共查询到19条相似文献,搜索用时 203 毫秒
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原料乳中嗜冷菌产脂肪酶条件的优化 总被引:1,自引:0,他引:1
研究了原料乳中嗜冷菌产生脂肪酶的几组影响条件。主要从pH值、培养温度、产酶培养基组成几个方面考虑。优化产酶条件,从而可提高脂肪酶的检测活力,为原料乳中嗜冷菌分泌的脂肪酶的研究奠定理论基础。 相似文献
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原料乳中嗜冷菌的检测 总被引:1,自引:0,他引:1
针对原料乳中嗜冷菌的一种快速检测方法进行了初步研究。由于嗜冷菌能在乳中产生大量的耐热性脂肪酶,所以我们在脂肪酶活与嗜冷菌数之间建立了一种线性关系,进而通过4-硝基苯酚游离释放法测定脂肪酶的活力来得到嗜冷菌数。 相似文献
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原料乳中嗜冷假单胞菌危害及控制研究进展 总被引:1,自引:0,他引:1
假单胞菌是对原料乳危害最大的嗜冷菌之一,极易在冷藏条件下成为优势菌群。大多数嗜冷假单胞菌有分泌蛋白酶和脂肪酶的能力,并导致原料乳及产品变质。本文对原料乳假单胞菌的危害特点,快速检测和新型控制工艺研究进展进行综述。最后探讨了嗜冷假单胞菌的研究方向。 相似文献
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乳是一种营养丰富的物质,同时也是微生物生长繁殖的理想培养基。生乳的质量是影响乳制品产业链的关键因素,随着低温储存和冷链运输技术的发展,生乳中大部分细菌的生长受到抑制,但嗜冷菌的生长并未受到抑制,并逐步成为生乳中的优势菌。生乳在冷藏运输或储存期间,嗜冷菌依旧可以生长繁殖,其分泌的蛋白酶和脂肪酶可耐高温,经过巴氏杀菌或超高温灭菌处理后依旧保持活性,因此,了解嗜冷菌的多样性及其产生的酶对提高乳及乳制品质量、减少腐败和浪费具有重要作用。本文通过介绍乳及乳制品中嗜冷菌污染现状及腐败危害研究,旨在为乳及乳制品行业的风险评估提供背景信息,从源头控制嗜冷菌对生乳的浪费,保证乳及乳制品的品质。 相似文献
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Effects of heating temperatures and addition of reconstituted milk on the heat indicators in milk 总被引:1,自引:0,他引:1
The objective of the present study was to evaluate the effect of heating temperatures and reconstituted milk on heat treatment indicators in milk by comparing the heat damage between raw milk and raw milk plus reconstituted milk (composite milk). The contents of lactulose, furosine, beta-lactoglobulin, and lactoperoxidase were determined after the heat indicators were heated to 65 to 115 °C for 15 s both in raw milk and composite milk. In the raw milk, the lactulose and furosine contents increased with increased heating temperature, while the beta-lactoglobulin content and lactoperoxidase activity decreased. The lactulose and furosine contents were increased after the addition of reconstituted milk. The reconstituted milk also significantly (P < 0.05) reduced the concentration of beta-lactoglobulin in the milk. Both heat treatment and an addition of reconstituted milk decreased the lactoperoxidase activity significantly (P < 0.05), and the lactoperoxidase activity was undetectable at 85 °C. The ratios of lactulose to furosine in pasteurized milk were higher than that in composite pasteurized milk. It is concluded that lactulose, furosine, and beta-lactoglobulin are suitable indicators of high heat pasteurization or raw milk, while lactoperoxidase may be used in monitoring mild heat pasteurization. Practical Application: Adequate heat treatment is necessary to destroy the microbes in raw milk. However, excessive heat treatment can result in inactivation of active compounds or loss of nutrients. The present study showed that the concentrations of lactulose, furosine, beta-lactoglobulin, and the activity of lactoperoxidase are sensitive to processing temperature and can serve as indicators of milk pasteurization. 相似文献
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Biochemical Characterization of an Extracellular Heat‐Stable Protease from Serratia liquefaciens Isolated from Raw Milk 下载免费PDF全文
François Baglinière Rafael Locatelli Salgado Cleonice Aparecida Salgado Maria Cristina Dantas Vanetti 《Journal of food science》2017,82(4):952-959
The protease Ser2 secreted by the psychrotrophic strain Serratia liquefaciens L53, a highly proteolytic strain isolated from Brazilian raw milk was purified and characterized. Using azocasein as substrate, Ser2 exhibited activity in a wide range of pH (5 to 10) and temperature (4 to 60 °C). The optimal activity was detected at pH 8.0 and at a temperature of 37 °C. This protease, still active at 4, 7, and 10 °C, was strongly inhibited by chelating agents and by dithiothreitol, a reducing agent. These results confirmed that Ser2 belongs to the peptidase family M10 and requires Ca2+, Zn2+, and disulfide