On incubation at 30degreesC, high pressure (HP)-treated (600 MPa for 30 min) pasteurised whole bovine milk, inoculated with lactic acid bacteria (LAB; Lactococcus lactis subsp. lactis and cremoris), acidified faster than its unpressurised equivalent. Faster acidification of HP-treated milk was due to the faster growth of LAB, although the numbers of LAB after 6 h of incubation at 30degreesC were similar in unpressurised and HP-treated milk. The buffering capacity of the milk was influenced only slightly by HP treatment. Faster growth of LAB in HP-treated milk was possibly due to HP-induced increases in the level of non-sedimentable (non-micellar) caseins, thereby enhancing the supply of accessible nitrogen for bacteria. Enhanced growth of the LAB in, and resultant faster acidification of, HP-treated milk may indicate possible applications of HP treatment of milk in the manufacture of fermented dairy products, such as cheese and yoghurt.
The aim was to study the effect of pasturing time (4 versus 9 hours) combined with restricted indoor feeding on fat content, fatty acid composition, concentration of ¿-tocopherol, ß-carotene, uric acid and ß-hydroxybutyrate in milk from Holstein Friesian dairy cows. Morning and afternoon milk samples were collected three times at the end of week 2, 4 and 6 of the experiment. Morning and afternoon milk from cows at pasture for 4 h varied significantly in medium and long chain fatty acids (C6-C14), C18:1 n-9, C18:2 n-6, C18:3 n-6 and cis 9, trans 11 CLA concentration for all the 3 weeks. Fat percentage, ¿-tocopherol, ß-carotene, milk uric acid and ß-hydroxybutyrate showed significant differences between morning and afternoon milk from 4-h pasture. In the contrary, there was no significant difference observed between morning and afternoon milk for most parameters studied in the 9-h pasture group. Similarly the difference between morning milk from 4- and 9-h was also non-significant for most parameters. Therefore, in general 4-h morning, 9-h morning and 9-h afternoon milk were very similar in their compositions for the parameters studied.
Foaming is an important process in the production of many food products. It usually involves mechanical agitation or gas injection. Foaming of milk for making cappuccino coffee, a common practice in many countries, involves the injection of steam into cold milk until the temperature reaches ̃ 65 °C. However, it is also possible to foam milk at this temperature using mechanical agitation or air bubbling. The objective of this research was to compare mechanical agitation, steam injection and air bubbling for foaming different types of milk. Five types of milk were chosen, namely reconstituted skim milk, pasteurized skim milk, pasteurized homogenized full-cream milk, UHT skim milk and UHT full-cream milk. Foaming characteristics were assessed in terms of foam stability and foam strength. There was little difference in the stability of the foams produced by the three methods of foaming but steam injection produced significantly stronger foams compared to air bubbling while the effect of mechanical agitation relative to steam and air bubbling varied considerably between milk types. Overall, foams with greater stability and strength were produced from the skim milks than from full-cream milks with the difference being most pronounced when mechanical agitation was used.
Enzyme detergents used in the food industry contain proteinase as the major enzyme but amylase may be present, either by design or inadvertently. Three commercial enzyme detergents and 3 enzyme preparations used in detergents were assayed for alpha-amylase activity by the Ceralpha method using the Megazyme kits. The amylase activities of the detergents varied from 3.2x 10(-6) to 32x 10(-6) mumoles ml(-1) h(-1) while the enzyme preparations had much higher activities ranging from 0.05 to 8.06 mumoles ml(-1) h(-1). When added aseptically to a simulated dairy dessert (2% starch solution) and stored for 42 days, the enzyme detergents caused an increase in viscosity; enzyme preparations at low concentrations caused an initial increase in viscosity followed by a decrease; and enzyme preparations at high concentrations caused an immediate decrease in viscosity. The increase in viscosity corresponded to formation of a distinct network of starch granules while the decrease in viscosity was characterised by a marked decrease in size of the granules and little or no network of granules. Decreases in viscosity corresponded to increases in reducing sugars but samples which increased in viscosity showed no measurable reducing sugars. The amylase activity in all sources was destroyed by heating at 75degreesC for 15 min at pH 1.8.
