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In the clarifixation method of homogenization, fat globules are disrupted by cavitation behind fixed teeth in centrifugally flowing cream. The machine clarifies and homogenizes in one operation. The process does not give the extreme degree of homogenization required for instance in sterile milk, but clarifixated milk satisfies the U.S. Public Health Service with respect to cream separation. The process involves comparatively lower power costs and capital investment.
A survey of the Foss Pro-Milk Mk II tester in use in Australia was made to collect and share information about operator experience with this protein-testing apparatus. In addition, a uniform check sample was used to measure the variation between the calibration of fifteen instruments. Results indicated that there were substantial variations between laboratories (SD 0.13 at 3.66% protein level). Differences in milk-to-dye ratios and in methods of estimating protein from Kjeldahl nitrogen explained some but not all of the variations between laboratories. Variations between determinations using the same instrument were negligible.
2162 milk samples from 1956 farms at 20 milk depots and factories in New South Wales, Victoria and South Australia were tested for contamination with sodium hypochlorite. Milk from 120 or 6.1 per cent of the farms gave positive results for hypochlorite by the Wright and Anderson test. Eighty-four or 4.3 per cent were estimated to contain less than 10.0 p.p.m. available chlorine. Twenty p.p.m. available chlorine in milk by two different methods of analysis was taken as presumptive evidence for culpable misuse or deliberate addition of hypochlorite; 15 or 0.7 per cent of the supplies came in this category.
Group N streptococci were found to possess both NAD-dependent and NAD-independent lactate dehydrogenases. The NAD-dependent enzyme, which was specific for the L(+) isomer of lactic acid, was markedly activated by fructose-1,6-diphosphate. Phosphate appeared to inhibit the activation by fructose-1,6-diphosphate. In the complete absence of phosphate or fructose-1,6-diphosphate the enzyme lost activity. The present of NAD-independent enzymes in species of Group N streptococci was variable. These enzymes were not activated by fructose-1,6-diphosphate. Some were specific for the L(+) and others for the D(-) isomers of lactic acid.
Authors: Sofroni Eglezos, Bixing Huang, Gary A. Dykes, Narelle Fegan, Kerry Bell and Ed Stuttard
An investigation of the microbiological quality of frozenunpasteurised goats' milk produced at three south-eastQueensland dairies was carried out. A total of 269 milk sampleswere examined. All samples were analysed for coliforms, 214 foraerobic bacteria, 74 for coagulase-positive Staphylococci andEscherichia coli, 63 for Campylobacter, 55 for Salmonella andListeria, and 34 for staphylococcal enterotoxin and Escherichiacoli O157:H7. No pathogens, toxins or faecal indicators (E. coli),were detected in any sample. A total of 90.2% of samples hadstandard plate counts (SPC) of greater than 2 log cfu/g. For thesamples with counts greater than 2 log cfu/g, the mean was 3.8log cfu/g, and counts at the 90th, 95th and 99th percentiles were4.2, 4.3, and 4.8 log cfu/g, respectively. The maximum numberof bacteria in any sample was 4.9 log cfu/g. Coliform counts weregreater than 1 log cfu/g in 7.4 % of cases. Of these samples,the mean was 1.4 log cfu/g, and counts at the 90th, 95th and99th percentiles were 1.9, 2.0, and 2.1 log cfu/g, respectively.The maximum number of coliforms in any sample was 2.3 logcfu/g. There were differences in mean bacterial counts betweenseasons, with SPC counts significantly higher in winter (p<0.05)and coliform counts significantly higher in summer (p<0.05). Themicrobiological quality of unpasteurised goats' milk as found in thepresent study is generally better than that reported in earlier work.These data can be used for risk assessments aimed at determiningthe safety of unpasteurised goats' milk in Queensland.
The naturally occurring iodide content of composite milks from individual cows was determined in seven herds on the Atherton Tableland in North Queensland. The selected farms did not use iodophors or iodine-containing feed supplements, and were geographically representative of the dairying region. Iodide was determined by a selective-ion electrode procedure. The mean iodide content of milk from 291 cows was 145 μ g/L. Statistical differences in iodide levels between localities and breeds were of no practical importance. The naturally occurring iodide level for the region was well below the legal limit for milk iodine in Queensland.