bridges for stability. This protease is able to hydrolyze three kinds of casein in the preferential order of κ→ β→ α‐casein. Highly heat‐stable in skimmed, semi‐skimmed, and whole milk at 140°C with D‐values of 2.8, 3.9, and 4.5 min, respectively, Ser2 showed a residual activity between 87 and 100 percent after heat‐treatment of 65 °C for 30 min, 72 °C for 20 s, and 140 °C for 4 s that are commonly used in dairy industries. As the protease AprX that is mainly secreted by Pseudomonas genus, Ser2 could be one of the main causes of UHT milk destabilization during storage. 相似文献
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Pseudomonas fluorescens UQM2490, resistant to 250 μg rifampicin/ml, was derived from P. fluorescens JC1, a proteolytic psychrotroph isolated from raw milk. Growth of UQM2490 was followed in raw and ultra heat-treated milk, by viable counting on rifampicin-containing agar medium. The growth curves obtained demonstrate slower growth in raw milk than in treated milk and the variation in growth with change in inoculum level. Generation times in ultra heat-treated milk ranged from 9.5 to 14.1 h compared with 9.6 to 33 h in raw milk. 相似文献
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《Food microbiology》1988,5(1):9-16
The advantages of storing raw milk, which is to be used for Cheddar cheese manufacture, at 2°C rather than at 6°C was examined. Storage of milk at the lower temperature effectively reduced the level of psychrotroph growth, and after 4 days the psychrotroph counts in samples stored at 2°C were 100-fold lower than those found in samples stored at 6°C. There was no advantage in terms of cheese yield in storing milks at the lower temperature, but an overall improvement in cheese quality was noted in samples produced from milk stored at 2°C. 相似文献
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《Journal of dairy science》2019,102(6):5005-5018
Thermization is a sub-pasteurization heat treatment of cheese milk (at 57–68°C for 15–30 s) aimed to reduce the number of undesirable microbial contaminants with reduced heat damage to the indigenous milk enzymes. In this work, the effects of milk thermization on the compositional parameters, proteolysis indices, free fatty acid levels, and low molecular weight metabolite profiles of ovine cheese were studied. Cheese samples at different ripening stages and produced in 2 different periods of the year were analyzed. While the effects of milk thermization on cheese macro-compositional parameters and free fatty acid levels were not evident due to the predominant effects of milk seasonality and cheese ripening stage, the gas chromatography-mass spectrometry based metabolomics approach of ovine cheese produced from raw and thermized milk highlighted strong differences at the metabolite level. Discriminant analysis applied to gas chromatography-mass spectrometry data provided an excellent classification model where cheese samples were correctly classified as produced from raw or thermized milk. The metabolites that mostly changed due to the thermization process belonged to the classes of free amino acids and saccharides. Gas chromatography-mass spectrometry-based metabolomics has proven to be a valid tool to study the effect of mild heat treatments on the polar metabolite profile in ovine cheese. 相似文献
