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Bulk milk from different areas of Victoria and New South Wales was examined for numbers and types of Bacillus spores. Four categories of organisms were considered, viz. total mesophiles, resistant mesophiles, total thermophiles and resistant thermophiles. The ranges of counts obtained were 40-9,000, <1-160, <20-> 1,800 and <1-50/100 ml., respectively. Pure cultures of spore-forming bacteria were isolated and identified when possible. Of 434 cultures studied, 69 per cent. proved to be B. licheniformis. The results show slight evidence of seasonal variation in numbers but not in types; the survey, however, was carried out over a limited period only.
Authors: F.L. Lehmann, P.S. Russell, L.S. Solomon and K.D. Murphy
Bacteriological aspects of continuous operation of commercial cheesemilk pasteurisers for extended times of up to 21 h were investigated. Total bacterial numbers in pasteurised milk increased slightly over the initial 8-9 h, then more rapidly, sometimes exponentially, over the remaining period of operation, reaching in excess of one million per mL and exceeding total bacterial numbers in the raw milk. The increase in total bacteria per mL of pasteurised milk was not observed in samples from the holding tube but was seen in samples from the cooling sode of the regenerative section, suggesting bacterial growth on plate walls of the regenerative section which seeded the pasteurised milk. Bacterial numbers in pasteurised milk were influenced by raw milk bacterial quality, which was in turn influenced by temperature and flow characteristics of raw milk in pre-pasteurisation balance tanks. A 20 min caustic miniwash of pasteurisers after 10 h continuous operation was shown to reduce bacterial numbers in pasteurised milk and is a recommended procedure to control bacteria buildup in commercial pasteurisers and contamination of pasteurised milk during prolonged operation.
Characteristic flavour of different cheese varieties is the result of a balanced breakdown of milk components including fat, casein, lactose and citrate. Several compounds are present in different varieties; while the proportion between them varies characteristically, only some compounds are exclusive for specific cheeses. The flavours result from activities of a changing microflora during ripening. This review describes the bacterial influence on flavour formation in semi-hard to hard cheese varieties with eyes, and which are made with mesophilic DL-starter. Influence of starter and non-starter lactic acid bacteria is described, as well as of propionic acid bacteria and thermophilic lactobacilli. Potent flavour compounds include amino acids, especially glutamic acid, umami and bitter peptides, ethyl esters of acetic and propionic acid from metabolism of lactose and larger carboxylic acids from fat catabolism, which also contributes to formation of methylketones and secondary alcohols. Diacetyl and acetoin are produced from citrate by DL-starter bacteria but also from aspartic acid by e.g. non-starter bacteria. Several aroma compounds are derived from ranched-chain, aromatic and sulphur amino acids. The total amount of aroma compounds typically increases during ripening, however, the amounts of secondary alcohols for example, may decrease while their corresponding methylketones increase during a long-time ripening. Thermophilic lactobacilli may intensify taste and stimulate metabolism of other bacteria by increasing release of amino acids. Propionic acid bacteria contribute specifically, along with propionic acid and its ethyl esters. Non-starter lactobacilli have been shown to have the potential to increase formation of aroma compounds from amino acid catabolism.
Non-thermal treatments and the use of natural antimicrobial compounds, whether deliberately added (ex situ) or produced in situ by food bacteria, are of considerable interest to the dairy industry. Foodgrade lactic acid bacteria (LAB), the majority of starter cultures applied in the dairy industry, possess an enormous antimicrobial potential. Bacteriocins, which are antibacterial peptides, are produced by all LAB species. Due to their antagonistic activities, bacteriocins can be used as non-thermal means to prevent spoilage, technical defects or safety problems in cheese, and to promote cheese quality. In the present review paper, a state-of-the-art is given of the best-studied bacteriocins that may help to combat undesirable bacteria in dairy applications, i.e. nisins, lacticins, macedocin and a range of non-lantibiotic bacteriocins, in particular enterocins. Although bacteriocins and bacteriocin-producing starter or adjunct cultures are already applied industrially by cheese manufacturers, several drawbacks hinder wider applications.
