Kaushik Khamrui Dairy Technology DivisionNational Dairy Research

Institute, Karnal

IntroductionSensory evaluation: measurement of a food

product’s quality based on information received from the five senses i.e., sight, smell, taste, touch & hearing.

Signals: transmitted via CNS to brain - integrated with past experiences, expectations, and other conceptual factors - response in summarized.

Four principal quality factors: appearance, flavour, texture & nutrition

First three are ‘sensory acceptability factors’ determined via sensory evaluation (Bourne, 2002)

‘Sensory acceptability factors’ – deciding factor for consumers’ acceptability

1.Proper sensory evaluation laboratory

2.Selection of sensory panel members/evaluators, and

3.Score-card4.Training of the panel

members.

Requirements of Sensory Evaluation

i. Meeting cum Briefing room

ii. Sample preparation roomiii.Testing boothsiv.Office

1. Sensory Evaluation Laboratory

Sensory Evaluation Laboratory

Sensory Evaluation Booths

Sensory Evaluation Booths

Conditions0.9m x 0.6m20-22°C 60-

62% RHFree from

odourAdequate

lightCounter with

opening

The evaluator: availability, interest & motivation. Qualities:Attitude towards foods: should not have strong

liking or disliking towards a dairy productAptitude and knowledge: have ability to

concentrate & unbiased. Should have: basic knowledge on the sensorial attributes .

Health: good health with normal organoleptic sensitivity, free from anosmia and ageusia.

Age: 18-50 years. Other requirements: smoking, chewing pan and

taking intoxicants - at least an hour before the test. Should not use odoriferous substances.

2. Selection of Sensory Panel Members

Sensory card: simple, brief, easy to follow and all important sensorial attributes are included in it.

Clearly printed and the matter should be arranged in logical sequence.

Terminologies used shall be clear and understandable.

Normally 3-5 samples with average intensity of flavour for each sitting are optimum.

The amount of each sample 50-100 ml or gm which is sufficient for one generous sip or bite.

The test should be carried out preferably one hour before or after lunch.

3. Score card, sample numbers and quantity

Evaluators: should like a calibrated instrument and provide reproducible results.

Training: detect, recognize and describe sensory stimuli

Acquainted with: desirable and undesirable attributescorrect terminologyuse of score cardscoring technique, &sequence of observations.

Must start with a large group of people : finally a trained panel comprising of 5-7 members should be retained

4. Training of the panel members

Desirable Sensorial Characteristics of Functional Fermented Dairy Products

Functional dairy products: as similar as possible to that of the original product

Sensory Attributes of Functional DahiColour & Appearance

Cow milk dahi: creamy-white with yellowish tinge

Buffalo milk dahi: creamy-whiteFree from browning & visible foreign matterSmooth & glossy surface w/o any free whey on sides or

topA cream layer on the top is indication of wholesomeness

& purity, hence considered as a desirable attribute

Desirable Characteristics of dahiFlavour

A pleasant, sweetish aroma & a clean acid taste are desirable in dahi

Derived from the overall blend of the delicate diacetyl aroma & clean acid taste of LA

Skimmed milk dahi lacks the natural rich flavour and considered as flat

Should not show any sign of bitterness, raw, yeasty, cheesy, sharp & unclean off-flavours

Desirable Characteristics of dahiBody & Texture

Good quality dahi is a weak gel like junket when made from whole milk

Body: firm, homogenous & free from gas holes/ air bubbles

On cutting it should appear clean/sharpGraininess/lumpiness, ropy, shrunken, thin &

wheying off should be absent in dahi

Desirable Characteristics of dahiAcidity

Range 0.75-0.85 % LA is appropriate for good quality dahi

Excessive acidity imparts too much sourness/sharp/astringent taste to the product

Low acidity is considered as raw/bland dahi

Score Card for Dahi

Score CardAttribute Perfect

Score

Container & closure 5

Flavour 45

Body & Texture 30

Acidity 10

Colour & appearance

10

Total 100

Technique for Sensory Evaluation of dahi1. First look at outside of container - for any smudges,

manufacturing date & batch no. is easy to read and in the proper place.

2. Open the container without disturbing the product, view the top, notice for any possible yeast or mould growth, discolouration, watery liquid exudates.

3. While opening notice the amount of force to peel-off the lid.4. Look the sides for possible indications that the product may

have sunken. 5. Tip the cup upside down on a plate puncture the cup bottom

lift the cup & scrape out of the remainder of any dahi in the cup bottom with the help of a spatula or spoon.

