寿命可靠性计算在食品货架期分析中的初步应用

以市售灭菌乳为研究对象,应用Weibull模型通过对食品非感官指标的分析,预测食品的货架期。灭菌乳分别在25、30、35、40℃环境下恒温储藏45d,并定期随机抽样进行感官检验和测定酸度。应用Weibull hazard analysis(WHA)方法分析非感官试验数据来预测样品货架期,并进行了寿命可靠性分析。     

应用Weibull Hazard Analysis方法预测食品货架寿命

本实验以市售灭菌乳为研究对象,应用Weibull模型通过对食品非感官指标的分析,预测食品的货架期。灭菌乳分别在25、30、35、40℃环境下恒温储藏,并定期随机抽样进行感官检验和测定酸度、细菌总数。应用Weibull Hazard Analysis(WHA)方法分析非感官实验数据来预测样品货架期,并与采用寿命加速方法ASLT和文献WHA方法得到的预测结果进行了比较。     

基于高通量测序解析UHT灭菌乳品质劣变关联微生物

针对超高温灭菌（ultra-high temperature treated,UHT）乳在货架期内出现的脂肪上浮、水乳分离、沉淀等品质劣变问题,利用高通量测序和生物信息学等技术方法,对大型乳企采集的9份在货架期内品质劣变的UHT乳和正常质量的UHT乳样品的理化指标、酶活性、微生物菌群进行了分析比较,并通过关联分析解析UHT灭菌乳品质劣变的关联微生物。结果表明：品质劣变UHT乳在理化指标、酶活性和微生物群分布方面与正常UHT乳有明显不同,假单胞杆菌、不动杆菌为品质劣变UHT乳中核心功能微生物且均属于常见的嗜冷菌,能够产生耐热酶,这可能是导致UHT乳腐败变质的主要原因。本研究为进一步解决UHT乳品质劣变问题提供了参考。     

基于Arrhenius模型预测无乳糖超高温乳的货架期

采用电子眼、电子鼻、电子舌等感官评价技术,结合货架期加速实验(ASLT)的阿伦尼乌斯公式(Arrhenius)模型,建立无乳糖超高温灭菌乳(UHT乳)的货架期预测模型。将无乳糖UHT乳分别贮存于37、27、4℃下,以色泽、气味、滋味为主要指标,在不同的贮存温度下,综合分析无乳糖UHT乳品质与贮存时间之间的变化,并应用Arrhenius公式建立货架期模型。结果表明:37、27℃下贮存的无乳糖UHT乳色泽的发生显著性变化(P<0.05)的时间为24、33 d;苦味发生显著性变化(P<0.05)的时间为24、27 d;而贮存60 d气味无显著性变化(P>0.05)。4℃下贮存60 d的无乳糖UHT乳色泽、气味、滋味均无显著性差异(P>0.05)。以苦味为指标,利用Arrhenius公式拟合的货架期模型为:t=0.109×e-5.1882。选取37、27℃验证模型准确性,与实际货架期之间的误差分别为9.5%、12.5%,误差较小。用此公式计算4℃下无乳糖UHT乳货架期为71 d。因此,以感官指标为依据建立货架期预测模型可预测无乳糖UHT乳的货架期。     

长货架期软包装灭菌乳工艺试验研究

立足国内现有的乳品加工设备，采用二次灭菌工艺技术、包装机械包装材料、超高温灭菌设备，对关键工艺技术进行研究，实现灭菌乳保质期３个月以上产品货架期。     

应用脂肪酶预测UHT乳货架期的研究

以市售UHT乳为研究对象,应用Arrhenius模型对脂肪酶进行分析,预测UHT乳的货架期.UHT乳分别在25、45℃环境下恒温储藏,并定期随机抽样,进行感官检验和脂肪酶含量测定.应用Arrhenius方法分析脂肪酶含量,来预测样品货架期,并建立了模型.     

金黄色葡萄球菌在生乳与灭菌乳中生长状况分析

目的 了解并比较金黄色葡萄球菌(S.aureus)在生乳与灭菌乳中的生长状况.方法 采用GB/T4789.37-2008<食品微生物学检验金黄色葡萄球菌检验>,测定不同温度下金黄色葡萄球菌在生乳和灭菌乳中的生长情况,利用MicroFit 1.0软件对所测数据进行分析,利用SPSS统计软件对该菌在生乳与灭菌乳中生长参数进行统计分析.结果 金黄色葡萄球菌在生乳中的最大生长速率明显低于在灭菌乳中的最大生长速率,二者的迟滞期、代时无明显差异.结论 金黄色葡萄球菌在生乳与灭菌乳中的生长情况差异显著.有统计学意义(P<0.05).     