The results of fifty bacteriological surveys of ten cheese factories over five sampling periods in three years, are reported. The overall average cheese factory hygiene indices were, in general, satisfactory, scoring over 300. The average milk, starter, and curd hygiene indices did not change greatly over the three years. The average water and equipment quality indices improved during the early periods, and remained at the higher level during later periods.
The numbers of samples passing the respective advisory standards for each type of samples are shown and discussed. The suitability of the standards is also discussed.
Cheese made from a particular source of high quality milk developed a characteristic unclean, bitter flavour. Compared to factory cheese the lactobacilli appeared much earlier in maturing and there was an unusually high population of micrococci. In Cheddar cheese made in Victorian commercial factories by the short time process (4Â½ to 4Â¾ hours), it was found that: (a) contrary to observations elsewhere the non-starter population never attained high numbers, reaching between 3 and 36 millions per g. The organisms consisted predominantly of lactobacilli (80 per cent) and micrococci (16 per cent) and did not proliferate until the starter organism population had dropped to low numbers. (b) individual cheeses of similar age and milk source showed considerable variability in the types of micro-organisms present. (c) starter strain influenced the growth of the non-starter flora.
The usual place to look for bacteriophages active on lactic streptococci is in or around a cheese factory. As part of a general study of this group of phages we have attempted to find other locations from which they can be isolated. In view of the fact that phage active on a wide variety of bacteria can be obtained from sewage effluent the isolation of lactic streptococcal bacteriophage was attempted from this source.
Some phages isolated from Cheddar cheese factories multiplied more rapidly on starter cultures in raw milk than in heat treated milk. Phage titres were reduced 102-108 fold depending on the severity of the heat treatment. Three such 'raw milk' phages showed highest multiplication rates at temperatures of about 35°C. These findings have significance for methods of detecting disturbing phage and also for methods of selecting phage-resistant starter cultures.
An organoleptically acceptable banana milk was formulated and manufactured by mixing ripe Cavendish bananas and whole or partially skimmed milk in the ratio of 1:5 by weight, heating to 38°C and single stage homogenising at 2,000 p.s.i. then H.T.S.T. pasteurising at 72°C for 15 seconds.
During preliminary trials, fat content of the milk, homogenisation pressure, banana type ripeness and concentration as well as fresh and preserved purees, were evaluated by a trained panel. Acceptability of banana milk containing additives was also assessed.
The product, when stored at 5°C or 10°C, has a keeping quality of two weeks. Chemical composition, nutritive value and consumer potential of the drink are discussed. When banana milk was made into yoghurt, manufacture was normal and the product was acceptable to tasters.
In many of the older countries, such as Britain and France, beef production is largely a complementary industry as such assumes a great importance. Beef cattle are used (1) to build up fertility on areas which are to be used for cropping or market gardening, and are, meantime, in temporary pasture; (2) to keep grass in order for sheep; (3) to utilise parts of dairy farms which are not required to depasture the dairy herd. They are for the most part "fertility builders" and as such are to greatest value. We have not yet reached the stage in Australia where they fill this major role, although the trend has started and can be expected to gain momentum as farmers become educated to their value.
Authors: B.C. Prasongsidh, K. Kailasapathy, G.R. Skurray and W.L. Bryden
The influence of pH at 4°C on 1 μg/mL of pure cyclopiazonic acid (CPA) was studied for a period of 30 days. Neutral pH affected CPA less than basic and acid environments. The concentration of CPA was reduced by the 30th day to 70% and 64% in pH 4 and 2 respectively. In contrast, yogurt made with artificially contaminated whole milk at 1 μg CPA/mL showed a reduction of more than 70% CPA on the first day of storage. However, more than 12% of the mycotoxin was still detectable in the yogurt on the 21st day of storage. Heating of milk to 85°C for 20 min before the inoculation of starter culture reduced the CPA content. A similar pattern of decrease of CPA was observed in chemically acidified milk but the decrease was less than in yogurt.
