共查询到19条相似文献,搜索用时 78 毫秒
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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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原料奶中嗜冷菌的测定 总被引:6,自引:4,他引:2
1概述如果UHT奶制品中发现有耐热蛋白酶存在(产品有凝块或发苦),或者有脂肪酶存在(产品有脂肪氧化味)时,则应对原奶中的嗜冷菌进行检验。2材料及仪器内装99ml无菌稀释液的烧瓶;氯化钠水溶液(浓度0.7%,用于制备稀释液);蒸馏水;无菌培养皿(预先灭... 相似文献
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J.C. Ribeiro Júnior A.M. de Oliveira F. de G. Silva R. Tamanini A.L.M. de Oliveira V. Beloti 《Journal of dairy science》2018,101(1):75-83
Refrigerated raw milk may contain psychrotrophic microorganisms that produce thermoresistant exoproteases and lipases, which may compromise the quality of processed fluid milk and dairy products during storage. The aim of this work was to quantify and identify the deteriorating psychrotrophic microbiota in Brazilian refrigerated raw milk using genetic diversity analysis. The mean psychrotrophic count was 1.1 × 104 cfu/mL. Of the total isolates, 47.8 and 29.8% showed deteriorating activity at 35°C within 48 h and 7°C within 10 d, respectively. Among the proteolytic species, more isolated by this study were Lactococcus lactis (27.3%), Enterobacter kobei (14.8%), Serratia ureilytica (8%), Aerococcus urinaeequi (6.8%), and Bacillus licheniformis (6.8%). Observed among lipolytics were E. kobei (17.7%), L. lactis (15.6%), A. urinaeequi (12.5%), and Acinetobacter lwoffii (9.4%). The isolates S. ureilytica, E. kobei, Pseudomonas spp., and Yersinia enterocolitica potentially produced alkaline metalloprotease (aprX). Despite the low counts, a considerable portion of the psychrotrophic microbiota presented spoilage potential, which reaffirms the need for rigor in the control of contamination and the importance of rapid processing as factors that maintain the quality of milk and dairy products. 相似文献
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Detection of the apr gene in proteolytic psychrotrophic bacteria isolated from refrigerated raw milk 总被引:1,自引:0,他引:1
Martins ML de Araújo EF Mantovani HC Moraes CA Vanetti MC 《International journal of food microbiology》2005,102(2):203-211
Bacteria of the genus Pseudomonas have been associated with the spoilage of raw milk and dairy products due to the production of thermostable proteolytic enzymes. The apr gene encodes for alkaline metalloprotease in Pseudomonas and other related bacteria. Its presence in psychrotrophic proteolytic bacteria isolated from raw milk collected from cooling tanks was verified. A polymerase chain reaction (PCR) technique was used with degenerate primers. Total DNA from 112 isolates was pooled in different groups and then used as template for the amplification reactions. Controls consisted of DNA extracted from 26 cultures. An expected DNA fragment of 194 bp was detected in groups that contained bacteria identified as Pseudomonas. The PCR product was observed only when DNA from control cultures of Pseudomonas aeruginosa, Pseudomonas fluorescens, Serratia marcescens and Aeromonas hydrophila were used. A detection limit assay indicated that the apr gene could be directly amplified from pasteurized milk inoculated with 10(8) CFU/ml of P. fluorescens. With this method it was possible to detect proteolytic bacteria at 10(5) CFU/ml in reconstituted skim milk powder if cells were recovered for DNA extraction before amplification. 相似文献
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Proteolytic activity among psychrotrophic bacteria isolated from refrigerated raw milk 总被引:1,自引:0,他引:1
MARIA F B L NÖRNBERG ROSANE S C FRIEDRICH RITA D N WEISS EDUARDO C TONDO ADRIANO BRANDELLI 《International Journal of Dairy Technology》2010,63(1):41-46
Psychrotrophic bacteria were isolated from refrigerated raw milk from a processing plant in Southern Brazil. Psychrotrophic counts were between 4.9 and 7.8 log cfu/mL, and 5.3 to 7.2 log cfu/mL, for samples collected at the truck and the milk storage silo, respectively. Among the bacterial isolates, 90% were Gram-negative. Most strains presented low proteolytic activity, but strains of Burkholderia cepacia, Klebsiella oxytoca and Aeromonas sp. showed higher than 20 U/mL on azocasein as substrate. Crude proteases from selected strains were resistant to conventional heat treatments and caused coagulation of UHT milk after 5 days storage at room temperature. 相似文献
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The aim of this study was to use molecular techniques to assess the microbiota of eight raw cow's milk samples at biotype and species level. Sixty-six isolates from raw milk samples were screened by Randomly amplified polymorphic DNA–PCR (RAPD–PCR) biotyping and representative strains of RAPD–PCR profiles were identified by 16S rRNA gene sequencing. Pseudomonas spp. were the most commonly occurring contaminants along with Enterobacteriaceae such as Hafnia alvei, Serratia marcescens and Citrobacter freundii. Moreover, Gram-positive isolates belonging to the genera Staphylococcus and Lactococcus were also found. Experiments of growth at different temperatures showed that more than 50% of the Gram-negative isolates could grow at chill temperatures and that 65% of the Pseudomonas spp. strains grew at 7 °C within 5 days. Only 13 Gram-negative isolates displayed proteolytic activity on milk agar, suggesting that not all the biotypes of milk contaminating species are able to perform this spoilage-associated activity. Among the Gram negative, the proteolytic strains were mainly Peudomonas spp. that displayed the activity at both 7 °C and 20 °C. A reliable molecular identification of raw milk microbiota is important for the study of the microbiological quality of raw milks and for the assessment of the ecology at species level in order to develop improved systems, preventing contamination and having the best conditions for the storage of milk. 相似文献
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利用API 20NE细菌鉴定系统快速鉴定出原料乳中主要的嗜冷菌。大大缩短常规嗜冷菌鉴定所用的时间。 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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Martins ML Pinto CL Rocha RB de Araújo EF Vanetti MC 《International journal of food microbiology》2006,111(2):144-148
The random amplified polymorphic DNA (RAPD) fingerprinting technique was used to assess the genetic diversity of 70 isolates of Gram-negative proteolytic psychrotrophic bacteria that were isolated from refrigerated raw milk. Three oligonucleotides, which generated 87 fragments of polymorphic DNA, were used in the amplification reactions. The genetic distance values calculated using Jaccard's coefficient showed there was high genetic variability among the isolates. Cluster analysis procedures suggested that the genetic variability among isolates belonging to the same species was as high as the variability among different species. Clustering by the UPGMA hierarchical method and data graph dispersion indicated a tendency of the isolates to group according to whether they did or did not ferment glucose. 相似文献