Milchwissenschaft Vol.65 Nr.4, 418-421 Excessive consumption of acid-containing drinks is associated with an increased risk of dental erosion. Milk has antierosive effects, and enrichment of acidic drinks with milk constitutes to reduce their erosive potential has been under increased interest. Our aim was to compare the erosive potential of conventional apple juice (85% juice), apple juice supersaturated with calcium phosphate (CaP), and apple juice enriched with calcium lactate gluconate (CaLG) in vitro. DeIonized water and citric acid (2%) were used as negative and positive controls. A total of 14-16 enamel specimens were incubated in each fluid for one hour. Erosion was examined by profilometry. One specimen per fluid was studied with a field emission scanning electron microscope for morphological changes. Citric acid caused erosion in all the specimens (100%), and conventional apple juice in 68.8% of the cases. One case in the CaP juice group showed visible erosion (6.7%), and the specimens incubated in the CaLG juice and water showed no visible erosion. Scanning electron microscopic data further confirmed the results. To conclude, addition of CaP and CaLG to apple juice reduced enamel erosion compared to conventional apple juice.
In this study, the effects of high pressure (HP) treatment on the mineral balance and pH of raw skimmed ovine milk were examined. HP treatment increased the level of non-sedimentable calcium and phosphate in ovine milk; such increases are probably the result of HP-induced solubilisation of micellar calcium phosphate. The HP-induced increases in the levels of non-sedimentable calcium and phosphorus were reversible on subsequent storage both at 5 and 20 degrees C for 4 or 24 h. As a result of HP-induced solubilisation of micellar calcium phosphate, an HP-induced increase in milk pH was observed, which was reversible on subsequent storage at 20 degrees C, but remained largely irreversible at 5 degrees C. HP treatment affected the mineral balance and pH of ovine milk in a manner analogous to that observed in bovine, buffalo and caprine milk, although there were considerable inter-species differences in the pressure at which specific effects occurred.
This study aimed to evaluate the effect of ultra high-pressure homogenisation (UHPH) on natural-occurring micro-organisms in bovine milk. Whole raw milk was standardised at 3.5% and was processed using a Stansted High Pressure Homogeniser (model FPG11300, Stansted Fluid Power Ltd., Essex, UK). The microbiological quality of raw, high pasteurized (90°C, 15 s) and pressure treated (200 and 300 MPa at inlet temperatures of 30 and 40°C) milks was studied by enumerating total bacteria, psychrotrophic bacteria, coliforms, lactococci, lactobacilli and enterococci. UHPH treatments were as efficient (99.99%) as high-pasteurization treatment in reducing the total bacterial population, reaching important reductions (3-4 log cfu/ml). Lactococci count behaviour was similar to that of total bacteria count, reaching the same reductions. Psychrotrophic bacteria counts were not detected in high-pasteurized milks and were reduced by 3-4 logs and on some occasions up to undetected levels in UHPH-treated milks. Coliforms, lactobacilli and enterococci were completed destroyed by both UHPH and heat treatments.
Five-week-old mice were given a diet consisting of ovalbumin alone (OVA, control diet) or a mixture of OVA, Escherichia coli, and its specific bovine milk IgG (IgG/E.coli added diet) as a protein source for 5 weeks, and mRNAs extracted from Peyer's patch cells of the mice were analyzed by means of DNA microarray. The gene expression of proteins relating to immunoglobulin production and development of immune diseases was reduced in mice given the IgG/E.coli-added diet compared with those given the control diet. In contrast, the gene expression of marker proteins on Th1, Th3, and negatively regulatory T cells was noticeably increased. On the other hand, Peyer's patch cells from mice that had not been given any E. coli or milk IgG were cultured with milk IgG, E. coli, or a mixture of E. coli and its specific milk IgG, and were subjected to a cell function analyzer. The numbers of CD19(+) cells and interleukin-4(+)CD4(+) cells increased significantly when the cells were cultured with either milk IgG or E. coli, while the mixture of E coli and its specific milk IgG hardly influenced the numbers of these cells. These results indicate that the result obtained by DNA microarray analysis is not due to free milk IgG or E. coli alone, but is attributable to a mixture of E. coli and its specific IgG, suggesting that a mixture of E. coli and its specific IgG in intestinal tracts would reduce the development of allergic symptoms and autoimmune diseases.
NaCl-induced changes in physicochemical properties of milk are widely reported but no information is available at present about the reversibility of such changes. In this study, the reversibility of NaCl-induced changes in the heat stability, ethanol stability, rennet coagulation time and the concentration of ionic calcium were examined. NaCl-induced reductions in the stability of milk against heat- and ethanol-induced coagulation and increases in the stability against rennet-induced coagulation were largely reversible on removal of excess NaCl by exhaustive dialysis against bulk milk. Some minor changes remained, which could be attributed to the lower level of ionic calcium in milk from which added NaCl was removed by dialysis than in control milk. The results of this study suggest that addition of NaCl has no irreversible effect on the physicochemical properties of casein micelles, but some changes in the mineral balance remained.
