Bsc Hons Degree in Food Science and Nutrition
Letterkenny Institute of Technology
2013-2014
Project Report
Comparison study of conventional hot-water and microwave
blanching at different time/temperature/power combinations on
the quality of potatoes.
Submitted by: David Smith
Supervisor: Aisling Coyle
i
Abstract
In the 1930s the technology Blanching arose as a way extending fresh produces shelf-life. It
deactivates enzymes in particular those which are associated with quality deterioration such as
those involved in browning, lipid oxidation and textural damages. The heat treatment generally
comprises of fresh produce being exposed to steam or hot water (75-100oC) for various lengths
of times. (Owusu-Apenten, 2005). Microwave blanching of vegetables has been established as
a trustworthy substitute technique to the typical heating method.
In this study conventional hot-water and microwave blanching were compared at different
time/temperature/power combinations on the quality of potatoes. The samples were blanched
using both methods and a number of quality tests were carried out before and after heat
treatment and compared. This analysis involved testing for;
Internal quality factors:
Peroxidase Tests on blanched samples to give indication of deactivation of
peroxidise enzyme and indication of effective blanching end point.
Ascorbic acid analysis on end blanched samples using end point times shown
by peroxidase test using DCPIP method, to determine Vitamin C loss after each
blanching type/combination.
External quality factors:
Weight loss to samples throughout heat treatment.
Texture/Hardness changes to samples throughout blanching.
Colour changes to samples throughout blanching.
The findings showed that; conventional blanching is the most straightforward. It has the least
damaging effects with regards to hardness/texture decrease. However conventional blanching
was also shown to lead to decreased quality including loss of ascorbic acid. It is considerable
slower when using temperatures lower than 100oC and has high energy costs.
Microwave blanching was shown to have more effective enzyme inactivation, less processing
time, and has the best retention of quality (ascorbic acid and other vitamin, minerals and other
properties). Its energy cost of production is almost of half compared with conventional.
However the equipment needed for microwave blanching is expensive and not commonly used
in food industry. This study has shown that microwave blanching could potentially be used in
the future if further research highlights and promotes the benefits of using microwave over
conventional blanching.
ii
Acknowledgments
I would like to take this opportunity to thank my project supervisor Ms Aisling Coyle for all
her help and excellent advice and guidance throughout the course of my project.
I would also like to acknowledge Dr. Brian Carney as well as Ken MacIntyre for their
assistance and for being so generous with their time throughout the duration of my project.
Lastly I would like to show my thanks and appreciation to everyone who helped in any way
this year and especially to my classmates for all their input, advice and continued
encouragement throughout the year and for making it enjoyable and cherished.
iii
Table of Contents
Chapter 1 - Literature Review Page
1.0 Introduction 2
1.1 Why we cook? 3
1.2 Methods of cooking vegetables 5
1.3 Blanching and its uses 7
1.4 Vegetables & Potatoes
1.4.1 Vegetables 9
1.4.2 Potatoes 10
1.5 Types of Blanching. (Boiling Water vs Microwave) 13
1.6 Quality of foods 14
1.7 Enzymatic activity effects on food and determination of peroxidase enzyme. 16
1.8 Vitamin C 17
1.9 Relationship between Time/Temperature/Power combinations on quality 20
1.10 Economic Statistics of Industrial blanching & benefits of new technologies.
20
Chapter 2 Methodology
2.0 Methodology 24
2.1 Sampling 25
2.2 Conventional Blanching Analysis at Various Time/Temp. Combinations
2.2.1 Pre Conventional Blanching Physical Characterization of Samples 25
2.2.2 Conventional Blanching of Samples 27
2.2.3 Post Conventional Blanching Physical Characterization of Samples 28
2.2.4 Peroxidase Tests on Conventional blanched samples 29
2.3 Microwave Blanching Analysis at Various Time/Temp. Combinations
2.3.1 Pre Microwave Blanching Physical Characterization of Samples 30
2.3.2 Microwave Blanching of Samples 30
2.3.3 Post Microwave Blanching Physical Characterization of Samples 32
2.3.4 Peroxidase Tests on Microwave blanched samples. 32
2.4 Ascorbic acid analysis blanched samples
33
Chapter 3 - Results
3.0 Results 36
3.1 Peroxidase Tests 36
3.2 Pre and Post Blanching Physical Characterization of Samples
3.2.1 Weight loss 39
3.2.2 Texture/Hardness 40
3.2.3 Colour 44
3.3 Ascorbic acid analysis on blanched samples
45
Chapter 4 - Discussion
4.0 Discussion
48
Chapter 5 - Conclusion
5.0 Conclusion
54
Bibliography 56
iv
List of tables
Table number Description Page
1.01 Comparison of segments of plants with vegetables that
grow on each respectively.
9
1.02 Nutritional Values for raw Potatoes
11
1.03 Enzymes responsible for quality deterioration
16
1.04 Advantages and disadvantages of both the Peroxidase
and Lipoxygenase enzyme indicators
17
1.05 Vitamin C content of Some Common Foods.
19
2.01 Conventional & Microwave blanching, parameters of
investigation
24
2.02 Conventional blanching, parameters of investigation
27
2.03 Peroxidase Activity Index Scale
29
2.04 Microwave blanching, parameters of investigation
30
3.01 Peroxidase Activity Index Scale
36
3.02 Peroxidase activity across Conventional blanching 80oC
and 100oC, with blanching endpoints shown in yellow
37
3.03 Peroxidase activity across Microwave blanching 600W
and 800W, with blanching endpoints shown in yellow
38
3.04 Hardness across conventional blanching at 80oC, blanch
endpoint shown in yellow
40
3.05 Hardness across conventional blanching @ 100oC,
blanch endpoint shown in yellow
41
3.06 Hardness across microwave blanching at 600W, blanch
endpoint shown in yellow
42
3.07 Hardness across microwave blanching at 800W, blanch
endpoint shown in yellow
43
3.08 Luminance scale measurements 44
3.09 Ascorbic acid in Control, Conventional 80oC & 100oC
and Microwave 600W & 800W
45
v
List of Figures
Figure number Description Page
1.01 Calcium, iron, zinc percentage uptakes in digestion of
raw, and traditional cooked and ready-to-eat legumes
4
1.02 Aerobic oxidation of phenol by polyphenoloxidase to
quinones (melanin) in chemical browning of potatoes
12
1.03 Boling water vs microwave blanching of turnip greens,
retention of water-soluble vitamins
14
1.04 Chemical Structure of L-ascorbic acid.
18
1.05 Cost comparison of hot water and steam use in
blanching
21
1.06 Effluent discharge comparison chart for hot water and
steam use in blanching
22
2.01 Sample sizes
25
2.02 Brookfield Texture Analyser
26
2.03 CR-400 Chrom-Meter
26
2.04 ELTAC EKA 179 Waterbath
28
2.05 Samples after heat treatment and cut in half prior
peroxidase testing
29
2.06 Microwave blanching
31
3.01 Top samples peroxidase level: 100%, Bottom samples
peroxidase level: 0%
36
3.02 Peroxidase activity across Conventional blanching 80oC
and 100oC, showing blanching endpoints at 0%
37
3.03 Peroxidase activity across Microwave blanching 600W
and 800W, showing blanching endpoints at 0%
38
3.04 Average sample size weight loss after Conventional
blanching @ 80oC and 100oC
39
vi
Figure number Description Page
3.05 Average sample size weight loss after Microwave
blanching @ 600W and 800W
39
3.06 Hardness decrease in Conventional blanching at 80oC,
in 1cm3, 2 cm3, 3cm3 samples
40
3.07 Hardness decrease in Conventional blanching at 100oC,
in 1cm3, 2 cm3, 3cm3 samples
41
3.08 Hardness decrease in Microwave blanching at 600W, in
1cm3, 2 cm3, 3cm3 samples
42
3.09 Hardness decrease in Microwave blanching at 800W, in
1cm3, 2 cm3, 3cm3 samples
43
3.10 Average L*a*b (Colour) measurements as conventional
& microwave blanching times increase.
44
3.11 Vitamin C measurements in Control and Conventional
blanched samples at 80oC & 100oC to endpoint
46
3.12 Vitamin C measurements in Control & Microwave
blanched samples at 600W and 800W to endpoint
46
4.01 Sample shape pre-blanching vs. misshaped samples
after blanching with considerable weight loss
50
1
Chapter 1
Literature Review
2
1.0 Introduction
The consumption of food is essential to all living things for nutritional support, energy and
body survival. Generally food is obtained through plants and animals which are comprised of
vital nutrients. These include; carbohydrates, fats, proteins, vitamins, and minerals. Living
things consume food in order to obtain these in an attempt to sustain life, yield energy and
promote growth. In the past food people have gained food by hunting & gathering, and through
farming. Now however most of the first world countries acquire food through the food industry.
The food industry is a global market of the sale and distribution of food & drink items in a vast
network across the world. It accompanies the majority of the worlds population as we are all
consumers purchasing nearly all of our daily food derived from the industry. Today as earlier
skills of manual food salvaging have died out in the general population, most of the world is
reliant on the food industry as a source of food. The system itself is made up of Agriculture,
Manufacturing, Food processing, Regulation, Wholesale and distribution, Marketing, Research
and development, Education and Financial services.
Cooking techniques have improved as centuries has passed and have become more advanced
in the present day. Now that we live in a world driven by the food industry these advancements
have grown exponentially as food is the largest global market for business. Today most of the
decisions taken in the production of current and new food products are taken for capital gain.
