Low of desirable food microorganism as practiced

Low temperature storage of food and it can be achieved Low temperature storage of food is done to prevent the growth of microorganisms, activity of enzymes, and purely chemical reactions. Benefits are• Low temperature can retard chemical reactions as well as the activity of food enzymes• It can also stop the growth/slow down activity of microorganisms• Preservation of food without any adverse effects on the nutritional values and flavour, colour and textural characteristics• Control of the rate of chemical/enzymatic changes in food due to spoilage organism and endogenous enzymes as in aging of beef• Control of the growth & metabolic activity of starter cultures of desirable food microorganism as practiced in cheese ripening & aging of winesFreezing and refrigeration are examples of the oldest methods of preservation Freezing prevents the growth of most foodborne microorganisms and refrigeration temperatures slow down the growth of microorganisms. Refrigeration below 5 °C effectively retards the growth of many foodborne pathogens. The cooling rate is important in controlling the growth of microorganisms. A slow cooling of food allows time to microbial growth. This can occur in a large volume of hot or warm food in a big container. Refrigerated foods have limited shelf life due to microbial growth. In frozen foods, microorganisms will not grow, but there will be survivors after long storage. Rapid thawing is desirable to control microbial growth. The killing rate of microorganisms is rapid at the beginning of freezing. • Refrigeration & freezing are distinguished based on temperature of operation• Refrigeration means storage at temp. above freezing of water in the food (16o C to -2.2 o C)• Refrigerators usually operate 4-7 o C• Pure water freezes at 0o C and most food will not begin until -2.2 o C/still lower temp is reached• Refrigerated/cool storage will preserve perishable/fresh foods for days or weeks depending on the type of foodFreezing/frozen storage refer to storage at temp where the food is maintained in solid frozen condition, generally at -18o C . Frozen storage will preserve foods for month or even yearsFactors Influencing Changes Occurred in Food• Harvest & slaughter• Sanitation• Damage to tissues• Mixture of foods in the storageToo low temperature which <-13o C slow down natural ripening and result in poor ripened colour? Loss in nutrient? Loss of sweetness of sweetcorn and vitamin for vegetable? Loss of crispness and firmness of vegetable and fruits? Loss of flavour? Caking of granular foodFactors of importance in refrigerated storage• Control of low temperature• Relative humidity and air circulation• Composition of atmosphere in the storage chamber• Food variability (to type of food)• Fruits and vegetable will produce heat due to respiration• Amount of heat expressed in term of British thermal unit• Most food store best at refrigerated temp when airFactors that affect freezing 5 factors are importance in the maintenance of the quality of foods in frozen storage? Solute concentration effects? Ice-Crystal Size? Rate of freezing? Final Temp? Intermittent thawingSolute Concentration Effects• Food must be frozen to a solid/nearly so to maintain good quality during frozen storage• A partially unfrozen are will deteriorate with respect to texture, colour, flavour and other properties Rate of FreezingRapid/instantaneous freezing produces ice crystals of small size and also minimizes concentration effects of solutes by decreasing the time of contact between solutes and food tissues and other constituentReferences Erkmen, O. and Bozoglu, T. F. (eds) (2016) Food Preservation by Low Temperatures, in Food Microbiology: Principles into Practice, John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9781119237860.ch29