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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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主要研究了牛乳中嗜冷菌数与其产生的耐热性胞外蛋白酶活性的相关性.从原料乳中分离出一株优势嗜冷菌,实验室初步鉴定后用API20NE系统进行鉴定,鉴定该菌为荧光假单胞菌(Pseudomonas Fluorescens),产酶实验结果表明,该菌产耐热性胞外蛋白酶.利用该菌株研究牛乳中单一嗜冷菌菌数与蛋白酶活性的关系,结果表明菌数与蛋白酶活性呈一定正相关,回归方程为Y=0.4548ln(X) 0.4178,决定系数R2=0.8172,相关系数R=0.9039,差异极显著(P<0.01);自然状态下,原料乳中嗜冷菌数与蛋白酶活性关系实验结果表明,原料乳在不同条件下贮存,嗜冷菌数有明显的增加趋势,但原料奶中嗜冷菌数和蛋白酶活性之间没有多少相关性. 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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原料乳中嗜冷菌超标会产生较高水平的耐热蛋白酶和脂肪酶,这两种酶是导致产品进入货架期后出现质量问题的重要原因。为探究牧场奶牛生活环境以及原料乳在流转过程中不同环节的微生物多样性,找出牧场中嗜冷菌的污染来源,本研究选取河北地区某规模化奶牛养殖场,采集TMR饲料、牛舍垫土、头三把奶、头三把奶之后的常规乳以及储奶罐中的原料乳等样品,利用宏基因组测序技术对所有样品的菌群结构、嗜冷菌种类及丰度进行分析。结果表明:在门水平上,主要微生物为变形菌门、厚壁菌门、放线菌门,在属水平上主要是无形体属、链球菌属、肠球菌属、短螺菌属、芽孢杆菌属、假单胞菌。此外对样品中的关键嗜冷菌(假单胞菌)进行分析,牛舍垫土的多样性最丰富的,包含了牧场中常规乳及储奶罐中乳假单胞菌种类的99.63%和96.39%,说明牛舍垫土是各类假单胞菌潜在的污染源。 相似文献
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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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Microbial and sensory quality of commercial fresh processed red lettuce throughout the production chain and shelf life 总被引:3,自引:0,他引:3
Red pigmented 'Lollo Rosso' lettuce was processed under usual and controlled conditions in an industrial plant. At different steps of the production chain (reception, shredding, washing, draining, rinsing, centrifugation, and packaging), microbial counts were evaluated. Following industrial practices, processed lettuce was packaged at 5 degrees C in sealed polypropylene (PP) bags with an initial atmosphere containing 3 kPa O(2) and 5 kPa CO(2). The numbers of psychrotrophic bacteria, coliform and lactic acid bacteria (LAB) were influenced by all the studied steps of the production chain of the fresh processed 'Lollo Rosso' lettuce. Shredding, rinsing and centrifugation in particular increased bacterial counts. During a storage period of 7 days at 5 degrees C, sensory attributes (general appearance, texture, aroma, translucency, initial and persistent off-odors, leaves superficial browning, leaves edges browning, and decay) as well as microbial counts (psychrotrophic and mesophilic bacteria, coliforms and lactic acid bacteria) were monitored. Due to high microbial counts and off-odors evaluation, a shelf life shorter than 7 days should be considered for fresh processed 'Lollo Rosso' lettuce. 相似文献
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The numbers of psychrotrophic bacteria in prerigor ground pork were slightly greater than in postrigor ground pork throughout an 11-day storage period at 2°C. Freezing both types of samples and subsequent thawing before storage at 2°C reduced the initial psychrotrophic counts but the freezing effects did not persist beyond 8 days of storage. Differences in psychrotrophic counts between prerigor and postrigor ground pork were not sufficiently great in any comparison to limit the use of prerigor grinding of pork. 相似文献
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G F Senyk S M Kozlowski P S Noar W F Shipe D K Bandler 《Journal of dairy science》1987,70(6):1152-1158
Standard plate counts, psychrotrophic bacterial counts, and coliforms were determined by conventional plating techniques and by Petrifilm TM plates, a dry culture medium, for 48 commercially processed milk samples (24 whole milk and 24 skim milk). The Petrifilm SM plate counts were compared with counts on standard methods agar for the standard plate count, psychrotrophic bacterial count, and rapid psychrotrophic bacterial count. The Petrifilm violet red bile plate counts were compared with counts on violet red bile agar for coliform test with a solid medium and the preliminary incubation method for detection of coliforms. Standard plate counts were determined within 24 h of packaging and after 7, 10, and 14 d of storage at 6.1 degrees C. Psychrotrophic bacterial counts and coliform counts were determined with 24 h of packaging and after 7 d storage. There was a strong linear relationship between Petrifilm SM and standard methods agar plates (excluding counts on samples plated within 24 h of packaging) and for the psychrotrophic bacterial count method. Petrifilm SM had a weak linear relationship with Standard Methods Agar plates for the rapid psychrotrophic bacterial count. Coliform counts determined on Petrifilm violet red bile plates were generally within the same range as counts on violet red bile agar plates. The positive predictive values for the Petrifilm violet red bile plates and violet red bile agar plates were essentially the same for samples plated within 24 h of packaging. 相似文献
