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Fifteen lactic acid bacteria (LAB) were screened for their ability to produce antimicrobial substances against Lactobacillus delbrueckii ssp. bulgaricus 2519, Lactobacillus helveticus 2700, Lactobacillus casei 2603 and Lactobacillus jugurti 2819. Of the fifteen LAB, L. helveticus 2700, Lactobacillus plantarum 2903 and Lactobacillus fermentum 5174 exhibited antimicrobial activity. The characteristics of the antimicrobial substance produced by L. helveticus 2700 were studied. The antimicrobial substance produced in fermented milk by L. helveticus 2700 inhibited seven strains of L. delbrueckii ssp. bulgaricus, the producer organism L. helveticus 2700, 14 strains of L. acidophilus and one strain each of L. plantarum 2903 and L. jugurti 2819, but not the other LAB, spoilage and pathogenic micro-organisms tested. The antimicrobial activity of L. helveticus 2700 was not due to organic acids or hydrogen peroxide. The molecular weight of the substance was less than 5000 daltons. The substance was active over a pH range of 3.0-10.0, and inactivation occurred at 70°C.
The antioxidant activity of a heated casein-glucose mixture (HCG) in full-cream milk powder (FCMP) was studied. FCMP with HCG added during processing showed a slower decline in flavour acceptability during storage compared to FCMP without added HCG. Analyses of peroxide and p-anisidine values and concentration of headspace volatiles supported the conclusion that the addition of HCG retarded the rate of fat oxidation in FCMP. The study showed that HCG was an effective antioxidant for FCMP.
Authors: L. Rosetti, L. Langman, G.M. Grigioni, A. Biolatto, A.M. Sancho, E. Comeron and A.M. Descalzo
In order to determine the effect feeding differences on natural antioxidant vitamin delivery, two contrasting diets, lucerne (ALF) and sorghum silage (SS), were analysed. Diets showed different profiles for fat-soluble vitamins. ALF was higher in α-tocopherol, β-carotene and retinol than the SS diet. On the contrary, SS diet was higher in γ- and δ-tocopherol, due to the soy expeller contribution in these isomers. The ALF diet favoured higher milk production and protein yield in comparison to SS, whereas the fat content was the opposite (p <0.01). The composition of the diets was partially reflected in milk. The ALF diet favoured the incorporation of α-tocopherol, retinol, β-carotene and Vitamin D3 intro raw milk. Meanwhile, a less abundant isomer of vitamin E, γ-tocopherol, was significantly higher in the SS than the ALF milk and δ-tocopherol was not deteced. In addition the ALF diet also promoted higher antioxidant activity. The ferric reduction antioxidant power (FRAP) was significantly higher in ALF than in SS milk, however oxidation determined by thiobarbituric acid reactive substances (TBARS) was similar for both types of milk. Also, no differences in ascorbic acid concentration were detected in either type of milk. The ALF and SS milks were clearly separated (100%) by their antioxidant status and odour profiles as a function of feeding into SS and ALF groups when the biochemical variables and sensor LY2/gCTI were analysed together. Two linear Fischer’s discriminant functions were defined according to dietary treatments using β-carotene and sensor LY2/gCTI. The success rate of correct classification of each sample was 100%, either for the original cases or after cross-validation (p,0.0001). The use of an electronic nose proved to be a useful instrumental method to discriminate the odour profile of milk samples with a different antioxidant status.
Authors: W.G. Whittlestone, L. Fell, B.O.E. Calder and R.H. Galvin
Automatic apparatus is described for simulating the milking and washing operations in a milking machine. The instrument consists of most of the components of a normal milking machine assembled so that milk and cleaning solutions pass throughout the unit at a fixed rate. An electrical controller which may be programmed for a wide variety of treatments caused the unit to be flushed with a standard sanitizer solution followed by simulated milking, cold water rinse, hot detergent rinse, hot water rinse, and a brief drying period. The cycle repeats itself every 50 minutes, thus bringing about the equivalent of 4 weeks' standard milking procedure in less than 48 hours. Preliminary tests have shown that the device does in fact produce conditions similar to those obtained in the field. It is intended primarily for the testing of detergents and for examining the performance of materials for the construction of milk handling equipment.
A method involving membrane filtration followed by culturing on selective agar was developed to improve the sensitivity of detecting Gram negative bacteria in pasteurized milk. The method involves enzymatic pretreatment of a milk sample at 43 to 49°C for 10 min and rapid filtration of 10 to 14 mL through a 47 mm diameter, 0.6mm pore size polycarbonate membrane filter, with minimal loss in apparent total number of bacteria recovered. A Gram negative selective medium (PBAC-ANS) allowed the growth of 98% of 50 Gram negative isolates and prevented the growth of 92.4% of 79 Gram positive isolates. Of the isolates which grew on the medium, 71.4% of the Gram negatives showed flurescent intensity of ≥ 2 and 83.5% of the Gram positives had fluorescent intensity of < 2.
