Man has always lost and continues to lose punitive quantities of food due to microbial activity. The sector of foods and beverages that the microbes were first gainfully employed to produce unique and more useful products, e.g., bread, cheese, butter curd and wine etc., even before the existence of microbes became known. Later, pure cultures microbes were isolated and improved for specific applications in processing of foods and beverages. Still later, purified enzymes and immobilized cells began to be used. More recently, microbial biomass production has been developed into an industrial activity to obtain protein-rich food/feed supplements.
Naturally occurring foods like fruits and vegetables contain some microorganisms. All kinds of foods are liable to contamination by microorganism during handling, and they all serve as a medium for microorganism growth, which may cause food spoilage. The foods may contain pathogenic organisms, and some microorganisms contaminating food may produce toxins, if they are allowed to grow in certain food products; these toxins may cause food poisoning. On the other hand, many microorganisms are used to prepare a variety of fermented foods.
The inner tissue of healthy plants and animals are free from microorganisms, but their surfaces are contaminated with a various types of microorganisms. The contaminations are depends on the microbial population of the plants and animals, environment, the condition of the raw product, the method of handling, and period or conditions of storage. It is desirable to maintain a very low level of microbial contamination on raw foods.
The inner tissues of fresh meat from a healthy animal are sterile, while the surfaces carry nominal contamination, the microorganisms being characteristic of the environment and the implement used. Meat held in a refrigerated room in chilled state is likely to retain these features. Considerable precautions must be adopted to prevent unacceptable contamination by the microorganisms during cutting and grinding of meats. The common bacterial contaminants are Pseudomonas, Staphylococci, Enterococci, and Col these microorganisms are psychrophilous nature; it means they grow at very low temperature.
Freshly dressed and eviscerated poultry have bacteria on their skin surface; these come from those present on live birds, and those contributed by the environment, implements and the personnel involved in the processing of the birds. Under good conditions, the bacterial count range from 100 to 1000 bacteria/cm of skin; it may increase 100-fold under less sanitary conditions. The Pseudomonas is the major contaminating microorganism.
|Food item||Microbiological features||Common contaminants|
|Meats (from healthy animals)||1. Minimal surface contamination from
environment., implements, etc.
2. Inner tissues are clean.
3. Cutting adds to contamination.
|Pseudomonas, Staphylococci, Micrococci, Enterococci and Col|
|Eggs||1. Interior of fresh egg is clean.
2. Microorganisms may enter eggs depending on hygiene, humidity, temperature, etc. during storage.
|Those present in the environment.|
|Fruits and vegetables||1. Tissues may be infected by bacteria, fungi and viruses.
2. Infection increases likelihood of spoilage during storage.
3. Bacterial growth is more likely in vegetables than in fruits.
|Bacteria and Fungi.|
|Milk||1. Several hundred to several thousand bacteria per milliliter (count highly variable).
2. Contamination due to bacteria that enter teat canal (main source), those present in the environment, on the equipment, personnel, etc.
|Streptococci, Lactobacilli, Coliforms, Micrococci, etc.|
Fruits and vegetables may be infected by bacteria, fungi and viruses during the various stages of their growth and development; such infections increase the likelihood of spoilage during storage. In addition, post harvest handling may produce breaks in the tissue, which would facilitate invasion by microorganisms. The pH fruit is in the acidic range (e.g., 2.3 for lemons and 5.0 for bananas); therefore, bacterial growth in fruits is restricted, while fungi can grow unrestricted. But the pH range of vegetables is usually between 5.0 and 7.0, which makes them more susceptible to bacterial attacks than the fruits.