长货架期饮用型酸奶的生产工艺

<正> 饮用型酸奶是一种低粘性的可饮用酸奶,无脂或含脂量极少,基本采用标准化牛奶作为原料,经热处理、均质并以酸奶发酵剂培养而成。 对于货架期要求只是2～3个星期的酸奶,一般只需进行均质和冷却处理,便已达到要求;要是所要求的货架期逾1个月以上,酸奶便要经过均质、巴氏杀菌和无菌灌装处理。发酵后的酸奶如要进行巴氏杀菌或高温灭菌,可添     

石榴风味乳饮料贮藏品质及货架期预测

以石榴汁和全脂奶粉为主要原料,添加低聚木糖,接种双歧杆菌（Bifidobacterium）进行发酵,制备石榴风味乳饮料。以不添加石榴汁和低聚木糖的普通乳饮料作为对照,分别考察4℃、25℃和35℃贮藏条件下乳饮料的品质变化。以酸度为评价指标,采用加速货架期实验（ASLT）法预测石榴风味乳饮料在4℃冷藏条件下的货架期。结果表明,石榴风味乳饮料在4℃、25℃和35℃条件贮藏期间酸度均逐渐增大,黏度和持水力均逐渐降低,双歧杆菌活菌数随着贮藏时间延长先升高后降低,且温度越高,变化幅度越大。石榴风味乳饮料在4℃冷藏条件下其酸度、黏度、持水力及双歧杆菌活菌数均优于对照乳饮料。经加速货架期实验预测,石榴风味乳饮料货架期可以达到24～40 d,优于市售的大部分酸乳的货架期21 d。     

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.     

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.     

Microbial quality of raw horse milk

Consumption of horse milk has become popular in developed countries, especially among people suffering from bowel problems and skin diseases. Since the positive effect is supposedly not observed after pasteurisation, the product is mostly consumed as raw milk. Since the microbiological quality of this milk has not been systematically surveyed, in this study we examined the presence of spoilage- and pathogenic microorganisms in 123 samples of horse milk collected in The Netherlands and Belgium. Hygiene and faecal indicators were found in a wide range of numbers. Although Salmonella, Campylobacter and Listeria were not found, these pathogens showed no reduction in challenge tests with artificially contaminated horse milk stored for 1 week at 7 °C. Since faecal indicators were present and able to grow at 7 °C, combined with the fact that pathogens may easily end up and survive in the milk, it is not advised to consume raw horse milk.     

Bioluminescence and impedimetric methods for assessing shelf-life of pasteurized milk and cream

The bacterial content of pasteurized milk and cream after incubation at 21°C for 25 h in the presence of crystal violet-penicillin-nisin solution is inversely proportional to the shelf-life of the product at 6°C. The bacteria may be enumerated by plate count, when results are obtained within 50 h, or by ATP estimation by bioluminescence, when results are obtained within 26 h of sampling. The regression coefficients ranged from ?0·76 to ?0.87. Impedance measurements on pasteurized milk and cream containing crystal violet-penicillin-nisin solution at 21°C using either modified plate count agar or milk agar showed that detection times are directly proportional to shelf-life; regression coefficients range from 0·62 to 0·82.Crystal violet-penicillin-nisin solution proved more effective than a mixture of benzalkon and crystal violet, especially for application to pasteurized milk.     

Results from raw milk microbiological tests do not predict the shelf-life performance of commercially pasteurized fluid milk

Analytical tools that accurately predict the performance of raw milk following its manufacture into commercial food products are of economic interest to the dairy industry. To evaluate the ability of currently applied raw milk microbiological tests to predict the quality of commercially pasteurized fluid milk products, samples of raw milk and 2% fat pasteurized milk were obtained from 4 New York State fluid milk processors for a 1-yr period. Raw milk samples were examined using a variety of tests commonly applied to raw milk, including somatic cell count, standard plate count, psychrotrophic bacteria count, ropy milk test, coliform count, preliminary incubation count, laboratory pasteurization count, and spore pasteurization count. Differential and selective media were used to identify groups of bacteria present in raw milk. Pasteurized milk samples were held at 6°C for 21 d and evaluated for standard plate count, coliform count, and sensory quality throughout shelf-life. Bacterial isolates from select raw and pasteurized milk tests were identified using 16S ribosomal DNA sequencing. Linear regression analysis of raw milk test results versus results reflecting pasteurized milk quality consistently showed low R² values (<0.45); the majority of R² values were <0.25, indicating small relationship between the results from the raw milk tests and results from tests used to evaluate pasteurized milk quality. Our findings suggest the need for new raw milk tests that measure the specific biological barriers that limit shelf-life and quality of fluid milk products.     