Authors: Kevin G. Wilkinson, Ron B. Brooks, Clare Balmer, David Halliwell, Laurence Palmowski, Jason G. Issa, S. Jeyaseelan, Barry Meehan and K. Baskaran
This paper reviews the waste management practices of 24 of the major dairy processing factories in Victoria, Australia. The identified total annual costs associated with waste management for the factories was more than AUD$36,760,000, which included the use of more than 11,000 t/year of cleaning-in-place (CIP) alkali and 3,000 t/year CIP acid cleaners at a cost of more than AUD$16,700,000. The total amount of water consumed annually by the factories was more than 10.5 GL, 78% of which was potable water. The recycling and reuse of water was common practice for pre-rinsing, CI P make-up, plant washdown, boiler feed/steam production or membrane washing. The relatively low cost of water and the ease of effluent disposal were found to be disincentives for factories attempting to use less water. The most common biological process for wastewater treatment was aerobic or facultative treatment in ponds or lagoons. Some 10 GL of wastewater was annually discharged in the following approximate proportions: surface-waterway 13%, land 44% and sewer 43%. The corresponding figure for sodium discharge was in the order of 3,400 t/year distributed thus: surface-waterway 8%, land 60% and sewer 32%. For factories providing enough data to conduct a reliable sodium balance (6), total sodium entering as CIP chemicals ranged from 21-64%, while sodium entering as raw material (e.g. milk) and salt varied from 19-67% and 1-57%, respectively. Of the sodium leaving these same factories, 29-64% was in the wastewater. Sodium analyses of many waste streams were not provided. Some waste streams, such as whey, sludges and product rejects, were reused or recycled as stockfeed to piggeries, while some were sent off-site for composting. The main concerns for these wastes were associated with the lack of long-term sustainable options for reuse and recycling.
Sweet buttermilk, skim milk and sweet whey were microfiltered on ceramic membranes to remove the residual fat. Pore diameters of membranes were 1.4, 0.8, 0.5, 0.2 and 0.1 Μm. The results exhibited a size-exclusion mechanism, approximately according to Ferry's law. There was a strong correlation between lipid and protein retentions. The correlation made possible a selective removal of lipids from sweet whey (86%) without a too high retention of protein (29%) using a 0.2 Μm membrane. Buttermilk ans skim milk contained casein and lipid particles with a diameter around 200 nm; therefore, a size-exclusion mechanism was unable to achieve selective separation of lipids. Chemical modification (pH adjustment, calcium and citrate addition) of buttermilk had little effect on lipid retention.
Authors: R. Portolesi, B.C. Powell and R.A. Gibson
Health authorities have recognised the importance of n-3 long chain polyunsaturated fatty acids (LCPUFA) in maintaining health and it is generally accepted that we need to increase our dietary intake of these fatty acids, particularly eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA). Common practice has been to increase our intake of fish, consume fish oil supplements or increase our intake of n-3 enriched foods. These practices rely heavily on a declining global fish supply. Alternative ways to increase our n-3 LCPUFA status are, therefore, imperative. The fatty acids found in dairy fat may provide an alternate source to increase our n-3 LCPUFA status. We examined the accumulation of EPA and DHA in HepG2 cells supplemented with α-linolenic acid (18:3n-3, ALA), EPA and docosapentaenoic acid (22:5n-3, DPA). There was a dosedependent increase in the level of ALA, EPA and DPA in HepG2 cell phospholipids following supplementation with these respective fatty acids. The accumulation of DHA, the long chain n-3 metabolite of fatty acid synthesis, was significantly higher in cells supplemented with EPA and DPA compared to those supplemented with ALA. Dairy fats uniquely contain greater amounts of EPA and DPA than ALA and no DHA. This study suggests that the fatty acids found in dairy fats have the capacity to elevate the level of DHA in cell membranes.
The acidification of milk is an integral step in the manufacture of many processed dairy products such as yogurts, acidified dairy desserts and sour creams. As pH is reduced, the milk develops viscosity. Acidification under quiescent conditions yields a set gel. A range of textures in milk products may be obtained depending on the nature of the acidifying agent, the final pH and the milk ingredients used. Generally, the acidifying agent is added to the milk during the manufacture of the dairy product. However, there are opportunities to provide food manufacturers with acidified powders. An example of this is yogurt powders, where cultured milk is dried. We have examined the use of a chemical acidulant, glucono-ÃÂ´-lactone (GDL), for production of acidified skim milk powders and investigated their functional properties.
A technique is described for investigating the factors responsible for the adhesion of press cloths to rindless cheese. It was found that high temperature of pressing, high moisture and low salt content of the curd increased the extent of adhesion. Treatment of the press cloths in a 2% solution of sodium tetraphosphate was effective in preventing adhesion even at a pressing temperature of 104°F. (40°C)