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Topic 1: Food Bio-Deterioration And Methods Of Preservation, Enzymes,…
Topic 1: Food Bio-Deterioration And Methods Of Preservation
Bio-Deterioration Agents
The term microorganism includes all small living organisms that are not visible to the naked eye. They are found everywhere in the atmosphere, water, soil, plants and animals.
Enzymes are complex globular proteins found in living organisms, which act as catalysts for speeding up the rate of biochemical reactions. Enzymes are naturally present in foods and can therefore catalyse reactions that lead to food bio-deterioration.
One further category of biodeterioration worthy of mention is that of non-enzymic browning. An important reaction in foods that takes place between the sugar constituents and amine-type compounds results in progressive browning and the development of off-flavours
Bio-Deterioration Reaction
Enzymes
The action of enzymes can be used to beneficial effect by the food industry to produce food products and are, for example, used in the manufacture of cheese, extraction of juice from tomatoes and apples, and beverage clarification.
In potatoes, enzyme inhibitors play an important role in balancing the rate of biochemical reactions in relation to sugar accumulation.
Another problem with fruits and vegetables is enzyme browning, which results from damage or cutting of the surface and exposure to the air.
Other complex reactions can occur, for example, the Rhizopus mould causes softening of canned fruits by producing heat-stable pectolytic enzymes that attack the pectins in the fruit
Microorganisms
Degrading organic material that food preservation techniques aim to counteract.
Psychrophilic (cold loving), in which organisms can reproduce in chilled storage conditions, sometimes as low as 4◦C, although 12–18◦C is the preferred growth range. However, having evolved to survive in extremes of cold, these are the easiest to destroy by heat.
Psychrotrophic (cold tolerant), in which the optimum growth temperature is 20–25◦C but slow growth can be achieved down to 8–10◦C.
Mesophilic (medium range), in which the optimum growth temperature is 30–45◦C. These are of greatest concern with packaged foods because many spore-forming organisms such as yeast and mould species are contained within the mesophile category.
Thermoduric (heat enduring), in which the organisms can survive above 70◦C, but cannot reproduce at these temperatures.
Non-enzymic
Foods in which this type of quality deterioration takes place is dehydrated foods, especially dried potato and vegetables, fruit juices (both dried and concentrated) and wine.
Reducing sugars react with the free amino groups of amino acids to form furfuraldehyde, pyruvaldehyde, acetol, diacetyl, hydroxydiacetyl and other sugar-degradation compounds that in turn react with amines to produce melanoid-type macromolecules (brown pigments
Enzymes
Microorganisms
Non-enzymic