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Authors: J.F. Horwood, G.T. Lloyd, E.H. Ramshaw and W. Stark
The 'plastic paint, kerosene' off-flavour in a sample of commercial Feta cheese was caused by approximately 200 ppm of trans-1,3-pentadiene and was associated with sorbic acid treatment. Trans-1,3-pentadiene had an odour threshold of 2.5 ppm above 10% sodium chloride and a flavour threshold of 4 ppm in a Feta cheese slurry.
Examination of a milk membrane fraction from when protein concentrates (WPC) has shown that components orginating from the skim milk membrane (SMM) system were present in lipoprotein complexes with a β-lactoglobulin and α-lactalbumin. This membrane fraction contained less than 3% of the total WPC protein, approximately 40% of the WPC phospholipid and less than 7% of the WPC triglyceride components. Isopycnic sucrose density gradient centrifugation showed that the lipoprotein complexes isolated in the membrane fraction covered a broad density range, but, in general, were higher in density than SMM lipoproteins and lower in density than the high density fraction of MFGM material. These complexes had apparently formed during processing in a similar manner to complexes between MFGM material and skim milk components observed in pasteurised milks and creams.
A simple technique for the extraction, paper chromatographic separation and quantitative determination of the free sugars from yoghurt is described. Typical mono- and di-saccharides contents of some commercial yoghurts are tabulated. No hydrolysis of sucrose was observed during storage of sweetened yoghurt for one month at 2°C.
High performance liquid chromatography (HPLC) has been applied to the analysis of whey proteins. Using a short alkyl chain (C6) reverse phase column with an acid saline / acetonitrile gradient the major whey proteins bovine serum albumin, α-lactalbumin and β-lactoglobulin have been completely resolved in a 30 min. analysis. In addition the A and B generic variants of β-lactoglobulin have been completely resolved to better than 70% in the same analysis. Reproducibly checks of peak retention times and peak areas yielded standard deviations of better than 1% and 3% respectively about mean values (n=5). Analysis of purified whey proteins by HPLC demonstrated the presence of levels of impurity not readily detected by electrophoresis. This technique has been applied to the analysis of whole Cheddar cheese whey and when protein concentrates (WPC) derived from Cheddar, hydrochloric acid and sulphuric acid casein wheys. Significant differences could be detected in the protein elution profiles of the whey proteins in the various WPC. Whey protein analysis by this HPLC method is sensitive enough to detect subtle changes in the whey protein which have occurred as a result of processing.
In order to obtain separation of the major whey proteins of bovine milk, β-lactoglobulin, α-lactalbumin and serum albumin and the generic variants of β-lactoglobulin in a single step, the technique of chromatofocusing was applied. Excellent separation of these milk components was obtained by this method. The pH values representing the apparent isoelectric points of the whey proteins were: β-lactoglobulin C, 4.66; bovine serum albumin, 4.61; β-lactoglobulin B, 4.55; α-lactalbumin, 4.45; β-lactoglobulin A, 4.36. Chromatofocusing was effective for both analytical and preparative separation of the whey proteins; at least a 1000-fold range of sample size was applicable to the same column system. The separated whey proteins could be recovered by gel filtration on an appropriate medium. Chromatofocusing was shown to be a useful technique for assessing the protein retentiveness of ultrafiltration systems.
Authors: D.J. Williams, S.M. Nottingham, M. Petroff and S.J. Veldhoven
The levels of alkaline phosphatase (AP) were determined in bulk goats' milk collected at two-weekly intervals from two dairies over twelve months. The AP levels in milk from both dairies varied widely and inconsistently over the year. Seasons of the year had only a limited effect on AP levels, while milk yield, solids-not-fat and fat percentages had no influence. Low AP activities of these milks allowed sizeable amounts of raw milk i.e. up to 1.6%, to contaminate the pasteurised product without detection by the standard Aschaffenburg and Mullen test. The use of a modification to enhance the sensitivity of the test (Williams, 1986) together with a change in the failure criterion is suggested to minimise the problem.
A number of milkfat components have demonstrated anticancerpotential in animal models of carcinogenesis. Conjugatedlinoleic acid and its natural isomer rumenic acid havemultiple anti-tumorigenic effects and is a potent inhibitor ofmammary tumour development. Vaccenic acid, the predominanttrans-monounsaturated fatty acid in milkfat, can beconverted endogenously to rumenic acid. Sphingomyelin andother sphingolipids suppressed colon tumour development inmice. Butyric acid, uniquely present in milk, can inhibitmammary tumour occurrence in rats, whereas 13-methyltetradecanoic acid suppressed cell growth in a numberof human cancer cell lines and inhibited the growth of humanprostate and liver cancer cells implanted in mice. Milk lipidsalso contain the common anticancer agents β-carotene andvitamin A. Pasture-derived components like β-ionone, phytoland gossypol may also help prevent cancer.
Authors: M.S. Carrasco, H.E. Scarinci and A.C. Simonetta
Antimicrobial activity of 27 strains of lactic acid bacteria isolated from artisanal and commercial Argentinian cheeses and other dairy products was tested against a set of bacterial species. Nine produced inhibition zones against indicator micro-organisms. Most of the substances excreted by lactic acid bacteria were active against Gram-positive bacteria including Listeria monocytogenes, and a wide range of Gram-negative bacteria including Pseudomonas sp., Escherichia coli, Salmonella enteritidis, Shigella sp. and Vibriocholerae O1. The substances were proteinaceous in nature as they were destroyed by trypsin, pepsin, papain and pronase E, but were resistant to heat (100°C for 30 min). They were produced during the growth phase and when tenfold concentrated cell-free supernatants were added to fresh culture of sensitive cells, inhibited the growth of most of the indicator organisms. These characteristics led to the conclusion that the inhibitory compounds are bacteriocin-like substances.
Lactoferrin inhibited the growth of food-borne pathogenic organisms Escherichia coli, salmonella typhi and Shigella dysenteriae appreciably at low concentrations. Addition of 0.2mg/mL of lactoferrin to the growth medium resulted in a gradual decline in the growth of the above organisms at various incubation periods ranging form 0 to 12 hrs. The maximum percent growth inhibition (94 per cent) was recorded in case of E. coli followed by Salmonella typhi (78 per cent) and Shigella dysenteriae (75 per cent).
Authors: Wayne M. Pitt, Terence J. Harden and Ron R. Hull
Raw bovine milk was shown to contain anti-Listeria monocytogenes activity. L. monocytogenes activity. L. monocytogenes inoculated into raw milk at 37°C to give an initial bacterial concentration of approximately 10,000 cfu/mL multiplied at a reduced rate for approximately 12 hours and then rapidly lost viability. Fifty-six hours after the inoculation of raw milk, no viable cells of L. monocytogenes were detectable. The anti-Listeria system was most active in raw milk incubated at 37°C. The activity was reduced at lower temperatures of 25°C, 7°C and 4°C; by heating the milk at 72°C for 15 seconds (pasteurisation); and by storing the milk at 4°C for 4 to 6 days. These preliminary results require further study to elucidate the mechanism of anti-Listeria activity in raw milk and also to determine the role of antimicrobial systems in the control of pathogenic and spoilage micro-organisms in milk products.