Effect of nisin and high temperature pasteurization on the shelf-life of whole milk

Two experiments were conducted to assess the effectiveness of nisin on the keeping quality of pasteurized whole milk. After pasteurization, milk samples were stored at 10°C and samples were analysed at intervals for total plate count (TPC), Lactobacillus count, calcium ion concentration, pH and total acidity (TA). In the first experiment nisin was added to milk samples in the range 0 to 50 IU ml^-1 prior to pasteurization at 72°C for 15 s. AH concentrations of nisin used were effective in controlling microbial growth. Milk containing 40 and 50 IU ml^-1 nisin had not spoiled after 41 days' storage compared to spoilage time of 14 days for the control milk. In the second experiment 40 IU ml^-1 of nisin was combined with three 'pasteurization' processes: 72°C for 15 s, 90°C for 15 s and 115°C for 2 s. The milk processed at 72°C for 15 s with nisin showed an increased keeping quality of about 7 days compared with the control and showed a significantly lower count for Lactobacillus. In contrast, nisin had a much greater effect on TPC counts in the milk pasteurized at 90°C for 15 s, and after 28 days' storage at 10°C the milk was still acceptable. Milks treated both with and without nisin at 115°C for 2 s were microbiologically acceptable after 28 days, with counts less than 10 ml^-1. However, the milk with nisin was superior in flavour, as no noticeable off-flavours were apparent after 32 days. All these results are consistent, as shown by the microbiological and chemical analyses. Addition of nisin to milk prior to pasteurization provides an opportunity to achieve extended shelf-life in regions with poor refrigeration.     

Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk

Milk was collected from eight Holstein cows four times before and four times after intramammary infection with Streptococcus agalactiae. Postinfection milk had significantly higher somatic cell count (SCC) (849,000 cells/ml) than preinfection milk (45,000 cells/ml). High SCC raw milk had more lipolysis and proteolysis than low SCC raw milk. Pasteurized, homogenized, 2% fat milks from pre- and postinfection periods were stored at 5 degrees C and analyzed for lipolysis, proteolysis, microbial quality, and sensory attributes at 1, 7, 14, and 21 d post processing. During refrigerated storage, the average rates of free fatty acid increase (i.e., lipolysis) and casein hydrolysis in high SCC milk were, respectively, three and two times faster than those in low SCC milk. In general, standard plate counts, coliform counts, and psychrotrophic bacterial counts of both the high and low SCC milks remained low (<100,000 cfu/ ml) during 5 degrees C storage. Low SCC milk maintained high organoleptic quality for the entire 21-d shelf-life period. However, for high SCC milk, between 14 and 21 d, sensory defects were detected, which resulted in low overall quality ratings. The sensory defects mainly included rancidity and bitterness and were consistent with higher levels of lipolysis and proteolysis. Hence, mastitis adversely affected the quality of pasteurized fluid milk. It is recommended that the fluid milk industry consider implementation of premium quality payment programs for low SCC milks.     

Development and shelf-life determination of pasteurized,microfiltered, lactose hydrolyzed skim milk

The segment of the world population showing permanent or temporary lactose intolerance is quite significant. Because milk is a widely consumed food with an high nutritional value, technological alternatives have been sought to overcome this dilemma. Microfiltration combined with pasteurization can not only extend the shelf life of milk but can also maintain the sensory, functional, and nutritional properties of the product. This studied developed a pasteurized, microfiltered, lactose hydrolyzed (delactosed) skim milk (PMLHSM). Hydrolysis was performed using β-galactosidase at a concentration of 0.4 mL/L and incubation for approximately 21 h at 10 ± 1°C. During these procedures, the degree of hydrolysis obtained (>90%) was accompanied by evaluation of freezing point depression, and the remaining quantity of lactose was confirmed by HPLC. Milk was processed using a microfiltration pilot unit equipped with uniform transmembrane pressure (UTP) ceramic membranes with a mean pore size of 1.4 μm and UTP of 60 kPa. The product was submitted to physicochemical, microbiological, and sensory evaluations, and its shelf life was estimated. Microfiltration reduced the aerobic mesophilic count by more than 4 log cycles. We were able to produce high-quality PMLHSM with a shelf life of 21 to 27 d when stored at 5 ± 1°C in terms of sensory analysis and proteolysis index and a shelf life of 50 d in regard to total aerobic mesophile count and titratable acidity.     

The shelf-life of dairy products: 2. Raw milk and fresh products

In the second of this series of articles, the specific factors controlling the shelf-life of raw milk, pasteurized milk and cream, cottage cheese and yogurt are considered. The shelf-life of raw milk depends on the quality of the milk ex-farm and on subsequent transport and storage conditions. Shelf-life may be enhanced by deep cooling or thermization. Post heat treatment contamination by Gram negative psychrotrophic bacteria is the major determinant of shelf-life of pasteurized products. In cultured dairy products, yeast and mould contamination is the most usual cause of spoilage.     

