金黄色葡萄球菌在生乳中生长预测模型的建立

目的建立生乳中金黄色葡萄球菌的生长预测模型。方法采用GB/T4789.37—2008第三法,测定不同温度下金黄色葡萄球菌在生乳中的生长曲线,利用麦夸特法和通用全局优化法将曲线数据分别拟合Gompertz方程、Logistic方程、Richards方程、Weibull方程、Baranyi方程和Monod方程,确定最适方程,建立一级模型。同时应用响应面方程建立二级生长预测模型。结果金黄色葡萄球菌在生乳中的最适预测模型为Gompertz模型。结论通过与多模型比较,建立了金黄色葡萄球菌在生乳中的生长预测模型。为该菌在生乳中的风险评估理论体系的建立提供理论基础,也为乳制品的安全生产和流通提供了科学依据。     

波动温度下原料乳中金黄色葡萄球菌的生长动力学模型

原料奶在实际运输过程中的温度是波动变化的。本文在建立10~37℃温度范围的金黄色葡萄球菌在原料乳中生长模型的基础上,得到温度变化对金黄色葡萄球菌生长状态的影响。采用"等效生长时间"理论,结合modified Gompertz模型得到波动温度下原料乳中金黄色葡萄球菌的生长模型。验证结果显示,R2,Af,Bf均接近于1,表明所建预测模型能够较好地预测波动温度下原料乳中金黄色葡萄球菌的生长状况。此外,将模型与Combase Predictor(CP)软件在相应条件下所建波动模型作比较,CP模型基于肉汤培养基而建,金黄色葡萄球菌的生长速率明显大于牛奶中培养的,表明预测软件应用于食品中进行波动温度建模时应作验证,在牛奶中建立的波动模型的适用性较高。     

生乳中金黄色葡萄球菌污染半定量风险评估研究

目的探索上海市生乳中金黄色葡萄球菌污染的风险。方法按微生物风险评估的程序,应用半定量风险评估软件(risk ranger)结合流行病学调查和微生物检测等。结果上海市金黄色葡萄球菌肠毒素性食物中毒列报告的细菌性食物中毒暴发事件第3位;金黄色葡萄球菌肠毒素性食物中毒的严重性中等、全人群易感;4—6月上海市生乳中金黄色葡萄球菌污染率为72.0%,乳及乳制品日均消费量达86.60 g/人;假设生乳在加工前金黄色葡萄球菌超过105 CFU/g的概率为1/1 000,则每人每天因食用污染金黄色葡萄球菌污染乳及乳制品引起食物中毒的概率为2.5×10-7,每年因金黄色葡萄球菌污染乳及乳制品食物中毒病例数862人,风险等级49。结论上海市生乳中金黄色葡萄球菌污染的风险程度属于中等,需加强监管。     

生乳中金黄色葡萄球菌污染快速微生物风险评估研究

应用快速微生物定量风险评估探索重庆市生乳中金黄色葡萄球菌污染的风险。方法利用重庆市生乳微生物风险监测数据、国内外相关研究资料,应用s QMRA快速微生物定量风险评估软件进行风险评估。计算得到重庆市因食用乳及乳制品导致金黄色葡萄球菌感染人数为12 619人,其中发生食源性疾病的人数为4 164人,食源性疾病发生概率为1.34×10-4,预估每人每天因食用金黄色葡萄球菌污染的乳及乳制品引起食源性疾病的概率为3.63×10-7。重庆市生乳中金黄色葡萄球菌污染的风险程度较高,应为重庆市食品安全风险优先监管领域之一。     

原料乳中金黄色葡萄球菌生长预测模型的建立

研究冬季、春季和夏季原料乳中金黄色葡萄球菌在15、25、37℃条件下的生长情况,并利用Logistic模型和Gompertz模型对生长数据进行建模。3个季节的原料乳中,金黄色葡萄球菌的Gompertz模型方根误差(RMSE)分别为0.0936(冬)、0.1057(春)和0.1032(夏),而Logistic模型相应的参数值为0.1498(冬)、0.1926(春)和0.1857(夏)。通过模型参数比较表明,Gompertz模型比Logistic模型更能准确的描述原料乳中金黄色葡萄球菌的生长情况;同时,建立以温度为自变量的平方根模型,以此来预测原料乳中金黄色葡萄球菌的生长速率。     

