External quality of food

Food quality is the quality characteristics of food including external factors (such as texture, flavor, origin and appearance: size, shape color) and internal factors (including chemical, physical, microbial).

External quality characteristics, those that can be perceived by the senses of sight and touch without ingesting the product, are important in product differentiation, particularly in purchase decision and food preparation.

For example, the totality of the sensory characteristics (such as appearance, smell, size, shape color, texture, aroma, taste, and mouth feel) of food influences the decision to buy fruit and vegetables to a greater or lesser extent.

There is a good deal of evidence that the sensory characteristics such as taste and aroma have a specific effect on the consumer’s food choice.

In the modern system, the appearance and external quality of the product can be evaluated automatically by machine vision systems. These have video cameras that take images of the units of the product traveling underneath and send them to a computer where they are conveniently analyzed.

Unfortunately, the computer system has some draw backs that make it unsuitable for certain industrial applications. It is inefficient in the case of objects of similar colors, inefficient in the case of complex classification, unable to predict quality attributes and it is inefficient for detecting invisible defects.
External quality of food

Shelf life of a product

The perception of quality of a product also depends on its form-fresh, frozen, canned or dried. Processing of fruits and vegetables extends the season of a perishable crop. Heat preservation (canning) provides a shelf-stable product, but usually at the cost of color, flavor, and texture. 

Better sensory quality is obtained in frozen foods but at a cost if increased energy requirement to maintain them, in a frozen state. Dried fruit products such as raisins and prunes offer very different attributes than their fresh counterparts. The consumer judges canned products with a different set of criteria than frozen or fresh items of the same commodity. 

Fresh fruits and vegetables are perishable, i.e., they have limited shelf life. They are living, respiring tissue that is also senescing and dying. Certain fruits such as bananas and tomatoes will ripen after harvest, developing desirable color, texture, and flavor during handling and storage. All other fruits and vegetables such as oranges, grapes, cucumbers, and carrots will show little or no improvement in quality within the postharvest system. 

Packing and handling systems have been developed to move the product from farm to consumer expeditiously to minimize quality degradation. Techniques used to extend shelf life of fresh products include 

Lowering the temperature to slow respiration and senescence 

Maintaining an optimal relative humidity to slow water loss without accelerating decay 

Adding chemical preservatives to halt physiological and microbial losses 

Maintaining an optimal gaseous environment to slow respiration and senescence

Longer shelf life can also be obtained by selecting cultivars that are more able to withstand the rigors of the handling system and by harvesting a crop at optimal maturity for storage and handling. 

Shelf life of a product