Post pasteurized milk's quality is tested by:
Ans. is 'a' i.e. Phosphatase test Pasteurization is defined as the heating of milk to such temperatures and for such periods of time as are required to destroy any pathogens that may be present while causing minimal changes in the composition, flavor and nutritive value.The process of pasteurization is named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk. Pasteurization uses temperatures below boiling point since at temperatures above the boiling point for milk, casein micelles will irreversibly aggregate (or "curdle").Pasteurization kills nearly 90 % of the bacteria in milk including the more heat-resistant tubercle bacillus and the Q fever organisms. It does not kill thermoduric bacteria nor the bacterial spores. Therefore, despite pasteurization, with subsequent rise in temperature, the bacteria are bound to multiply. In order to check the growth of microorganisms, pasteurized milk is rapidly cooled to 4 deg C. It is kept cold until it reaches the consumer. Hygenically produced pasteurized milk has a keeping quality of not more than 8 to 12 hours at 18 deg C.Note that unlike sterilization, pasteurization is not intended to kill all pathogenic micro-organisms in the food or liquid. Instead, pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurization product is refrigerated and consumed before its expiration date). Commercial-scale sterilization of food is not common because it adversely affects the taste and quality of the product.Methods of pasteurization:1 )Holder (Vat) method:In this method, milk is kept at 63-66 deg C for at least 30 min. and then quickly cooled to 5 deg C.This method is recommended for small and rural communities.HTST method (High Temperature and Short Time method):In this process, milk is rapidly heated to a temperature of nearly 72 deg C, is held at that temperature for not less than 15 seconds, and is then rapidly cooled to 4 deg C.This is now the most widely used method.UHT method (Ultra-high temperature method)Milk is rapidly heated usually in 2 stages (the second stage usually being under pressure) to 125 deg C for a few seconds only. It is then rapidly cooled and bottled. UHT increases the shelf life of milk.Tests of pasteurized milk: a .Phosphatase test: Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milks, which is used as an indicator of proper milk pasteurization. Complete pasteurization will inactivate the enzyme to below levels which are detectable by conventional methods. Because the heat stability of ALP is greater than that of pathogens which may be present in milk, the enzyme serves as an indicator of product safety.The phosphatase test shows whether milk has been properly pasteurized or it has been contaminated with raw milk after pasteurization.Standard plate count: The bacteriological quality of pasteurized milk is determined by the standard plate count. Most countries in the West enforce a limit of 30,000 bacterial count per ml of pasteurized milk.Coliform count: Coliform organisms are usually completely destroyed by pasteurization, and therefore, their presence in pasteurized milk is an indication of improper pasteurization or post pasteurization contamination. The standard in most countries is that coliform be absent in 1ml of milk.Also Know:Methylene blue reduction testThis test is carried out on the milk accepted for pasteurization.It is an indirect method for detection of microorganisms in milk.The methylene blue reduction test is based on the fact that the color imparted to milk by the addition of a dye such as methylene blue will disappear more or less quickly. The removal of the oxygen from milk and the formation of reducing substances during bacterial metabolism causes the color to disappear. The agencies responsible for the oxygen consumption are the bacteria. Though certain species of bacteria have considerably more influence than others, it is generally assumed that the greater the number of bacteria in milk, the quicker will the oxygen be consumed, and in turn the sooner will the color disappear. Thus, the time of reduction is taken as a measure of the number of organisms in milk. Thus in this test, the milk which remains blue the longest is considered to be of the best quality.
Phosphatase test
Methylene blue test
Catalase test
Oxidase test
Nutrition and Health