新含气调理食品的品质及其应用前景

新含气调理食品保鲜技术是针对目前普遍使用的真空包装、高温高压灭菌等常规方法存在的不足之处而开发出来的一种适合于加工各类新鲜方便食品或半成品的新技术。由于采用原材料的减菌化处理和多阶段升温的温和式灭菌方式，能够比较完美地保存烹好食品的品质和营养成分，加之采用充氮包装，食品原有的色泽、风味、口感和外观几乎不发生改变。新含气调理食品可在常温下贮运和销售，货架期长达6～12个月。这不仅解决了高温高压。真空包装食品的品质劣化问题，而且也克服了冷藏、冷冻食品的货架期短、流通领域成本高等缺点。新含气调理食品保鲜…     

应用游离氨基氮预测UHT乳货架期的研究

以市售UHT乳为研究对象,应用Arrhenius模型通过对游离氨基氮的分析,预测UHT乳的货架期.UHT乳分别在25℃和45℃环境下恒温储藏,并定期随机抽样进行感官检验和游离氨基氮质量浓度测定.应Arrhenius方法分析用游离氨基氮质量浓度来预测样品货架期,并建立了模型.     

出口日本的食品将受放射线辐射检查

日本厚生劳动省近日发布通报,决定对今年中国进口食品加强放射线辐射相关项目的检查。辐照食品加工技术是利用一定剂量的γ射线、x射线或电子加速器产生的电子束辐照食品的方法以达到抑制发芽、杀虫、灭菌、调节成熟度、保持食品鲜度和延长食品货架期的一项物理保藏技术。此灭菌原理是以电磁波辐射的能量破坏生物体中的DNA结构,使得微生物无法再继续繁殖,同时也能造成植物胚芽停止生长分化。     

Ninsin在延长豆奶保质期方面的研究

本试验初步证明了Nisin作为天然食品防腐剂,应用于豆奶生产中具有较明显的延长保质期的作用,并且有利于提高豆奶的质量,降低能源消耗。结果表明,使用以Nisin为主的复合防腐剂可以延缓豆奶的腐败,保质期可达3个月。     

HACCP系统在UHT鲜奶生产中的应用

<正> 近年来,我国乳制品工业迅猛发展,尤其是UHT鲜奶已经越来越受到广大消费者的喜爱。但在UHT鲜奶的无菌生产中常易出现质量不稳定的问题,从典型的UHT灭菌乳的生产流程上可以看出UHT鲜奶的加工工序多、影响因素多、控制参数多、涉及面广、运用知识多。     

Age Gelation,Sedimentation, and Creaming in UHT Milk: A Review

Demand for ultra‐high‐temperature (UHT) milk and milk protein‐based beverages is growing. UHT milk is microbiologically stable. However, on storage, a number of chemical and physical changes occur and these can reduce the quality of the milk. These changes can be sufficiently undesirable so as to limit acceptance or shelf life of the milk. The most severe changes in UHT milk during storage are age gelation, with an irreversible three‐dimensional protein network forming throughout, excessive sedimentation with a compact layer of protein‐enriched material forming rapidly at the bottom of the pack, and creaming with excessive fat accumulating at the top. For age gelation, it is known that at least two mechanisms can lead to gelation during storage. One mechanism involves proteolytic degradation of the proteins through heat‐stable indigenous or exogenous enzymes, destabilizing milk and ultimately forming a gel. The other mechanism is referred to as a physico‐chemical mechanism. Several factors are known to affect the physico‐chemical age gelation, such as milk/protein concentration, heat load during processing (direct compared with indirect UHT processes), and milk composition. Similar factors to age gelation are known to affect sedimentation. There are relatively few studies on the creaming of UHT milk during storage, suggesting that this defect is less common or less detrimental compared with gelation and sedimentation. This review focuses on the current state of knowledge of age gelation, sedimentation, and creaming of UHT milks during storage, providing a critical evaluation of the available literature and, based on this, mechanisms for age gelation and sedimentation are proposed.     

Short communication: Variation in the composition and properties of Swedish raw milk for ultra-high-temperature processing

The composition and properties of raw milk are of great importance for the quality and shelf life of the final dairy product, especially in products with a long shelf life [e.g., ultra-high-temperature (UHT)-treated milk]. The objective of this study was to investigate the compositional variation in raw milk samples before processing at the dairy plant. Moreover, we wanted to investigate the effect of the UHT process on this variation (i.e., if the same variation could be observed in the corresponding UHT milk). The quality traits analyzed included detailed milk composition, counts of total and psychrotrophic bacteria, proteolytic activity, and color, as well as predictive measures of stability (i.e., ethanol stability and heat coagulating time). Samples of raw milk and the corresponding produced UHT milk were collected and analyzed on a monthly basis during 1 yr. Principal component analysis was used to identify months showing similarities and differences with respect to total variation. In contrast to previous studies, we observed only small variations between months and no clear effect of season for the raw milk. For the UHT milk, July and the winter months (December, January, and February) tended to separate from the other months. Quality traits showing significant variation were only to some extent identical in raw milk and UHT-processed milk. A better understanding of the natural variation in raw milk quality will provide opportunities to improve the shelf life of UHT-treated milk products.     

