Nisin在巴氏消毒乳中的应用

本文研究了不同浓度的Nisin对巴氏消毒乳的保藏作用,结果表明在巴氏消毒乳杀菌前加入一定量的Nisin,能够大大延长巴氏消毒乳的保质期。     

牛油火锅底料冷藏储存过程中品质变化

以牛油火锅底料为研究对象,测定在冷藏(4℃)条件下其水分、酸价、过氧化值、辣椒素类似物、脂肪酸组成及相对含量随时间变化情况。结果表明:样品的水分、酸价、过氧化值随时间延长均呈上升趋势,且氧化速度逐渐加快。辣椒素类似物含量随时间延长而下降,且降解速度逐渐减慢。气相色谱质谱分析得出不饱和脂肪酸含量下降,低级脂肪酸含量升高。因此,控制牛油火锅底料油脂在冷藏期间的劣变有利于维持产品品质,延长其货架期。     

巴氏消毒乳加工工艺及原理

巴氏杀菌是指杀死引起人类疾病的所有病原微生物及最大限度破坏腐败菌和乳中酶的一种加热方法,以确保产品的安全性。     

巴氏杀菌乳门店冰箱冷藏贮存售卖期间的温度及品质变化

为了研究巴氏杀菌乳在门店冰箱贮存售卖期间的温度和品质变化特点;通过对玻璃瓶装巴氏杀菌乳在冷藏贮存售卖冰箱温度波动变化的情况下,实测获取冰箱箱体温度和时间参数,以不开启售卖同条件的冷藏贮存冰箱为对照,考察过程中的微生物指标、理化指标和感官品质变化情况。研究表明,在1~5 d时间内,不同贮存条件下,样品的蛋白质、脂肪、乳糖、非脂乳固体、酸度几乎不变,感官品质不变差异不明显,大肠菌群、金黄色葡萄球菌及沙门氏菌未检出,而菌落总数增长速度试验组冰箱明显快于对照组冰箱,存在统计学显著性差异(p0.05),但两组都符合国家标准。说明样品在冰箱冷藏贮存售卖期间温度的波动,对产品品质会造成影响,低的贮存温度及相对短的贮存时间有利于巴氏杀菌乳优良品质的保持。建议玻璃瓶装巴氏杀菌乳在售卖贮存过程,要控制温度波动,保证在保质期内冷藏贮存产品超6℃累积时间不超过7 h,温度在8℃以下,贮存环境箱体累积超过6℃不超过9 h,温度在9℃以下。     

基于粮食储存过程中品质的变化与控制

我国是一个人口大国,解决人口的粮食问题是国民发展的关键所在。因此,粮食的储存关乎农业经济的发展与民生工作的稳定,如何解决粮食在储存过程中容易发生变质的问题已经成为相关工作单位和人员的重点研究方向。本文以粮食在仓库内存储环节中的品质变化为析课题,结合实际工作经验,对解决粮食变质的措施进行综合总结,意在降低粮食损耗,提高粮食储存效益。     

巴氏杀菌乳冷藏配送期间的温度及品质变化

为研究巴氏杀菌乳配送期间的温度和品质变化特点,通过跟车实测获取牛乳配送温度和时间参数,以2℃恒温过程为对照组,考察巴氏杀菌乳在8℃和10℃恒温过程中的菌落总数、酸度和蛋白质含量的变化情况。结果表明,冷藏车车厢内各个部位温度不均;车厢门口和车厢中部的乳温低于车厢最内部乳温;配送时间超过12h后牛乳品质变化有加快趋势。      

巴氏杀菌机消毒过程的控制

运用先进的水处理方法，解决了巴氏杀菌机使用过程中产生水垢和沉淀，导致腐蚀速度加速，水耗量加大等弊端。     

巴氏杀菌乳冷藏配送期间的温度及品质变化

为研究巴氏杀茵乳配送期间的温度和品质变化特点,通过跟车实测获取牛乳配送温度和时间参数,以2℃恒温过程为对照组,考察巴氏杀菌乳在8℃和10℃恒温过程中的菌落总数、酸度和蛋白质含量的变化情况.结果表明,冷藏车车厢内各个部位温度不均;车厢门口和车厢中部的乳温低于车厢最内部乳温;配送时间超过12h后牛乳品质变化有加快趋势.     

