Concentration of milk

The concentration of milk protein is controlled by the rate of milk protein synthesis (milk protein yield) in relation to milk yield (milk volume). The... 

Table 5.1 Concentration of milk salt constituents (mg litre 1 milk (from various sources)...

Feed has relatively little effect on the concentration of most elements in milk because the skeleton acts as a reservoir of minerals. The level of citrate in milk decreases on diets very deficient in roughage and results in the Utrecht phenomenon , i.e. milk of very low heat stability. Relatively small changes in the concentrations of milk salts, especially of Ca, Pj and citrate, can have very significant effects on the processing characteristics of milk and hence these can be altered by the level and type of feed, but definitive studies on this are lacking. 

In addition to the general decrease in viscosity with increasing temperature, heating milk can also influence its rheology by heat-induced denatura-tion of cryoglobulins and/or other whey proteins. Concentration of milk, e.g. by ultrafiltration, prior to heating results in a greater increase in f/app than in milk heated before concentration. 

Many different kinds of milk and milk products are available (USDA 1978 NDC 1976,1983A, 1983B). Milk has two major components fat, including fat-soluble vitamins, and milk-solids-not-fat (MSNF), which contain protein, carbohydrate, water-soluble vitamins, and minerals. The specific nutrient contribution of each of these milk products is related largely to the concentrations of milk fat and MSNF of the product. If the percentages of milk fat and MSNF are known, the values in Table 7.2 may be used to determine the nutrient contribution of a particular milk product. 

Tillmans, J. and Obermeier, W. 1920. The hydrogen-ion concentration of milk. Z. Unter-such Nahr u. Genussm 40, 23-34. 

Torssell, H., Sandberg, V. and Thureson, L. E. 1949. Changes in viscosity and conductivity during concentration of milk. Proc. 12th Int. Dairy Congr. 2, 246-258. 

Heat denaturation of protein solutions is normally retarded by concentration. Concentration of milk to total solids levels of 9, 28 and 44% decreases apparent denaturation by 40, 60, and 80% (Whitney 1977). Individual proteins are affected differently by concentration, a-lactal-bumin being denatured more easily as solids are increased and both A and B genetic variants of /3-lactoglobulin being denatured less easily (Hillier et al 1979). 

The ability to accurately determine the onset of oestrus in cattle is of great value in enabling artificial insemination to be carried out efficiently and therefore cost-effectively. One way to monitor the oestrus cycle is by measuring variation in progesterone production and in dairy cows this can be achieved by measuring progesterone levels in their milk. Oestrus onset is indicated by a rapid fall in the concentration of milk progesterone to below 2-5ng/mL [3]. 

The earliest efforts to modify the composition of milk fat used an insoluble formaldehyde-crosslinked protein to encapsulate unsaturated vegetable oils. In numerous studies using this approach, linoleic acid was increased to as high as 35%, w/w, of the total milk fatty acids (reviewed by McDonald and Scott, 1977). Bitman et al. (1973) fed increasing amounts of safflower oil encapsulated in formaldehyde-treated casein. The content of milk fat increased linearly from 3.5 to 4.6% as supplemental protected oil was increased from 0 to 1320 g/day per cow. The concentration of linoleic acid increased to 33% of total milk fatty acids, with a compensating decrease in Ci6 o and a smaller decrease in Ci4 0. The concentration of milk fat decreased to lower than pretreatment levels when the supplement was removed, a common observation (Pan et al., 1972). A typical milk fatty acid profile from cows fed a protected sunflower/soybean (70/30) supplement is shown in Table 2.1. 

Drew, P.G., Maimers, J.G. 1985. Microbiological aspects of reverse osmosis concentration of milk. Aust. J. Dairy Technol. 40, 108-112. 

The feasibility of increasing the a-tocopherol concentration of milk by supplementation of the feed has been investigated in many studies (Dunkley et al., 1966, 1967 King et al., 1966 St. Laurent et al., 1990 Barrefors et al., 1995 Focant et al., 1998 Granelli et al., 1998). These studies showed that when feed was supplemented with varying levels of a-tocopheryl acetate, the a-tocopherol content of the milk was increased with consequent increased resistance to spontaneous and copper-induced oxidation. King et al. (1967) reported that when feed was supplemented to achieve an intake of 1 g a-tocopherol per day per cow, oxidation was effectively controlled in milk... 

Concentration of Milk (w/w, %) (Velez-Ruiz and Barbosa-Canovas, 1998) Storage Time (weeks) /3q fi- 02... 

However, the procedures used in the dairy industry, rennet and acid casein, have the disadvantages to produce large volume of chemical effluents due to the addition of bases and acids during treatments, and to generate inherent risk linked to handling, stocking, and transportation of concentrated bases and acids. In acid casein production, milk pH is decreased to the isoelectric point of the casein by addition of strong acid (hydrochloric, sulfuric, nitric, lactic, etc.). H" " concentration of milk is increased... 

The analysis of human milk for the distribution of iron into the various components found iron in three fractions of lipid, low molecular weight form and lactoferrin (16). The total concentration of milk iron varied from 0.26 to 0.73 mg/ml with 15 to 46% of the iron bound to the lipid fraction, and 18 to 50% found in a low molecular weight fraction. Surprisingly, only a small amount of iron was bound to the lactoferrin, which was saturated at 1-4%. These results even further complicate the role of lactoferrin in iron absorption by infants. Further experimental work needs to be done to define the role of lactoferrin in iron absorption, if any at all. 

Prefiltration for UF. In most cases, MF is too expensive for use as a prefilter. However, there are some feed streams which severely foul UF membranes and where prefiltration with cross-flow MF is cost effective. For example, in the UF of milk or cheese whey fat, casein fines, coagulated protein, and microorganisms all cause severe membrane fouling. In the concentration of milk, the use of tubular MF as a prefilter increased the UF flux by 100% on the average. CFF is required because TFF (through-flow filtration) would plug the MF membrane immediately. 

The evaporation of milk has been known for many years, even as early as 1200 when Marco Polo described the production of a paste-like milk concentrate in Mongolia [6.4.1.1]. Approximately 600 years later the concentration of milk and of other liquid food products, for example extracts such as coffee, was taken-up as an industrial technology, eventually ending in the production of a dry powder. During water removal, pronounced changes in physical structure and appearance take place. Since the process starts with a thin, water-like liquid and ends with a dry powder, it was found that one method of liquid removal is not optimal for all conditions In the food and dairy industry, the methods listed in Tab. 6.4-2 have been adopted for liquid removal. 

The two main types of condensed milk are unsweetened and sweetened. The unsweetened condensed milk contains about twenty per cent of sugar due to concentration of milk constituents. Sweetened condensed, milk contains about forty per cent of sugar, cane sugar having been added. 

Table 23.1. Specific gravily vs, concentration of milk of lime Specific gravity at l.S C g/ml...

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