For this reason there is a large strive for new, innovative, improved and most importantly more
profitable techniques to how food is processed.
Cooking is one of many processes carried out to food for many desired purposes. Cooking
methods differ largely around the world, due to contrasting environments, economies, and
cultures. As new cooking technologies have progressed so has the approach to cooking. It is
now more intuitive, radical, scientific and cutting-edge. This new scientific approach to food
has become known as Food science. A sub-discipline of Food science exists as Molecular
gastronomy which aims to study, illustrate and make functional use of the physical and
chemical changes of ingredients that happen during cooking, and also the social, creative and
practical features of culinary and gastronomic phenomena as a whole (This, 2006).
3
Some modern methods and inventions such as the oven, microwave, refrigerator, atmosphere
packing, canning, pasteurization and sterilisation, have revolutionised the food industry and
household consumption of food.
Methods of cooking vary from a wide range of alternatives and combinations. Most of these
include; baking, frying, roasting, barbecuing, smoking, grilling, microwaving and boiling.
Boiling uses water as a heating medium. Types of boiling can be steaming, poaching, steeping,
simmering, braising, and blanching. Many types of cooking techniques use various amounts of
heat and moisture and can differ in cooking times also. The amount of heat, moisture and
lengths of time used will considerably influence the final product. For this reason cooking
differences are often experimented with to investigate different end results. The aim of doing
this is usually to improve quality, find a quicker cooking method, or to identify a cheaper or
more economic technique among other agendas.
1.1 Why we cook?
Cooking is the preparation of food using heat. It is generally carried out to destroy or deactivate
organisms which can cause damaging effects if consumed, for example bacteria, moulds,
viruses and parasites. The act of ingesting harmful microorganism can cause food poison to
those subjected to the agents. Susceptible or contaminated foods which have not been properly
cooked can lead to food poisoning by presence of infectious agents. Examples includes
Salmonella in foods containing bacteria, Peronopora hyoscyami in moulds, Norovirus in
viruses and Toxoplasma gondii which is a parasite. Generally parasites are established in foods
like salads, incorrectly cooked meats and contaminated water.
Cooking inhibits most sicknesses caused by food pathogens, which would subsequently cause
illness if the food was consumed fresh and uncooked. The use of cooking increases the number
of potential foods which can be eaten as it allows otherwise harmful produce to be safely
digested.
Generally the types of food which are consumed are from animal origins such as meat, fish,
eggs, and dairy products or from plant origins such as fruit, vegetables, grains, nuts, herbs and
spices. The mostly consumed plant derived foods are fruit and vegetables.
4
Cooking some foods can improve their nutritional quality for example cooked beans when
compared to raw beans. This usually involves increasing the efficiency of absorption of
nutrients by the body in food which has undergone a cooking process in comparison to which
has not been cooked. This is to say that cooking increases the bioavailability of nutrients. For
example traditional cooking significantly increases the intake of zinc, calcium & iron from
white beans, and of calcium in lentils. When mineral uptakes from raw, traditionally cooked,
and ready-to-eat lentils (they already been steamed, therefore they keep their shape and texture
when cooked) are compared, the highest uptake values correspond to the ready-to-eat product,
which is attributed to cooking under pressure (Viadel, Barber, & Farr, 2006).
Figure 1.1: Calcium, iron, zinc % uptakes in digestion of raw, cooked & ready-to-eat legumes
In addition, cooking is also carried out in some fruit and vegetables to deactivate enzymes. In
particular enzymes which are associated with food safety and quality deterioration such as
those involved in browning, lipid oxidation and textural damages. Sensory, nutritional quality
and shelf life of fresh vegetables are affected by the action of endogenous enzymes. In the
5
1930s the technology called Blanching arose as a way extending fresh produces shelf-life by
the application of a mild heat which inactivates enzymes and halts adverse changes in fresh
fruit and vegetables quality. Blanching generally comprises of fresh produce being exposed to
steam or hot water (75-100oC) for various lengths of times (Owusu-Apenten, 2005).
The method of cooking application depends on what the end result intends to be. Different
techniques and methods use varying amounts of heat, power and cooking times. The type of
cooking process used will considerably effect the final product. They will effect foods quality
(taste, weight loss, shrinkage, texture, colour, enzyme inactivation, & nutrient retention) shelf-
life, and level of safety from a present of pathogens point of view.
1.2 Methods of cooking vegetables
Baking/Roasting involves sustained dry heat by convection, instead of thermal radiation. It is
usually carried out in an oven. In roasting, the vegetables are placed onto a roasting tray, usually
fat or oil is added to give the final product and adds flavour. The addition of butter, lard or oil
also aims to reduce moisture loss by evaporation.
Roasting and baking are both cooking in hot air. They are very similar in process but the term
baking is generally referred to dough foods whereas the phrase roasting describes to the
treatment of dry heat to all other products (Berk, 2013).
Smoking is a another method of flavouring, cooking, or preserving food by subjecting it to the
smoke from burning or smouldering plant materials, generally charcoal or wood. Meats and
fish are the most smoked foods. However vegetables and other foods are often smoked also.
Commonly smoked vegetables are peppers, onions, corn, potatoes, asparagus, mushrooms and
paprika. Smoking food can be done either through a cold smoke or a hot smoke. Cold smoking
is carried out for increased flavour and retain moisture. Cold smoking will not cook foods. Hot
smoking subjects foods to smoke and heat. They are fully cooked, moist, and flavourful.
However smoking at high temperatures decreases yield due moisture and fat being lost (Berk,
2013).
Frying is the cooking process when fat/oil is used as the heat transfer agent in direct contact
with the product (Varela, Bender, & Morton, 1988). There are a number of types;
6
Pan frying. This type of frying is used on flat, wide and moderately thin cuts of food,
like bacon, egg and fillets. The food is cooked by contact without agitation with a small
amount of fat usually oil.
Stir frying. This applies to small to medium-size food pieces which are quickly cooked
with constant agitation in a small quantity of fat generally oil.
Deep frying. Here food pieces are submerged in hot fat or oil, and heat transfer occurs
evenly over the complete surface of the food.
Today deep-fat frying has grown to a big sized industrial process. Fried chips are undoubtedly
the most important industrial foods produced by immersion frying (Berk, 2013).
Microwaving is carried out in a microwave where the food is placed and cooked. It uses high
frequency radio waves, which penetrates the food molecules causing them to vibrate. The
vibrating of these molecules leads to friction, which causes heat formed, thus cooking the food.
The phrase microwaves refers to electromagnetic radiation in the wavelength range of 0.1-1 m
in air, corresponding to a frequency range of 0.3-3 GHz.
The technology is generally used in household and food service (for example; restaurants,
planes) ovens, to defrost frozen products, to heat food, to cook, to bake and to boil water. They
were originally launched in the 1950s, and now they have grown to be the foremost food
heating device in modern houses and in range of classes of food service institutions (Datta,
2001).
Subsequently, the food manufacturing industry devotes extensive resources to developing
products and packages compatible with the capacities and restrictions of the household
microwave unit. In industrial uses, the practice of microwave heating continues to be limited
to small numbers of instances where the technology gives defined technological and economic
advantages over traditional heating methods (Berk, 2013).
Boiling involves cooking through use of moisture, mainly water. Heat is transferred via
convection through the liquid and/or steam. It comprises of the heating of water which contains
the food to be cooked to its boiling point of 100oC. Food can either be completely covered by
the water and then heated, however this can result in high losses of vitamins and mineral
through a leaching activity. Moderate boiling helps to break down tough fibrous structures of
some foods which would be less tender if cooked using other techniques. When boiling is
7
carried out for the least amount of time possible, then the maximum colour and nutritive value
can be retained.
A particular study was undertaken on the effects of water while boiling (Sikora, Cielik,
Leszczyska, Filipiak-Florkiewicz, & Pisulewski, 2008). It showed that the smallest amount
of water capable of being used to cook is the amount that should be used to keep leaching of
vitamins and minerals to a minimum (Foskett, Campbell, Ceserani, & Paskins, 2009).
Potatoes can be blanched by boiling or steam to help to peel the skin, to maintain their quality
and colour, decrease microorganisms and preserves the potatoes for freezing. This is done to
retain fresher looking potatoes with improved taste (Buckner, 2013).
1.3 Blanching and its uses.
Blanching deactivates enzymes in particular those which are associated with quality
deterioration such as those involved in browning, lipid oxidation and textural damages. It
shrinks the product giving it a better fill. As well as this, blanching expels air/gas from a product
being canned which produces a vacuum in the closed can.
The process can also be carried out just to soften many fruit & vegetables or to partially or
completely cook them, or to eliminate sharp tastes e.g. in onions, bacon, and cabbage (Child,
Bertholle, & Beck, 2001).
Concerning potatoes chips, blanching frequently applies to the pre-cooking of potato chips in
oil at a low temperature before completing them at a high temperature. The benefit is that the
blanching stage cooks the potato. The following stage at a high temperature leaves the outside
of the chips crispy (Blumenthal, 2012).
Vegetables such as green beans are sometimes blanched to increase their natural green colour.
Studies have shown that the reduction or removal of peroxidase activity to be the best indicator
of blanching completion in relation to the retaining of quality after process has been carried out
(Joslyn & Berkeley, 2006). Lipoxygenase has also been shown to be an indicator of blanching
end point. Peroxidase is responsible for off-flavour development, lipoxygenase is responsible
for colour changes, and ascorbic acid has been shown to be linked with nutritional changes.