低温储存期间原料乳微生物预测模型建立

本研究对秋季低温储存原料乳进行预测微生物学研究。使用Gompertz模型建立4~14℃储存的秋季原料乳中总菌落和嗜冷菌的生长动力模型。模型可以有效的模拟秋季原料乳中微生物的生长情况,模型的相关系数均大于0.972,可以用来预测微生物生长情况和达到控制下限的时间。研究表明嗜冷菌是低温储存的原料乳中优势微生物,在4~8℃储存温度下总菌落数与嗜冷菌的数量呈很好的相关性(R~2=0.931),可以通过总菌数推算出嗜冷菌的数量,保证乳制品的品质。      

应用PCR-DGGE对巴氏消毒乳中腐败细菌的污染溯源研究

运用PCR-DGGE技术分析了巴氏杀菌乳从原料乳到杀菌、灌装这两个加工关键控制点的微生物动态变化和差异性,容易发生污染的环节是挤乳环节、杀菌后的加工管道和包装环节。原料乳中易携带的细菌是乳酸链球菌（Lactococcus lactis subsp.）和乳酸杆菌（Lactobacillus sp.）;挤乳环节中易受无乳链球菌（Streptococcus agalactiae）污染;杀菌后的加工管道易受热杀环丝菌（Brochothrix thermosphacta）、钻黄肠球菌（Enterococcus casseliflavus）、瑞士乳杆菌（Lactobacillus helveticus）和2株非培养的假单胞菌属（Uncultured Pseudomonas sp.）污染;肉杆菌属（Carnobacterium sp.）和产乳酸菌素的肉杆菌（Carnobacterium maltaromaticum）则在挤乳环节、杀菌后的加工管道或包装环节都可能被污染。      

巴氏杀菌奶微生物风险评估的研究进展

本文从常见的可能引发巴氏杀菌奶食用风险的食源性致病菌——金黄色葡萄球菌和单核细胞增生李斯特菌,概述了微生物风险评估的内容,从微生物风险评估程序的四个步骤,即危害识别、危害特征描述、暴露评估及风险描述,分别对国内外金黄色葡萄球菌和单核细胞增生李斯特菌进行了综述,并就国内外微生物风险评估在巴氏杀菌奶及其相关乳制品中的研究进展进行了综述,最后对巴氏杀菌奶的微生物风险评估在中国未来的发展方向作了展望。     

Chemical,microbiological and sensory changes of dried Acetes chinensis during accelerated storage

Chemical, microbiological and sensory changes of dried Acetes chinensis during 28 days of accelerated storage at 37 °C were studied. Eighty volatile components including alcohols, aldehydes, acids, ketones, esters, alkanes, nitrogen-containing components, aromatic components and terpenes were identified by headspace sampling and gas chromatography–mass spectrometry (GC–MS) method during storage. Among these volatile components, the relative content of trimethylamine was the highest during storage, which increased from 11.36 ± 1.02% at day 0 to 14.60 ± 0.58% at day 28. Values of total volatile base nitrogen (TVB-N), trimethylamine (TMA), thiobarturic acid reactive substances (TBARS), total viable mesophilic count (TVC) and sensory characteristics of colour and odour for dried A. chinensis changed significantly during storage. Volatile components, TVB-N, TMA, pH, TBARS, TVC, colour and odour characteristics at different storage time were statistically interpreted by principle component analysis (PCA) method in order to found the main indices for the freshness of dried A. chinensis. The results suggested that colour, TMA, TVB-N, TBARS, odour, TVC and some volatile components could reflect the quality changes perfectly.     

Survey of the microbiological quality of the raw cow milk in the Tadla area of Morocco

Cow milk samples were collected during three periods and from four milk collection centres located in four different geographical zones. Samples were analysed for their standard plate count, enterococci, total coliform and feacal coliform, lactic acid bacteria, spoilage bacteria and some of the pathogenic bacteria. The most contaminated cooperatives were those located essentially in the irrigated zones. The less contaminated ones belong to semipublic farms. It seems that transportation, milking and pre‐storage conditions constitute the main basic relevant factors for heavy bacterial contamination. This is the first survey of the microbiological characteristics of raw milk produced in the Tadla area of Morocco.     

