Evaluation of food quality
Introduction
Quality is the ultimate criterion of the desirability of any food product. Food quality can be evaluated by sensory and objective methods.
Sensory Evaluation
When the quality of food product is assessed by means of human sensory organs the evaluation is said to be sensory or subjective.
Sensory characteristics of food
Appearance
Surface characteristics of food products contribute to the appearance. Interior appearance can also be evaluated. Perception of the size, shape and colour, transparency can judge by external appearance. Lumps in a pudding or gravy, which are not desirable, can be judged by the eye.
Colour
In addition to giving pleasure, the colour of foods is associated with other attributes. Colour is used as an index to the quality of a number of foods. Ripeness of fruits like banana, mango, tomato, guava can be assessed by the colour.
Flavour
The flavour of food has three components- odour, taste and a composite of sensations known as mouth feel.
i) Odour
The odour of food contributes immeasurably to the pleasure of eating. Aroma is able to penetrate even beyond the visual range when comparatively volatile compounds are abundant in it.
ii) Taste
We value food for its taste. The sensation known as sour is associated with hydrogen ions supplied by acids like vinegar. Salt taste is due to ions of salt. Sweet taste is related to presence of organic compounds.
iii) Mouth feel
Texture and consistency can be found out by mouth feel. Hotness or burning sensation of pepper can also be found out by mouth feel. Mouth feel depends upon temperature, texture, and tenderness of food products.
Reasons for testing food quality
To know the consumer preference
This helps the producer to discover which qualities of the product need to be developed and emphasized. Consumer's preference panel tests the product and the results are considered to represent the taste of the significant portion of the population and are used to predict market outlook for a product.
Effect of variation in processing on quality
Tests are done to investigate the influence of factors in production. The members of the panel are not required to taste the product. It is also used to test the effects of storage and packaging of two items originally alike but subjected to different storage environment.
To detect the presence of off quality
Here the panel members are usually trained to recognise and to evaluate the standard flavours of food so that they can use their powers of discrimination consistently, e.g. rancidity in fats and butter.
Types of tests
Different sensory tests are employed for food evaluation. The tests are grouped into four types.
Difference tests
Rating tests
Sensitivity tests
Descriptive tests
The selection of a particular test method will depend on the defined objective of the test, accuracy desired and personnel available for conducting the evaluation.
Tests used for objective evaluation
Chemical methods
Chemicals are estimated in food spoilage like peroxides in fats. Adulterants in food like presence of starch in milk, metanil yellow in turmeric powder and loss of nutrients during cooking can be estimated.
Physico-chemical methods
Measurement of Hydrogen ion concentration can be found out by the use pH meter.
Sugar concentration can be found by refractometer.
Polariscope is used for quantitative analysis of sugar.
Microscopic examination
Some properties of foods depend on their structure and valuable information can be obtained by microscopic examination. Some examples are give below
Type of organisms present in fermented products like idli batter.
Examination of starch cells under the microscope for identification.
Spoilage of the food can be found out by observing the organisms under the microscope.
Size of crystals in sugar is related to smoothness of the product.
Number and size of the air cells in batters and foams.
Physical methods
Weight
Weight of a food indicates the quality like in case of apple or egg.
Volume
Liquid volumes can be measured by using measuring cups. Solid food volume can be found by displacement method.
Specific volume
The volume may be measured by displacement with solvents like kerosene.
| Specific volume = | bulk volume |
| -------------------- | |
| Wt. of the substance |
Instruments used for texture evaluation
Various instruments are used to measure the texture of liquids, semi solids and solids. Rheology is defined as the science of deformation and flow of matter. It has three aspects elasticity,viscous flow,plastic flow. Rheological properties of foods is important for two reasons.
1.To determine the flow properties of liquid food stuffs.
2.To ascertain the mechanical behavior of solid foods when consumed and during processing.
Instruments used for liquids and semisolids
Measurement of this factor for the raw material or the product at various stages of manufacture serves as an aid in checking or predicting the consistency of the final product. Further, such quality control measurements also serve as indicators. In calculating the amount of an ingredient that should be added in a particular food product.
Percent sag
Stormer viscometer
Brookfield synchrolectric viscometer
Bostwick consistometer
Efflux-Tube Viscometer
Adams Consistometer
Penetrometer
Brabender Farinograph
Instruments used for solids
Food texture can be reduced to measurements of resistance to force.
If we squeeze food so that it remains as one piece this is called compression e.g. bread.
If we apply a force so that one part of the food slides past another it is shearing e.g. chewing gum.
If the force goes through the food so as to divide it well call it cutting e.g. cutting an apple.
If the force is applied away from the material, the food pulls apart by which we measure tensile strength e.g. chapathi.
Magness- Taylor Pressure tester
Succulometer
Tenderometer
Fibrometer
Shortometer
Christal texturometer
Voldokevich bite tenderometer
Kramer shear press
Tensile strength
