Some effects of processing and storage on the nutritive value of milk and milk products

Abstract

Milk is an excellent food and its composition makes it an ideal medium for the growth of micro-organisms, including pathogens, which may be present in raw milk, either as a result of infections in the cow or pathogens introduced adventitiously during subsequent handling. T o ensure a safe product of good keeping quality it is necessary to control microbial contamination. This is normally effected by some form of heat-treatment or by the conversion of liquid milk into a dry powder or a moist product, such as cheese or yoghurt, with its own built-in protection against spoilage. Such treatments may impair the nutritive value of milk by causing losses of the more labile constituents, and it is the purpose of this paper to outline recent work concerned with the nature and extent of the losses that occur during the heatprocessing and storage of liquid and dried milks, and during the preparation of some of the new products now being made from milk.Processing of liquid milk Pasteurization of milk, either by the holder process, in which milk is heated to 61-65" for 30 min, or by the high-temperature short-time (HTST) process, in which it is heated to 71-73' for 15 s, gives a product almost unchanged in flavour that will keep for several days if kept cool. For longer-term storage more vigorous sterilization is necessary. In-bottle sterilization, which involves heating bottled, homogenized milk to I I O -I I~O for 20-40 min, imparts a marked cooked flavour due to browning. This older procedure is now rarely used : instead, ultra-high temperaturesterilized (UHT) milk is bottled and resterilized by heating at 110-IIZ' for 15-20 min, a procedure that imparts Iess of a cooked flavour. I n the UHT process milk is sterilized by heating it to 13o-150~ for I s, either by the indirect process, in which the milk passes through a heat exchanger, or by the direct process, in which the milk is mixed with steam, the condensate being removed under reduced pressure (cf. Burton, 1969). UHT processing gives a safe product with less change of colour and flavour than does in-bottle or in-can sterilization; this is because at these high temperatures the rate of destruction of micro-organisms increases faster with increasing temperature than does the rate of browning. When filled aseptically into suitable containers such as Tetra Pak (London) Ltd (Richmond) cartons lined with aluminium foil, the milk can be kept for several months without refrigeration.

Effect of Storage Duration on Physicochemical and Antibacterial Activities of Sweet Corn-based Synbiotic Yogurt with Honey

“…According to Resnawati, lactose is an energy source for the growth of LAB in fermented milk, which in the next process, will act as a producer of acid levels in fermented milk. The longer fermented milk is stored, the energy source, in the form of lactose, will be overhauled by LAB, and there will be an increase in the total acidity of the fermented milk [22].…”

Nutritional, Microbiological, and Sensory Qualities of a Peanut Beverage Prepared Using Various Processes

“…The browning reaction proceeds more rapidly at water activities of 0.3-0.5 than at higher ones, and in the presence of pentoses or hexoses than of disaccharides (Wolf et al, 1982). Dworschak (1980) cites the work of Rolls and Porter (1973) which indicated that UHT (130-150°C for 1 set) heating of milk produced no detectable loss in available lysine or methionine. Conversely, Kisza et al (1967) found methionine in milk to be reduced from 3.26 to 2.64% by pasteurization.…”

Shelf Life of Spray-Dried Milk Formulations Supplemented With N-3 Fatty Acids

“…Initial quality of milk with respect to microbial load and the extent of deterioration before processing can have an adverse effect on the stored products (Ispen and Hansen 1988). Milk foods containing high levels of protein, unsaturated fats and reducing sugars tend to undergo browning reactions, resulting in rancidity of products (Rolls and Porter 1973). Sensory quality of the products decreases mainly as a result of off flavor caused by oxidation of milk fat (Badings and Neeter 1980).…”