These can be used as indicators of blanching efficiency (Barrett & Theerakulkait, 1995).
8
After undergoing blanching, food quality can vary considerably depending on the
time/temperatures combination use as well as the size of the food blanched. Under-blanching
will increase the activity of enzymes and is more adverse than if no blanching was carried out.
Over-blanching results in loss of texture, colour, phytochemicals and minerals (Jaiswal, Gupta,
& Abu-Ghannam, 2012). Industrial blanching is generally carried out at combinations of 70 to
95 C for not longer than 10 minutes while for household purposes vegetables are usually
blanched at combinations of 98100 C for of 1012 min (Morales-Blancas, Chandia, &
Cisneros-Zevallos, 2002).
Blanching is mostly commonly carried out in a water bath where the food is exposed to; hot
water, hot air, or steam at the above range of time/temperature combinations. The food is the
cooled very quickly to remove any retained heat which may cause the fruit or vegetables to
continue cooking.
Blanching is often carried out as a precursor to canning. The objective of blanching as a pre-
treatment of vegetables for canning is the removal of tissue gases; the shrinking of the material
so that adequate fills can be contained in the can; and the heating of the material prior to filling
so that a vacuum will be obtained after heat processing and boiling (Lee, 1958).
Studies by (Afoakwa & Yenyi, 2006) have shown that blanching has considerable influences
on the moisture content, ash content, leached solids, phytates, tannins and the hardness of the
canned vegetables. In this study, blanching lead to increased moisture content and leached
solids while significant decreases were shown for the phytates, tannins and hardness of the
canned vegetables. The research also showed that the optimal pre-processing blanching
conditions required to achieve the optimum quality canned product from the vegetables was 5
minutes. These conditions were proven to give the best quality canned product with improved
nutritional quality and acceptable product quality characteristics, according to (Afoakwa &
Yenyi, 2006)
Blanching is also necessary as a part of the preparation for freezing preservation to inactivate
the enzymes in the tissues and to shrink the material so as to conserve space in packing. The
inactivation of the enzymes is very important in this process. This is because no final cook or
sterilization is used previous to freezing, therefore their inactivation is the only step taken to
prevent undesirable deterioration in flavour, odour, and colour on the part of the enzymes in
the tissues (Lee, 1958).
9
Microwave blanching of vegetables has been established as a trustworthy substitute technique
to the typical heating method used in the vegetable canning industry. The microwave treatment
of vegetables leads to an efficient enzyme inactivation, faster, and improved retention of
vitamin C (Ruiz-Ojeda & Peas, 2013).
1.4 Vegetables & Potatoes
1.4.1 Vegetables
In regards to cooking, a vegetable plant or part of one which can be eaten, used for cooking or
consumed raw. In relation to biology, a vegetable refers to members of the plant kingdom.
Vegetables are segments of plants which can be eaten and in nature occur in an array of forms.
Table 1.1: Comparison of segments of plants with vegetables that grow on each respectively.
Segment of Plants Vegetable
Flower bud Broccoli, Cauliflower, Globe artichokes,
Leaves Kale, Collard Greens, Spinach, Beet Greens, Turnip Greens,
Lettuce, Mustard Greens, Watercress, Garlic Chives,
Leaf sheaths Leeks
Buds Brussels sprouts
Stem Kohlrabi, Galangal, and Ginger
Stems of leaves Celery, Rhubarb, Cardoon, Chinese celery
Stem shoots Asparagus, Bamboo Shoots
Tubers Potatoes, Jerusalem Artichokes, Sweet Potatoes, and yams
Whole-plant sprouts Soybean, Mung Beans, Urad, and Alfalfa
Roots Carrots, Parsnips, Beets, Radishes, and Turnips
Bulbs Onions, Shallots, Garlic
10
Vegetables for consumption are prepared in a number of methods. Vegetables nutritional value
differs from food to food with a range of vitamins (e.g. A, B, C, & K), provitamins, dietary
minerals and carbohydrates. Generally they contain very little fat and protein. Vegetables are
also composed of additional phytochemicals, several of which have been declared to have
antioxidant, antibacterial, antifungal, antiviral and anticarcinogenic properties (Steinmetz &
Potter, 1996). Certain vegetables have fibre, which plays a vital role in gastrointestinal
function.
The Food Safety Authority of Ireland recommends 3 to 5 servings of vegetables per day
(Ireland, 2011). The risk of cardiovascular disease and diabetes has been shown to be lowered
in people who diets consume the recommended amounts of fruits and vegetables (Sangita, Vik,
Pakseresht, & Kolonel, 2013). These diets have been shown to defend from certain cancers and
reduce loss of bone (Mirmiran, Hosseini-Esfahani, & Azizi, 2013) (Chen & Ho, 2010). The
potassium derived from fruits & vegetables could aid in the prevention of the development of
kidney stones (Grieff & Bushinsky, 2013).
Vegetables post-harvest should be properly storaged to extend their shelf life and quality.
Whilst being stored, leafy vegetables have moisture loss, and ascorbic acid content also
decreases quickly. Vegetables should be stored for short times, in cold conditions and in an air
controlled environment.
1.4.2 Potatoes
The potato is full of starch, it is a tuberous plant from the perennial nightshade Solanum
tuberosum. They are high in carbohydrates, contain a lot of starch and dietary fibre consisting
of insoluble cellulose, lignin in the skin and soluble pectins in the flesh. Table 1.2 shows this.
The proteins in potatoes are restricted to the essential amino acids methionine and cysteine.
They are a great source of the vitamin B and ascorbic acid. Fresh potatoes have more ascorbic
acid than potatoes which have been in storage.
One 170 g baked potato with its skin has 4 g dietary fibre, 4 g protein, 0.2 g total fat, 48 mcg
folate (12 percent of the RDA), and 16 mg vitamin C (21 percent of the RDA for a woman, 13
percent of the RDA for a man) (Ireland, 2011).
11
Table 1.2: Nutritional Values for raw Potatoes
Nutrient Value
Calories 278
Fat
12
the brown pigment melanin (Mathew & Parpia, 1971). This process is otherwise seen as the
involved in chemical browning of potatoes
Figure 1.2: Aerobic oxidation of phenol by polyphenoloxidase to quinones (melanin)
The reaction can be slowed by immersing the peeled sliced fresh potatoes in water containing
ice, however several vitamins in the potatoes will leach out into the water. Alternatively the
sliced potatoes can be submerged in an acid solution (lemon juice & water, or vinegar & water),
they have a low pH, and will denature the polyphenol oxidase but will also alter the taste.
Studies have shown that heat application from blanching will denature the enzymes
polyphenoloxidase and peroxidase involved in this reaction (Ndiaye, Xu, & Wang, 2009).
The starch in potatoes comprises of granules loaded with the molecules of amylose and
amylopectin. When potatoes are cooked, the starch particles absorb water molecules that
adhere to the amylose and amylopectin molecules, this results in swelling of the granules. If
the granules soak ample water, they can burst and the nutrients inside will escape. If the
potatoes are cooked in a soup or stew, the amylose & amylopectin compounds that are released
from the broken starch granule will bind water molecules in the liquid, this thickens the
product. Potatoes which have undergone a cooking stage have more nutrients available than
raw potatoes do. Cooked potatoes can additionally be a different colour to raw potatoes.
Potatoes also possess pale anthoxanthin pigments which react with metal ions to produce green,
brown or blue compounds (Rinzler, 2009).
Due to its characteristic taste and texture, french fries (chips) remain to be the most popular
processed potato product. In general, the preliminary steps in regular cut French fry production
include washing of raw potatoes, peeling, sorting, and cutting into strips. After this point, potato
strips are blanched, partially dehydrated, deep-fat par-fried, frozen, deep-fat finish-fried and
served (Bingol, Wang, Zhang, Pan, & McHugh, 2014).
In industrial production, the potato strips are generally blanched with water (6085 C) for
more than 10 min mainly to inactivate enzymes (lipoxygenase, polyphenoloxidase, peroxidase
ect.) and to obtain a uniform colour, and then pre-dried with warm air to improve texture. The
13
blanched potato strips are par-fried in hot oil (170190 C), cooled at room temperature, frozen,
packaged and distributed. (Nonaka, Sayre, & Weaver, 1977), (Tajner-Czopek, Figiel, &
Carbonell-Barrachina, 2008).The process of finish-frying is usually accomplished in
restaurants or at home and each of these steps is important for the final product quality and its
oil content.
Conventional blanching and pre-drying are two separate processes and have the drawbacks of
having low energy efficiency, long processing time (Tajner-Czopek et al., 2008). In a typical
water blanching operation, firstly the water needs to be procured and heated and secondly after
a certain amount of blanching operations this water needs to be replaced since it becomes
saturated with sugars leaching from the potato strips. This results in not only excessive energy
consumption due to re-heating of the water to the blanching temperatures but also consumption
of high amounts of water (Bingol et al., 2014).
1.5 Types of Blanching. (Boiling Water vs Microwave)
Blanching is an efficient method of preserving fruits & vegetables. Hot steam/ boiling water is
the most common method of blanching, although microwave blanching is increasingly in use
today (Bingol et al., 2014). Its recognised that conventional blanching of vegetables leads to
leaching of water-soluble B and C vitamins. Traditional blanching is carried out using boiling
water or steam. Conversely microwave blanching could be a practical alternative method which
may result in better overall quality and retention of essential vitamins & minerals. Still the
equipment needed for microwave blanching is expensive which results in the method not
commonly used in food industry. Conventional water blanching is generally used home
cooking. It is straightforward and cost-effective, but has greatest possibility of leaching water-
soluble B and C vitamins and minerals compared to microwave balancing. Traditional steam
blanching is presently the most frequently used technique in the food industry today. It is
reasonably cheap and retains minerals and water-soluble vitamins over boiling water and
microwave blanching.