6. Dahi “mound” left on a plate. Notice is made of any unusual aromas.

Technique for Sensory Evaluation of dahi7. After the dahi has been placed on the plate, first notice how

the dahi appears on the plate. The dahi should resemble a thick mass with little no running.

8. Notice the colour. Should resemble from the type of milk from which it is prepared otherwise the product is criticized as “atypical color”.

9. Place a spoonful of Dahi in the mouth & notice how the dahi clings or sticks to the tongue and sides of the mouth.

10.While moving around the dahi inside the dissipate fast, it is perceived to be ‘weak’.

11. If is sticks or sticks to the tongue and sides of the mouth and requires some force to be applied to move around it is perceived to be ‘thick’.

Technique for Sensory Evaluation of dahi12.After noticing the texture the flavour sensations are

perceived and where in the mouth they are observed are recognized.

13.One of the first sensations is acidity of dahi. The sensation is on the sides of tongue. Sensing too high an amount of acid can cause this flavour note to be over-powering.

14.Notice other strong off-flavours also e.g., oxidized, atypical (foreign), old ingredient, unclean and yeasty.

15.Expectorate (split it out) the dahi. After the acid and sweet sensations, the next flavours that are noticed are cooked, too high or low flavouring.

16.Finally, after expectorating some off-flavours that are noticed. These include rancid, bitter, old ingredient, lacks freshness, unnatural flavors, and acetaldehyde.

17.Different penalties are prescribed for different attributes and defects.

Scoring Guide for Functional Fermented Milk ProductsQuality according to the Grade of Dairy Products

Grade Defect & Intensity Approximate Score (% of the Perfect Score)

Excellent A No defect More than 90%Good B Flavour: Flat, slight

cooked/stale/acidic/rancid/insufficient/ salty Consistency/Texture: defects of only slight intensityPackage: Smudgy print but readable

More then 80%But less then 90%

Fair C Flavour: Definite cooked/ flat. Slight rancid/oxidized/metallic/ fishy/ yeasty/mouldy/ acidicConsistency/Texture: Any texture defect of definite intensityPackage: Slightly smudgy print & deformed container

More then 60%But less then 80%

Poor D Flavour: Any flavour defect of the higher intensity as given above for grade C Consistency/Texture: Pronounced defectPackage: Pronounced smudgy print & deformed container

Less then 59%. The products are generally unacceptable at this score

Undesirable Attributes of dahi Flavour related

1.High acidic: Certain amount of acid needed to coagulate the proteins & form coagulum typical to dahi. If acid level too high taste become sharp, harsh & offensive. Caused by:

I. Higher set temperatureII. Slow/insufficient cooling after settingIII. Temperature abuse during distribution/storage

2.Low acid: Dahi should exhibit an acid taste. Consumers can easily detect the ‘low-acid’ taste of dahi. Caused by low culture activity:

I. Residual cleaning/sanitizing compoundII. Antibiotic in the milk supplyIII. Result of bacteriophage attack

3. Lacks freshness: Fresh ingredients should be used in dahi making. Ingredients should be stored at low temperature.

Undesirable Attributes of dahi Flavour related

4. Insufficient flavour: Absence of typical dahi flavour. Caused by low citrate level in milk and destruction of diacetyl. Rapid cooling after setting helps to prevent this defect.

5. Bitter: Offensive aftertaste sensed at the back sensed at the of tasting sequence. Caused by:

i. use of poor quality/old milk contaminated with psychrotrophic or spoilage bacteria

ii. starter culture with proteolytic activity iii. finished product being stored too high a temperature

6. Cooked: a slight amount of cooked flavour is desirable. Gives an aroma like caramelized sugar, butterscotch, egg-like odour to dahi.

Undesirable Attributes of dahi Texture related

1.Wheying off/Syneresis/Free whey: Translucent, greenish- yellow liquid on the surface & around the sides of the cup: Causes:I. Too low pHII. disruption of the coagulum before settingIII. Heat shock of dahiIV. Rough transportation after settingV. Freezing/thawing of dahi

2.Gel like/too firm: has the appearance of a formed gel in the cup, and a very firm set. Using excessive Exo-polysaccharide (EPS) producing cultures.

3.Weak: appears “runny” or liquid like or no residence time in the mouth. Caused by: 1. Insufficient heat treatment 2. Dahi SNF too low

Undesirable Attributes of dahi Texture related

4. Ropiness: placing the bottom of spoon on the top of the dahi mass, lifting the spoon. Trail of rope >2 inch: ropiness. Causes of culture contamination or EPS producing strains.

5. Chalky/powdery texture: caused by too much SMP use in dahi making.