In this study, effects of high pressure (HP) on the casein micelles and whey proteins of ovine milk were examined. Treatment at 100-400 MPa for 30 min did not denature a-lactalbumin, but treatment at 600 MPa denatured similar to 70% of this protein. Denaturation of beta-lactoglobulin occurred > 100 MPa, reaching > 90% after treatment at 400 MPa; most denatured P-lactoglobulin was associated with the casein micelles. Treatment of milk at 100 or 400 MPa did not affect average casein micelle size, but treatment at 250 increased it by similar to 40% whereas treatment at 600 MPa reduced it by similar to 45%; the HP-induced reduction of micelle size at 600 MPa was partially reversible on subsequent storage at 5 or 20 degrees C. As a result of HP-induced disruption of casein micelles, the L-value of milk decreased with pressure; reduction of the L-value was irreversible on subsequent storage at 5 degrees C, but partially reversible at 20 degrees C. HP treatment affected the proteins of ovine milk in a manner analogous to in bovine, buffalo and caprine milk, although some inter-species differences in the pressure at which specific effects occur are apparent.
Presence of lipase in milk, curd, whey and cheese was studied. A small amount of the product was added to a large volume of lipase-free whole milk that had been made sensitive to lipolysis by homogenization. Increase of the acidity of the fat in the mixture, determined after incubation, was interpreted as enzyme activity being present in the product concerned. Results obtained in this way showed that lipase was present in raw milk and in the curd and whey made of it, but that the bulk of the enzyme disappeared quickly from the curd during Gouda cheese making, as a result of several factors including scalding of the curd, whey removal and pH decrease. By using this method no lipase could be detected in ripened Gouda cheese, made of raw milk. Furthermore, no potential lipolytic activity was measured in ripened danish blue cheese, but it was in ripened Camembert and Brie, all of these cheeses being made of pasteurized milk. Obviously, the presence of active milk lipase in ripening cheese is by no means self-evident.
Five-week-old male mice were divided into 2 groups in which they were orally given sterile saline solution (control solution) or cow's colostrum powder prepared from milk produced 6 to 7 days after parturition in sterile saline solution (colostrum solution). The mice were given the solution once a day for 5 weeks. The level of intestinal total IgG was significantly lower in the mice given the colostrum solution than in the mice given the control solution, and the intestinal IgA and serum IgG levels tended to be lower in the mice given the colostrum solution. The numbers of spleen CD11b(+), CD19(+), and IFN-gamma(+)CD4(+) cells were also significantly lower in mice given the colostrum solution. DNA microarray analysis of mRNAs extracted from Peyer's patch cells showed that the gene expression of proteins relating to T cell activation of acquired immune responses or Fc epsilon-mediated mast cell activation was obviously lower in the mice given the colostrum solution than in the mice given the control solution, whereas that of proteins relating to T regulatory cells or intestinal innate immune system was noticeably higher in mice given the colostrum solution. These results suggest that the oral ingestion of cow's colostrum suppresses the acquired immune system and type I allergic reactions, and enhances the innate immune system.
On the basis of the milk flow profiles analysed at the level of single quarters and whole udder relationships between the duration of the decline phase of milk flow and somatic cell counts (SCC) were investigated. 39 Holstein cows, free of clinical mastitis and in their first to third lactation, were used. A total of 1760 quarter and 440 whole udder milk flow curves were recorded during 6 consecutive days. At the last evening and morning milking of this period milk samples from all quarters were collected for SCC determination. At the whole udder level no relation between duration of the decline phase and SCC was found. The decline phase increased with increasing milk yield. At the single quarter level the cows with longer duration (over 80s) of quarter decline phase had significantly higher SCC in their milk. Single quarter decline phase increased with peak milk flow rate. The duration of the quarter decline phase was not related to the duration of blind phase (overmilking) and milk production. No correlation was found between duration of blind phase and SCC on a single quarter level.
Whole fresh goat's milk was heat treated at 135 degrees C for 4 s using a miniature UHT plant. The temperature of the milk in the preheating and sterilizer sections, and the milk flow rate were monitored to evaluate the overall heat transfer coefficient (OHTC). The decrease in OHTC was used to estimate the extent of fouling. Goat's milk fouled very quickly and run times of the UHT plant were short. The use of sodium hexametaphosphate, trisodium citrate and cation exchange resins to reduce ionic calcium prior to UHT processing, increased the pH and alcohol stability of the milk and markedly increased the run time of the UHT plant.
