7th International Conference of Food

Industry at the Service Tourism. March 31-April 3, 2017, Hurghada, Egypt.

Dr. Adel Gabr Abdel-Razek

Fats and Oils Dept., National Research Centre,

Cairo, Egypt.

adelgabr2@gmail.com

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IntroductionDEEP FRYING

Art and Science

• Egypt’s Fats & Oils Profile

Oils and fats are staple products in the diet

of Egyptian consumers.

• Frying is one of the common and principal methods for food preparation at homes; restaurants and food ingredient factories.

• In this way, oil is not only act as a heat transfer, but also it interacts with proteins and carbohydrates in the food matrix and induces favorable odor and taste.

• Consumption of fried food should be considered as part of an overall balanced diet, and in this context, fried foods should be eaten with moderation.

Originated - Frying foods - Middle East –

two millennia before the birth of Jesus.

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Sautéing Shallow frying Deep frying

• Shallow frying:

• is cooking process in highly heated oil, promoting browning of battered or

non battered foods.

• Deep Fat frying:

• is a cooking process that involves submerging a food in extremely hot oil in

the presence of air at a high temperature of 150°C to 190°C.

• Par-frying:

• is an industrial process, food is partially dehydrated in an industrial fryer

and flash frozen at -20°C and packaged par-fried food stored at -5°C to -

10°C before distribution in freezer trucks

• Frying oil plays a great role in quality of the fried product, acts as a heat

transfer medium and contributes to texture and flavor of fried food.

• Frying oil role in frying

Texture

Fried food flavor

Mouthfeel

Aftertaste

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Deep-frying process –

Product safety and quality

During deep-frying not only desired changes occur, like

crusting of the outer area, cooking processes within the

food and the formation of typical flavor components.

Deep-frying also leads to unwanted changes, which

finally results in the deterioration of the frying oil/fat.

• These changes affect both the quality of the deep-

frying medium (Oil) and the quality of the fried food.

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• In Food

Loss of moisture

Development of dark color, firm texture and fried flavor

• In Oil

Bland flavor at initial frying, later develops fried food flavor in oil

Changes due to chemical reactions

Dark and viscous

• Oil and food both passes through an optimum stage after which quality of oil and

product flavor declines

• Unsaturated fatty acids decreases with increasing number or time of frying

Oil and food both undergo severe changes due to frying, difficult to relate every change

in different frying process, because of the variables of oil, food and process conditions

Understanding new compounds and their dependence on the main variables of the

frying process - Important

CRUST

CORE

Starch degradation

Non

enzymatic

browning

High

temperatures

Frying oil

thermal

degradation

Beneficial

compounds

degradation

Water vaporization

Atmospheric conditions

Frying oil

oxidation

Frying oil

hydrolysis

Moisture

loss

Oil uptake

Key

structural

components

changes

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Changes in Product During DFF

OIL CONTENT IN SELECTED FRIED FOOD

Food Oil content (%)

Potato chips

Corn chips

Tortilla chips

French fries

Frozen pre-fried French fries

Battered products (chicken, fish)

Breaded products (chicken, fish)

Instant noodles

Doughnuts

30 - 40

33 - 38

22 - 26

12 - 15

4 - 7

14 - 17

13 - 20

18 - 21

15 - 24

Fresh oil - Fried food appears bland

Reused oil – Fried flavor

New compounds formed in oils during frying process

Frying is a complex process to understand completely and thoroughly.. 11

Causative agent Change effect New compounds

Moisture Hydrolysis Free fatty acids

Diaclyglycerol

Monoaclyglycerol

Air and Metals Oxidation Oxidized monomers

Oxidized dimers & polymers

Volatile compounds (aldehydes, ketones,

hydrocarbons)

Sterol oxides

High temperature Polymerization Dimers and non-polar polymers

Cyclic monomers

Trans isomers and position isomers

13Physical and Chemical changes of oil during deep fat frying

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“...As significant amount of frying oil is

becoming part of the fried food, oil

quality and stability is of major

concern to consumers...”

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SELECTION OF SUITABLE OIL IS AN IMPORTANT

FACTOR THAT AFFECTS THE QUALITY OF FRIED FOODS.

Product flavor

Product texture

Product appearance

Mouthfeel

Aftertaste

Shelf life of the product

Availability of the oil

Cost

Nutritional requirements

To meet current market desire, frying oil must be

Low in saturated fat

Low in linolenic acid

High oxidative and flavor stability

Non hydrogenated (trans-fat free)

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• Polymers formed affects the quality of frying oil

Accelerate further degradation of oil

Increase oil viscosity

Reduce heat transfer

Induce foaming

Develops undesirable color in fried food

Increase absorption of oil in food

• Stability of oil for frying can be determined by relating to its

inherent stability to oxidation

• Inherent Stability relate to relative reaction rates of unsaturated

fatty acids with oxygen, hence oil with low inherent stability is

less susceptible to oxidation during frying

• Hence frying quality of oil with high unsaturated fatty acids and

free fatty acids is not as good as oil with low unsaturated fatty

acids and free fatty acids

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• Selection of oil is dependent on factors other than their frying

Appearance

Fat retention

Ex. Doughnuts for serving fresh or packaged

• Depending upon the application, solid fats are sometimes blended with refined

vegetable oil (like shortenings).

