Unit 6 - EVALUATION OF FOOD

Introduction

Quality is a desired attribute for any food product.
Consumer choose food on the basis of its quality and their individual likes and dislikes.
When consumer makes a selection they basically look for food that is attractive in terms of colour, flavour, texture, the nutritional quality and shelf  life.
Keeping quality and cost factor are other criteria which may affect their selection .
Today’s consumers are discerning, demanding and more knowledgeable about food.
Therefore knowing consumer’s preferences of the sensory characteristics of food and beverage products is vital to food manufacturers as well as caterers.
Without appropriate evaluation, there is high risk of market failure.

Objectives of Food Evaluation

The major objectives of evaluation of food are:
(1) To develop new products – the food industry depends on evaluation in developing new products and maintaining quality in existing products.
(2) To observe consumer reactions – how the consumer reacts to particular food dictates the quality of the product.
(3) To identify changes in menus to make food acceptable – catering supervisors in institutional food service depend on evaluation to identify changes in menus to make food acceptable.
(4) To collect information of food acceptability –the studies on plate waste provide valuable information regarding food acceptability.
(5) To assist in determining the shelf life of a product.
(6) To understand how the product competes in the market.
(7) To determine whether or not consumers can detect differences between products due to recipe modification.

QUALITY can be evaluated by
(1)sensory methods i.e. by sensory organs like eyes, nose
and mouth
(2)objective methods i.e. by use of instruments.

Sensory Evaluation of Food

When quality of food is assessed by means of human sensory organs the evaluation is said to be SENSORY OR SUBJECTIVE OR ORGANOLEPTIC EVALUATION.
 The method of judging of food is done by a panel of judges.
The evaluation deals with measuring, analyzing, and interpreting the qualities of food as they are perceived by the senses of sight, taste, touch, etc.
By the senses of sight the size shape and colour of the food and other characteristics like transparency, opaqueness, turbidity, dullness or gloss can be perceived.
Other sensory organs i.e. nose and mouth are utilized to obtain information on flavor.
Flavour of a substance is due to the combined senses of taste and a composition sensation known as mouth feel.

The various attributes to be judged are:
APPEARANCE: - The surface characteristics of food product contribute to the appearance
          Example: surface of a chocolate is smooth.

COLOUR – Colour provides variety to the diet and used as an index of quality for a number of foods
          Example: Ripeness of fruits and the strength of tea and coffee.

FLAVOUR – Flavor has 3 components odour, taste, and mouth feel. Mouth feel consists of texture, consistency and temperature of food.
The texture of the food can be smooth or velvety as that of an ice cream or can be coarse as that of corn flakes.

Classification of Methods of Evaluation

Sensory Evaluation

Sensory evaluation is the evaluation of the sensory properties of food (appearance, flavour, texture)
• It can be carried out by the following steps:
Look at the food and describe the overall appearance
Smell the food and describe its aroma
Cut the food and feel its texture
Chew the food and describe the taste and mouthfeel

Sensory properties of food are
Appearance
Involves the sense of sight
Can be described in terms of colour, size, shape, consistency and crumb
• Example: golden brown, small, round, smooth

Texture
• Involves the senses of sight and touch
• Mouthfeel is the sensation when we bite and chew food
•Different cooking methods produce different textures  Example: soft, chewy, crispy, sticky, grainy, coarse etc.

Flavour
• Flavour is produced by a combination of taste and aroma
• Taste – The taste buds on our tongue enable us to detect the different tastes of food – Example: sweet, spicy, bland, buttery, nutty
• Aroma – Involves the sense of smell – Detected by the nose – Example: fragrant, burnt, floral, fishy, fruity

Conducting Sensory Evaluation

A panel of judges is selected. They should be unbiased for tasting.
Physical, psychological and environmental conditions should be maintained as these affect one’s judgement.
The sampling has to be done homogenously.

Preference Test

Judging should be done in individual booths.
This assures independent judgement and communication between panel members should be allowed except for consultation with the panel leader on any point of doubt.
The best time of day for sensory testing is morning 10.00 am to 12 noon and 3 to 5 pm.
The size of the panel is usually 50 to 100 people to avoid any experimental error.
Judgement should be done quickly, but not hurriedly.
They are valuable in developing new foods and in evaluating quality.
These tests are designed to provide information on selected characteristics and to indicate preference or acceptability of products.

