Milk heat effects

Effect of milk heating on peptide formation during cheese ripening... 

In the case of concentrated UHT milks, physicochemical effects appear to predominate, although proteolysis also occurs, e.g. the propensity of UHT concentrated milk reconstituted from high-heat milk powder to age gelation is less than those from medium- or low-heat powders, although the formation of sediment is greatest in the concentrate prepared from the high-heat powder (see Harwalkar, 1992). 

Tamsma, A., Mucha, T. J. and Pallansch, M. J. 1962. Factors related to flavor stability of foam-dried milk. II. Effect of heating milk prior to drying. J. Dairy Sci. 45, 1435— 1439. 

Heating milk to > 100°C for 15 to 20 min, as in the forewarming of milk for evaporated milk manufacture, effectively denatures and complexes whey proteins with casein micelles and causes simultaneous aggregation and disaggregation of these complexed milk protein aggregates (Morr 1975). 

Experimental Cookery. —Examination of the chemical and physical natures of various food stuffs, e.g., flour, fat, fish, meat, eggs, vegetables, pulses, milk. The effects of heat, and of different methods of cooking on these food stuffs. Study of yeast and its action in bread making. Examination of sugar substitutes. Experiments to attempt the solution of problems encountered in the kitchen. 

Hunt, J.A. and Dalgleish, D.G. (1995) Heat stability of oU-in-water emulsions containing milk proteins effect of ionic strength and pH. /. Food ScL, 60,1120. 

Fig. 10.18. Chemical reactions in heat-treated milk. ( Chemical effect C = 1 losses of approx. 3% thiamine and approx. 0.7% lysine and formation of approx. 0.8 mg/1 HMF) commonly used heat treatments 1 high heat, 2 short time heating, 3 prolonged heating, 4 UHT treatment, 5 boiling, 6 sterilization (according to Kessler, 1983).

In the semidirect process, (Fig. 23) the taw coke oven gas is cooled to condense tar and ammonia Hquor. The heavy layer, tar phase, is pumped to storage and the aqueous layer containing free and fixed ammonia is subsequendy processed in a stiH operation. Free ammonia is that which is in a form which readily dissociates by heat. Fixed ammonia is in a form which requites the presence of an alkaH, such as milk of lime, to effect the ammonia release. 

Patel, H. A., Singh, H., Anema, S. G., and Creamer, L. K. (2006). Effects of heat and high hydrostatic pressure treatments on disulfide bonding interchanges among the proteins in skim milk. /. Agric. Food Chem. 54, 3409-3420. 

There have also been reports [36, 37] that racemization of amino acids occurs more rapidly using MW heating than conventional heating at the same temperature. Chen et al. [36] observed that racemization of amino acids in acetic acid the presence of benzaldehyde was accelerated by MW heating. Lubec et al. [37] reported that some D-proline and ris-4-hydroxy-D-proline were found in samples of infant milk formula when they were heated in a MW oven. On the other hand, conventionally heated samples did not contain these unnatural D-amino acids. This report caused concern, and received media attention because D-proline is neurotoxic and suggested that MW heating of some foods could have deleterious effects on their nutritional value and the health of the consumer. 

In the jet spray dryer, cold feed is introduced(42) into preheated primary air which is blown through a nozzle at velocities up to 400 m/s. Very fine droplets are obtained with residence times of around 0.01 s, and an air temperature of 620 K. This equipment has been used for evaporating milk without adverse effect on flavour and, although operating costs are likely to be high, the system is well suited to the handling of heat-sensitive materials. 

Similar results were obtained in a study of the combined effect of ultrasound (20 kHz) and heat treatment on the survival of two strains of Bacillus subtilis in distilled water, glycerol and milk [17]. When spores, suspended in water or milk, were subjected to ultrasonic waves before heat treatment little or no decrease of the heat resistance was observed. However when heat and ultrasound were applied simultaneously the heat treatment times in milk were reduced by 74% for B. subtilis var, niger-40 and by 63 % for B. subtilis var, ATCC 6051 and similar results were obtained in glycerol. Thermosonication in water was more marked reducing the heat resistance of the spores by up to 99.9 % in the 70 - 95 °C range. The effect of thermosonication was slightly diminished to 75 % as the temperature reached the boiling point of water. 

Heat processes reduce the allergic properties of milk, as temperature and exposure time increase. A similar effect is produced by fermentation carried out by Lactobacillus sp. (Wroblewska and J rychowski, 1994 van Beresteijn et al., 1995). Moreover, the allergenicity of milk may be also reduced by chemical modifications and application of high pressure (Nakamura, 1993 Nakamura et al., 1993). 

Kebary, K.M.K., El-Sonbaty, A.H. and Badawi, R.M. (1999). Effects of heating milk and accelerating ripening of low fat Ras cheese on biogenic amines and free amino acids development, Food Chem., 64, 67. 

No milk can be considered hormone free as natural hormones are always present. The question that has been under heated debate since approximately 1995 is whether the bovine somatotropin hormone (BST) injected into cows to increase milk production results in harmful levels of hormone in milk. The use of BST, which is based upon an economic return rather than any health benefit to the animal, raises two important questions what are the health risks to the human consumer, primarily children and what are the effects on the animals It is fairly well accepted that the use of BST increases the incidence of mastitis and therefore the potential for increased residues of antibiotic and antimicrobials in milk. Because of this Canada, Australia, Japan, the U.K., and other European Union countries decided that the health impact on animals was unacceptable and that BST was not to be used in their jurisdictions. Their decisions were not based upon any human health concerns, but strictly on concerns for animal health. 

It has been suggested that lactoferrin may only confer beneficial immune effects when consumed in the form of breast milk (Lonnerdal, 2003). When added to infant formula, lactoferrin may be affected by its prior bioactivity how it was added (blended or dissolved) and extent of heat treatment of the formula (Lonnerdal, 2003). There is evidence that lactoferrin can be inactivated by invading pathogens or even enhance microbial pathogenicity. For example, the pneumococcal surface protein A of Streptococcus pneumoniae was reported to bind to lactoferrin and protect the bacteria from the killing action of lactoferrin (Ward et ah, 2005). 

---