新乡市生乳中菌落总数和金黄色葡萄球菌及β-内酰胺酶调查

目的了解新乡市规模化奶牛养殖场生乳中菌落总数、金黄色葡萄球菌和β-内酰胺酶的基线数据,为生乳安全性风险评估及国家标准更新提供资料。方法以新乡市3家规模化奶牛养殖场(A、B、C场)为观测基地,2016年5月—2017年4月每月采集2家生乳样品各29份和1份混合样品。分别按照GB 4789.2—2010《食品安全国家标准食品微生物学检验菌落总数测定》和GB 4789.10—2010《食品安全国家标准食品微生物学检验金黄色葡萄球菌检验》测定菌落总数和金黄色葡萄球菌,胶体金法测β-内酰胺酶残留。结果 3家奶牛养殖场单份样品菌落总数的中位数分别为13 000、4 450、130 000 CFU/ml,明显低于GB 19301—2010《食品安全国家标准生乳》中的限量(2×10~6CFU/ml),差异有统计学意义(P0.01),3家奶牛养殖场的菌落总数之间差异有统计学意义(P0.05)。各奶牛养殖场单份样品的菌落总数与混合样品比较,仅B场差异有统计学意义(P0.05)。7~8月菌落总数较高。3家奶牛养殖场样品中金黄色葡萄球菌检出率分别为1.1%(4/360)、16.7%(30/180)和0.0%(0/180),计数结果为50~42 000 CFU/ml。3家奶牛养殖场的所有样品中均检出β-内酰胺酶,检出率为6.1%~10.6%。结论 GB 19301—2010生乳菌落总数限量远高于新乡市实际情况,建议修订标准;个别奶牛养殖场生乳中存在一定程度的金黄色葡萄球菌污染,需加强监管;筛查出的β-内酰胺酶需进一步鉴定其来源,同时要加强对β-内酰胺酶检测方法的研究。     

清蛋糕中金黄色葡萄球菌生长预测模型的建立

目的建立清蛋糕中金黄色葡萄球菌生长预测模型。方法选用清蛋糕和金黄色葡萄球菌作为研究对象,比较了6、15、25、35℃条件下金黄色葡萄球菌在糕点中生长情况,分别采用修正Gompertz模型(SGompertz)和修正Logistic模型(SLogistic)进行拟合,建立清蛋糕中金黄色葡萄球菌一级生长动力学模型,采用平方根模型和二次多项式模型描述温度与最大比生长速率(μmax)及延滞期(λ)的关系,并进行验证。结果SLogistic模型作为一级模型,能更好描述6～35℃条件下清蛋糕中金黄色葡萄球菌生长变化;平方根模型是拟合温度与最大比生长速率的最适二级模型;二次多项式模型是拟合温度与延滞期的最适二级模型。结论本研究建立的生长预测模型能够有效预测金黄色葡萄球菌在清蛋糕中的生长情况,为清蛋糕的定量风险评估提供参考。     

营养肉汤中不同因素影响下金黄色葡萄球菌生长模型的构建

采用营养肉汤培养基,研究不同温度、pH值和水分活度对金黄色葡萄球菌生长规律的影响,并构建金黄色葡萄球菌菌落数的一级生长模型和最大比生长速率、延滞期的二级生长模型,其中一级模型通过Baranyi模型来拟合;二级模型包括单因素二级模型和多因素二级模型,分别通过Belehradek平方根模型和二次多项式回归模型来拟合。结果表明:金黄色葡萄球菌生长速率随着温度、PH值和水分活度的增加而增加,而延滞期随着温度、PH值和水分活度的增加而降低,并且温度与PH值,温度与水分活度以及PH值与水分活度之间存在明显的交互作用。一级Baranyi模型、二级平方根模型以及多项式回归模型拟合性较好(R~2>0.85)。通过数学检验参数精确因子(A_f)、偏差因子(B_f)、均方根误差(RMSE)对模型进行数学检验,表明构建的一级、二级模型适用性、可靠性和拟合性均在可接受范围内,在建模设定的范围内能预测金黄色葡萄球菌建模范围内的延滞期和最大比生长速率。     

