Spoilage of fish: Definition and characteristics

Fish is highly perishable due to high moisture content, availability of the nutrients for the growth of microorganisms and ambient temperature. Fish spoilage results from three basic mechanisms:
*Enzymatic autolysis (reactions caused by the activities of the fish’s own enzymes)
*Oxidation (oxidation of unsaturated lipids)
*Microbial growth (metabolic activities of microorganisms)

One-fourth of the world's fish supply and 30% of landed fish are lost through microbial activity alone.

Fresh fish spoilage can be very rapid after it is caught. The spoilage process (Rigor mortis) will start within 12 h of their catch in the high ambient temperatures of the tropics.

Spoilage of fish can be considered as any change that render the product unacceptable for human consumption. When fish dies, the biochemical changes responsible for anabolism stop. As an inevitable consequence of this process of cessation of anabolism, catabolism starts bringing spoilage to fish flesh. The digestive enzymes still being active, instead of acting on the food present inside the gut, begin to digest tissue components such as lipids, carbohydrates and proteins. This process is called “autolysis”.

One important action determining the onset of spoilage in freshly caught fish is rigor mortis, the stiffening of the body. Usually, this develops within 1-7 hours after death. Rigor mortis sets in and passes quickly in very active fish but slowly in inert fish.

Characteristics of spoiled fish
*The flesh is soft to touch. When the flesh is pressed it leaves a permanent indentation.
*The skin looks dull and has slime on the surface.
*The gills look brownish.
*It gives a bad smell.

With the ever-growing world population and the need to store and transport the food from one place to another where it is needed, food preservation becomes necessary in order to increase its shelf life and maintain its nutritional value, texture and flavour.
Spoilage of fish: Definition and characteristics

Water quality characteristics

Water quality is relative and is defined as the characteristics of a water that influences its suitability for a specific use. Quality is defined in terms of physical, chemical and biological characteristics.

Water quality cannot be monitored without adequate laboratory facilities. Some laboratory work is routinely performed at the water treatment plant.

Normally sophisticated Health Authority’s approved laboratory, be it private or part of the community administration, must be available to the public health engineer and water manager so that physical, chemical, microbiological and radionuclide parameters can be analyzed routinely.

The various chemicals dissolved in the water, as well as the temperature and other physical attributes of water, all combine to form what is called water quality. Water is one of the few materials that is liquid at ambient temperatures; the only others are elemental mercury and some hydrocarbons. This surface tension strongly limits diffusion of gases into and out of the water. Water has a high specific heat, which makes it resistant to change in temperature.

In certain dimension (e.g., visible phenomena such as the extent of algal growth; the clearness of the water and the existence of suds, foam or debris and smells such as hydrogen sulfide from anaerobic conditions), people at large found it easy to perceive changes in water quality.

Water quality characteristics

Taste of spoiled food

To the public, off-tastes and smells in food are probably the least noticeable consequence of microbial spoilage, depending of the perspicacity of the tasters and their familiarity with what the food should normally taste like.

The tastes of spoiled foods range from loss of good characteristic taste to the development of objectionable tastes.

Thus, when a pear or an orange spoil, the sweet characteristics tastes of either is lost, and when milk spoils, it develops an acidic taste, sometimes also bitter. Spoiled food can also make people sick if they eat it.

The feel of spoiled foods reflects the spoilage in different ways, depending on the type of food and the microbe involved in the spoilage, so some spoiled foods feels slimy while others may feel mushy.

Spoiled foods is usually produced by bacteria called pseudomonas and colophons that feast upon poultry, red meats, fish and cheese and thereby impart to these foods the typical off-odor, taste, color and feel with which every homemaker familiar.

In theory, microbial growth and metabolism can influence the flavour and smell of food in one of two ways; ether by removal of flavorsome food components; or by production of off-flavors or off-odors.
Taste of spoiled food 

Foods characteristics suitable for human consumption

The composition and the chemical nature of the food components affect all aspects of food quality. Some of the essential characteristics that individually or in combination, identify and designate materials as foods suitable for human consumption are:
*Harmless
*Edibility (acceptable flavor, ease of chewing and swallowing)
*Nutritiousness
*Ease of digestion and social acceptability
*Palatability or pleasantness draws both on factors related to edibility and on aspects of social acceptability.