Studies on the results of microwave blanching versus. boiling water blanching on retention of
selected water-soluble vitamins ion vegetables have shown microwave blanching in certain
circumstances to be more effective in the retaining the selected water-soluble B and C vitamins
and nutrients in vegetables (Osinboyejo, Walker, Ogutu, & Verghese, 2003).
14
In another study comparing traditional hot-water and microwave blanching on quality of green
beans, microwave blanching of green bean pods has been shown to be a reliable alternative to
the conventional heating process used in the vegetable canning industry. The microwave
treatment of pods, in addition to an effective enzyme inactivation in less processing time, led
to a better retention of ascorbic acid (Ruiz-Ojeda & Peas, 2013).
Research in the assessment of microwave methods in blanching of broccoli as an alternative
for traditional blanching has also proven that microwave blanching uses less energy on an
industrial scale to conventional blanching. Microwave blanching consumption and energy cost
of production is almost of the half in compare with the conventional (Patricia, Bibiana, & Jos,
2011).
The investigation of the results of microwave pre-treatment on the kinetics of vitamin c loss
and peroxidase deactivation in various parts of green asparagus during water blanching proved
that microwaves could be an reliable pre-treatment method for use before water blanching to
reduce the loss of vitamin c and to speed up the deactivation of peroxidase and therefore
preserve quality (Zheng & Lu, 2011).
(Osinboyejo et al., 2003)
Figure 1.3: Traditional versus microwave blanch, retention of turnip green water-soluble
vitamins
1.6 Quality of foods
Quality of foods is the quality features of food that is satisfactory to buyers. This incorporate
external factors such as appearance (size, shape, weight loss, shrinkage, colour, gloss, and
15
consistency), texture, & flavour; and internal (chemical, physical, microbial, enzyme
inactivation, and ascorbic acid retention.
Quality of food also involves all the attributes of excellence that create acceptable food for
consumers. Food buyers put a high priority on eye appeal of fresh foods in the market. Well
coloured fruits and vegetables, uniform sizes and products that are free of any kind of damage
will get a good rating from most food buyers. Exterior colour often has little to do with whats
inside and uniform sizes do not indicate how good or bad a food is from a nutritional point of
view, but is important factor for the quality and therefore saleability of the fruits or vegetables
(Ferree, 1973).
The nutritional value of fruits & vegetables is dependent on its components, which contains a
broad array of variation depending on the species, cultivar, and maturity stage. Overall,
vegetables contain more minerals than fruits, but both fruit and vegetables are recognised as
nutrient-dense foods because they release considerable quantities of micronutrients, such as
minerals and vitamins, but moderately little calories. Minerals have both direct and indirect
effects on human health. From a direct nutrition view, potassium and ascorbic acid has the
biggest presence in both fruits and vegetables (Vicente, Manganaris, Sozzi, & Crisosto, 2009).
Quality of foods can be drastically adversely affected by food decay. This is a process which
is vital to remove or decrease in food production. Decay is the method where food deteriorates
to the stage where it is not acceptable to be eaten by humans or is unsafe to be eaten. There are
three type of food decay also known as food spoilage; putrefaction, fermentation and rancidity.
The spoilage that happens in food is down to a reaction/breakdown of the chemical composition
of the product, involving its lipids, carbohydrates and proteins. The degree at which the
chemical reactions are undertaken is dependent on a number of elements, for example;
temperature, exposure to light, water activity, pH or oxygen.
A number of techniques to prevent food decay may be employed that may either completely
prevent, delay, or else decrease food spoilage. These include; use of preservatives or
refrigeration, freezing can preserve food even longer, canning, lactic acid fermentation, drying
and blanching.
In blanching the application of a mild head inactivates enzymes and halts adverse changes in
fresh fruit and vegetables quality. Blanching also deactivates enzymes in particular those which
are associated with quality deterioration such as those involved in browning, lipid oxidation
16
and textural damages. After undergoing blanching, food quality can considerably depend on
the time/temperatures/power combination use as well as the size of the food blanched.
1.7 Enzymatic activity effects on food and determination of peroxidase enzyme.
Many of the quality changes that vegetables undergo are catalysed by enzymes, therefore it is
reasonable to choose an enzyme as the indicator of the efficiency of the blanching method.
From about 1949 to 1975, catalase was used as the indicator enzyme for English green beans
and a number of other vegetables, while peroxidase served as the indicator enzyme for all other
vegetables. In 1975 the U.S. Dept. of Agriculture suggested that peroxidase inactivation was
necessary to reduce deterioration of quality during storage of vegetables and that catalase
inactivation was not an adequate indicator.
A number of enzymes can be used as an indicator of quality in vegetables. There is no sole
essential enzyme which is accountable for all the vegetable quality changes possible during
storage. However most studies agree that the two widely used and most effective enzyme
indicators of blanching are peroxidase and lipoxygenase (Gkmen, Sava Baheci, Serpen, &
Acar, 2005) (Garrote, Silva, Bertone, & Roa, 2004) (Gne & Bayindirli, 1993).
Table 1.3: Enzymes responsible for quality deterioration
Quality defect Responsible enzymes
Off-flavour
development
Lipoxgenase
Lipase
Protease
Textural
Changes
Pectic enzymes
Cellulose
Colour
changes
Polyphenol oxidase
Phlorophyllase
peroxidase
lipoxygenase
Nutritional
changes
Ascorbic acid
Oxidase
Thiaminase
(Williams, Lim, Chen, Pangborn, & Whitaker, 1986)
17
Research has shown that the biggest problem with using lipoxgenase as an indicator is that a
quick test is generally unavailable or not readily utilized by the food industry. Lipoxygenase
analysis may be carried out in a laboratory using either a spectrophotometric or a polarographic
method, however both can pose difficulties and neither would be feasible in a processing
facility environment (Barrett & Theerakulkait, 1995).
According to the research presented in table 1.4, peroxidase appears to be a more practical,
quicker, less expensive, simpler alternative to lipoxygenase. Other studies support this and have
shown that the reduction or removal of peroxidase activity to be the best indicator of blanching
completion in relation to the retaining of quality after process has been carried out (Joslyn &
Berkeley, 2006).
Table 1.4: Advantages and disadvantages of both the Peroxidase and Lipoxygenase indicators
Enzyme
Indicator
Advantages Disadvantages
Peroxidase
Wide distribution in vegetable
tissues.
Correlation to quality un clear
Resistant to destruction by heat Inactivation may require overheating
Simple and rapid test quantitative
test possible
Regeneration is possible
Lipoxygenase
Wide distribution in plants
Rapid assay either unavailable or not
utilisd
Good evidence to support
involvement in off-flavour
development and colour loss
Interference common in the
spectrophotometric assay
Polarographic method may not be
sensitive
Non-enzymatically catalysed lipid
oxidation may occur
(Barrett & Theerakulkait, 1995)
1.8 Vitamin C
Vitamin C or L-ascorbic acid, is an essential dietary nutrient for humans. Ascorbic acid is a
water-soluble vitamin which is vital for growth and repair of teeth, gums, bones, tendons
ligaments and skin, as it is required for the production of collagen. Vitamin C helps wounds
heal also and is required for normal immune system function. It works as an antioxidant which
defends the cells of the human body from free-radical damage.
18
L-ascorbic acid deficiency may lead to scurvy, a severe disease identified by anaemia, skin
hemorrhages (blood spots) and gingivitis (gum disease). Generally it is uncommon, however it
may take place in the extremely malnourished or alcoholics (Jegtvig, 2013).
(Sigma-Aldrich, 2013)
Figure 1.4: Chemical Structure of L-ascorbic acid.
Vitamin C is readily used in the food industry for two main uses, the first being as an additive
to increase a food products nutritious quality and the second is to act as a preservative. As an
additive it may be added in order to replace vitamin loss during processing. Examples of such
products would be in fruit juices, canned fruit and vegetables, etc. Vitamin C acts as a
preservative by preventing oxidation, increasing the acidity of the product and acts as a
stabiliser. It is widely used in bread making, where it is present as a flour improver, by
improving bread texture and size of resulting bread along with an increased elasticity of the
dough and increased gas retention. All of these factors make it a very useful additive in the
food industry (Davies, Partridge, & Austin, 1991).
Vitamin C cannot be manufactured in the body and must be acquired through our diet. Our
bodies benefit more from L-ascorbic acid than that of L-dehydroascorbic acid, which is of no
use to the bodies system and is removed during excretion. It is a very heat unstable vitamin and
is extremely soluble in water (Whitney & Rolfes, 2002).
Therefore the vitamin must be sourced through food. FSAI recommends a daily vitamin C
intake of 60 mg/day. Vegetables and fruit are a great source of ascorbic acid. The below table
shows you which foods are sources of vitamin C.
19
Table 1.5: Vitamin C content of Some Common Foods.
