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Milk fat was separated into three fractions, low melting fraction (LMF), middle melting fraction (MMF) and high melting fraction (HMF) by crystallisation from acetone in yields of 70%, 24% and 6% respectively. These fractions, milk fat and fully hardened milk fat were studied by differential scanning calorimetry and X-ray diffractometry to determine their phase behaviour and polymorphism. The melting curve of milk fat showed three peaks which were shown to be related to the three fractions. Both MMF and HMF showed polymorphism. MMF was shown to crystallise at 3-5°C in the α-2. The α form transformed into a mixture of β'-2 and β'-3 forms after 7 days at 30°C and finally stabilised in a single β'-2 form on storage at 30°C in the presence of LMF. HMF also showed α and β'-2 forms. The β'-2 form was very stable and did not change on storage at 40°C for 31 days. It could be transformed to a β form on storage at 40°C only in the presence of LMF. Milk fat showed less marked polymorphism than the individual fractions and easily transformed to, or crystallised as, a mixture of β' and β forms. It was concluded that the phase behaviour and polymorphism of milk fat can be understood as the sum of the phase behaviour and polymorphism of three groups of glycerides which behave approximately as independent solid solutions. Although the solid fat content of milk fat was observed to be dependent on its HMF content, the effect of HMF was no greater than expected for a high melting fat. Addition of a given percentage of HMF raised the solid fat content by the same percentage at 10-15°C and slightly less at 0°C and 30°C. The melting curve of fully hardened milk fat showed clear evidence of polymorphism. After tempering at 40°C a simple, two-peak melting curve was obtained. The fat crystallised as an α form at 3-5°C which transformed to a stable β' + β mixture on tempering at 40°C.
Blends of milk fat with beef tallow were studied by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and X-ray diffraction techniques. Solid fat contents determined by NMR were used to construct isosolid diagrams which indicated eutectic and compound interactions at temperatures below about 20°C. The stable polymorphic form of both milk fat and beef tallow was found to be predominantly B' together with small amounts of B. Mixtures of the two fats developed a B polymorphic form which was related to the compound interaction observed in the isosolid diagram. This B form increased on storage, but was eliminated by interesterification. Beef tallow and blends of beef tallow with milk fat which contained 20% or more beef tallow showed an exothermic transition in the DSC melting curve. This transition was attributed to an a to B' polymorphic change; it could be eliminated by tempering at 25°C. Blends of milk fat with beef tallow stearine and oleine were qualitatively similar to blends with beef tallow.
The effects of some processing variables on the plasticizing of milkfat in a laboratory plant have been studied. Precooling and recycling softened the product but had a slightly adverse effect on appearance. Double working had little effect on any parameter while tempering the product after manufacture was shown to increase firmness, decrease plasticity and improve the appearance.
The fatty acid profile of milkfat fatty acids obtained by gas liquid chromatographic analysis on polar columns showed a component eluting after C18:1 and before C18:2. Isothermal GLC analysis showed this component had an ECL of 19.0. The component was found to be concentrated in the high-melting glyceride fraction of milkfat and was present in the fraction representing trans fatty acids.
On the basis or ECL, co-chromatography and permanganate-periodate oxidation it is included that the component is trans-octadec-16-enoic acid and contributes along with n-non-adecanoic acid to the peak with ECL 19.0
Maintenance of a thrust limited to 1,000-1,200 lbs is necessary in gang presses to achieve close-texture in 40 lb rectangular cheese. Studies with a volumetric load cell showed that serious losses of thrust, resulting in inadequate pressing of the cheese, can arise from frictional losses in the spring heads, from friction in the hoop itself particularly if it is bulged. A gauge to indicate total thrust by the extent of spring compression is described.
With the cessation of long-term contracts with the United Kingdom Ministry of Food and the present search for alternative markets, Australian manufacturers and selling agents of roller dried milks are appreciating that the consistent production of a high quality article carries with it a good deal of bargaining power in the face of competition from overseas. A common and serious defect in quality is the presence in the powder of charred particles. Although there is available a wealth of published data covering the chemical and technological aspects of milk drying by the roller process, the elimination of charred particles has often represented a problem to those engaged in production. It is the aim of this article to set out certain requirements designed to assist in the drying of milk powder free from charred particles.
