Intrinsic factors of food spoilage are those inherent factors that are associated with the food and which in several ways affect the overall physical and chemical composition of the food. Intrinsic factors are food related factors; and they are generally referred to as the physico-chemical properties of food. The composition of a particular food is a significant factor in the spoilage of that particular food or food product. These intrinsic factors of food spoilage include the nutrient makeup of the food, the acidity or alkalinity of the food, water activity, moisture content, buffering capacity and the pH of the food. Some food or food products also contain antimicrobial agents as intrinsic factors; and these antimicrobial constituents and the aforementioned intrinsic factors play several roles in the spoilage of food. It is noteworthy that low pH favours the growth of fungi particularly yeasts and moulds; and foods with high moisture content favour the growth of food spoilage organisms than foods with low moisture content. Production of odours or offensive smell is usually associated with foods with high protein content; and such foods or food products undergo putrefaction.
Putrefaction is the microbial decomposition of organic matter (such as the anaerobic breakdown of proteins) with the production of foul-smelling compounds. Amines and hydrogen sulphide are typical examples of some foul-smelling compounds produced in the microbial degradation or decomposition of food or food products with high protein content. Food or food products with high fat content are usually rendered rancid due to the production of short-chain fatty acids from fats by lipophilic or lipolytic microbes (e.g., bacteria).
Rancidity is defined as a type of food spoilage that occurs in food or food products with high lipid content; and it is mainly characterized by the production of fatty acids as aforementioned. It is worthy of note that foods with high salt and sugar content prevent the growth of some food spoilage organisms. Nevertheless, osmophilic and xerophilic organisms can still grow under high salt and sugar concentration. Osmophilic organisms are organisms that have the ability to grow in environment with very high concentration of solutes such as sugar and salt. They can also be known as osmophiles. Xerophilic organisms or xerophiles are organisms that have the ability to grow in environment with low water activity (aW). Xerophiles thrive very well in food or food products with little or no water activity; and such organisms are responsible for the spoilage of foods with low moisture content. Since microorganisms are ubiquitous and they play critical roles in the processing or production of food, and in the handling and distribution of food and food products; it is important to ensure proper food storage in order to the prevent food spoilage due to microbial activity.
EXTRINSIC FACTORS OF FOOD SPOILAGE
Extrinsic factors of food spoilage are the non-substrate factors that affect the spoilage of foods and food products and which are not innately found in the foods. These factors are the environmental factors that are implicated in food spoilage occurrences. The extrinsic factors are those factors that interact with the microbial activities that normally go on in food or food products. Typical examples of extrinsic factors that affect microbial growth in foods are temperature, relative humidity, gases and the amount or number and type of microorganisms present in the food. The gases in this case include oxygen and carbondioxide which favour the growth of particular microbes. Temperature and humidity are amongst the most critical extrinsic factors that affect microbial growth in foods; and when foods/food products are improperly preserved in terms of the temperature and humidity level they are kept, such food products are likely to undergo spoilage due to microbial activity in them.
When food or food products are stored in conditions of high humidity and low temperature levels, such foods or food products are bound to undergo spoilage due to the intense microbial activity going on in it. Frosted foods or food products (i.e. foods stored in the refrigerator and in a frosted state) can last more than foods stored in defrosted states in the refrigerator. Nevertheless, some psychrotolerant microorganisms (i.e., microorganisms that can withstand low temperatures or cold conditions) can thrive efficiently at a very low temperature as obtainable in the refrigerator (e.g. 3oC). Most perishable fresh foods may undergo thawing and lose their physical storage during storage especially when they are not stored at temperatures below freezing temperature (e.g. –20oC). Storage of perishable foods like meat, vegetables and fruits at –20oC over a long period of time is possible but expensive and thus they are not routinely used for food storage. However, when grains for example are not properly stored, moulds can rapidly grow on them thus causing their spoilage. Claviceps purpura, an ascomycete is a typical example of a fungus that infects grains to cause the disease condition known as ergotism.
Ergotism is the toxic condition or disease that is caused by the consumption of grains infected with ergot or ascomycete. Ergot is the dried sclerotium of C. purpurea. Psychotic delusions, gangrene, abortion, convulsions and nervous spasms are symptoms associated with ergotism in both man and animals. Extrinsic factors play critical roles in food spoilage and thus foods should be properly stored after processing in order to contain and minimize their contamination by microbes that initiate food spoilage.
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