Vegetables Serving size Vitamin C (mg)
Cabbage, red, raw 250 mL (1 cup) 54
Brussels sprouts, cooked 125 mL (4 sprouts) 38-52
Broccoli, raw 125 mL ( cup) 42
Cabbage, cooked 125 mL ( cup) 30
Caulifower, cooked 125 mL ( cup) 29
Cauliflower, raw 125 mL ( cup) 26
Potato, with skin, cooked 1 medium 17-24
Sweet potato, with skin, cooked 1 medium 22
Asparagus, frozen, cooked 6 spears 22
Turnip greens, cooked 125 mL ( cup) 21
Tomato, raw 1 medium 16
(Dietitians.ca, 2012)
Potatoes are a commonly eaten vegetable in Ireland. They contain considerable amounts of
vitamin C, however the majority of it is lost because of the high heat temperatures for long
times in cooking. To avoid this, blanching a precursor to cooking can be used to help retain
Vitamin C before the actual cooking for longer times is undertaken. For this reason blanching
is a carried out on potatoes. Its quick processing time, and quick cooking step leads better
retention of ascorbic acid. Studies have proven that well-controlled blanching techniques can
add to the overall retention of vitamins in vegetable foods (Selman, 1994).
Methods of detecting Vitamin C in foods have evolved in recent years. Biological techniques
have been commonly used in vitamin C analysis, but have gradually been replaced with
chemical methods which were more sensitive and selective. However, the titrimetric method
(DCPIP) is commonly used due to its simplicity and for its rapid technique (Davies et al., 1991).
The official method used for the analysis of vitamin C is the 2, 6-dichloroindophenol titrimetric
methods, which is an Association of Official Analytical Chemistry method. This technique is
commonly used as it is a quick test for a variety of products such as vegetables (Helrich, 1990).
The determination of vitamin C content using the 2,6 -dichloroindophenol method works on
the principle that vitamin c reduces the indicator dye to a faint pink colour for 10 seconds and
then to a colourless solution. The titre of the dye can then be established using a standard
ascorbic acid solution. Food samples can then be titrated with the dye and the volume for the
titration used to calculate the vitamin C content of the sample (Nielsen, 2010). The type of
blanching (microwave or water) can have varying effects on Vitamin C retention.
20
1.9 Relationship between Time/Temperature/Power combinations on Quality
After undergoing blanching, food quality can vary considerably depend on the
time/temperatures combination used as well as the size of the food blanched. Under-blanching
will increase the activity of enzymes and is more adverse than if no blanching was carried out.
Over-blanching results in loss of texture, colour, phytochemicals and minerals (Jaiswal et al.,
2012). Industrial blanching is generally carried out at combinations of 70 to 95 C for not
longer than 10 minutes while for household purposes vegetables are usually blanched at
combinations of 98100 C for of 1012 min (Morales-Blancas et al., 2002).
Numerous investigations (Klein, Rastogi, Perry, & Brewer, 1994) on microwave blanching of
vegetables and fruits have been published. investigated the effect of different blanching
methods on the ascorbic acid content and the peroxidase activity in 225 g-batches of green
beans, and they concluded that a 3-min microwave treatment at 700 W resulted in a product
similar to that obtained by steam blanching. Muftugil, (1986) showed that the time to complete
the peroxidase inactivation in green beans was less with microwave blanching than with water
and steam treatment, whereas a higher greenness remained with the two latter methods.
(Brewer & Begum, 2003) investigated the effects of power and irradiation time on ascorbic
acid, colour, and peroxidase activity in microwave blanching of various vegetables. Compared
to raw unblanched samples, they found that the optimum conditions (2 min at 490 W, or 1 min
at 700 W) led to a peroxidase activity reduction up to 88%, and an ascorbic acid retention of
about 70%. Although, in spite all of this research, there are not many comparison studies of
microwave blanching with conventional industrial blanching.
The most efficient blanching time/temperature/power combinations, depends greatly on the
type of food blanched, why blanching is being carried out, the desired end result, and the type
of heating medium used.
1.10 Economic Statistics of Industrial blanching & benefits of improved technologies.
Both water and steam blanching have one thing in common, product is exposed directly to
food-grade water that typically ranges in temperature from 70oC to 100oC. With microwaving
blanching, the process is carried out in a microwave where the food is placed and cooked. It
uses high frequency radio waves, which penetrates the food molecules causing them to vibrate.
21
The vibrating of these molecules leads to friction, which causes heat formed, thus cooking the
food. The phrase microwaves refers to electromagnetic radiation in the wavelength range of
0.1-1 m in air, corresponding to a frequency range of 0.3-3 GHz (Berk, 2013).
With steam blanching, product is exposed directly to food-grade steam that is typically 100oC
as it is conveyed within a chamber. Some steam blanchers use convection technology that
forces the steam through the bed of product to increase the heat transfer efficiency, other steam
blanchers present the product in a single layer to achieve Individual Quick Blanching (IQB).
To minimize the product's exposure to heat, some steam blanchers follow the heat penetration
stage with a holding stage that allows the core temperature of the product to rise without the
addition of more steam.
Most water blanchers and steam blanchers require the steam to be produced by a boiler. With
water blanching, the steam heats the water and the product. With steam blanching, the steam
is applied directly to the product. Because the boiler is one of the most expensive pieces of
equipment pieces to operate in a food processing plant, given the high cost of energy, steam
consumption as a direct and significant effect on energy costs (Johnson, 2011).
Figure 1.5: Cost comparison of hot water and steam use in blanching of carrots or peas
Like energy costs, water use and wastewater effluent are directly correlated to the volume of
steam used. Steam blanchers require half the steam of water blanchers, therefore needing half
the volume of water.
22
Figure 1.6: Effluent discharge comparison chart for hot water and steam use in blanching
Overall, the use of microwave ovens in the food industry is limited. Currently, the most
expensive blanched foods are using microwave balancing. Although it has shown to be energy
saving in the case of potato fries (Bingol et al., 2014). The hugely high frequencies used in
microwave heating permits for quick energy transfers and thus high rates of heating. This is an
important feature of this method.
Research (Patricia et al., 2011) in the assessment of microwave methods in blanching of
broccoli as an alternative for traditional blanching has also shown that microwave blanching
uses less energy on an industrial scale to conventional blanching. Microwave blanching
consumption and energy cost of production is almost of the half in compared with the
traditional. (Patricia et al., 2011).
However microwave blanching is not as widespread as the conventional types, as soon as it has
exhibited its worth, it may be drawn to the freezing and canning industry. Replacements of
existing water or steam blanchers is not likely to happen. The vegetable industry would be
hesitant to substitute examples of equipment before full depreciation and particularly if their
market niche is stable. Lastly, it continues to appear that the shorter processing times of
microwave ovens will lead to reduced operating costs and higher value products, thus
compensating for equipment cost (Reyes De Corcuera, Cavalieri, & Powers, 2004).
23
Chapter 2
Methodology
24
2.0 Methodology
Samples of potatoes are blanched using both methods and a number of quality tests are carried
out before and after heat treatment and compared. This analysis involves testing for;
Internal quality factors as Conventional and Microwave blanching is carried out across
different time/temperature/power combinations.
Peroxidase Tests on blanched samples to give indication of deactivation of
peroxidise enzyme and indication of effective blanching end point.
Ascorbic acid analysis on end blanched samples using end point times shown
by peroxidase test using DCPIP method, to determine Vitamin C loss after each
blanching type/combination.
External quality factors as Conventional and Microwave blanching is carried out across
different time/temperature/power combinations.
Weight loss to samples throughout heat treatment.
Texture/Hardness changes to samples throughout blanching.
Colour changes to samples throughout blanching.
This below table is the time and temperature/power parameters for conventional and
microwave blanching that is used in this investigation.
Table 2.1: Conventional & Microwave blanching, parameters of investigation
Sample Size
Time
Conventional Blanching Microwave Blanching
x 3 Temperature (oC) Power (Watt)
1cm3, 2 cm3, 3cm3 30 secs 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 1 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 2 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 3 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 4 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 5 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 6 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 7 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 8 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 9 mins 80oC, 100oC 600W, 800W
1cm3, 2 cm3, 3cm3 10 mins 80oC, 100oC 600W, 800W
25
2.1 Sampling
Rooster Potatoes were purchased fresh on the morning of each day of testing from a local
Tescos. All potatoes were non-organic and were checked prior to purchasing to make sure that
they were all free from any damage or bruising. Just samples which were free from
irregularities or any defects which could affect the result were chosen for use.
2.2.1 Pre Conventional Blanching Physical Characterization of Samples
Conventional Blanching Sample Preparation;
Method:
1. Potatoes selected, peeled, washed, sliced & diced into around:
(1cm x 1cm x 1cm), (2cm x 1cm x 1cm), (3cm x 1cm x 1cm),
(1cm3) (2cm3) (3cm3)
Figure 2.1: Sample sizes
2. Each sample size is done in triplicates, ie for each test
x (1cm3), 3 x (2cm3), 3 x (3cm3)
3. Soak samples in iced water and covered with cloth to prevent air exposure
The following determined:
Weight (to determine weight loss)
Texture/Hardness
Colour
Methods:
Weight (to determine weight loss)
1. Samples weight measured using a mass balance and recorded in grams.
2. Length of samples measured using a stainless steel ruler, which was cleaned using sterilized
wipe before and after use.
26
Texture/Hardness
CT3 Texture Analyser used along with TA-MTP Magness-Taylor Probes (puncture
test) to measure hardness.