Frozen concentrated cheese starters were prepared by batch cultivation of starter strains used in Australia. Growth media were made from dilute skim milk containing added lactose and 1% yeast autolyzate; the casein was dissolved with trypsin before sterilizing, or with sodium citrate before harvesting. Best results were obtained with most strains in a medium which contained 3.5% lactose and was neutralized with NH4OH, and when cells were harvested at a lactose concentration of 1%.
The concentrated starters performed satisfactorily in the vat, and the cheese quality was equal to that of cheese made with control bulk starters. In one strain, E8, activity tests on the concentrate were not a reliable guide to acid development in the cheese milk.
Concentrated cheese starters prepared by batch culture methods were examined for their stability on storage at -30°C and -40°C against controls stored at -110°C.
After storage for 3 months the concentrated starters at -30°C showed appreciable losses in viability and activity whilst those at -40°C were similar to the controls in retaining full viability and activity.
The production of acetic, propionic and butyric acids together with proline and diacetyl was studied throughout the ripening period of a Swiss-type cheese. Grading trials indicated that the most desirable flavour was exhibited by cheese having the following composition: acetic acid 38 to 120 mg per 100 g cheese, propionic acid 417 to 555 mg per 100 g, butyric acid less than 5 mg per 100 g, proline 115 to 215 mg per 100 g and diacetyl 11 to 29mg per 100 g.
The levels of the volatile sulphur compounds hydrogen sulphide, carbonyl sulphide, methanethiol and dimethyl sulphide were determined in normal Cheddar cheeses and also in cheeses that had been subjected to accelerated ripening treatments. Hydrogen sulphide and methanethiol levels increased until the cheeses were approximately 6 months of age and then decreased. Carbonyl sulphide levels appear to increase regularly over the ripening period while dimethyl sulphide levels did not vary systematically with the age of the cheeses. Correlation and regression analyses were carried out on the levels of volatile sulphur compounds and flavour assessments. The highest correlation coefficients were obtained for methanethiol but these correlations were considered to be due to the independent increases in both methanethiol levels and flavour with the age of the cheeses. None of the volatile sulphur compounds was considered to be useful as a reliable indicator of flavour development.
The use of Yoghurt as a milk food originated in the Balkan countries. Its production, and even manufacture on an industrial basis, is now widespread throughout the world. It has an attractive mild acid flavour and a fine aroma. Popular attention has recently been directed to Yoghurt by Gayelord Hauser in his book on diet, "Look Younger, Live Longer", a best-seller in the USA in 1950. Hauser, who describes Yoghurt as one of his five wonder foods, states, "It is a must in the Live Longer diet. Among the Bulgarians, where Yoghurt is a part of each meal but where diet is not outstanding in other respects, the life span is longer than that of any other people in the world; Bulgarians are credited with retaining the characteristics of youth to an extremely advanced age. "I recommend Yoghurt, which is definitely not fattening; it tastes much better than milk, remains in the stomach a long time and prevents 'hunger pains'." Hauser goes on to recommend alternative to the quart of milk fortified with skim milk solids to be consumed every day.
The softening point and fatty acid composition of milkfats from two dairy herds supplying market milk were determined at monthly intervals for one year. Throughout the year one herd produced soft milkfat with softening points ranging from 29.7°C to 30.8°C (average 30.4°C), while the other herd produced hard milkfat with softening points ranging from 36.9°C to 39.9°C (average 38.4°C). For each herd there was little variation in fatty acid composition of the milkfat throughout the year. There were, however, significant differences in fatty acid composition between the two herds. The herd producing soft milkfat had higher levels of short and medium chain length fatty acids and lower levels of the C18:0 fatty acid than the herd producing hard milkfat.
The herd producing hard milkfat had a high positive correlation between the content of the C18:0 fatty acid and softening point. The correlation between the C18:0 fatty acid and softening point for the herd producing soft milkfat was not as significant.