Evaluation of polyethylene terephthalate as a packaging material for premium quality whole pasteurized milk in Greece

Chemical, microbiological and sensorial changes in premium quality whole pasteurized milk stored at 4 °C under fluorescent light was studied for a period of 13 days. Milk containers tested included 1 l bottles made of (a) clear PET + UV blocker, 350–400 μm in thickness bearing a transparent label, (b) clear PET + UV blocker, 350–400 μm in thickness bearing a white colored label, (c) clear PET 350–400 μm in thickness. Milk packaged in 1 l coated paperboard cartons and stored under the same experimental conditions served as the “commercial control” sample. Data were obtained for lipid oxidation, lipolysis, proteolysis, vitamin A, E and riboflavin content, microbial growth including mesophilic and psychrotrophic counts and sensorial attributes (odor and taste) of whole pasteurized milk. Results showed satisfactory protection of milk packaged in all containers with regard to microbiological and chemical parameters assessed over the 13-day period. Based on sensory analysis, the shelf life of premium quality whole pasteurized milk tested in the present study was 10–11 days for both samples packaged in clear PET + UV bottles and in paperboard cartons and 8–9 days for clear PET bottles. Vitamin E losses recorded after 10 days of storage were respectively 42.7, 53.6 and 43.9% for samples packaged in clear PET + UV protected bottles, clear PET and control samples. Respective losses for riboflavin were 38.7, 52.5 and 35.0%. Average losses for vitamin A were 20.6% for all packaging materials. Clear PET + UV provided equal or better protection to milk as compared to the paperboard carton. Clear PET was the least effective in retaining light-sensitive vitamins. Based on spectral transmission curves of packaging materials tested, it is suggested that the use of a UV blocking agent in combination with a dark color pigmentation (blue, green etc.) in fresh milk packaging will provide a better protection to light-sensitive vitamins in cases where the expected shelf life of milk exceeds 5–6 days.     

Evaluation of polyethylene terephthalate as a packaging material for premium quality whole pasteurized milk in Greece

Chemical, microbiological, and sensorial changes in premium quality whole pasteurized milk stored at 4 °C under fluorescent light for one day followed by storage in the dark for an additional 12 days was studied. Milk containers tested included 1 l bottles made of (a) clear PET + UV blocker, 350–400μm in thickness bearing a transparent label, (b) clear PET + UV blocker, 350–400 μm in thickness bearing a white colored label, (c) clear PET 350–400 μm in thickness. Milk packaged in 1 l coated paperboard cartons and stored under the same experimental conditions served as the “commercial control” sample. Data were obtained for lipid oxidation, lipolysis, proteolysis, vitamin A, E, and riboflavin content, microbial growth including mesophilic and psychrotrophic counts and sensorial attributes (odor and taste) of whole pasteurized milk. Results showed satisfactory protection of milk packaged in all containers with regard to microbiological and chemical parameters assessed over the 13 day period. Based on sensory analysis, the shelf life of premium quality whole pasteurized milk tested in the present study was 10–11 days for samples packaged in clear PET+UV bottles and 9–10 days for clear PET bottles and paperboard cartons. Vitamin A losses recorded after 10 days of storage were respectively 15.9, 20.6, and 14.3% for samples packaged in clear PET+UV protected bottles, clear PET, and control samples. Respective losses for Vitamin E were 26.4, 36.6, and 35.0% and for riboflavin 32.9, 38.3, and 32.5%. Clear PET + UV provided equal or better protection to milk as compared to the paperboard carton. Clear PET was the least effective in retaining light-sensitive vitamins. Based on spectral transmission curves of packaging materials tested, it is suggested that the use of a UV blocking agent in combination with a dark color pigmentation (blue, green etc.) in fresh milk packaging will provide a better protection to light-sensitive vitamins in cases where the expected shelf life of milk exceeds 5–6 days.     

