贮藏温度对全脂羊奶粉品质稳定性的影响

本文主要研究了贮藏温度(5、25和35℃)对全脂羊奶粉品质稳定性的影响。通过测定全脂羊奶粉的酸值(AV)、过氧化值(POV值)、硫代巴比妥酸值(TBA值)、溶解度、色值等指标反应贮藏期间品质的变化。结果表明,贮藏在35℃的全脂羊奶粉贮藏期间酸值、过氧化值、TBA值变化速率较快,分别于第4个月后、第2个月后、第3个月后显著高于贮藏在5℃和25℃的全脂羊奶粉(p<0.05);所有样品的溶解度和色值变化规律相似,但差异不显著(p>0.05)。因此降低贮藏温度可提高全脂羊奶粉品质稳定性。      

全脂核桃乳及稳定性的研究

通过实验确定了全脂核桃乳研制的工艺参数,探讨了乳化剂和稳定剂对核桃乳稳定性的影响,并对产品的营养成分和储存稳定性进行了分析.     

Effect of temperature on raw whole milk density and its potential impact on milk payment in the dairy industry

The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T² (R² = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T² (R² = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm⁻³, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm⁻³ at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally.     

乳蛋白ACEI酶解工艺条件的研究

通过测定牛乳蛋白酶解液的ACE抑制活性，确定了蛋白酶水解牛乳蛋白产生ACE抑制肽（ACEI）的工具酶及其最佳酶解工艺备件。结果表明：在胰蛋白酶，蛋白酶A，蛋白酶M，肽酶R四种酶中，蛋白酶A为酶解牛乳蛋白制备ACEI工具酶；其最佳酶解工艺条件为温度50℃，pH值为7．0，酶用量为3％，底物浓度为5％，酶解时间10h，在该条件下得到的酶解液1C50为0.8987g／L；在最佳酶解工艺条件下得到的酶解液经柱层析分离，在2个较大洗脱峰处得到的ACEI活性较高，其抑制活性分别为84．98％和85．35％，相对分子质量分别为1340u和439u。     

Long-term effects of ad libitum whole milk prior to weaning and prepubertal protein supplementation on skeletal growth rate and first-lactation milk production

Our objectives were to determine the effects of rapid growth rate during the preweaning period and prepubertal protein supplementation on long-term growth pattern and milk production during the first lactation. Forty-six Israeli Holstein heifer calves were fed either milk replacer (MR) or whole milk (WM) from 4 to 60 d age. Calves had free access to WM or MR for 30 min twice daily and free-choice water and starter mix for the entire day. From weaning until 150 d of age, all heifers were fed the same ration. At 150 d of age the heifers were divided into 2 subgroups, with one subgroup supplemented with an additional 2% protein until 320 d of age. Thereafter, all heifers were housed and fed together until calving. Another cluster of 20 heifers was raised on MR and WM treatments and 3 animals from each nursery treatment were slaughtered at 60 d and 10 mo age to determine effects of nursery treatment on organ and adipose tissue mass. Prior to weaning, the MR heifers consumed 0.12 kg/d more DM than the WM heifers, but metabolizable energy intake was not different. Body weight at weaning and average daily gain during the preweaning period were 3.1 kg and 0.074 kg/d higher, respectively, in the WM treatment than in the MR treatment, with no differences in other measurements. Nursery feeding treatment and added protein had no effect on growth rate in the prepubertal period, but the postweaning difference in BW between the WM and MR heifers remained throughout the entire rearing period. The age at first insemination was 23 d earlier and age at pregnancy and first calving was numerically lower for the WM heifers than for the MR heifers. Adipose tissue weights at weaning were doubled in the WM calves. First-lactation milk production and 4% fat-corrected milk were 10.3 and 7.1% higher, respectively, for WM heifers than for MR heifers, whereas prepubertal added protein tended to increase milk yield. In conclusion, preweaning WM at high feeding rates appears to have long-term effects that are beneficial to future milk production. The positive long-term effects of feeding WM on first-lactation milk production were independent of their effects on skeletal growth. Enhanced milk production observed with WM treatment may be related to the milk supply, paracrine or endocrine effects of fat tissues on mammary parenchyma, or a combination of both factors.     

