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1.
SARA A SCOTT JOHN D BROOKS JASNA RAKONJAC KYLIE M R WALKER STEVE H FLINT 《International Journal of Dairy Technology》2007,60(2):109-117
A survey was undertaken at a whole milk powder manufacturing plant to determine the origin and the rate of spore formation of thermophilic bacteria. Spores were generally not detected (< 10 cfu/mL) in either the pasteurization process or the pasteurized milk directed into the powder plant. The predominant sites of spore formation were the preheater plate heat exchanger and the evaporator. Spores began to be detected approximately 9 h into an 18-h manufacturing run. Spore isolates were identified as Anoxybacillus flavithermus and Geobacillus species. A. flavithermus predominated in the preheat section, whereas a mix of both organisms was present in the later manufacturing stages. 相似文献
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Skim milk powders with various levels of sodium hexametaphosphate (NaHMP) were prepared. Reconstituted skim milk samples were prepared from these powders. NaHMP slightly reduced the pH, markedly reduced the serum and ionic calcium and markedly increased the serum phase orthophosphate levels of the milks. This shift in the mineral equilibrium resulted in a drastic reduction in casein micelle integrity, with a marked dissociation of casein from the micelles. κ-Casein was the predominant casein dissociated, although significant levels of αS-casein and β-casein were also transferred to the serum phase. This dissociation of the casein micelles caused a marked decrease in size and scattering properties of the casein micelles. In addition, a small decrease in the zeta potential of the casein micelles in the milk was observed. Heat treatment of the milks with added NaHMP induced further dissociation of κ-casein, although much of the αS-casein and β-casein re-associated with the micelles. 相似文献
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Growth of thermophilic spore forming bacilli in milk during the manufacture of low heat powders 总被引:3,自引:0,他引:3
PATRICK M MURPHY DAVID LYNCH PHILIP M KELLY 《International Journal of Dairy Technology》1999,52(2):45-50
The survival and growth of Bacillus stearothermophilus and Bacillus licheniformis, naturally present (30–300 colony forming units/ml) in late season skim milk, was monitored in a three effect evaporator during low heat skim milk powder manufacture. Substantial growth was shown to occur in the preheating stages prior to direct steam heating. A typical heat treatment (77°C, 15 s) used in the manufacture of low heat powder did not inactivate the bacteria, which continued to grow in the heater. The importance of preheaters in influencing thermophile growth in the evaporator is demonstrated by the finding that growth in the preheater stages was accompanied by growth in subsequent evaporator effects which significantly exceeded that observed when the final two preheaters were bypassed. A mid-run mini-clean procedure incorporating 0.2% hydrogen peroxide for decontaminating the evaporator was tested and may prove useful in extending evaporator run times 相似文献
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Direct gas-fired heating experiments were carried out during spray drying of milk using a 'low-NOx ' burner in order to minimize contamination of the drying air by the combustion products in the flue gases from the burner. The burner, model CXA (Urquhart Engineering Co Ltd, England) was of the 'excess air' type, and was fuelled by natural gas. There was no significant difference between the mean values of the nitrate content of the skim milk powders produced by direct firing, electrical heating and the factory produced (indirect heating) sample. Only with nitrite content (NO2 ) was there a significant difference between the direct gas fired (0.811 ppm NO2 -) and the factory (0.460) samples, but the range of values encountered was very small (0.24–1.68). Direct gas-fired heating using the low NOx burner did not contribute to the levels of N-nitrosodimethylamine (NDMA) detected in the test powders when compared to the levels found in the control samples (trace-1.3 μg/kg NDMA). 相似文献
5.
The traditional process of manufacturing whole milk powder has some negative aspects: high heat treatment of the milk and, owing to fouling during evaporation, loss of product. To reduce these negative aspects an alternative way of producing whole milk powder was investigated in pilot-plant experiments. Milk was first separated into skim milk and cream and then treated further. Skim milk was subjected to a low heat treatment and concentrated by evaporation. The cream was subjected to a high heat treatment and mixed with the concentrated skim milk. The standardized whole milk concentrate was then spray dried. This process of manufacturing whole milk powder compared favourably with the traditional process with respect to product losses, the physical properties of the whole milk powder and the flavour of the reconstituted milk. 相似文献
6.
