Chapter 6 :- Evaluation of Food

 (A.) Objectives:-

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 a particular food dictates the quality to be produced. 
3. To indentify 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 info. Regarding food acceptability.
5. To assist in determining the shelf life of a product.
6. To understand how their product performs against competitors products. 
7. To determine whether or not consumers can detect differences between products due to recipe modification.

(B.) Sensory assessment of food quality:-

• When the 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 food by a panel of judges.
• The evaluation deals with measuring, analysing 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 utilised to obtain info. On flavour
• Flavour of a substance is due to the combined senses of taste and a composition sensation known as mouthfeel.

The various attributes to be judged are-

1. APPEARANCE-The surface characteristics of food product contribute to the appearance. Example: the surface of a chocolate is smooth.
2. 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.
3. FLAVOUR-Flavour has 3 components odour, taste and mouthfeel. Mouthfeel consists of texture, consistency and temperature of food.
4. The texture of the food can be smooth or velvety as that of an ice-cream or can be coarse.
5. Astringency- It is the puckering sensation that is felt on the tongue due to precipitation of certain substances on the tongue.

Format of score card:-

(C.) Methods:-

Evaluation of foods involves instrumentation and use of physical and chemical techniques to evaluate food quality.  Food quality has both subjective and non-subjective aspects. Appearance, texture, and flavour are largely subjective attributes, whereas nutritional and bacterial quality is not. Major methods of food evaluation include

• Discrimination tests
• Rating tests
• Sensitivity tests
• Objective Evaluation

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.

Classification of methods of Sensory Evaluation

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Discrimination tests

They are also known as difference tests carried out by small group of trained judges. The judges are asked to describe differences in the samples presented to them in any of the following ways:

1. Triangle test-three samples one different and two identical. Panellist has to identify the odd sample.
2. Duo-trio test- this test also uses three samples, one different two identical. First the panellist is presented with one of the identical sample known as the reference. subsequently the other two are presented in random order. The panellist has to match one of these to reference sample.
3. Paired comparison test-two samples in a pair are presented to the panellist who is asked to indicate if there is any difference between them.

Rating tests

These are quantitative and are very often used for consumer testing. They employ more than two sample and can tell which one is better.

1. Ranking test-the panellists are presented 2-7 samples to rank them in an increasing or decreasing order based on one or more attributes such as flavour, colour or texture.
2. Hedonic rating test-this can measure food acceptability by different groups of consumers eg school canteens, mess. The panellist rate the food on a 9 or 5 point hedonic scale ranging from like extremely to dislike extremely. 
   

   1	2	3	4	5	6	7	8	9
   Dislike extremely	Dislike very much	Dislike moderately	Dislike slightly	Neither like nor dislike	Like slightly	Like moderately	Like very much	Like extremely

   

   For children a facial hedonic scale- the smiley scale is used.
   
   

3. Numerical scoring test- score system is used to evaluate the foods.eg score of 90 may be awarded to excellent quality, whereas a score of 20 may be assigned to the poor quality product.
4. Composite scoring- this rates every quality attribute such as colour, texture and flavour separately and then scores are compounded. Total scores represent overall acceptability of the product.

Scorecard using descriptive ratings:

Sensitivity tests

They assess the ability of individuals to identify and detect different aspects of food quality. They help in training panellists for evaluating specific food products.

1. Threshold test- any food item or water with salt or sugar in increasing concentration.
2. Dilution test- this test is used to detect the presence of unknown substance added in a small amount to a natural food product.

Objective Evaluation

It consists of various physical and chemical tests to measure physical features, such as volume, viscosity, specific gravity and chemical composition such as nutrients present and pH of food.

These tests supplement the data obtained through sensory evaluation.

Test/Instrument	Description	Product
Physical methods
Penetrometer	Measures tenderness	Meat
Compressimeter	Measures Firmness or softness of a cooked product
Shortometer	Determines texture of a baked product	Cookies, pastries
Farinograph	Determines consistency	Dough
Chemical methods
Nutrient analysis	Determines nutrient content in food	Kilocalories, protein, fat etc.
pH- pH meter	Shows degree of acidity or alkalinity of the food

(D.) Introduction to proximate analysis of Food constituents:-

The proximate principles, namely, proteins, fats, and carbohydrates are chemically analysed. The value for fat in a food can be assessed directly by extracting the lipid chemically in ether, which is a fat solvent. Protein value is estimated by measuring the nitrogen content and the factor used is 6.25 for all foods as proteins contain 16 per cent nitrogen. The carbohydrate content given is the difference between 100 and the sum of moisture, protein, fat,crude fibre, and ash content. 

(E.) Rheological aspects of food:-

Rheology is the study of the relation between forces exerted on a material and ensuring deformation as a function of time.

In the food industry, rheology provides a scientific basis for subjective measurements such as mouthfeel, spreadability and pourability.

It is the study of stress and strain or in other words, it is the study of flow and deformation of materials, both solid and liquid under stress and strain condition.

Primarily rheology deals with three aspects-elasticity, plasticity and viscosity.

ELASTICITY  is a property exhibited by solids. It is a characteristic of importance in baked products such as crumb of bread and cake especially when they are fresh. Elastic deformation is reversible. Solid does not flow, however, some solids can be deformed by force and recover when the force is removed. Gels like those of pectin, gelatine and starch are the example of elastic solids. Elasticity can be depicted by spring model, spring clip model and shear pin model.

PLASTICITY-a material that is plastic resists the flow until a force is applied, plastic flow is irreversible. It is exhibited by foods such as cream icing, peanut butter. A plastic food resists changing position until a certain amount of force is applied.

VISCOSITY is a resistance to the flow of a liquid. 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.

Key Terms:-

• Objective Evaluation:- Evaluation of various characteristics of food such as texture, viscosity, and colour by accurate testing devices, often used to supplement sensory evaluation. 
• Organoleptic:- Affecting an organ or the senses; used to evaluate the taste and aroma of a food. Used interchangeably with the term sensory or subjective evaluation. 
• Proximate analysis:- Analysis of protein, fat,and ash content of food, and calculating carbohydrate content by subtracting the value obtained from the total. Carbohydrate value may be corrected for crude fibre. 
• Score card:- Numerical evaluation of various characteristics of food on cards which are specific for each recipe with appropriate descriptive terms for which numerical scores are assigned.