原料奶中病原菌的调查及代表性病原菌的研究

对榨乳过程进行了采样分析,确定了原料奶中的主要致病菌为金黄色葡萄球菌,并分析了原料奶在不同温度储存时金黄色葡萄球菌的生长情况以及金黄色葡萄球菌在酸奶发酵和冷藏过程中的存活情况。研究发现,酸奶的低酸性环境并不能有效的抑制金黄色葡萄球菌的生长,所以为了确保产品的安全性,要对奶牛的乳房炎和隐性乳房炎进行有效防治,并严格控制榨乳的卫生条件及原料奶的储存温度。     

低温储存原料乳中金黄色葡萄球菌风险研究

以新鲜原料乳为研究对象,研不同季节的原料乳中金黄色葡萄球菌在不同储存温度下的生长情况和产肠毒素情况,对低温储存原料乳中金黄色葡萄球菌在储存过程中风险评估。研究表明品质合格的原料乳在低温储存过程中,金黄色葡萄球菌的危害不明显。     

毛细管电泳法对乳及乳制品中乳源蛋白的研究

采用毛细管电泳方法对原料乳、市售鲜奶、不同厂家的巴氏灭菌乳、不同厂家和产地超高温灭菌乳(UHT)、调味乳、乳酸饮料、复原乳、酸奶、奶粉中蛋白成分进行检测。选择聚乙烯醇涂层毛细管,采用柠檬酸缓冲体系,在紫外检测214nm、分离电压20kV条件下对乳及乳制品中的α一乳白蛋白(α-La)、β一乳球蛋白(β-Lg)、α-酪蛋白(α-CN)、β-酪蛋白(β-CN)和k-酪蛋白(k-CN)进行分离测定。结果表明:五种蛋白的含量在原料乳(巴氏灭菌乳、市售鲜奶)、UHT乳、酸奶、调味乳、乳酸饮料、复原乳中依次降低,而UHT乳含量随保质期的增加而减少,奶粉中蛋白质含量因其适应人群而有差异。乳及乳制品中蛋白质的含量与其存在形式、产地及加工工艺相关。     

原料奶中病原菌的调查及代表性病原菌的研究

对榨乳过程进行了采样分析，确定了原料奶中的主要致病菌为金黄色葡萄球菌，并分析了原料奶在不同温度储存时金黄色葡萄球菌的生长情况以及金黄色葡萄球菌在酸奶发酵和冷藏过程中的存活情况。研究发现，酸奶的低酸性环境并不能有效的抑制金黄色葡萄球菌的生长，所以为了确保产品的安全性，要对奶牛的乳房炎和隐性乳房炎进行有效防治，并严格控制榨乳的卫生条件及原料奶的储存温度。     

Copper, zinc, tin and lead in canned evaporated milk, produced in Lithuania: the initial content and its change at storage

The study has been carried out to elucidate what contents of heavy metals were typical for canned milk products - evaporated (TS 25.5-28.5%) sterilized milk and condensed sweetened milk, produced in Lithuania in the period 1983-1997. The influence of storage time upon the level of Sn, Pb, Cu and Zn in the products has also been determined. The results show that the most considerable changes occurred in Cu concentration, which gradually decreased from the maximum level in 1983-1985 (2.23±0.18mg/kg) to the minimum level in the latest years (0.44±0.01 mg/kg). Such variation of copper content in canned milks can be closely connected with its changes in raw milk. Zinc content in canned milk products also was in good agreement with raw milk. The content of tin and lead in the canned products many times exceeded their concentration in raw milk and ranged from 28±2 and 0.093±0.005 to 114±4 and 0.29±0.01 mg/kg, respectively. It has been determined that the dependence of the concentration of tin and lead on the storage time of concentrated (or evaporated) sterilized milk is nearest to the parabolic, and in sweetened condensed milk to the exponential function, whereas the small increase of copper and zinc concentrations can be described by straight-line function. The functional dependence obtained enables one to predict the Sn and Pb level in canned evaporated milk products after storage and to foresee the safe initial concentration of these metals in freshly produced evaporated milk, assigned for storage.     