《Food microbiology》1996,13(4):275-280
Three species of bifidobacteria, namelyBifidobacterium bifidum, Bifidobacterium longumandBifidobacterium adolescentiswere used in pure culture and in combination with yoghurt bacteria (B3 and SBI cultures) for the production of fermented milks. The number of bacteria during fermentation and the level of acid produced during fermentation and storage were assessed using Rogosa's modified selective agar and high performance liquid chromatography (HPLC). It was found that during fermentation all bifidobacteria exhibited growth uncoupled from acid production. Two of the species examined produced only low levels of acids when grown individually and onlyB. adolescentisproduced appreciable amounts. In mixed cultures, the level of acid was a reflection of the combination of yoghurt culture and species ofBifidobacterium, and this, observation suggests that there is a degree of influence between the cultures. During storage, the acid concentration remained quite stable in most samples. The prevention of post-production acidification that normally occurs during storage of yoghurt can be attributed to the presence of bifidobacteria, and it could be that acetic acid has a marginally inhibitory effect on theLactobacillusandStreptococcusspp. 相似文献
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In this study, skim milk powder was produced from cow's milk contaminated artificially with aflatoxin M1 (AFM1) at two different levels, 1.5 and 3.5 microg/liter (ppb), and the effects of process stages on the AFM1 contents were investigated. Pasteurization, concentration, and spray drying caused losses of about 16, 40, and 68%, respectively, in AFM1 content of the milk contaminated with 1.5 microg/liter AFM1, and losses of 12, 35, and 59%, respectively, in the milk contaminated with 3.5 microg/liter AFM1. These losses were found to be statisticially significant at the level of P < 0.01. After 3- and 6-month storage periods, AFM1 content of the skim milk powder produced from milk with 1.5 microg/liter AFM1 decreased by 2 and 5%, respectively, whereas these rates were 2 and 4%, respectively, for the skim milk powders made from milk with 3.5 microg/liter AFM1 (after adjustment for sample weight). Changes in AFM1 content of milk powder samples were found statistically insignificant (P > 0.05 and P > 0.01) for 3- and 6-month storage periods. 相似文献
8.
《International Dairy Journal》2005,15(5):501-511
Skim milk powder was manufactured in a milk powder plant using different preheating temperatures, concentrate heating temperatures and spray drying temperatures. Varying the preheating conditions from 70 °C for 52 s to 120 °C for 52 s had a marked effect on the denaturation of -lactoglobulin A, -lactoglobulin B, -lactalbumin, bovine serum albumin (BSA), and immunoglobulin G. In contrast, varying concentrate heating temperature (65–74 °C) and inlet/outlet air dryer temperature (200/101 °C–160/89 °C) had a minimal effect on whey protein denaturation. Most of the whey protein denaturation and association with the casein micelle occurred in the preheating section of the powder plant. Aggregation of β-lactoglobulin (β-lg) and BSA predominantly involved disulphide bonds. Although, greater than 90% of the β-lg and BSA was denatured after preheating at 120 °C for 52 s, the extent of association with the casein micelle was lower, 50% for β-lg and 75% for BSA. 相似文献
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Fanny Guyomarch Franoise Warin D. Donald Muir Jeffrey Leaver 《International Dairy Journal》2000,10(12):863-872
Extensive lactosylation of milk proteins in standard skim milk powder dried against air between 185 and 90°C (inlet and outlet temperatures of the air) was detected by capillary electrophoresis. Optimisation of the drying conditions included keeping the outlet temperature low (preferably <80°C), since this was the parameter which most affected the extent of lactosylation of milk proteins. The inlet temperature was set in order to obtain the best compromise between a low extent of lactosylation and a high drying rate (170–175°C). These conditions allowed the manufacture of low-lactosylated skim milk powder. Storage of freeze-dried and control low-lactosylated skim milk powder at different temperatures showed that both temperature and moisture content affected the progress of lactosylation during storage. Further drying to less than 2.5% moisture content (w/w) and storage at low temperatures were required to prevent the development of lactosylation in the low-lactosylated skim milk powder. 相似文献
11.