The effect of legume protease inhibitors on native milk and bacterial proteases

Protease inhibitors from legume seed extracts (soybean, cowpea and marama beans) and purified soybean protease inhibitor were evaluated with regards to their abilities to inhibit proteases produced by important milk contaminating bacteria, i.e. Bacillus spp. and Pseudomonas spp., and native milk protease, plasmin. Although heat treatment is the most common mean of inactivating enzymes, some heat-stable enzymes can survive the ultra-high temperature (UHT) processing of milk and cause sensory and consistency defects during storage at room temperature. The legume protease inhibitors reduced the activity of plasmin and proteases produced by Bacillus spp. by up to 94% and 97%, respectively, while it showed low inhibitory activity towards Pseudomonas fluorescens proteases (19%) in a buffer system. The protease inhibitors reduced the activity of plasmin (41%) and Bacillus proteases (50%) in UHT milk, however to a lesser extent as compared to inhibition in the buffer system; while it had little or no effect on proteases form Pseudomonas spp. Legume protease inhibitors show great potential in preventing or reducing proteolytic activity of Bacillus proteases and plasmin and may be exploited in various applications where these proteases cause sensory or consistency defects in the product.     

水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响

采用加速氧化的方法研究水分活度对全脂羊奶粉贮藏期间脂肪稳定性的影响。通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、颜色等指标评价全脂羊奶粉贮藏期间的氧化状况。结果表明,水分活度为0.32的全脂羊奶粉贮藏期间酸值、TBA值显著高于水分活度为0.11和0.23的全脂羊奶粉(p<0.05),且水分活度为0.32的全脂羊奶粉过氧化值变化速率较快(p<0.05),且褐变严重。因此,降低全脂羊奶粉的水分活度可以提高其贮藏稳定性。      

乳清蛋白酶解条件优化

用二次回归正交旋转组合设计对乳清蛋白酶解条件进行优化,建立酶法水解乳清蛋白的水解度与水解温度、水解时间、加酶量等三因素的正交回归模型。结果表明:在反应温度57℃、加酶量8 214U/g·蛋白条件下酶解114min,可获得中性蛋白酶水解乳清蛋白的最大水解度11.72%,与模型值基本相符。     

充氮包装对全脂羊奶粉贮藏期间脂肪氧化稳定性的影响

采用加速氧化的方法研究充氮包装对全脂羊奶粉贮藏期间脂肪氧化稳定性的影响。通过测定全脂羊奶粉的酸值、过氧化值、硫代巴比妥酸值(TBA)、色度值等指标评价全脂羊奶粉贮藏期间脂肪的分解氧化状况。结果表明:充氮包装的全脂羊奶粉贮藏期间酸值、TBA值和色度值变化趋势较慢,分别于第6周后、第3周后、第7周后显著低于普通包装的全脂羊奶粉(p<0.05);充氮包装的全脂羊奶粉的过氧化值于第7周达到最高值13.54mmol/kg脂肪,变化速率显著小于普通包装的全脂羊奶粉(p<0.01)。说明充氮包装可延缓酸值、过氧化值、TBA值和色度值的变化速率,显著提高全脂羊奶粉脂肪的氧化稳定性。      

巴氏牛奶中蜡样芽孢杆菌的风险评估

为了了解巴氏牛奶中蜡样芽孢杆菌的风险状况，调查研究了北京地区乳品企业巴氏牛奶的运输和销售的总体情况以及北京地区居民牛奶消费的相关情况，结合预测微生物学的方法建立了巴氏牛奶中蜡样芽孢杆菌在流通领域的暴露评估模型。从整个评估过程来看，流通领域的温度和时间是影响巴氏奶安全性的主要因素。     