Genetic analysis of herd life in Quebec Holsteins using Weibull models

Survival analysis methodologies were used to study herd life in Canadian Holstein cows. Herd life was defined as true herd life or the length of time between first calving and censoring. True herd life adjusted for 305-d milk production was defined as functional herd life. Lifetime record (censored or completed) were from 331,147 Holstein cows registered in the Programme d'Analyse des Troupeaux Laitiers du Québec (PATLQ) that calved for the first time between March 1, 1981 and March 31, 1995. The Weibull (proportional hazards) model used to analyze true herd life and functional herd life contained a Weibull baseline hazard function and the time-dependent effects of year of first calving, lactation number by stage of lactation, annual change in herd size and herd-year (random), and the time-independent effects of the milk recording option (supervised or not) and age at first calving. The model for functional herd life included also the time-dependent effect of herd-year-parity class of 305-d milk production. Genetic differences between sires with regard to the hazard function of their daughters was clearly demonstrated. The hazard rate followed a different pattern in later lactations, particularly in the first 240 d in milk. Older age at first calving was found to be associated with higher risks of culling. Changes in herd size had a small impact on the hazard function of animals. The hazard decreased as production of the cow increased. Heritability in the log scale was 0.09 for true herd life and 0.08 for functional herd life, but when heritability was expressed on the original scale, the estimates for the two traits were 0.19 and 0.15, respectively. The difference in the median survival between a bull with an estimated transmitting ability of 0.6 and another bull with an estimated transmitting ability of 1.3 was 690 d or 1.7 lactations. Rank correlations between the official estimated transmitting abilities for true herd life and functional herd life and those obtained in this study were 0.62 and 0.66, respectively.     

IMPROVED SHELF LIFE ESTIMATION OF UHT MILK BY PREDICTION OF PROTEOLYSIS

ABSTRACT

During growth in raw milk, many psychrotrophic bacteria produce proteases that can retain activity following ultra‐high temperature (UHT) treatment. In this study, casein and skim milk powder assays for detecting very low levels of protease in UHT milk were optimized, and the suitability of azocasein and fluorescein isothiocyanate‐casein (FITC‐casein) as substrates was investigated. The strongest correlations of protease activity with proteolysis in stored UHT milk were observed when FITC‐casein was used as substrate in the assays. Assays using casein and FITC‐casein as substrates yielded the highest activities. To determine sensitivity, crude protease was added at low concentrations to UHT milk, and the milk was assayed for progress of proteolysis over 12 months and for protease activity using the casein and FITC‐casein assays. With long assay incubation times, the FITC‐casein assay was more sensitive than the casein assay and may be suitable for detecting very low levels of protease activity and predicting progress of proteolysis in stored UHT whole milk.

PRACTICAL APPLICATIONS

This study contributes to the development and evaluation of practical assays for the detection of protease activity in the industry to identify potential premature spoilage of contaminated UHT milk before it is distributed for sale. The developed assays are also useful for assessing the quality of milk powder as active protease can persist in milk powder to cause spoilage in reconstituted milk. Although the assays require up to 14 days to complete, this is not an excessive time, compared with the time required for microbiological clearance and total shelf life of the product. High protease activity can be identified with less incubation time. The cost of protease detection assays developed during this work is quite low and, although 20 min analysis time is required per sample, the tests can be very cost efficient when run in batches, as would be expected in a commercial testing facility.

     

UHT Milk Processing and Effect of Plasmin Activity on Shelf Life: A Review

Abstract: The demand for ultra‐high‐temperature (UHT) processed and aseptically packaged milk is increasing worldwide. A rise of 47% from 187 billion in 2008 to 265 billon in 2013 in pack numbers is expected. Selection of UHT and aseptic packaging systems reflect customer preferences and the processes are designed to ensure commercial sterility and acceptable sensory attributes throughout shelf life. Advantages of UHT processing include extended shelf life, lower energy costs, and the elimination of required refrigeration during storage and distribution. Desirable changes taking place during UHT processing of milk such as destruction of microorganisms and inactivation of enzymes occur, while undesirable effects such as browning, loss of nutrients, sedimentation, fat separation, cooked flavor also take place. Gelation of UHT milk during storage (age gelation) is a major factor limiting its shelf life. Significant factors that influence the onset of gelation include the nature of the heat treatment, proteolysis during storage, milk composition and quality, seasonal milk production factors, and storage temperature. This review is focused on the types of age gelation and the effect of plasmin activity on enzymatic gelation in UHT milk during a prolonged storage period. Measuring enzyme activity is a major concern to commercial producers, and many techniques, such as enzyme‐linked immunosorbent assay, spectrophotometery, high‐performance liquid chromatography, and so on, are available. Extension of shelf life of UHT milk can be achieved by deactivation of enzymes, by deploying low‐temperature inactivation at 55 °C for 60 min, innovative steam injection heating, membrane processing, and high‐pressure treatments.