Quality changes of burnt aromatic coconut during 28-day storage in different packages

The shelf-life of unwrapped, film-wrapped and vacuum-packed burnt aromatic coconut was studied at 5±1 °C and 80-90% relative humidity. Regardless of the packaging treatments, weight loss of whole burnt coconut increased with storage time. Transmittance and lightness (L*) values of coconut water decreased (P<0.05) with longer storage time. The pH of coconut water and coconut meat from the vacuum-packed treatment decreased as storage time increased. Sensory analysis showed that, for all treatments, the yellowness intensity of coconut water increased whereas its transparency decreased with time. The sourness intensity of vacuum-packed coconut water increased on later days of storage. Only the film-wrapped coconut, having the shortest shelf-life, had mold on its shell and husk at the end of storage. This study showed that the unwrapped, film-wrapped and vacuum-packed burnt coconuts could be stored for up to 14, 18 and 28 days, respectively, under the conditions used in this study.     

Survival of Helicobacter pylori in artificially contaminated ultrahigh temperature and pasteurized milk

Helicobacter pylori (H. pylori) is a very important bacterial pathogen of humans which may cause gastrointestinal illnesses ranging from gastric and duodenal ulcers to neoplastic diseases such as MALToma and gastric cancer. Transmission via contaminated food is still uncertain but several authors believe this can realistically occur and milk may act as a vehicle of infection. This paper reports the results of H. pylori survival trials in pasteurized and ultrahigh temperature (UHT) milks artificially contaminated and aerobically stored at 4 degrees C. The results obtained showed that the four strains used in this study (H. pylori nat 18-19-20 and H. pylori ATCC 43504), had a progressive reduction in bacterial load with a median survival of 9 days in pasteurized milk and 12 days in UHT milk, with approximate average of initial inoculum of 10(5) and 10(6)cfu/ml, respectively. These findings are very important to clarify the route of transmission of H. pylori to humans via food and for implementation of a correct risk analysis for food safety purposes.     

Effect of technological parameters on the characteristics of kasseri cheese made from raw or pasteurized ewes' milk

Two groups of kasseri cheese (pasta filata type) were manufactured from raw or pasteurized ewes' milk, without starter cultures. Cheeses of each group were divided into two subgroups: the first was ripened and stored at 4°C and packaged in plastic film; the second ripened and stored at 15°C and coated with paraffin wax. Milk pasteurization and technological parameters had a significant effect on the pH ( P  < 0.05), while only technological parameters had an effect on the total solids content. At day 120, the range of mean cfu/g counts for the mesophilic aerobic flora was 9.5 × 10⁷−1.4 × 10⁸; for the thermophilic streptococci, the range was 2.6 × 10⁷−7.6 × 10⁷; and for the thermophilic bacilli, 9.8 × 10⁶−1.7 × 10⁷. Changes in the N fractions became significant after 30 days of ripening. For mature 120-day-old cheeses, the percentage of total N soluble at pH 4.6 was 22.7%–22.9% in raw milk cheeses and 19.0%–21.7% in pasteurized milk cheeses. The percentage of total N soluble at 12% TCA was 10.1%–12.2% in raw milk cheeses and 7.3%–11.5% in pasteurized milk cheeses; the percentages of total N soluble at 5% PTA were 3.1%–4.0% and 2.6%–3.6%, respectively. The residual α_s-casein percentages at day 120 ranged between 63% and 78% of the respective area at day 1; the residual β-casein ranged between 67% and 75%. There were some characteristic differences in the reverse phase-HPLC peptide profiles of the four cheeses. In general, the effect of the different ripening conditions was more pronounced in cheeses made from pasteurized milk.     

Proteolysis of ultra-high pressure homogenised treated milk during refrigerated storage

Plasmin residual activity and its relation to proteolysis of milk subjected to ultra-high pressure homogenisation (UHPH; 200–300 MPa, inlet temperature = 30 °C and 40 °C) and to a high-pasteurisation treatment (90 °C, 15 s) were studied during refrigerated storage. Proteolysis was examined by capillary electrophoresis, HPLC peptide profiles, pH 4.6-soluble nitrogen and free amino acids. Inactivation of plasmin increased as homogenisation pressure did. Extensive proteolysis, was observed in 200 MPa 40 °C milk, due to its higher native and microbial enzyme contents, compared with the other samples. In general, hydrolysis of β-casein, hydrophobic peptide and pH 4.6-soluble nitrogen levels increased with higher residual plasmin activity, while hydrophilic peptides were not affected by the different treatments applied. β-Lactoglobulin was denatured to a greater extent by thermal treatment than by UHPH treatments. This study provides further insight into how UHPH treatments influence milk properties.