In the programmes of milk quality payment, the milk casein content is generally calculated (crude protein × 0.77 = casein). The aim of the research was to verify the validity of such criterion of evaluation. The survey was carried out on 696 herd milk samples collected throughout an entire year (58 samples per month). Only in 49% of the cases a good correspondence (±0.02 g) between calculated casein and casein determined by Kjeldahl was observed. Casein content resulted underestimated and overestimated by at least 0.04 g per 100 g milk in 36% and 15% of the cases, respectively.
Loop-mediated isothermal amplification (LAMP) allows a rapid amplification of nucleic acids under isothermal conditions. It can be combined with a chemosensor for much more efficient, field-friendly detection of Escherichia coli 0157. In this report, LAMP was performed at 65 °C for 10 min, followed by a rapid reaction of DNA amplification byproduct, pyrophosphate ion, with a chemosensor resulting in red disappearance. The detection limit of E. coli 0157 by the LAMP-Chemosensor was 3-5 copies, and the total assay time including 10 min for rapid DNA extraction was approximately 30 min. Data on naturally contaminated raw milk samples indicated that the LAMP method was highly specific and sensitive, giving 100% concordance with the ISO 16654:2001 reference method. The results showed that the LAMP-Chemosensor method had the advantages hierhin ich of better sensitivity and speed and less dependence on equipment than the standard (PCR) for specifically detecting low levels of E. coli 0157 DNA, and this can be useful in the field as a routine diagnostic tool.
To investigate antimutagenic activity of Lactobacillus casei ADA 03 (a dairy isolate), and its cell wall components against 2-aminofluorene L. casei ADA 03 live cells, heat killed cells, cell wall components (whole cell wall preparation and peptidoglycan) and skim milk fermented with L. casei ADA 03 were examined using Salmonella reverse mutation assay. In the presence of test substances, histidine revenants (frame shift mutations) of Salmonella typhimurium TA 98 were determined, and compared with positive and negative controls. Antimutagenicity was expressed as the percentage inhibition of Salmonella growth by each test substance. Fermented milk culture with L. casei ADA 03 had the highest antimutagenic activity; it reduced the occurrence of mutation by about 50%. Live cells also showed antimutagenic activity, while heat killed cells and cell wall components showed no considerable activity. Incorporation of peptidoglycan at higher concentrations, (800 -1000 μg/plate), inhibited the mutation only by about 5%. Milk fermented with L. casei 03 has a considerable antimutagenic activity against 2-aminofluorene. It is likely that the products generated during the fermentation of milk play a major role in the antimutagenic action. However, cell wall components of L. casei ADA 03 are unlikely to participate in antimutagenic activity in vitro.
The ability of the proteinase-negative Lactococcus lactis FH 041 to utilize amino acids and peptides, and its peptidase activities were examined. Strain FH 041 and its parent strain UC 317 exhibited similar growth rates in a medium with casein hydrolysate as the sole nitrogen source. Growth of strain FH041 in media containing different amino acids, each as the sole nitrogen source, indicated a preference for hydrophilic over hydrophobic amino acids. It also preferentially utilized cheese peptides of less than 2 kDa. Strain FH041 exhibited strictly intracellular general aminopoeptidase and X-propyldipeptidyl aminopeptidase activities, and most of its endopeptidase and dipeptidase activities were also intracellular.
In this cross-sectional study the effect of the parity and the stage of lactation on the prevalence of mastitis pathogens in quarters with high somatic cell count (SCC ≥ 100.000/ml) was analyzed by applying the model of logistic regression. The prevalence of minor pathogens (coagulase-negative staphylococci, Corynebacterium bovis) and major pathogens was significantly influenced by both factors. High SCC of primiparae was most likely caused by minor pathogens, primarily by coagulase-negative staphylococci. They were isolated from 24.4% of cultured quarters of primiparae and from 10% of cultured quarters of multiparae. Older cows being 5 or more lactations in milk had the highest risk of infection caused by major pathogens. High SCC of cows being more than 90 days in milk was most likely caused by minor pathogens, primarily by Corynebacterium bovis. This pathogen was isolated from 12.7%, 25.6% and about 40% of quarters of cows with 8 to 90, 91 to 180 and more than 180 days in milk, respectively. The prevalence of major pathogens in quarters with SCC ≥ 100.000/ml decreased in the course of lactation: 33.1%, 25.4% and 19% were isolated from cows being 8 to 90, 91 to 180 and more than 180 days in milk, respectively.