Authors: H. Jiang, P.A. Grieve, R.J. Marschke, A.F.Wood, D.A. Dionysius and P.F. Alewood
Recent advances in the analysis of complex biomolecules by mass spectrometry (MS) provide researchers in dairy science with powerful techniques for characterisation of dairy proteins and peptides. We have applied ionspray MS, MS/MS, liquid chromatography MS (LC/MS) and LC/MS/MS to the identification of proteolytic breakdown products of cheeses.
The performance of the Milko-tester was investigated with a view to its application for routine fat testing of ten day preserved composite milk samples. The Milko test was found to be more reproducible than the Babcock test and calibration of the instrument was possible to give excellent correlation with the Babcock test.
Consideration was given to the effects of concentration of mercuric chloride preservative, daily shaking of composite samples and length of conditioning time at 40°C. A comparison was made of ten day composite samples and the means of the daily samples. Practical points of importance in any proposed introduction of the Milko-tester for routine factory testing are discussed.
Dilution methods were developed to make whole milk and cream filterable through tortuous pore membrane filters so that the toluidine blue-membrane filter method could be applied to these substrates. Bacteria and somatic cells in milk and cream were spread evenly and uniformly over the filter by the addition of 1mL of substrate to 9 mL of either 5% Triton X200 (TX) or a mixture of 2.5% TX and 2.5% Tween 80 (TX-T80) at 60°C, mixing vigorously and followed immediately by the addition of 1 mL of 10% sodium tripolyphosphate before filtration. Some fat remained on the filter but it could be removed by dipping the filter in diethyl ether after filtration. The effects of TX and TX-T80 diluents on four organisms were compared by measuring the absorbance of stained cells. The TX diluent caused a 6% reduction in absorbance values when compared with TX-T80 and the latter is recommended as a consequence. It may be possible to use this procedure with the toluidine blue-membrane filter method to measure somatic cells in milk.
The toluidine blue-membrane filter method was used to measure the growth of Streptococcus cremoris ML1 on a dry mass basis in M17 broth, reconstituted skim milk (RSM), whole milk and cream. Results for the estimates of the maximum dry mass concentration achieved in batch cultures in RSM at the stationary growth phase were comparable with published values based on turbidity measurements. Metabolic functions for the organism derived from the data were also comparable with published values. Growth in whole milk was uncoupled from acid production throughout the growth cycle but became uncoupled later. Lactic acid production and bacterial concentration were compared directly. This showed that the organism went through a change in lactic acid metabolism during the growth period in M17 broth and RSM. The change was not related to pH of the medium. There was no change in lactic acid metabolism during growth in whole milk and cream in which growth ceased abruptly at pH 5.0.
Compressive properties of composite gels consisting of 13% whey protein isolate (WPI) and 10-30% selected milkfat fractions were investigated at different temperatures. Compressive properties of gels were significantly affected by melting properties of the filler. Maximum compressive strength of composite gels was proportional to filler load and proportion of solid lipids. Compressive strength of composite gels was higher than that of WPI only gels and the relative increase in hardness ranged from about 5 to 91%. Viscoelastic properties of full-and reduced-fat curds containing anhydrous milk fat (AMF) or selected fraction of AMF were investigated. Results indicated that replacing AMF with milkfat fractions with lower melting rage allowed both viscoelastic properties of reduced-fat curds to be adjusted to those of full-fat curd. Results may open new applications for fractionated milkfat in fabricated foods containing milkderived components and may offer opportunities in modulating rheological properties of cheese. Results may offer means to overcome textural difficulties associated with reduced-fat cheese.
Authors: Ranjan Sharma, Peerasak Sanguansri, Rachel Marsh, Luz Sanguansri and Mary Ann Augustin
Omega-3 fatty acids are reported to have an important role inbrain development, cardiovascular disease, cancer and inflammatorydiseases such as arthritis. Due to their high level ofunsaturation, the omega-3 fatty acids are highly susceptible todeterioration. Such deterioration leads to the development of offflavours and limits their use as direct additives to food products.MicroMax®, a patent pending microencapsulation technology(Sanguansri and Augustin, 2001) developed at FoodScience Australia by collaborative research between Food ScienceAustralia and Clover Corporation has been successfullyemployed in the manufacture of microencapsulated omega-3fatty acids. This study investigates the application ofmicroencapsulated omega-3 fatty acids in dairy products andreports on the consumer evaluation of selected dairy products.
In recent years, a number of new technologies have emerged which present alternative processing strategies to conventional approaches such as heat treatment; these include the use of high pressures, pulsed electric fields, and ultrasound. Each technology has specific and sometimes unique advantages over existing technologies in terms of microbial inactivation or effects on proteins, enzymes or other food constituents. This review considers the possible application of some of these technologies for functional dairy products, including reducing allergenicity of proteins and preserving probiotic products or colostrum. While many of the technologies mentioned have not yet been widely implemented by the food industry, specific examples of commercial adoption of high-pressure processing are described.