Figure 2.2: Brookfield Texture Analyser
Instrument calibrated and samples tested as per Brookfield Texture Analyser Operating
Instructions, Manual No: M08-372-C0113 (Brookfield, 2012)
Settings:
Probe: 4 mm diameter cylinder probe
Test type: Compression
Test Speed: 1.0 mm/s
Target Type: Distance: 5mm
Target value: 110.0 mm
Trigger Load: 10 g
The procedure produces a plot of force (N) vs. time (s) which is used to establish the value of
hardness in Newton (N).
Colour
CR-400 Series Colorimeter used to measure Luminance (colour). Tests as per Konica
Minolta CR-400 Chrom-Meter Catalogue No: 9242-4889-11 (Minolta, 2013)
Figure 2.3: CR-400 Chrom-Meter
After blanching samples of cubes are cut in half prior to peroxide tests and their colour
is measured internally using the Luminance CR-400 Series Colorimeter.
27
*** Following Pre Conventional Blanching Physical Characterisation of Potatoes, the
samples were placed back into iced water and covered with cloth to prevent air exposure
2.2.2 Conventional Blanching of Samples using Hot-water method using different
blanching Times/Temperature combinations and post blanching cooling step.
Table 2.2: Conventional blanching, parameters of investigation
Samples x 3 Time Temperature
1cm3, 2 cm3, 3cm3 30 secs 80oC, 100oC
1cm3, 2 cm3, 3cm3 1 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 2 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 3 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 4 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 5 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 6 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 7 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 8 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 9 mins 80oC, 100oC
1cm3, 2 cm3, 3cm3 10 mins 80oC, 100oC
Materials & Equipment:
ELTAC EKA 179 Waterbath
Vegetable baskets
Thermometer
Ice
Basins
Timer
Method:
1. ELTAC EKA 179 Waterbath is filled from bottom (enough to submerge the samples
which will be placed in and allowed to heat to specific temperature.
28
Figure 2.4: ELTAC EKA 179 Waterbath
2. Samples 3 x (1cm2), 3 x (2cm2), 3 x (3cm2) are removed from iced water and placed into
baskets, before being placed into the waterbath for scheduled times. Ensure lid is only
removed on entering of samples and quickly replaced on during blanching. Accurately
record the blanching time for accurate results.
ie first blanch is carried out at 800C for 30 seconds.
last blanch is carried out at 1000C for 10 minutes.
The sample sizes and quantities remain the same on each blanch.
3. On blanching completion remove lid and retrieve samples. Quickly place into fresh iced
water once again prior to enzyme testing.
2.2.3 Post Conventional Blanching Physical Characterization of Samples
Method:
In the same manner as the pre characterization of samples, the following determined:
Weight (to determine weight loss)
Texture/Hardness
Colour
These tests should be carried out as quickly as possible to reduce air exposure to samples
Again place back samples back into iced water on completion.
29
2.2.4 Peroxidase Tests on Conventional blanched samples to give indication of
deactivation of peroxidise enzyme and indication of effective blanching end point.
Materials & Equipment:
Pipette filers.
3% Hydrogen Peroxide
1% Guaiacol Solutions
Method:
1. Remove samples from iced water and place on three different sheets of white paper
designated by the sample size & time/temperature combination used.
Figure 2.5: Samples after heat treatment and cut in half prior peroxidase testing
2. Cut the cubes from each treatment in half and saturate the cut surface with equal volumes
of 3% H2O2 and 1% guaiacol solutions.
3. After three minutes at room temperature note the extent of any colour change in terms of
percentage area of the cut surface.
4. The degree of surface colouring gives an indication of the peroxidase activity in the
sample.
Table 2.3: Peroxidase Activity Index Scale
Coloured Score
80 100% 5
60-80% 4
40-60% 3
20-40% 2
0-20% 1
0% 0
30
2.3 Microwave Blanching Analysis at Various Time/Temp. Combinations
2.3.1 Pre Microwave Blanching Physical Characterization of Samples
Methods:
Conventional Blanching Sample Preparation:
Potatoes selected, peeled, washed, sliced & diced into around:
(1cm 3), (2cm3), (3cm3)
Each sample size is done in triplicates, ie for each test
3 x (1cm3) 3 x (2cm 3) 3 x (3cm3)
Soak samples in iced water & covered with cloth to prevent air exposure
The following determined:
Weight (to determine weight loss)
Texture/Hardness
Colour
*** Following Pre Microwave Blanching Physical Characterization of Potatoes, the
samples were placed back into iced water and covered with cloth to prevent air exposure
2.3.2 Microwave Blanching of Samples using different blanching Times/Power
combinations and post blanching cooling step.
Table 2.4: Microwave blanching, parameters of investigation
Samples x 3 Time Power (Watt)
1cm3, 2 cm3, 3cm3 30 secs 600W, 800W
1cm3, 2 cm3, 3cm3 1 mins 600W, 800W
1cm3, 2 cm3, 3cm3 2 mins 600W, 800W
1cm3, 2 cm3, 3cm3 3 mins 600W, 800W
1cm3, 2 cm3, 3cm3 4 mins 600W, 800W
1cm3, 2 cm3, 3cm3 5 mins 600W, 800W
1cm3, 2 cm3, 3cm3 6 mins 600W, 800W
1cm3, 2 cm3, 3cm3 7 mins 600W, 800W
1cm3, 2 cm3, 3cm3 8 mins 600W, 800W
1cm3, 2 cm3, 3cm3 9 mins 600W, 800W
1cm3, 2 cm3, 3cm3 10 mins 600W, 800W
31
Materials & Equipment:
Bosch Gourmet HFT879 HME9751GB Combination Oven & Microwave
Plastic microwavable container & lid.
Thermometer
Ice
Basins
Timer
Method:
1. Microwavable plastic container is filled way is (enough to submerge the samples)
with room temperature water
2. Samples 3 x (1cm2), 3 x (2cm2), 3 x (3cm2) are removed from iced water and placed
into plastic container, before being placed into the Bosch Gourmet HFT879
HME9751GB for scheduled times. Ensure lid is only placed on container before heat
treatment starts.
3. Accurately record the blanching time using the timer on microwave for accurate results.
ie. first blanch is carried out at 600W for 30 seconds.
last blanch is carried out at 800W for 10 minutes.
4. The sample sizes and quantities remain the same on each blanch.
Figure 2.6: Microwave blanching
5. On blanching completion remove lid and retrieve samples. Quickly place into fresh iced
water one again prior to enzyme testing.
32
2.3.3 Post Microwave Blanching Physical Characterization of Samples
Method:
In the same manner as the pre characterization of samples, the following determined:
Weight (weight loss),
Texture/Hardness (quality),
Colour (quality)
These tests should be carried out as quickly as possible to reduce air exposure to samples
Place back samples back into iced water on completion.
2.3.4 Peroxidase Tests on Microwave blanched samples to give indication of
deactivation of peroxidise enzyme and indication of effective blanching end point.
Materials & Equipment:
Pipette filers.
3% Hydrogen Peroxide
1% Guaiacol Solutions
Method:
1. Remove samples from iced water and place on three different sheets of white paper
designated by the sample size and time/temperature combination used.
2. Cut the cubes from each treatment in half and saturate the cut surface with equal volumes
of 3% H2O2 and 1% guaiacol solutions.
3. After three minutes at room temperature note the extent of any colour change in terms of
percentage area of the cut surface.
4. The degree of surface colouring gives an indication of the peroxidase activity in the
sample.
33
2.4 Ascorbic acid analysis blanched samples using end point times shown by peroxidase
test using DCPIP method, to determine Vitamin C loss after each blanching
type/combination (to be carried out in triplicates).
After the peroxidase test has been completed, the most suitable blanching time/temperature
combinations based on quality of the vegetable will be determined. Using these, new samples
can be balanced at each temperature/power for the lengths of time determined by the end points
needed to remove enzyme activity. These new samples are tested for Ascorbic acid, using the
2, 6-dichloroindophenol titrimetric method, which is an Association of Official Analytical
Chemistry method (AOAC Method 967.21, 45.1.14).
The results of the peroxidase test will yield the optimum time/temperature combination in the
case of conventional blanching and the optimum time/power combination in the case of
microwave blanching. These are the samples that will be tested for ascorbic acid along with
control samples which have not undergone any blanching.
For this the two optimum time/temperature and time/power combinations are redone with fresh
potatoes samples.
Materials & Equipment
Test samples & control samples 30g each
250 ml solution of 0.1g of 2,6-Dichlorophenol indophenol
1000ml solution of 0.1g of ascorbic acid dissolved in 3% metaphoric acid solution
(Concentration of standard vitamin C solution- 0.1mg/ml)
Beakers 250ml
Burette 50 ml
Erlenmeyer flasks 125ml
Funnel
Glass rods
Measuring cylinders 100ml,1000ml
Pipettes
Volumetric flasks 250ml, 200ml,50 ml
Analytical balance
34
Method:
Sample Preparation
Weigh and extract by homogenizing test sample in metaphoshoric acid-acetic acid solution
(i.e., 15 g HPO3 and 40 ml of HOAc in 500ml of deionized H20). Filter (and/or centrifuge)
sample extract, and dilute appropriately to a final concentration of 10-100 mg of ascorbic
acid/100 ml.
Standard Preparation
Weigh 50 mg of USP L-ascorbic acid reference standard and dilute to 50 ml with HPO3-HOAc
extracting solution.
Titration
Titrate standard, test samples, and blank with indophenol reagent (prepared by dissolving 50
mg of 2,6-dichlorindophenol sodium salt and 42 mg of NaHCO3 to 200 ml with deionized H20)
to a light but distinctive rose pink endpoint lasting > 5 seconds.