巴氏杀菌奶的微生物生长动力学模型研究

目的通过初级模型和二级模型来描述巴氏杀菌奶中微生物的生长动力学模型。方法样品放置在4、8、16、25、30、37、40和43℃条件下培养,使用IPMP 2013软件进行拟合,初级模型采用Huang模型和Baranyi模型分析不同温度下的生长动力学特征,二级模型采用Ratkowsky平方根模型、Huang平方根模型和Cardinal模型描述温度对其生长速率的影响。结果在所有温度下都能观测到微生物的生长,综合比较2种初级模型的均方根误差(root mean squared error,RMSE)、均方误差(mean squared errorMSE)、赤池信息量准则(Akaike information criterion, AIC)和生长速率,得到2种初级模型具有同等拟合效果;而3种二级模型得到的最低生长温度和最高生长温度分别是-3.191、0.56、-4.962和47.309、45.277、44.408℃。结论 Baranyi模型和Huang模型均适合描述巴氏杀菌奶中微生物菌群的生长,3种二级模型都能用于评价温度对其生长速率的影响,但Ratkowsky平方模型覆盖的温度范围更广,可能更适合描述温度对巴氏杀菌奶中微生物菌群生长的影响。     

Improvement of shelf-life and wholesomeness of ground beef by irradiation 1. Microbial aspects

Various doses of ionizing radiation (cobalt-60) were used to improve the microbiological quality of commercial ground beef. The study included the isolation and identification of the natural microbial flora. The radioresistance of the individual strains was investigated. D(10) values, obtained in a saline solution, showed values ranging from 0·035 to 1·827 kGy. Treatment of ground beef with gamma radiation at doses of 1·0, 2·5 and 5·0 kGy resulted in extended shelf-life at 4°C of 4, 10 and 15 days, respectively while the control samples already exceeded 10(7) colony forming units (CFU)/g on day 0. Dominant groups of bacteria shifted from Gram-negative bacilli to Gram-positive cocci as the irradiation dose increased. Gram-negative cocci as well as yeasts and moulds also developed in greater proportion during storage of the irradiated samples.     

货架期内液态奶中结合型羟甲基糠醛生成的动力学分析

液态乳在货架期内发生的美拉德反应对产品品质变化有很大影响,对美拉德反应主要产物生成的动力学分析有助于反应机理的研究。文中采用同一品牌的3种液态奶产品,分别在4、25、37℃贮存5个月,跟踪分析产品中结合型羟甲基糠醛(B-HMF)的含量变化,建立基于贮存温度和贮存时间的预测模型。结果表明:液态乳中B-HMF的生成整体符合动力学零级反应模式,并最终建立各样品中B-HMF生成的动力学预测模型。     

浅谈影响UHT奶货架期的各类因素及控制措施

针对目前UHT奶常出现的质量问题,着重阐述了原料奶、生产工艺各个环节和关键控制点对UHT奶货架期的影响及相应的预防措施。     

The shelf-life of dairy products: 1. Factors influencing raw milk and fresh products

This review forms the first part of a series of four articles which will consider factors affecting the shelf-life of dairy products. In this report factors influencing the shelf-life of raw milk and fresh products are highlighted. Potential methods of controlling bacterial growth are discussed in detail.     

Electrophoretic characterization of protein interactions suggesting limited feasibility of accelerated shelf-life testing of ultra-high temperature milk

Accelerated shelf-life testing is applied to a variety of products to estimate keeping quality over a short period of time. The industry has not been successful in applying this approach to ultra-high temperature (UHT) milk because of chemical and physical changes in the milk proteins that take place during processing and storage. We investigated these protein changes, applying accelerated shelf-life principles to UHT milk samples with different fat levels and using native- and sodium dodecyl sulfate-PAGE. Samples of UHT skim and whole milk were stored at 20, 30, 40, and 50°C for 28 d. Irrespective of fat content, UHT treatment had a similar effect on the electrophoretic patterns of milk proteins. At the start of testing, proteins were bonded mainly through disulfide and noncovalent interactions. However, storage at and above 30°C enhanced protein aggregation via covalent interactions. The extent of aggregation appeared to be influenced by fat content; whole milk contained more fat than skim milk, implying aggregation via melted or oxidized fat, or both. Based on reduction in loss in absolute quantity of individual proteins, covalent crosslinking in whole milk was facilitated mainly by products of lipid oxidation and increased access to caseins for crosslinking reactions. Maillard and dehydroalanine products were the main contributors involved in protein changes in skim milk. Protein crosslinking appeared to follow a different pathway at higher temperatures (≥40°C) than at lower temperatures, making it very difficult to extrapolate these changes to protein interactions at lower temperatures.