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The activities and rates of inactivation of four enzymes in raw buffalo milk were measured in relation to the process of heating to determine the value of these enzymes as markers for the evaluation of milk pasteurization. The activities of the enzymes alkaline phosphatase (ALP), lactic dehydrogenase (LDH), gamma-glutamyltransferase (GGT), and aspartate aminotransferase (AST) were measured before and after heating at 50, 60, 70, and 80 degrees C for 1, 3, 5, 10, 20, and 30 min. The enzyme GGT showed the highest activity (712 +/- 601 IU/liter), followed by LDH (386 +/- 183 IU/liter), ALP (295 +/- 164 IU/liter), and AST (18 +/- 4 IU/liter). Heating the milk at 50 degrees C for 1 to 30 min resulted in no effect on the activity of any of the enzymes. At 60 degrees C, ALP showed the highest sensitivity to heat inactivation, whereas all other enzymes showed resistance. At 70 degrees C, ALP activity was abolished completely after 1 min, whereas GGT and LDH lost most activity after 10 min, and AST still maintained 50% activity even after 30 min. At 80 degrees C, the activities of LDH and GGT were lost, whereas AST still retained some of its activity. The results suggest that in addition to ALP, LDH and GGT, but not AST, are potential markers for heat denaturation in buffalo milk, with GGT having the advantage that its concentration is the highest. 相似文献
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The detection of alkaline phosphatase (ALP) activity is used as a legal test to determine whether milk has been adequately pasteurized or recontaminated with raw milk. However, a wide variety of microorganisms produce both heat labile and heat stable ALPs which cannot be differentiated from the milk ALP by current enzymatic methods. Monoclonal antibodies specific of the bovine milk ALP were obtained in mice from a raw bovine milk ALP preparation. Coated in microtitre plates, these antibodies specifically capture the bovine milk ALP from dairy products. After washing, the enzymatic activity of the captured ALP is revealed by adding p-nitrophenyl-phosphate as a substrate. This simple immunoassay does not react with ALPs of intestinal or bacterial origin and, once optimized, was found to be the first immunoassay suitable to detect raw milk in boiled milk down to a 0.02% dilution. Moreover, in contrast with competitive indirect ELISA formats, the capture immunoassay does not require purified ALP. 相似文献
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The temperature at which raw milk was stored, within the range 4°-8°C, affected the rate of growth of bacteria and the release of free fatty acids. The effects were of both statistical and practical significance and it was shown that, by maintaining milk temperatures at 4°C, a useful extension of the storage time of raw milk could be achieved. Lipolysis in stored milk was not closely related to the total concentration of psychrotrophic bacteria, but lipolytic rancidity was not observed when the psychrotroph count was below 5 × 106 colony forming units/ml. 相似文献
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The evolution of free fatty acids (FFA) was monitored over 168 d of ripening in Cheddar cheeses manufactured from good quality raw milk (RM), thermized milk (TM; 65°C × 15 s), and pasteurized milk (PM; 72°C × 15 s). Heat treatment of the milk reduced the level and diversity of raw milk microflora and extensively or wholly inactivated lipoprotein lipase (LPL) activity. Indigenous milk enzymes or proteases from RM microflora influenced secondary proteolysis in TM and RM cheeses. Differences in FFA in the RM, TM, and PM influenced the levels of FFA in the subsequent cheeses at 1 d, despite significant losses of FFA to the whey during manufacture. Starter esterases appear to be the main contributors of lipolysis in all cheeses, with LPL contributing during production and ripening in RM and, to a lesser extent, in TM cheeses. Indigenous milk microflora and nonstarter lactic acid bacteria appear to have a minor contribution to lipolysis particularly in PM cheeses. Lipolytic activity of starter esterases, LPL, and indigenous raw milk microflora appeared to be limited by substrate accessibility or environmental conditions over ripening. 相似文献