Milk powder taken to Antarctica on Shackelton's British Antarctic Expedition in 1907 was produced in New Zealand by a roller drying process in the first factory in the world dedicated to this process. Thermophilic bacilli are the dominant contaminants of modern spray-dried milk powders and the 1907 milk powder allows a comparison to be made of contaminating strains in roller-dried and spray-dried powders. Samples of milk powder obtained from Shackelton's Hut at Cape Royds had low levels of thermophilic contamination (< 500 cfu ml-1) but the two dominant strains (Bacillus licheniformis strain F and Bacillus subtilis) were typical of those found in spray-dried powders. Soil samples from the floor of the hut also contained these strains, whereas soils distant from the hut did not. Differences in the RAPD profiles of isolates from the milk powder and the soils suggest that contamination of the milk from the soil was unlikely. It is significant that the most commonly encountered contaminant strain in modern spray-dried milk (Anoxybacillus flavithermus strain C) was not detected in the 1907 sample. 相似文献
12.
在现代乳粉生产中大多数采用两段干燥,即喷雾干燥塔和流化床结合,流化床的普遍使用完成了对乳粉的二次干燥、附聚、冷却和连续出料等工序.本文对流化床的结构、工作原理进行了分析,并说明了流化床在乳粉生产中的应用过程. 相似文献
13.
Contamination of milk and its products with Yersinia enterocolitica at various stages of the production process was studied for the first time. Yersinia were detected in fresh milk (at dairy farms, in tanks at reception compartments of dairy plants) and in pasteurized milk (in tanks at the plant, in paper-bags on sale). All Yersinia strains isolated from milk are pathogenic for man and highly resistant to antibiotics. A possible role of man, in particular of workers at dairy farms and plants, in Yersinia dissemination, is shown. Unlike milk, sour milk foodstuffs virtually do not participate in propagation of the infection. 相似文献
14.
《International Dairy Journal》2000,10(1-2):7-15
Bacteriocin-producing lactic acid bacteria were isolated from 298 samples of raw ewes', goats’ or cows’ milk. Eighty-two bacteriocin producers were phenotypically and genotypically identified as L. lactis subsp. lactis (59 isolates), L. lactis subsp. cremoris (2 isolates), L. lactis subsp. lactis biovar diacetylactis (6 isolates), E. faecalis (7 isolates), E. faecium (1 isolate), L. paracasei subsp. paracasei (4 isolates), L. plantarum (1 isolate) and Leuconostoc spp. (2 isolates). By means of PCR-techniques, nisin was characterized in 39 of the 67 bacteriocin-producing lactococci and lacticin 481 in 23 isolates, some of which presented antilisterial activity. Enterocin AS-48 was produced by four enterococcal isolates. Four non-identified bacteriocins produced by 16 isolates showed a broad inhibitory spectrum. Nisin-producing lactic acid bacteria were the most abundant, but lacticin 481-producing lactococci and AS-48-producing enterococci were found at relatively high rates. 相似文献
15.
