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Studies on the solubility of purified β-lactoblobulin and α-lactalbumin as a function of temperature, pH and protein concentration indicated that α-lactalbumin aggregated more extensively under certain conditions than β-lactoblobulin and that both the aggregates were totally resolubilized by readjustment of the pH and temperature. The investigation was extended to fresh Cheddar cheese whey, concentrated whey an protein enriched whey under similar conditions to establish the feasibility of separating whey proteins on the basis of differences in solubility. The conditions for maximum precipitation of α-lactalbumin in whey and optimum separation of the proteins were about 65°C in the pH range 4.1 to 4.3 for several minutes. Total depletion of α-lactalbumin was attained by treatment of whey with a protein content increased by a factor of 2 to 5 by ultrafiltration. After this heat treatment, immunoglobulins, bovine serum albumin and some unidentified highly aggregated material coprecipitated with the α-lactalbumin, thus resulting in a supernatant fraction enriched in β-lactoglobulin. The aggregation behaviour of α-lactalbumin under these experimental conditions is discussed with respect to the known denaturation states of the protein and the mechanisms of folding and unfolding. It is suggested that this behaviour of the major whey proteins may form the basis for a process for manufacturing enriched α-lactalbumin and enriched β-lactoglobulin fractions as the separate functional properties may offer advantages over the natural mixture.
Electro-deposited tin-nickel alloy has been tested for corrosion resistance under a wide range of conditions in the laboratory and in the field. It has been found to be superior to pure tin. Under field conditions tin-nickel cleans more readily than pure in and when chlorine-releasing detergent sanitisers are used in more readily cleaned than polished stainless steel. Tin-nickel may be electrically coupled with stainless steel without significant increase in corrosion rate, due to the rapid polarisation of the couple. Because of its stability tin-nickel alloy is suggested for the coating of de-tinned components such as claw pieces, cup nipples, end of milking indicators, milk inlets, strongly made releasers and coolers as a means of eliminating copper contamination of milk by old milking machinery.
Atomic absorption spectroscopy was used to determine the levels of trace metals in samples of market milk and a range of dairy products from 33 Queensland dairy factories. A year-long survey showed that the mean values for homogenized market milk were: cadmium 0.006 ±S.E.0.003 ppm; chromium 0.017 ± 0.0006 ppm; copper 0.233 ± 0.0069 ppm; iron 0.729 ± 0.0251; lead 0.039 ± 0.0014 ppm and zinc 4.878 ± 0.0858 ppm. Results for mercury were all less than 0.002 ppm and those for nickel were all less than 0.01 ppm. In general it was concluded that during the manufacture of various dairy products from milk further trace metal contamination was minimal. No significant geographical differences were found, but significant seasonal differences were found for cadmium, chromium, iron and lead with the highest results being recorded in the winter period.
To improve the quality of commercial dairy ingredients and consumer products, including cheese, fluid milk, milk powders and others, it is important to identify and then control factors that contribute to their degradation. The uncontrolled presence of spoilage bacteria is a common cause of loss of sensory and functional properties in dairy products. With the ultimate goal of developing effective intervention strategies, a DNA sequence-based bacterial subtyping method was developed and applied to characterise and track milk spoilage microbes in dairy systems in New York State and across the United States. The resulting studies have identified the sporeforming bacteria that represent the biological barrier presently limiting further shelf-life extension of high temperature-short time (HTST ) pasteurised milk in the United States. Identification of the targeted spoilage microbes, along with their entry points in milk production and processing systems, will enable development of practical tools for improving the bacterial quality of dairy products.
According to the US Centers for Disease Control and Prevention (CDC), each year about 76 million cases of foodborne illness occur in the United States (Mead et al. 1999). That means that annually, one in four Americans contracts an illness by eating food that has been contaminated with such pathogens as E. coli, Salmonella, hepatitis A, Campylobacter, Shigella, Norovirus and Listeria. Most of those illnesses are relatively minor. But about 325,000 individuals will be hospitalised and 5,000 will die. Billions of dollars will be spent on medical treatment and billions more lost in decreased food sales and, for the families of sick people, wages will be lost (FDA/CFSAN 2004). When careless business practices poison customers, and when regulatory agencies do not have the manpower or ability to help business perform, people die and market share is lost, nationally and internationally.
Authors: Ana I. Pintado, TÃ¢nia G. Tavares, Freni K. Tavaria and F. Xavier Malcata
There is a long tradition of artisanal cheesemaking in Portugal. A number of cheese varieties are indeed manufactured locally from raw ewes’ or goats’ milk (or a mixture of both) at the farmhouse level, which are traded chiefly within their production area. Despite the current dominance of industrial cheeses on the world market obtained from pasteurised cows’ milk, farmhouse ewes’ and goats’ milk cheeses still have an important market niche in that country, and are in increasingly higher demand owing to their organoleptic uniqueness. The most outstanding Appéllation d’Origine Protegée (AOP) cheeses are Azeitão, Castelo Branco, Évora, Nisa, Serpa and Serra da Estrela, for which the milk is clotted with a plant coagulant without deliberate addition of any starter or non-starter culture. The aforementioned coagulant is a crude aqueous extract from the flowers of Cynara cardunculus (cardoon) – a kind of thistle related to the globe artichoke, which can be found in dry, stony areas in Southern Portugal. Its (aspartic) proteinases possess an unusually wide specificity towards cleavage of peptide bonds; their activity spectra account for an extensive primary proteolysis of caseins to medium- and small-sized peptides. On the other hand, the adventitious microflora entail several lactic acid bacteria, e.g. Leuconostoc lactis and L. mesenteroides ssp. dextranicum, Lactobacillus paracasei ssp. paracasei, Lactococcus lactis ssp. lactis and Enterococcus faecium; their contribution to flavour development throughout ripening is crucial, especially owing to secondary proteolysis followed by amino acid catabolism toward small volatile molecules with a very low odour threshold.