豆奶粉生产及品质变化研究进展

豆奶粉是一种营养健康粉状植物蛋白饮料。该文综述目前豆奶粉生产工艺,分析其品质变化原因,并对其存在问题和今后重点研究方向进行总结和展望。     

全脂牛乳粉中糖基化酪蛋白分析

研究全脂牛乳粉中糖基化酪蛋白,探讨其酶解特性。重点考察了不同pH、酸及提取方法对酪蛋白提取质量百分数的影响,并通过SDS-PAGE电泳分析酪蛋白,高碘酸—希夫碱染色法及莫氏试验鉴定糖基化酪蛋白,木瓜蛋白酶水解酪蛋白,测定其氨基酸含量。结果表明,pH 4.6时提取酪蛋白的质量百分数显著高于其他组(P0.05);质量百分数为2%的乙酸(pH 3.58)提取酪蛋白的质量百分数为(40.45±0.66)%,显著高于其他组(P0.05);鞣酸提取酪蛋白的质量百分数为(46.13±0.46)%,显著高于其他方法(P0.05);酪蛋白SDS-PAGE电泳结果表明,不同酸、不同方法提取的酪蛋白均有3条带,其分子量均分别为34,24,60ku;高碘酸—希夫碱染色结果表明,分子量为34,24ku的酪蛋白是糖基化酪蛋白;莫氏试验结果表明,乳粉酪蛋白中存在糖基化酪蛋白;酶解结果表明,乳粉酪蛋白经木瓜蛋白酶水解后游离氨基酸含量显著高于鲜乳酪蛋白(P0.05)。说明全脂牛乳粉中有糖基化酪蛋白,其分子量分别为34,24ku,易于水解。     

Assessment of quality and technological characterization of lactose-hydrolyzed milk

The intensity and sequence of heat and hydrolytic treatments as well as storage stability of lactose-hydrolyzed milk was assessed during processing and storage in 15 different commercial samples by monitoring the glycidic fraction (glucose, lactose and galactose) and selected thermal treatment markers (furosine, lactulose and fructose). The use of an additional indicator (fructose) together with classical process indicators (lactulose and furosine), was useful to better understand the quality of this dietetic milk and the processing procedures utilized. The results confirmed the high reactivity of lactose-hydrolyzed milk to the Maillard reaction and the more limited chemical stability of this milk typology when stored at 20 °C. In addition, a wide variability in the quality of commercial samples of lactose-hydrolyzed milk was found, which underlines the necessity to establish definite thresholds for this milk to defend both consumers and product quality.     

全脂乳粉和脱脂乳粉在1kHz～10MHz下的介电特征研究

分别研究了各4种不同品种的全脂乳粉和脱脂乳粉在1kHz～10MHz波段的介电特性。结果发现:随着频率的增加,全脂乳粉和脱脂乳粉的ξ’和ξ″值呈单调递减趋势;全脂乳粉的ξ’和ξ″值都高于脱脂乳粉,相同类型乳粉各品种间的ξ’和ξ″差异不大;全脂乳粉的ξ″值在103～105Hz频率段减小趋势明显,且ξ″值的对数与频率的对数成线性反比关系,而脱脂乳粉无此规律;全脂乳粉和脱脂乳粉的穿透深度Dp随频率的提高而减小,两类乳粉的介电特性差异可能与它们各自的脂肪和乳糖含量有关。     

豆浆加工工艺对全子叶豆腐品质影响的研究

为研究豆浆加工工艺对全子叶豆腐(Whole Cotyledon Tofu,WCT)品质的影响,以传统工艺作对照,选用去皮大豆为原料,比较研究两种豆浆加工工艺即湿法工艺(泡豆打浆)和干法工艺(制粉调浆)对制备WCT的组成成分、出品率、表观形态、色泽、质构特性的影响。结果表明:干法工艺和湿法工艺生产出的WCT的基本成分没有显著差异(p<0.05);与传统工艺相比,湿法工艺和干法工艺分别提高产量41.23%和46.67%,但后者比前者效率更高;干法工艺获得的WCT比湿法工艺外观更为顺滑细腻;两种工艺生产的WCT色泽无明显差异;干法工艺获得的WCT硬度、弹性、内聚性和咀嚼性均高于湿法工艺,且整体质构特性接近传统工艺豆腐。由此表明干法工艺比湿法工艺更适合生产品质优良的WCT,并能有效提高出品率。      