Calculations
Calculations can be carried out to determine the amount of ascorbic acid per 10 g of potato
sample.
Mg of ascorbic acid / g or ml of sample = (XB) x (F/E) x (V/Y)
Where:
X = average ml for the test solution titration
B = average ml for test blank titration
F = mg ascorbic acid equivalents to 1.0ml indophenol standard solution
E = sample weight (g) or volume (ml)
V = volume of initial test solution
Y = volume of test solution titration
Note: The (V/Y) term represents the dilution factor employed. (Nielsen, 2010)
35
Chapter 3
Results
36
3.0 Results
3.1 Peroxidase Tests on blanched samples to give indication of deactivation of
peroxidise enzyme and indication of effective blanching end point.
Figure 3.1: Top samples peroxidase level: 100%, Bottom samples peroxidase level: 0%
Table 3.1: Activity Index Scale
Coloured Score
80 100% 5
60-80% 4
40-60% 3
20-40% 2
0-20% 1
0% 0
37
Table 3.2: Peroxidase activity across Conventional blanching 80oC/100oC, endpoints in yellow
Time/Temp.
Combo.
Peroxidase Level Time/Temp.
Combo.
Peroxidase Level
1cm3 2cm3 1cm3 1cm3 2cm3 3cm3
Raw: 0 min 5 5 5 Raw: 0 min 5 5 5
30 secs @ 80oC 5 5 5 30secs @ 100oC 4 4 4
1 min @ 80oC 5 5 5 1 min @ 100oC 3 3 3
2 min @ 80oC 4 4 4 2 min @ 100oC 2 2 2
3 min @ 80oC 4 4 4 3 min @ 100oC 1 1 1
4 min @ 80oC 3 3 3 4 min @ 100oC 0 0 0
5 min @ 80oC 3 3 3 5 min @ 100oC 0 0 0
6 min @ 80oC 2 2 2 6 min @ 100oC 0 0 0
7 min @ 80oC 2 2 2 7 min @ 100oC 0 0 0
8 min @ 80oC 1 1 1 8 min @ 100oC 0 0 0
9 min @ 80oC 1 1 1 9 min @ 100oC 0 0 0
10 min @ 80oC 0 0 0 10 min @ 100oC 0 0 0
Figure 3.2: Peroxidase activity across Conventional blanching 80oC/100oC, endpoints at 0%
5
4
3
2
1
0 0 0 0 0 0 0
5 5 5
4 4
3 3
2 2
1 1
00
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 1 2 3 4 5 6 7 8 9 10
PER
OX
IDA
SE L
EVEL
(5
-0, 1
00
%-0
%)
TIME (MINTUES)
CONVENTIONAL BLANCHING: PEROXIDASE LEVEL IN SAMPLES @ 80 OC & 100 OC
100*C 80*C Blanching end point.
38
Table 3.3: Peroxidase activity across Microwave blanching 600W/800W, endpoints in yellow
Time/Temp.
Combo.
Peroxidase Level Time/Temp.
Combo.
Peroxidase Level
1cm3 2cm3 1cm3 1cm3 2cm3 1cm3
Raw: 0 min 5 5 5 Raw: 0 min 5 5 5
30secs @ 600W 5 5 5 30secs @ 800W 5 5 5
1 min @ 600W 4 4 4 1 min @ 800W 4 4 4
2 min @ 600W 3 3 3 2 min @ 800W 3 3 3
3 min @ 600W 3 3 3 3 min @ 800W 2 2 2
4 min @ 600W 2 2 2 4 min @ 800W 1 1 1
5 min @ 600W 1 1 1 5 min @ 800W 0 0 0
6 min @ 600W 1 1 1 6 min @ 800W 0 0 0
7 min @ 600W 0 0 0 7 min @ 800W 0 0 0
8 min @ 600W 0 0 0 8 min @ 800W 0 0 0
9 min @ 600W 0 0 0 9 min @ 800W 0 0 0
10 min @ 600W 0 0 0 10 min @ 800W 0 0 0
Figure 3.3: Peroxidase activity across Microwave blanching 600W/800W, endpoints at 0%
0
1
2
3
4
5
0 2 4 6 8 10 12
PER
OX
IDA
SE L
EVEL
(5
-0, 1
00
%-0
%)
TIME (MINUTES)
MICROWAVE BLANCHING: PEROXIDASE LEVEL IN SAMPLES @ 600W & 800W
600W 800W Blanching end point.
39
3.2 Pre and Post Blanching Physical Characterization of Samples
3.2.1 Weight Loss
Refer to Appendix 1 for weight loss data tables.
Figure 3.4: Average sample size weight loss after Conventional blanching @ 80oC and 100oC
Figure 3.5: Average sample size weight loss after Microwave blanching @ 600W and 800W
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 1 2 3 4 5 6 7 8 9 10
We
igh
t lo
ss (
gram
s)
Time (minutes)
Average sample size weight loss after Conventional blanching @ 80oC and 100oC
80*C
100*C
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 1 2 3 4 5 6 7 8 9 10
We
igh
t lo
ss (
gram
s)
Time (minutes)
Average sample size weight loss after Microwave blanching @ 600 and 800 W
800W
600W
40
3.2.2 Texture/Hardness
Table 3.4: Hardness across conventional blanching at 80oC, blanch endpoint shown in yellow
Time/ Temp Combo.
Sample Size: 1cm3 Sample Size: 2cm3 Sample Size: 3cm3
Force (Newtons) Force (Newtons) Force (Newtons)
Raw: 0 min @ 100oC 4,304 N 4,299 N 4,303 N
30 secs @ 80oC 4,300 N 4,294 N 4,296 N
1 min @ 80oC 4,292 N 4,283 N 4,284 N
2 mins @ 80oC 4,279 N 4,271 N 4,274 N
3 mins @ 80oC 4,263 N 4,259 N 4,263 N
4 mins @ 80oC 4,248 N 4,233 N 4,236 N
5 mins @ 80oC 4,219 N 4,209 N 4,214 N
6 mins @ 80oC 4,188 N 4,186 N 4,186 N
7 mins @ 80oC 4,159 N 4,152 N 4,152 N
8 mins @ 80oC 4,128 N 4,129 N 4,129 N
9 mins @ 80oC 4,093 N 4,101 N 4,097 N
10 mins @ 80oC 4,057 N 4,065 N 4,062 N
Figure 3.6: Hardness across conventional blanching at 80oC, 1cm3, 2 cm3, 3cm3 samples
3,900
4,000
4,100
4,200
4,300
4,400
0 0.5 1 2 3 4 5 6 7 8 9 10
Har
dn
ess
(N
ew
ton
s)
Time (minutes)
Sample Texture/Hardness measurement as Conventional blanching is carried out @ 80oC
1cm3 2cm3 3cm
Blanching end point indicated by peroxidase test.
41
Table 3.5: Hardness across conventional blanching @ 100oC, blanch endpoint shown in yellow
Time/ Temp Combo.
Sample Size: 1cm3 Sample Size: 2cm3 Sample Size: 3cm3
Force (Newtons) Force (Newtons) Force (Newtons)
Raw: 0 min @ 100oC 4,302 N 4,294 N 4,306 N
30 secs @ 100oC 4,291 N 4,287 N 4,301 N
1 min @ 100oC 4,266 N 4,278 N 4,284 N
2 mins @ 100oC 4,247 N 4,251 N 4,257 N
3 mins @ 100oC 4,117 N 4,122 N 4,125 N
4 mins @ 100oC 4,075 N 4,079 N 4,089 N
5 mins @ 100oC 4,032 N 4,028 N 4,054 N
6 mins @ 100oC 4,002 N 3,996 N 4,012 N
7 mins @ 100oC 3,975 N 3,968 N 3,984 N
8 mins @ 100oC 3,941 N 3,929 N 3,956 N
9 mins @ 100oC 3,898 N 3,888 N 3,928 N
10 mins @ 100oC 3,857 N 3,849 N 3,894 N
Figure 3.7: Hardness across conventional blanching at 100oC, 1cm3, 2 cm3, 3cm3 samples
3,600
3,700
3,800
3,900
4,000
4,100
4,200
4,300
4,400
0 0.5 1 2 3 4 5 6 7 8 9 10
Har
dn
ess
(N
ew
ton
s)
Time (minutes)
Sample Texture/Hardness measurment as conventional blanching iis carried out @ 100oC
1cm3 2cm3 3cm3
Blanching end point indicated by peroxidase test.
42
Table 3.6: Hardness across microwave blanching at 600W, blanch endpoint shown in yellow
Time/ Power Combo.
Sample Size: 1cm3 Sample Size: 2cm3 Sample Size: 3cm3
Force (Newtons) Force (Newtons) Force (Newtons)
Raw: 0 min @ 100oC 4,302 N 4,304 N 4,297 N
30 secs @ 600W 4,286 N 4,289 N 4,288 N
1 min @ 600W 4,251 N 4,263 N 4,266 N
2 mins @ 600W 4,232 N 4,238 N 4,248 N
3 mins @ 600W 3,995 N 4,004 N 4,023 N
4 mins @ 600W 3,947 N 3,962 N 3,992 N
5 mins @ 600W 3,893 N 3,933 N 3,951 N
6 mins @ 600W 3,861 N 3,887 N 3,928 N
7 mins @ 600W 3,824 N 3,848 N 3,892 N
8 mins @ 600W 3,785 N 3,799 N 3,855 N
9 mins @ 600W 3,748 N 3,752 N 3,817 N
10 mins @ 600W 3,703 N 3,719 N 3,779 N
Figure 3.8: Hardness across microwave blanching at 600W, 1cm3, 2 cm3, 3cm3 samples
3,400
3,600
3,800
4,000
4,200
4,400
0 0.5 1 2 3 4 5 6 7 8 9 10
Har
dn
ess
(N
ew
ton
s)
Time (minutes)
Sample Texture/Hardness measurment as microwave blanching is carried out @ 600W
1cm3 2cm3 3cm
Blanching end point indicated by peroxidase test.