Butter from Maleny, Kingston and Gympie Queensland Factories, and from a factory selected at random were sampled at fortnightly intervals during the period mid-July 1967 to mid-October 1968. The trans unsaturation content of the 116 samples of milkfat collected ranged from 4.27 to 7.64% with a mean of 6.01%. Maximum values occurred in the spring-summer period, minimum values in the winter.
A lack of correlation was found between C18 monoethenoic acid content and trans unsaturation for 23 samples for which the C18 monoethenoic acid content was known. It is considered that the level of trans unsaturation in milkfat is influenced by the amount of unsaturated dietary lipids consumed. The lack of correlation between C18 monoethenoic acid content and trans unsaturation was due to the fact that maximum C18 monoethenoic acid values did not occur at the period of time when unsaturated pasture lipids were at their highest levels.
Authors: F. Vosinakos, A. Moumtizis, A. Kesidou, S. Ganatsios, A. Bizopoulos and P. Karakoltsidis
The transfer of artificially added 121I and 137Cs, from cow milk, to cheese curd, cheese whey, mytzithra (a traditional Greek whey cheese) and lactose serum was studied. The contamination was introduced directly to the milk in doses amounting to those Greece received during the Chernobyl's accident. The average values recovered for 121I in cheese curd and cheese whey were 28.9% and 71.1% respectively. The average values for 137Cs were 17.6% and 82.4%. In mytzithra production the amount of radioactivity transferred was 17.1% for 121I and 21.1% for 137Cs with the rest remaining in lactose serum. The results of our work demonstrate that these radioisotopes follow the water phase during processing of contaminated milk. They also show that as the contamination of milk increases the higher proportion of 137Cs and 121I is retained in the cheese curd. The radioactivity does used were up to 6000 Bq/kg.
A method was developed to characterise the transit time of curd in a pilot-scale mozzarella cooker/stretcher before undertaking studies on the influence of thermal treatment on the properties of the cheese during storage at 4°C.
Authors: Lydia Ong, Raymond R. Dagastine, Sandra E. Kentish and Sally L. Gras
Milk processing prior to cheesemaking serves a number of functions, but may also irreversibly change the structure of the milk components. The effect of processing parameters on the microstructure of several milk preparations was assessed using transmission electron microscopy (TEM). Our TEM results confirmed the presence of the native milkfat globule membrane on fat globules within raw milk, within raw milk ultrafiltration retentate and within pasteurised and standardised milk for cheddar cheesemaking. Sodium dodecyl sulphate – polyacrylamide gel electrophoresis confirmed the identity of the native MFGM proteins isolated from the surface of fat globules. In contrast, homogenisation produced the greatest changes in the microstructure of the fat globules, where the native MFGM could not be detected using TEM. The fat globules within homogenised milk had mostly casein present on the fat globule surface. These changes in the microstructure of the milk components may alter the microstructure of downstream products. Our results highlight the potential use of TEM to complement previously reported techniques such as confocal laser scanning microscopy (CLSM) to provide valuable information about membrane integrity and changes associated with milk preparation for cheddar cheese production.
Experiments were conducted to ascertain the minimum treatment necessary for good quality cream. Useful economies in terms of reduced fat losses and steam consumption derived from minimising the degree of deodorizing. A relatively high pasteurizing temperature was found useful in providing better bacterial destruction.
To enable slightly defective rennet casein to be usefully disposed, a limited investigation was made of treatments which might allow preparation of a satisfactory glue from rennet casein. Preliminary tests indicated that phosphoric acid treatment was slow and not very effective. Treatment of the casein with other acids was therefore investigated.
Our understanding of the microbiology of milk and dairy products continues to evolve rapidly. The magnitude of the advances is illustrated well by some of the changes that have taken place since an International Dairy Congress was last held in Melbourne in 1970. Dairy microbiologists were not concerned with Listeria monocytogenes two decades ago, nor had they heard of Escherichia coli 0157. Pathogens were not considered capable of growth in correctly refrigerated dairy products. Ingestion of a large number of cells of Salmonella was believed necessary to cause foodborne illness. As a result of these changes the food industry must deal with a much wider range of microbiological hazards with important consequences for both the day-to-day maintenance of existing processes and the development of new products and processes. We have no reason to believe that this process of change will not continue during the next two decades. Scientific ressearch and the development of new quality management techniques have enabled the industry to respond the new hazards effectively. HACCP is a well established component of the dairy industry's quality management systems, providing improved control of all microbiological hazard. The continuing development of sophisticated laboratory assays for antigens and nucleic acid sequences is providing more rapid, sensitive and reliable methods for detecting pathogens in environmental samples and products.
Authors: Duncan A. Rouch, Peter Roupas and Hubert Roginski
A statistical analysis was performed on results produced by a range of methods used to calculate the value of the protein content of infant formulae that were quoted in a report by the European Commission (2003, Report of the Scientific Committee on Food on the Revision of Essential Requirements of Infant Formulae and Follow-on Formulae). This report recommended that the nitrogen conversion value be reduced from 6.38 to 6.25. It appears that the data presented in the report do not support this recommendation. Nevertheless, the report's data underscore the importance of true protein and Non-Protein Nitrogen analyses of milk products. For Australia to gain the most benefit from true protein analysis, a number of standards will need to be revised.