抗菌肽cp1对蜡样芽孢杆菌的抑菌作用及在巴氏杀菌乳中的应用

目的 探究抗菌肽cp1对蜡样芽孢杆菌的抑菌作用,并进一步分析抗菌肽cp1在巴氏杀菌乳中的应用。方法 以蜡样芽胞杆菌为研究对象,通过测定抑菌圈直径(diameter of inhibition zone, DIZ)、最小抑菌浓度(minimal inhibitory concentration, MIC)、最小杀菌浓度(minimum bactericidal concentration, MBC)评价抗菌肽cp1对蜡样芽胞杆菌的抑菌效果。通过分析生长曲线、细胞内三磷酸腺苷(adenosine triphosphate, ATP)、膜电位、内容物渗出和细胞形态的变化,来揭示可能的作用机制。在此基础上,并探究抗菌肽cp1在巴氏杀菌乳贮藏中的应用。结果 当抗菌肽cp1质量浓度为10μg/mL时,其对蜡样芽胞杆菌的DIZ为(16.19±1.29) mm;抗菌肽cp1对蜡样芽孢杆菌的MIC、MBC分别为4μg/mL和8μg/mL;当抗菌肽cp1质量浓度为2 MIC时,蜡样芽胞杆菌几乎不生长;抗菌肽cp1导致细胞内ATP含量降低,细胞膜超极化,细胞液(包括核酸和蛋白质)漏出,细胞形态破坏;在巴氏杀...     

Effect of high-pressure-jet processing on the viscosity and foaming properties of pasteurized whole milk

The processing of milk using high-pressure technologies has been shown to dissociate casein micelles, denature whey proteins, and change the appearance and rheological properties of milk. A novel high-pressure processing technology called high-pressure-jet (HPJ) processing is currently being investigated for use in the food industry. Few studies have evaluated the effects of HPJ technology on dairy foods. The present study investigated the physicochemical and foaming properties of homogenized pasteurized whole milk processed at pressures from 0 to 500 MPa using HPJ processing. The apparent particle size exhibited a monomodal distribution in whole milk samples processed up to 125 MPa and a bimodal distribution for samples processed at 250, 375, and 500 MPa. The viscosity increased from approximately 2 to 5 mPa·s when whole milk was processed using HPJ at 375 MPa, and foam expansion increased from approximately 80 to 140% after processing at >125 MPa. Foam stability was limited to pressures in the 375 to 500 MPa range. We hypothesized that the increase in apparent particle size was due to the dissociation of casein micelles into surface-active casein protein monomers, and the formation of casein–casein and casein–fat particles. Ultracentrifugation of samples into 3 milk fractions (supernatant, serum, and precipitate), and subsequent fat and protein analysis on the 3 fractions, showed that a strong interaction between casein proteins and fat triglycerides occurred, evidenced by the increase in fat content associated with the precipitate fraction with increasing pressure. This suggests that stable casein–fat aggregates are formed when whole milk is processed using HPJ at pressure >125 MPa.     

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.     

改性大豆分离蛋白对液态奶研制工艺及品质的影响

实验采用改性大豆分离蛋白作为奶粉的部分替代品制成了中性和酸性两种双蛋白奶,分析了调配方法、均质条件和灭菌条件对产品色泽、口感和稳定性的影响.选用的改性大豆分离蛋白为低氧化性蛋白,不仅具有好的凝胶性,还具有较好的乳化性和热稳定性.采用Lab色彩空间表征色泽变化,通过沉淀率和稳定系数来表征产品的稳定性.结果表明:研制过程中,均质条件和灭菌条件对产品的质量有很大的影响.对酸性奶而言,除了以上工艺条件需要考虑,糖酸比对稳定性和口感同样重要.65℃、25MPa的均质务件适用于两种条件下的产品.中性和酸性双蛋白奶分别选择121℃、20min和65℃、30min为灭菌条件.