Staphylococcus aureus growth and enterotoxin production during the manufacture of model Saint-Nectaire, Registered Designation of Origin Saint-Nectaire, and Registered Designation of Origin Salers cheeses, three types of uncooked, semihard, raw milk cheese, were investigated. Coagulase-positive staphylococci (SC+) grew rapidly during the first 6 h. Between 6 and 24 h, counts increased by less than 0.5 log CFU/ml. Raw milk counts ranged from undetectable (<10 CFU/ml) to 3.03 log CFU/ml. Maximal levels reached in cheese on day 1 ranged from 2.82 to 6.84 log CFU/g. The level of SC+ after 24 h was mainly influenced by the milk baseline SC+ level (correlation coefficient, r > 0.80) but pH at 6 h influenced the SC+ growth observed between 6 and 24 h (r > 0.70). Thus, the initial level of SC+ in raw milk should be maintained below 100 CFU/ml and best below 40 CFU/ml. To limit growth, acidification should be managed to obtain pH values around or below 5.8 at 6 h in Saint-Nectaire cheeses and around or below 6.3 at 6 h in Salers cheeses. Enterotoxins were only detected in two Salers cheeses whose SC+ counts on day 1 were 5.55 log CFU/g and 5.06 log CFU/g, respectively, and whose pH values at 6 h were high (approximately 6.6 and 6.5, respectively). 相似文献
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为了建立同时检测婴幼儿奶粉中阪崎肠杆菌、金黄色葡萄球菌、蜡样芽孢杆菌的多重PCR方法,根据阪崎肠杆菌ompA基因、金黄色葡萄球菌nuc基因、蜡样芽孢杆菌hblA基因分别设计3对引物进行多重PCR扩增,并对反应条件进行优化。结果多重PCR扩增出长度为514、156、235bp的特异性目的条带。不增菌的情况下,多重PCR同时检测3种病原菌的灵敏度是103cfu/mL,3种病原菌在奶粉中的检出限是104cfu/g。建立的多重PCR反应准确、快速、高效,为同时检测婴幼儿奶粉中的阪崎肠杆菌、金黄色葡萄球菌、蜡样芽孢杆菌提供了新方法。 相似文献
19.
Histamine production by bacilli bacteria, acetic bacteria and yeast isolated from fruit wines 总被引:1,自引:0,他引:1
Eleven red wines imported from foreign country and 40 domestic fruit wines, including 15 red wines, 4 white wines, 7 plum wines, and 14 other fruit wines, sold in the supermarkets in Taiwan were purchased and tested to determine the occurrence of biogenic amines and histamine-forming bacteria. The levels of pH, total soluble solids (TSS), titratable acidity (TA), reducing sugar (RS), total sugar (TS), sulphites, methanol (milligram per liter of pure ethanol), ethanol and Pb in all samples ranged from 3.0 to 4.1, 6.8 to 24.4 °Brix, 0.3 to 1.7 g/100 mL, 0.2 to 17.6 g/100 mL, 1.6 to 28.4 g/100 mL, <2 to 260.5 mg/L, <1 to 2559 mg/L, 5.0 to 15.6 g/100 mL and <1 to 46.2 μg/L, respectively. The levels of TSS, TA, RS, and TS in plum wine samples were significantly higher than those of the other wines samples, whereas the pH value in plum wine samples was lower than that of the other wines samples. The average content for each of the nine biogenic amines in all samples was less than 5.2 mg/L. However, higher levels of histamine and spermine were detected in domestic fruit wine samples than the imported red wine samples. Five histamine-forming isolates isolated from domestic red wine and jackfruit wine, capable of producing 13.0 mg/L to 69.1 mg/L of histamine in trypticase soy broth (TSB) supplemented with 2 g/100 mL l-histidine (TSBH) or MRS broth supplemented with 2 g/100 mL l-histidine (MRSH), were identified as Bacillus pumilus (one strain), Bacillus sp. (two strains) and Acetobacter pasteurianus (one strain) by 16S rDNA sequencing with PCR amplification, and Zygoascus hellenicus var. hellenicus (one strain) by internal transcribed spacer sequencing with PCR amplification. To our knowledge, this is the first report to demonstrate the occurrence of histamine-forming bacilli bacteria, acetic bacteria and yeast in fruit wine. 相似文献
20.
C. Vernozy-Rozand C. Mazuy G. Prevost C. Lapeyre M. Bes Y. Brun J. Fleurette 《International journal of food microbiology》1996,30(3):271-280
An antigen related to the Enterotoxin E from Staphylococcus aureus was produced by ten of 187 coagulase-negative staphylococci (CNS) isolated from goats' milk, whey and cheese in quantities ranging from 10 to 90 ng/ml supernatant. The enterotoxin-producing strains were identified at the species level as S. simulans, S. xylosus, S. equorum, S. lentus and S. capitis. Detection of the enterotoxins was done by the VIDAS SET test (bioMérieux) and by an indirect double-sandwich ELISA technique using anti-enterotoxin monoclonal antibodies. The results obtained were further confirmed by Southern blotting, using two radioactive oligonucleotide probes that hybridized specifically with the gene of S. aureus coding for the enterotoxin E. 相似文献