Methods of Food Evaluation

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

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.