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It has been recognized that biogenic amines (BA) content in meat can be considered a freshness marker. Considerable amounts of some BAs can appear during food storage under certain conditions, according to the handling of the raw material, technology applied, storage temperature and time, packaging condition, mainly if amino acid - decarboxylase positive microorganisms are present. The aim of this study was to evaluate the psychrotrophic bacteria growth and metabolic production of BAs during chill storage of beef. The vacuum packed beef cuts (Longissimus dorsi muscle) were analyzed during storage at 7 °C at 0, 15, 30, 45, and 60 d, to determine the psychrotrophic bacteria growth and the BAs amount. The BAs considered were: putrescine, cadaverine, histamine, spermidine, and spermine. The BAs quantitative determination was carried out by reversed phase high-performance liquid chromatography (HPLC) with UV detection. Statistic procedures were performed using SAS statistical software. The growth parameters of psychrotrophic bacteria including lag phase, maximum specific growth rate, maximum bacterial cell density, initial population, mean square error, and coefficient of determination were determined according to Baranyi and Roberts model. The values of histamine and spermidine increased significantly (P < 0.0001) during storage time, while the levels of spermine decreased (P < 0.0001). Psychrotrophic bacteria counts increased significantly (P < 0.0001) reaching 7.6 log cfu/g over time. The counts of this group positively correlated to histamine and spermidine (r = 0.68 and 0.61, respectively), while spermine showed a negative correlation (r = -0.70). Conversely, no significant correlation was found between psychrotrophics counts and putrescine or psychrotrophics counts and cadaverine. 相似文献
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Comparison of the heat resistance of bacterial lipases and proteases and the effect on ultra-high temperature milk quality 总被引:3,自引:0,他引:3
Thirty-four of 49 isolates of psychrotrophic bacteria produced extracellular lipase or protease when grown in rehydrated nonfat dry milk. The cell-free crude preparation from 50% of these had either heat-resistant lipase or protease; in 30% both enzymes were heat resistant. Eight isolates were selected for further evaluation of effect on ultra-high temperature processed milk. Free fatty acids and free amino groups of milk precultured with the bacteria increased at different rates depending on the isolate. Partially purified lipase from one of these bacteria (Acinetobacter sp.) caused free fatty acids to increase following ultra-high temperature processing when the milk was stored at 10, 21, or 32 degrees C for 4 wk. The increase was temperature dependent. Lipase activity of .0012 units/ml added prior to processing caused significant increases in free fatty acid at 21 and 32 degrees C in 4 wk. 相似文献
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《Food microbiology》2005,22(2-3):227-231
White croaker (Micropogonias furnieri) were submitted to a direct electric current post-mortem and stored refrigerated at 4°C for 16 days. Flesh and surface of electrically treated fish exhibited higher mesophilic bacteria counts than controls on the 3rd and on the 6th day of storage, respectively. Conversely, electrical treatment reduced flesh and surface psychrotrophic bacteria counts on the 12th and on the 16th day of storage, respectively. These changes had no influence on fish shelf life since they occurred when microbial counts were higher than the recommended limit for human consumption. Electrical treatment significantly reduced total count of mesophilic but did not affect psychrotrophic bacteria in the water used in fish treatment. These results suggest that although post-mortem application of electric current does not increase fish shelf life, it may reduce microbial counts in the water used in fish processing. 相似文献
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Effectiveness of chitosan edible coatings to improve microbiological and sensory quality of fresh cut broccoli 总被引:3,自引:0,他引:3
The effects of chitosan edible coating on microbiological and sensory quality of refrigerated broccoli were studied. The antimicrobial effects of chitosan on the native microflora (mesophilic, psychrotrophic, yeast and molds, lactic acid bacteria and coliforms) and on the survival of E. coli O157:H7 inoculated in broccoli were evaluated.Chitosan treatments resulted in a significant reduction in total mesophilic and psychrotrophic bacteria counts with respect to the control samples during the entire storage period. There was an immediate decontaminating activity of chitosan. At the end of the storage, yeast and molds was the most dominant flora representing the largest part of the total aerobic counts. Lactic acid bacteria (LAB) numbers remained relatively low during the whole storage in all samples. Chitosan coating inhibited the growth of total coliform throughout the storage time. Also, chitosan treatments resulted in a bactericidal effect on E. coli endogenous and a significant decreased in total E. coli counts (endogenous and O157:H7). The application of chitosan coating on fresh cut broccoli inhibited the yellowing and opening florets. The results of this experiment showed that the use of chitosan coating is a viable alternative in controlling the microorganisms present in minimally processed broccoli, improving its sensory quality. 相似文献