Risk evaluation for staphylococcal food poisoning in processed milk produced with skim milk powder

The growth of S. aureus and the production of staphylococcal enterotoxin A (SEA) in skim milk concentrates stored at inappropriate temperatures in a recovery milk tank (tank for excess concentrated skim milk) used in the manufacture of skimmed milk powder were investigated. Also, it was estimated if a possible outbreak of food poisoning would occur if the contaminated skimmed milk powder was used in the manufacture of processed milk. Skim milk concentrates with milk solid content of 15, 25, and 35% were inoculated with S. aureus at 1-2 log CFU/ml and incubated at 15, 25, or 35 degrees C for 0 to 24 h with or without shaking. Bacterial growth and the level of SEA production were measured. At 35 degrees C with shaking, there was a significant difference (p<0.05) in one way layout analysis of variance, and it was demonstrated that the growth of S. aureus and SEA production could be milk solid content-dependent. Shaking accelerated the growth of S. aureus and SEA production at 35 degrees C. Generally, skim milk powder is produced by mixing a set percentage of skim milk concentrates (recovery milk) from the recovery milk tank into raw milk. If recovery milk contaminated with S. aureus at levels of 1-2 log CFU/ml is kept at 15 to 35 degrees C due to a power failure, it was estimated that processed milk consumption of 670-1200 ml, 420-1500 ml and 18-83 ml would trigger the onset of food poisoning symptoms when skim milk concentrates (recovery milk) are stored at 25 degrees C for 24 h, 35 degrees C for 10 h, and 35 degrees C for 24 h, respectively, during the production of the skim milk powder. Based on these consumption levels, it was concluded that, if recovery milk cannot be refrigerated and is stored at room temperature (25 to 35 degrees C), it must be used within 8 h and preferably within 6 h.     

广州市牛奶中抗生素残留的现状分析

为了控制牛乳中抗生素的残留,对广州市牛奶中抗生素残留进行监测。结果表明不同给药途径及剂量可造成不同的残留时间;生牛奶及奶粉中抗生素残留阳性率显著比消毒牛奶高;出口生牛奶抗生素残留阳性率显著比内销生牛奶高;进口消毒牛奶及奶粉中未检出抗生素。     

PAHs concentration in heat-treated milk samples

In this study the presence of residual levels of Polycyclic Aromatic Hydrocarbons (PAHs) in milk samples from Calabria was evaluated. A comparative analysis of PAHs concentrations was conducted on raw, pasteurized, UHT semi-skimmed and whole milk.Quantitative determination of PAHs was performed by HPLC using a fluorescence detector and analysis in HPLC-MS was conducted to confirm the presence of these compounds.Residual levels of PAHs were found in all milk samples analyzed, showing higher concentrations in pasteurized and UHT milk than in raw milk samples.The results obtained demonstrate that PAHs presence also in raw milk is dependent from environmental pollution but pasteurization and UHT treatments of milk can influence PAHs formation; the differences found between whole and semi-skimmed samples can be due to different fat content of milk.     

