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Food bio-deterioration and methods of preservation, It occurs in fatty…
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- It occurs in fatty foods with high levels of unsaturation due to breakdown of fats and oils resulting into production of off
flavour and off odour.
- Lipid oxidation rate and course of reaction is influenced by light, local oxygen concentration, high temperature the presence of catalysts (generally transition metals such as iron and copper) and water activity. Control of these factors can significantly reduce the extent of lipid oxidation in foods.
- This occurs when sugars and amino acids present in the food go through a series of reactions producing a brown colour in the food
- This is referred to as Maillard Reaction
- Highly undesirable when it develops in dried milk during storage
- For examples include syrups, candied fruits, jams and jellies. There is also the oxidation of ascorbic acid on exposure to oxygen that may occur in foods high in this nutrient
- A typical example is an unappealing brown discoloration, which is seen when peeled ripe bananas or sliced apples, pears or some vegetables are exposed to the air.
- Enzymatic spoilage also causes the production of off-odours and off-flavours in foods such as meats and meat products.
- type of spoilage, the enzyme in the food must be inactivated before storage.
- The microorganisms attack virtually all food constituents. Some of them may lead to ferment sugars and hydrolyse starches and cellulose, where as others hydrolyse fats and produce rancidity still others digest proteins and produce putrid and ammonia like odours.
- Some produces acid and make food sour while others produce gas and make food foamy. Some form pigments and a few produce toxins giving rise to food borne illnesses.
- Biodeterioration is defined as the breakdown of food by agents of microbiological origin, either directly or indirectly from products of their metabolism.
- Microbiological sources can be present in foods prior to packing and on surfaces of packaging materials
- Therefore, the shelf life will depend on their types and numbers, in
addition to the hurdles to growth offered by the preservation techniques
- 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
- Enzymes can be used to beneficial effect by the food industry to produce food products
- Microorganisms can play a very important role in breaking down organic material, but it is this very action degrading organic material that food preservation techniques aim to counteract.
- Temperature is the most commonly used method to kill or control the numbers of microorganisms present within foods and on packaging surfaces.
- Bacillus cereus and Camplylobacter. These can be controlled by the use of sterilising solutions
- This critical pH limit is an important determinant as to whether heat-preserved foods receive a pasteurisation or sterilisation treatment
- Sterilisation processes (typically 115–135◦C) using heat have greater cooking effects on product quality than the relatively mild heat treatment of pasteurisation processes (typically 75–105◦C)
- Bacteria are single-celled microorganisms that normally multiply by binary fission, in which each cell divides into two cells following a period of growth
- The simplest method of identifying bacteria is according to their appearance, which approximates to spherical (cocci), rod and spiral shapes.
- lactic acid bacteria for the fermentation of milk to produce yoghurts.
- Lactic acid bacteria can be either bacilli or cocci and are facultatively anaerobic
- Their energy source during growth is the milk sugar lactose, and during fermentation this is converted to lactic acid.
- The result is that the level of acidity increases until a predetermined pH value is reached whereby the yoghurt is ready to be packaged.
- Fungi are a group of microorganisms that are found in nature on plants, animals and human beings.
- The Peni cillium family of moulds produces powerful lipases and proteases (fat- and protein degrading
enzymes) that make them key agents in the ripening of blue cheeses.
- Another fungi, Oospora lactis, which displays char acteristics of both yeasts and moulds, occurs on the surfaces of cultured milk.