Acceptance Preference Test

In this method, a single sample or two samples may be tested.
It is used to find out whether a product will be used by consumers and this also shows their preference for the sample being tested.
If a new food is introduced, only one sample is offered to the panel, but if a food is modified then two samples are offered and their preference is seen.
The HEDONIC SCALE is most commonly used for evaluation.
In this scale ratings of preference or liking and disliking are measured.
It is generally used with untrained assessors.

HEDONIC SCALE
There is also a Facial Hedonic Scale consisting of 5 to 9 faces depicting varying degrees of pleasure and displeasure , it may be used with young children.

Fact Scale

FACT SCALE – food action rating scale

It is a more sensitive method made up of a nine point food action rating scale.
The codes used clearly indicate the action the panelist would take regarding the food i.e. how often the subject would like to eat the food.
FACT Scale

DIFFERNCE TESTING

These tests are designed to determine whether the difference in two or more food products can be detected.
The result of these tests are more precise and reproducible. Tests in this category are:
(1) Discrimination tests
(2) Descriptive tests
Discrimination tests

Paired comparison test 

Prepare two different samples of the food product you wish to test.
Compare one attribute, e.g. which one is smoother?
 Record the response from the tasters.

Duo-trio test

In this test, three samples are to be tested of which two are control samples and one is variable sample.

One of the control sample is presented first followed by the other two sample, and evaluator is requested to identify which of the two sample is different from the control.
The chances of guessing correctly are 50%.

Triangle Test

Prepare three food samples, two of which are the same.
Arrange the samples in a triangle.
Ask the tasters to decide which of the samples is the odd one out.
Record the responses from the tasters
Two Samples A and B can be presented in two combinations AAB and BBA and for replication in six different- AAB,ABA,BAA,BAB,ABB and BBA.

Dilution test

This test is used to measure the quality of an ingredient which has been substituted.
A standard sample is presented to the judges followed by other samples which may or may not contain the unknown at a definite level of dilution.
Example: use of dried egg powder with fresh eggs. If of good quality the product quality will be difficult to get detected, if poor quality the product will be detected at low concentration or high dilution.

Taste threshold test

This test determines the lowest concentration of a substance that can be detected.
It also indicates the lowest concentration of a substance required to be able to identify it.
The taste threshold of sweet, salty, sour, and bitter tastes can be detected.
Sweet - usually indicates energy rich nutrients.
Umami - the taste of amino acids (e.g. meat broth or aged cheese).
Salty – the taste of common salt.
Sour - typically the taste of acids.
Bitter - allows sensing of diverse natural toxins.
Ranking order

 DESCRIPTIVE TESTS

These tests describe the sensory attributes of food in exact words and the judge / evaluator is asked to select the exact word description from the score card which matches with the sample.
These tests are superior to preference tests which provide information about acceptability of a food sample and discrimination tests which detect deviations between samples.
Accurate descriptions of each characteristic of the sample to be evaluated by the judges is described over a range.
The score cards needs to be carefully designed for descriptive testing.
These are two types of descriptive tests.

 Profiling

In this, a panel of experts sit together and formulate a very detailed word description, generally of flavors which is used as a standard for evaluating further product.

Score cards

In this method food samples are individually evaluated by judges with the help of score cards which have a series of descriptive terms or levels of a characteristic.
Numerical values or scores are assigned to each descriptive term.
FOR EXAMPLE : The juiciness of meat which is a textural characteristic is evaluated on the basic of one of the following terms:

Extremely juicy     - 6
Moderately juicy   - 5
Slightly juicy          - 4
Slightly juicy          - 3
Moderately dry     - 2
Extremely dry        - 1

Score cards

While evaluating the food, the judge should think of the appropriate descriptive adjective and take a decision and not decide on the basis of the score.
It is preferable not to mention the numerical score on the score card which is given to the evaluator.
All score cards should have columns to fill the name of the judge and date of evaluation, and this should be filled in advance.

The following are the point to be kept in mind while preparing score cards.