• Comprehensive oil specification studies are needed to address any performance,

nutritional and labeling issues that may arise

Criterion Specification

Color Light

Flavor Bland

Phosphorus <1mg/kg

Trace metals Fe<0.1mg/kg Cu

<0.02mg/kg

Free fatty acids <0.05%

Peroxide value <1 meq O2/kg

Smoke point >220°C

Linolenic acid <2%

Dimethylpolysiloxane 2mg/kg

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• NO ideal oil or shortening that satisfies each and every frying application

Types of food products

Frying conditions

Further processing

Storage

Expected shelf life

• Any oil that is selected may compromise of at least these three factors

Ideal

Frying Oil?

Nutrition

Functionality

Cost

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• A questionnaire for the appropriate oil chosen for any particular frying process

• Score different oils and fats for the above concerns, and you will have the best oil

selected for your application with the highest score

Area of Concern Factors to be considered

Nutrition Low Saturated FA content?

Level of trans-fats accepted?

Additives acceptable?

Process Frying temperature?

Continuous or discontinuous frying?

Turnover rate?

Oil storage facilities?

Product Type of product?

Fresh or stored?

Shelf life desired?

Sensory attributes?

Commercial Cost?

Packaging type?

Environmental Availability?

Properties Conditions

Free fatty acid < 0.1%

Peroxide value < 4 meq kg-1

Smoke point > 200oC

Polymer compounds < 1%

Lauric acid content (C12:0) < 1%

Linolenic acid content (C18:3) < 2%

Colour Light yellow

Flavour Bland

SPECIFICATIONS OF FRYING OIL

LIMITS OF USED FRYING OIL

Parameter Conditions

Free fatty acid (FFA) 0.5% (Potato chips, Instant noodles)

1% (Pre-fried French fries)

2 to 2.25% (Coated food)

Smoke point Minimum 170 oC

Polar compounds 25 - 27%

Polymer compounds 10 - 16%

Total Polar Compounds

In Egypt the common oils used for

frying are:

• Cottonseed oil ???

Soybean oil

Sunflower oil

Palm olein

One of the usual ways for increasing the oxidative

stability of soft oils (soybean and sunflower) is

blending with other oils that have less unsaturated

compounds and high oxidative stability [Chu & Kung, 1998].

Palm olein is one of the suitable oils for blending

with other sensitive oils.

Heat-stable frying medium

Good oxidative, hydrolytic and flavor stabilities

Better or similar frying stability with other oils/fats

As a blending oil

Abundance supply

Competitive price

WHY IS PALM OLEIN CHOSEN?

FATTY ACID PROFILES OF SELECTED OILS

FA (%) PO POo SBO CSO CNO CO SFO HOSFO

C12:0

C14:0

C16:0

C18:0

C18:1

C18:2

C18:3

Others

SFA

MUFA

PUFA

-

1.0

46.0

4.0

37.8

10.0

0.5

0.7

51.0

37.8

10.5

0.4

1.2

40.5

4.1

41.5

11.1

0.4

0.8

46.2

41.5

11.5

-

0.1

11.0

3.6

24.7

53.5

6.4

0.7

14.7

24.7

59.9

0.2

0.8

23.4

2.5

16.6

55.4

0.2

0.9

26.9

16.6

55.6

-

0.1

5.1

2.0

60.2

23.6

6.2

2.8

7.2

60.2

29.8

-

0.1

11.0

2.0

27.0

58.5

0.5

0.9

13.1

27.0

59.0

-

0.1

6.8

3.1

36.1

52.8

0.7

0.4

10.0

36.1

53.5

-

-

3.6

2.5

84.3

8.0

0.1

1.5

6.1

84.3

8.1

Stability

(110 oC, h)

27 23 5 5 6 7 5 15

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Check list for deep-frying

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Before deep-frying

• Preheat the deep-frying fat with a max of 60°C for some

minutes before start up.

• Control the oil temperature using an external thermometer

• The deep-frying quantities: the ratio of food to deep-frying oil

or fat should not exceed 1:10.

• Separate deep-fryers should be used for fish, potato

products and finally meat, chicken and vegetables

• Wet food products should be dried

• Frozen food products should be defrosted and dried

• Avoid salt and other spices before deep-frying

• Shake off any crumbs from food products that have been

coated in breadcrumbs

• All fire extinguishers must be check every 2 years for

suitability of use

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During deep-frying

Ideally the temperature should lie between 150°C –175°C,

and preferably not exceed 180°C.

The deep-frying temperature should be continually

controlled using an external thermometer.

Avoid adding salts and other spices to the deep fryer.

All control checks and changing of the deep-frying oils/fats

must be strictly documented

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After deep-frying

The fat should be allowed to drip off while still warm

During long breaks in deep-frying the temperature should be

reduced, during short breaks the deep-frying temperature

should be maintained.

During breaks the deep-fryer should be covered

The deep-frying oil or fat quantities should be supplemented

The deep-frying oil or fat should be filtered to remove any

remaining food rests

The deep-fryer should be thoroughly cleaned

Replace the deep-frying oil or fat before total degradation

occurs

Unused deep-fryers should be emptied and cleaned carefully

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Fat Evaluation

Sensory evaluation (smell and taste): gritty, rancid taste,

smoke development, increased foam formation.

Note! – darkening is not a measure for fat degradation

Quick tests for rough orientation

Laboratory tests – determination of polar components and

polymer triacylglycerols.

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