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Authors: A.T. Griffin, M.W. Hickey, L.F. Bailey and J.T. Feagan
The effects of preheat and pH adjustment in the manufacture of recombined evaporated milk were examined for their influence on heat stability. The experiments demonstrated that preheating will increase maximum heat stability of the milk where the pH of the milk is lower than the pH of maximum heat stability. Where the pH of the milk is greater than that of maximum heat stability, preheating will tend to reduce the heat stability. Preheating caused a narrowing of the peak on the pH-heat stability curve making pH adjustment of the milk to the maximum heat stability more difficult to attain. Seasonal variation in milk components was also shown to be important. It was found that the combined effect of pH adjustment and manipulation of preheating conditions allowed the production of milk powder which met the Australian heat stability specification for recombined evaporated milk powder.
Solubilities were studied by determining softening points of appropriate mixtures. The systems studied were: (i) milk fat with soyabean, sunflower or cottonseed oils, (ii) fully hardened milk fat with sunflower oil, (iii) milk fat or a hard fraction of milk fat with a soft fraction of milk fat. In the range 0-60% liquid oil or soft fraction, the results fitted the ideal solubility equation, except for system (ii). However, heats of fusion determined using the equation were always higher than corresponding heats of fusion determined by differential scanning calorimetry. It is suggested that the higher heats of fusion are attributable to the more saturated, higher melting triglycerides which are not completely dissolved at the softening point. Deviations from ideal solubility are discussed in terms of molecular weight differences between milk fat and vegetable oil triglycerides, solid solutions and imperfect crystals.
For mixtures of butter oil with liquid vegetable oils, an approximate version of the ideal solubility equation is proposed:
log10 (% weight / 100) = C.?T
where % weight is the percentage of milk fat in the mixture. C is a constant and equals 0.0589 and ?T is the difference in the softening points of the milk fat and the mixture. This equation is independent of either the milk fat or the liquid oil. It may be used (i) to deduce the composition of a mixture from a knowledge only of its softening point and the softening point of the original milk fat, or (ii) to deduce the oil addition required to yield a mixture with a given softening point.
The A.O.M. or Swift times for fats from 508 samples of Australian butter ranged from 10 to 36 hours with 75 per cent in the range of 17 to 24 hours. The average value for Queensland samples was 24 hours compared with the average of 20 hours for other States. A marked seasonal variation was found in Queensland butters, maximum values occurring in summer and minimum values in winter and early spring. Similar but less obvious seasonal trends were found in samples from other States.
Authors: J.G. Zadow, J.F. Hardham, H.R. Kocak and J.J. Mayes
In the initial pH of goat's milk subjected to UHT processing is below about 6.9, rapid and severe sedimentation occurs in the product. This problem may be controlled by either adjustment of the pH of the milk to well above 7.0, or by the addition of 0.2% di-sodium phosphate to the milk before processing. The higher ionic calcium content of goat's milk compared to cow's milk is probably responsible for the greater instability of goat's milk to UHT processing.
Evaporated milk was fortified with vitamin C at high levels, for special requirements of the armed services, by addition of sodium ascorbate. There was a marked increase in the rate of destruction of ascorbate with increasing temperature of storage. Differences in the level of addition between 490 and 930 p.p.m. ascorbic acid did not affect the rate of destruction. There was no visible effect on the physical properties of the milk.
Vitamin A had good stability in sweetened condensed milk for six months at 30°C and 40°C. In one brand of milk, 11 per cent was lost after nine months, but in another brand there was little change in one year.
The exposure of whole milk for 3 hours in plan glass bottles to mercury-vapour lamps resulted in a loss of about 15 per cent of vitamin A. Under comparable conditions, the extent of loss in reconstituted non-fat milk powder fortified with vitamin A ranged from 26 to 51 per cent. The addition, with homogenization, of hydrogenated coconut fat in increasing concentrations progressively reduced the extent of destruction of vitamin A. In reconstituted milk made from fresh non-fat milk and fully hydrogenated coconut fat fortified with vitamin A, tocopherol and lecithin, vitamin A was as stable as in normal milk. Plain glass by filtering out light of short wave-length had some protective effect but with milk in bottles the large exposed surface to volume ratio resulted in much greater destruction of vitamin A than in stainless-steel cans.