• Select the different characteristics of a food product which need to be evaluated – example – appearance , colour , flavor , texture.
• Select appropriate descriptive terms pertaining to the characteristics chosen and arrange in sequence.
• Give numerical values to the descriptive terms.
• All products which are to be evaluated should be given a code. Codes could be symbols, colours or randomly selected three digit numbers.
• Score cards should be descriptive.

Score cards

Score cards

Environment for conducting sensory test

• Separate sensory booths should be provided so that judges do not interact with each other except when preparing profiles because judges work together to develop vocabulary needed to describe food samples.
• Controlled air and lighting so that food is correctly visible and booth is free from odours other than the sample . Temperature should be comfortable and non-smoking zone observed.
• Small sinks should be provided for spitting out samples or rinsing ones mouth

Sample preparation and presentation

• Samples should be of identical size.
• They should be in identical shape or from identical portions e.g.  edge of cake from one sample and centre slice from another sample should not be taken.
• It should be served at the customary temperature example. e.g.Soup should be served hot.
• Sample plates should be marked.
• Plates or containers used should be of identical size and colour.
• Necessary cutlery, glass of water should be provided at room temperature.
• Only a limited number of samples should be evaluated at a time to avoid fatigue and for efficient judging.

Members of the Panel

• The judge should neither be too hungry or too well fed.
• Smoking, chewing gum or nibbling snacks 20 minutes prior to the test should not be permitted.
• The judges should be healthy and not suffering from a cold as this will affect their sense of taste and smell.

PROXIMATE ANALYSIS

A method for the quantitative analysis of the different macronutrients in food is the proximate analysis
Proximate Analysis is a partitioning of compounds in a food into categories based on the chemical properties of the compounds. The categories are:
moisture
ash
crude protein
crude lipid
digestible carbohydrates &  crude fibre
Purpose of proximate analysis
Estimation and determination of how much of the major food components, which are Moisture, CHO,
Lipids, Proteins, Ash, Crude Fiber, exist in a given food.
It is important to remember that proximate analysis is not a nutrient analysis, rather it is a partitioning of both nutrients and non-nutrients into categories based on common chemical properties.
Purpose of proximate analysis
Moisture Analyses
Crude Fat Analyses
Crude Protein - (Non-protein nitrogen also included) most proteins contain 16% nitrogen. Therefore the general “protein factor” is 100/16=6.25. If we multiply the percent nitrogen by 6.25, we obtain crude protein.
Ash - residue after burning all organic material. Some minerals become volatile at high temperatures of burning and therefore can be lost. Also some minerals occur in the form of salts of organic acids like citrates which contain carbon and are lost.
CHO and Crude Fiber Total carbohydrate = 100 - [moisture + crude fat + crude protein + ash].
Crude fiber: residue left after alkaline and acid digestion of organic matter. If we subtract the total of 1-5 from 100, we get the digestible carbohydrates.

RHEOLOGICAL ASPECTS OF FOOD

It is the science of measuring forces, which are needed to deform food materials or to study the flow properties of liquid foods. It deals with the viscous behaviour of a system.
Solid food can be chopped up, ground, minced, sliced, torn apart or broken while it is being prepared or eaten, the texture is determined as crisp, tough, chewy, creamy, sticky, spongy etc.
Liquid foods are fluid or viscous. Viscosity is defined as the resistance of a liquid to flow. It is measured by an instrument called viscometer. This property of liquid is seen in batters, sauces and syrups.

REOLOGICAL PROPERTIES OF FOOD

ELASTICITY is the tendency of solid materials to return to their original shape after being deformed. Solid objects will deform when forces are applied on them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. Elasticity is a characteristic of importance in baked products such as cake especially when they are fresh. Elastic deformation is reversible.

PLASTICITY- is the tendency of food items to be moulded into shape while soft, and then set into a rigid or slightly elastic form.

VISCOSITY is resistance of a liquid to flow. It is a measure of the resistance of a fluid to deformation under shear stress. It describes a fluid’s internal resistance to flow and maybe thought of as a measure of fluid friction. Thus water is thin having low viscosity while vegetable oil is thick having a high viscosity.