Textural characteristics that render a food difficult to control in the mouth are likely to cause it to be rejected. Fish with many small bones, e.g herring, exemplify the problem. On the other hand the texture of cod, in which soft, juicy flakes of flesh come away easily from the cooked fish, is an example of a food for which oral control is easy.

Some of these quality characteristics are covered in food laws and regulations. For instance, failure of a food to meet regulatory requirements relating to a standard of identify, the declared quantity, declared ingredients or label claims, can be considered as misinterpretation, misbranding or fraud.

Unacceptable levels of foreign matter or extraneous materials that are not necessarily harmful to health or do not cause injury can also be considered as failure to meet food quality requirements.
Foods characteristics suitable for human consumption

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

Fruit quality characteristics

Quality of food refers to the composite characteristics which differentiate individual units and enable determination of the degree of acceptability by the consumer.

Quality is fitness for use and to consume. Quality of fruit is to meet the expectations of the consumer.

The overall quality may be broken down into component characteristics such a color, texture, flavor, nutritional value freedom from harmful microorganism and undesirable substances.

Fruit quality is strongly affected by temperature. Temperature directly influences metabolism and indirectly, cellular structure and other components that determine fruit quality such as color, texture, size and organoleptic properties.

The color of the fruit is critical for initial consumer acceptability but is quickly replaced by sweetness and a firm texture upon consumption.

However, there is increasing appreciation that quality of fruits means more than just taste, texture, and appearance.

Nutritional properties of fruit such as vitamins, minerals and perceived health benefits (e.g. antioxidants) are becoming factors in consumer preference.

Fruit quality means different things to different people: for grower, achieving high yield and large fruit: for transporter, long storage potential and continuity of supply.

For consumer, they consider good quality fruits to be those that look good, are firm and offer good flavor and nutritive value.

Consumer acceptability tends to be based on appearance and sensory properties associated with texture and flavor rather than on laboratory measurements such as titratable acidity, dry matter and firmness.
Fruit quality characteristics

Quality Characteristics of Raw Milk

Quality Characteristics of Raw Milk
Good raw milk quality is the basis for the production of high quality dairy products. The raw milk quality is controlled by the following characteristics:

Level of nutrient and reagents

Chemical physical characteristics

Level of total plate count and composition of the flora, e.g. level of spore formers, coliform, psychotrophs and thermosresistant microorganisms in the total plate count as well as level of somatic cells (cell count)

Presence or absence of pathogenic organisms such as those that cause tuberculosis, brucellosis or mastitis

Presence or absence of disease such as pus particles or toxins

Presence or absence of deleterious substances such as inhibitors or other foreign substances

Taste and flavor

Cleanliness of milk

Quality Characteristics of Raw Milk

Raw Materials for the Markets

Raw Materials for the Markets Both conventional breeding and more particularly the promise of direct genetic modification of genotype offer the potential for changing the marketing dynamic of fresh produce, milk and meat.  

Fruit and vegetables marketed to the consumer are still predominantly producer led; what is offered is what can be grown. Quality criteria reflect, not what is desired but the limits within which a product is acceptable or tolerated. 

By using advanced breeding techniques the food industry would want the potential to match a fruit or vegetable to the consumers’ preference and the consumers’ mode of using the product. This would be true of fresh produce for manufacture, too. 

The dream is to be able to specify the ideal quality criteria of a fruit or vegetable and know that a grower is able to match the characteristics accurately and consistently. The desirable characteristics would include flavor, sweetness, texture, nutrient content and durability in storage. No doubt the growers would want to specify such characteristics as yield drought tolerance, insect resistance and ease of harvest. 

Similar scenarios can be imagined for milk and meat. As the market demand for butter fat, casein and whey protein moves, one or other component is in surplus, another is dearth. Although some changes in gross composition have been achieved through conventional breeding and feed regimes, could milk composition be more closely tailored to market demand by a better understanding of feed conversion or by altering the genotype? 

In the livestock market, the demands for the different cuts of meat must be managed. Chickens yield a fairly steady ration of leg to wing to breast meat. However, the market does not necessarily reflect this balance. Beef muscle is selected from different parts of the animal according to the desire for leanness, tenderness and flavor, but the market for hind and fore quarter does not necessarily reflect the fat that for every forequarter there is exactly one hindquarter. Raw Materials for the Markets