Authors: S.B. Mittal, J.A. Hourigan, J.G. Zadow and M.H. Nguyen
Changes occurring in various characteristics (pH, titratable acidity, viscosity, heat stability, ethanol stability, sedimentation, gelation, colour, dissolve oxygen, freezing point, lipolysis, fat separation and phosphatise enzyme activity) of UHT recombined and UHT recombined lactose hydrolysed milks were studies during six months storage at 5°C and 30°C. The degree of lactose hydrolysis versus enzyme activity was also determined. Except for heat stability, no significant difference in these variants was observed between recombined and lactose hydrolysed milks immediately after UHT treatment. During storage, changes in some parameters were more pronounced in lactose hydrolysed milk followed by partially lactose hydrolysed and recombined milk, but the extent was not so marked as to affect the overall quality. No relation was observed between pH and ethanol stability of between ethanol stability and heat stability. A sharp rise in viscosity and a fall in ethanol stability (50% or less) indicated onset of gelation. The establishment of a semi-logarithmic relationship between degree of hydrolysis and lactase activity allows an easier prediction of the amount of enzyme required for hydrolysis. One seventh and one third as much enzyme is required to attain degrees of lactose hydrolysis of 50% and 70% than 98%. Partially lactose hydrolysed milk was found to be better in terms of cost of production and storage stability than completely lactose hydrolysed milk. On the basis of this study, it is suggested that UHT recombined and lactose hydrolysed milks can be prepared and stored for prolonged periods without significant deleterious effects on the overall quality.
β-Lactoglobulin (β-lg) occurs at high concentrations in dairyfoods. The crystal structure of β-lg shows a primary binding sitein the central cavity of the molecule and other surface hydrophobicregions capable of interacting with organic molecules.This binding property could be exploited in using the protein asa 'carrier' to protect and stabilise organic compounds that arebeneficial to health and to food quality. Vanillin is used as aflavouring agent by the food industry. Many studies have showna decrease in vanillin perception in food systems containing wheyproteins (Hansen and Heinis 1991) that suggest some form ofinteraction between the proteins and vanillin. Research aimed atunderstanding the mechanism(s) of interaction between the wheyproteins and vanillin is required to control flavour loss andensure product quality, and to provide a sound basis for use ofthis binding capacity in 'carrier' applications that could extendto other flavours, colours and nutriceuticals.We have investigated the interaction of β-lg (variant AB) withvanillin as monitored by tryptophan fluorescence in differentphysicochemical conditions.
Milk proteins are known for their high nutritive value and diverse functional properties. Beyond these functions, milk proteins have attracted growing scientific and commercial interest as a source of biologically active molecules. Such proteins are found both in casein and whey protein fractions and can be enriched and purified industrially. The best characterised whey-based bioactive proteins include immunoglobulins, lactoferrin, lactoperoxidase and growth factors. The native milk proteins exhibit a wide range of biological activities that influence the digestive function, metabolic responses to absorbed nutrients, growth and development of organs and disease resistance. Whey-derived proteins, in particular, have proven beneficial in reduction of the risks of many chronic human diseases reflected by the metabolic syndrome. To this end, commercial applications are now being developed extensively. Other applications include preservation of foodstuffs and prevention of infectious diseases in humans and domestic animals. Over the past decade, a great number of peptides with specific bioactivities have been identified in major milk proteins. Such peptides can be liberated during gastrointestinal digestion or fermentation of milk by starter cultures. The efficacy of a few peptides has been established in animal and human studies and a number of commercial products have been launched on global markets. The great potential of bioactive milk peptides in promotion of human health has been realised and more commercial products are envisaged.