Antibacterial activity of a chitooligosaccharide mixture prepared by cellulase digestion of shrimp chitosan and its application to milk preservation

The antibacterial activity of a chitooligosaccharide mixture prepared by digestion of shrimp chitosan with cellulase at 50 degrees C for 14 h was evaluated. Sugars with 1 to 8 degrees of polymer (DP) were found in this chitooligosaccharide mixture, and the weight percentage of sugars with DP > or = 6 was 44.3%. Minimal lethal concentrations of this mixture against Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, Shigella dysenteriae, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus in nutrient broth were 5 to 29 ppm, which were much lower than those of the chitosan reactant (50 to 1,000 ppm). The antibacterial activity of this mixture in the sterilized milk against E. coli O157, L. monocytogenes, Salmonella Typhimurium, and S. aureus was much stronger at 4 degrees C than at 37 degrees C. When raw milk was supplemented with either 0.24% or 0.48% (wt/vol) of this oligosaccharide mixture and stored at 4 degrees C for 12 days, its mesophilic and psychrotrophic counts were reduced by at least 3 log cycles, and there was very little change in pH. In addition, this mixture retarded the growth of Salmonella species and caused quicker reduction of Staphylococcus species in raw milk. Accordingly, the shelf life of raw milk at 4 degrees C was extended by at least 4 days.     

Comparison of the Baird-Parker agar and 3M Petrifilm Staph Express Count plate methods for enumeration of Staphylococcus aureus in naturally and artificially contaminated foods

The recently developed 3M Petrifilm Staph Express Count plate (PFSE) method was compared with the U.S. Food and Drug Administration Bacteriological Analytical Manual's Baird-Parker agar spread plate (B-P) method for enumeration of Staphylococcus aureus in naturally contaminated, mechanically separated poultry (MSP; n = 92) and raw milk (n = 12). In addition, mozzarella and Parmesan cheeses and hot-smoked rainbow trout and chub were surface inoculated with a three-strain mixture of S. aureus, stored at 5 degrees C, and periodically analyzed with both methods for numbers of S. aureus. For naturally contaminated raw milk and MSP samples, the PFSE method yielded counts that were not significantly different (P > 0.05) from counts obtained using the B-P method. From raw milk and MSP samples, 60% (21 of 35) and 55% (124 of 226), respectively, of confirmed (DNAse-positive) isolates from PFSE plates were identified by further testing as S. aureus. Corresponding S. aureus identification rates for isolates forming typical colonies on B-P plates were 53% (19 of 36) and 50% (125 of 248). For both methods, other staphylococci composed the vast majority of tested isolates that were not identified as S. aureus. For inoculated hot-smoked fish, S. aureus counts from the PFSE method were not significantly different from counts from the B-P method. Compared to the B-P method, significantly lower numbers of inoculated S. aureus were recovered using the PFSE method in analyses of mozzarella cheese stored 28 and 42 days at 4 degrees C. The PFSE and B-P methods were not significantly different for inoculated cheeses at all other sampling times. DNAse-positive isolates from PFSE analyses of inoculated cheeses and smoked fish were identified as S. aureus 98% (51 of 52) and 86% (36 of 42) of the time, respectively, as compared with 100% (58 of 58) and 95% (40 of 42) of the time for typical B-P isolates. Overall, the PFSE and B-P methods appeared to perform similarly in enumeration of S. aureus in animal-derived foods.     

Discrimination of Staphylococcus aureus strains from different species of Staphylococcus using Fourier transform infrared (FTIR) spectroscopy

Staphylococcus aureus is a widespread opportunistic pathogen that can cause food-borne illness and is sometimes associated with raw milk and raw milk cheese products. The traditional taxonomic procedures for classification of staphylococcal species are time consuming and often several tests are required. FTIR spectroscopy offers a rapid method for the discrimination and identification of S. aureus strains isolated from raw milk and raw milk cheeses. FTIR spectroscopy was used to discriminate S. aureus from other species of Staphylococcus. This was achieved by using a model composed of 39 species and subspecies of Staphylococcus. The model was validated using a set of spectra of strains isolated from raw milk and different varieties of French raw milk cheese. S. aureus was successfully discriminated from the other species of Staphylococcus and all the strains of S. aureus isolated from raw milk and different varieties of French raw milk cheese were also successfully identified as such. These results demonstrated that FTIR spectroscopy is a rapid (results obtained within 24 h starting from a pure strain or a single colony) and robust method for the identification of S. aureus isolates of dairy origin and food-borne origin in general.