The practice of boiling milk in the home, common in many tropical countries, leads to losses of vitamin A which are more serious with reconstituted than with fresh milk. Losses ranged from 2 to 20 per cent after 2 minutes' boiling of milk reconstituted from vitamin A fortified non-fat milk powder, and rose to 30 per cent after 30 minutes heating.
A number of methods used for the staining of animal serum lipo-protein bands obtained on electrophoresis or iso-electric focusing have been evaluated for their applicability to staining lipo-proteins from whey protein concentrates. The commonly used post-staining techniques employed for the visualisation of animal serum lipo-proteins after electrophoresis were not satisfactory, as the stains employed all bound strongly to the major protein fractions in whey. A pre-staining method based on Sudan Black was, however, found to be satisfactory. It was essential to use gels on low total solids content (< 3.5% T) to permit the entry into the gel of the high molecular weight lipo-proteins from whey protein concentrates. To prevent the adsorption of lipo-protein fractions onto the paper wicks normally used in iso-electric focusing, it was essential that samples be applied in slots cast in the gels.
Figures are given for the estimation of calculation of maximum steam loads in butter, cheese, casein, milk treatment and milk powder factories. Steam charts from portable recording steam meter are presented to show the type of load in each factory. A table giving a simple if approximate guide to the boiler requirements of the various types of factories is presented.
The sterol content of milkfat, animal fats, margarines and vegetable oils was determined by gas liquid chromatography of sterol trimethylsilyl ethers after isolation of the sterols in the unsaponifiable fraction by preparative thin layer chromatography.
The cholesterol content of 13 samples of Australian milkfat ranged from 236.9 mg/100 g to 270.6 mg/100 g, average 257.6 mg/100 g. The sterol content of cooking, soft-spread, table, industrial, and polyunsaturated margareines, together with sunflower, safflower, soybean, cottonseed, corn, olive and peanut oils, beef dripping and lard is presented.
Bitterness is commonly found in protein-rich foods such as cheese to which proteolytic enzymes have been added as an aid to manufacture. This paper reviews the structure of bitter peptides and discusses factors important in their formation in dairy products.
Yoghurt bacteria viability is important in providing a number of therapeutic benefits to consumers. The survival of AB-culture (Lactobacillus acidophilus and Bifidobacterium spp.) in traditional commercial yoghurts was reported to be unsatisfactory (Rybka, 1994). Two batches of yoghurt were prepared fermented with: (i) L. acidophilus, Bifidobacterium spp. (mixed B. bifidum and B. longum 10:90) and Streptococcus thermophilus (yoghurt with ABS-culture); (ii) as in (i) plus L. delbrueckii subspp. Bulgaricus (traditional yoghurt with AB-culture). In yoghurts with ABS culture, L. acidophilus, Bifidobacterium spp. and S. thermophilus were; after fermentation: 4.0x107, 9.0x106 and 2.8x109 cfu/mL; after 36 days of refrigerated storage: 107, 4.9x105 and 4.5x108 cfu/mL correspondingly. In traditional yoghurt with AB culture, L. acidophilus, Bifidobacterium spp., L. bulgaricus and S. thermophilus were; after fermenation: 4.0x106, 8.6x106, 1.2x108 and 1.6x109 cfu/mL; after 62 days of refrigerated storage: 1.2 x 106, 1.5x106, <102, 108 cfu/mL respectively. The strain of L. bulgaricus used wasa slow lactic acid producer not sufficiently antagonistic towards AB-culture. ABS-culture counts in a commercial yoghurt did not decrease during 48 hours of freeze drying at -40°C. After 21 days of storage of the freeze dried yoghurt powder only L. acidophilus population met the suggested minimum levels (106 cfu/mL). In freshly prepared experimental yoghurt powders (freeze-dried for 96 hours at -50°C) yoghurt bacteria populations were from 0.25 to 2 log lower than in the fresh liquid product. L. bulgaricus count was reduced from 1.2x108 to 3.0x105 cfu/mL and these species were the most sensitive to freeze-drying. Viable counts of the acidophilus and Bifidobacterium spp. in both commercial and experimental yoghurt powders were less than the suggested minimum levels after27 days of storage. Reincubation of the powder did not increase viable population of yoghurt bacteria.