43
Table 3.7: Hardness across microwave blanching at 800W, blanch endpoint shown in yellow
Time/ Power Combo.
Sample Size: 1cm3 Sample Size: 2cm3 Sample Size: 3cm3
Force (Newtons) Force (Newtons) Force (Newtons)
Raw: 0 min @ 100oC 4,298 N 4,295 N 4,300 N
30 secs @ 800W 4,244 N 4,249 N 4,238 N
1 min @ 800W 4,202 N 4,207 N 4,205 N
2 mins @ 800W 4,138 N 4,134 N 4,142 N
3 mins @ 800W 4,076 N 4,072 N 4,088 N
4 mins @ 800W 3,943 N 3,964 N 3,999 N
5 mins @ 800W 3,896 N 3,932 N 3,958 N
6 mins @ 800W 3,865 N 3,889 N 3,924 N
7 mins @ 800W 3,829 N 3,843 N 3,895 N
8 mins @ 800W 3,781 N 3,797 N 3,850 N
9 mins @ 800W 3,746 N 3,751 N 3,819 N
10 mins @ 800W 3,700 N 3,716 N 3,776 N
Figure 3.9: Hardness across microwave blanching at 800W, 1cm3, 2 cm3, 3cm3 samples
3,400
3,600
3,800
4,000
4,200
4,400
0 0.5 1 2 3 4 5 6 7 8 9 10
Har
dn
ess
(N
ew
ton
s)
Time (minutes)
Sample Texture/Hardness decrease as microwave blanching times increase @ 800W
1cm3 2cm3 3cm3
Blanching end point indicated by peroxidase test.
44
3.2.3 Colour
Table 3.8: Luminance scale measurements
L Brightness scale (from 0 - dark to 100 = white)
a Red-Green scale (+a for red; -a for green; the higher the numerical value, the more
intensive the colour impression)
b Yellow-Blue scale (+b for yellow: -b for blue; the higher the numerical value, the more
intensive the colour impression).
Refer to Appendix 2 for colour data tables.
Figure 3.10: Average L*a*b (Colour) measurements as conventional & microwave blanching
times increase.
45
3.3 Ascorbic acid analysis on blanched samples using end point times shown by
peroxidase test using DCPIP method, to determine Vitamin C loss after each
blanching type/combination. (To be carried out in triplicates).
Table 3.9: Ascorbic acid in Control, Conventional 80oC/100oC & Microwave 600W/800W
No. Samples 10 g each Vitamin C/10g Avg. Vit. C/100g
1.
Control Raw
Raw 2.18 mg
22.90 mg 1. Raw 2.32 mg
1. Raw 2.37 mg
2.
Conventional 800C
800C for 10 mins 1.12 mg
10.83 mg 2. 800C for 10 mins 1.05 mg
2. 800C for 10 mins 1.08 mg
3.
Conventional
1000C
1000C for 4 mins 0.83mg
8.33 mg 3. 1000C for 4 mins 0.89mg
3. 1000C for 4 mins 0.78 mg
4.
Microwave 600w
600w for 7 mins 1.92 mg
18.97 mg 4. 600w for 7 mins 1.81 mg
4. 600w for 7 mins 1.96 mg
5.
Microwave 800w
800w for 5 mins 1.43 mg
15.17 mg 5. 800w for 5 mins 1.58 mg
5. 800w for 5 mins 1.54 mg
46
Figure 3.11: Vitamin C in control & conventional 80oC & 100oC samples blanched to endpoint
Figure 3.12: Vitamin C in control & microwave 600W & 800W samples blanched to endpoint
22.9
10.83 8.33
0
5
10
15
20
25
0 20 40 60 80 100
Vit
amin
C c
on
ten
t/1
00
g (m
g)
Temperature (oC)
Vitamin C measurment across conventional blanching at: (0oC for 0 mins), (80oC for 10 mins) & (100oC for 4 mins)
22.9
18.97
15.17
10
12
14
16
18
20
22
24
0 100 200 300 400 500 600 700 800
Vit
amin
C c
on
ten
t/1
00
g (m
g)
Power (Watt)
Vitamin C measurement across microwave blanching at: (0W for 0 mins), (600W for 7 mins) & (800W for 5 mins)
47
Chapter 4
Discussion
48
4.0 Discussion
Quality refers to the characteristics of food that is acceptable to consumers. The
characteristics are made up of external and internal factors. External factors include;
Appearance (size, shape, weight loss, shrinkage, colour, gloss, & consistency), texture and
flavour. Internal factors include; chemical, physical, microbial, enzyme inactivation, and
ascorbic acid retention. Quality is adversely effected by food decay. Blanching deactivates
enzymes (polyphenoloxidase and peroxidase) which are associated with quality deterioration
such as those involved in browning, lipid oxidation and textural damages. In doing this
blanching delays decay (Mathew & Parpia, 1971).
After undergoing blanching, food quality can considerably depend on the
time/temperature/power combination used as well as the size of the food blanched. Under-
blanching will increase the activity of enzymes and is more adverse than if no blanching was
carried out. Over-blanching results in loss of texture, colour, phytochemicals and minerals
(Jaiswal et al., 2012).
This study was carried out to compare conventional hot-water and microwave blanching at
different Time/Temperature/Power combinations on the quality of potatoes. The parameters of
the investigation was 0 10 mins at 80oC & 100oC for conventional and 0 10 mins at 600W
& 800W for microwave blanching. The objects of this study was to answer the following:
Can a quicker, more economic processing time/temperature/power combination be
established between conventional and microwave blanching while maintaining
acceptable quality?
Which method is less damaging to product texture?
To test the efficiency of peroxidase activity testing as an indicator of blanching
completion.
Identify the relationship between blanching effectiveness and the size of the food which
undergoes the process.
Which method of blanching convention or microwave, best retains ascorbic acid?
On completion of each blanching sample, they were tested using the peroxidase test for an
indication of peroxidase level. The level of enzyme activity was measured from 100% to 0%
and scored 5 1 respectively. A result of 0% showed no peroxidase activity and thus the
endpoint of the blanching. The first blanch time/temperature combination at 80oC yielded an
49
endpoint of 10 minutes. The second time/temperature combination at 100oC yielded an
endpoint of 4 minutes. The third time/power combination 600W showed an endpoint of 7
minutes and the final fourth time/power combination showed an endpoint of 5 minutes. Sample
size did not appear to influence the rate of decrease in peroxidase activity. The sample sizes
used were 1cm3, 2cm3, 3cm3. They all decreased in peroxidase activity at the same rate from
100% to 0% at each time/temperature/power combination, i.e. for 4 minutes at 80oC, each
sample size was reduced to 40-60% peroxidase activity. If however larger intervals of size
were used, the relationship between size and decreased rate of enzyme activity in potatoes
during blanching could be investigated.
From this initial data, it could be noted; the most economic option would be microwave
blanching at 600W for 7 minutes as the energy cost of production is almost of half with
microwave compared with conventional (Patricia et al., 2011). For this reason the faster,
slightly less economic microwave alternative (800W for 5 minutes) of the two could be used if
time was a factor and still be a better method over the conventional styles cost wise. However
the quickest method is conventional blanching at 1000C for 4 minutes but the high costs
associated with heating water and the consumption of large volumes of water needed make this
method less economical. Research from the literature review indicated that microwave
blanching is faster than conventional blanching (Ruiz-Ojeda & Peas, 2013). This was not the
case of conventional blanching at 100oC (4 minutes) as it was the fastest, but was the case with
the other time/temperature/power combinations as microwave blanching was faster (600W for
7 minutes, 800W for 5 mins) than conventional blanching at 80oC (10 mins). This analysis
showed a visual change in samples by the peroxidase indicator that was used in alignment with
the scale shown in Table 3.2 to determine peroxidase activity after blanching. This use of the
peroxidase test was successful in showing peroxidase activity and therefore efficiently
indicates peroxidase activity as an indicator of blanching completion.
Further data was collected focusing more on quality of the potatoes after being subjected to the
different times and type of heat treatments. The first of these was a measure of weight loss/
shrinkage. Weight of vegetables is an important factor to both food producers and customers.
Most fresh produce contains from 65 to 95 percent water and potatoes contain around 79
percent water (Vicente et al., 2009). Cooking removes water content of vegetables. It is in the
interest of food producers to use a method of blanching which retains the most weight to
maintain as much value to the vegetables as possible. In this investigation sample size (1cm3,
2cm3, 3cm3) did appear to influence weight loss with relation to blanching times/methods. For
50
example conventional blanching at 80oC for 4 minutes was reduced by 227 N, 215 N, 217 N
for 1cm3, 2cm3, 3cm3 respectively. Blanching time and method of heating also had different
effects on weight loss of the samples. The conventional method at 100oC produced the least
weight loss with respect to blanching end point (quick at 4 minutes). The combination which
produced the second least amount of weight loss
Top Related