Microstructure of fat globules in whole milk after thermosonication treatment

The structure of fat globules in whole milk was studied after heat and thermosonication treatments to observe what happens during these processes at the microscopic level using scanning electron microscopy. Raw whole milk was thermosonicated in an ultrasonic processor-Hielscher UP400S (400 W, 24 kHz, 120 microm amplitude), using a 22-mm probe at 63 degrees C for 30 min. Heat treatment involved heating the milk at 63 degrees C for 30 min. Color and fat content were measured to correlate the images with analytical measurements. The results showed that the surface of the fat globule was completely roughened after thermosonication. Ultrasound waves were responsible for disintegrating the milk fat globule membrane (MFGM) by releasing the triacylglycerols. Furthermore, the overall structure of milk after sonication showed smaller fat globules (smaller than 1 microm) and a granular surface. This was due to the interaction between the disrupted MFGM and some casein micelles. Minor changes in the aspect of the globules between thermal and raw milks were detected. Color measurements showed higher L* values for sonicated samples. Sonicated milk was whiter (92.37 +/- 0.20) and generally showed a better degree of luminosity and homogenization compared to thermal treated milk (88.25 +/- 0.67) and raw milk (87.82 +/- 0.18). Fat content analysis yielded a higher value after sonication (4.24%) compared to untreated raw milk (4.04%) because fat extraction is more efficient after sonication. The advantages of thermosonicated milk are that it can be pasteurized and homogenized in just 1 step, it can be produced with important cost savings, and it has better characteristics, making thermosonication a potential processing method for milk and most other dairy products.     

超声波灭酶机制及其在食品加工中的应用

超声波是一项新型食品加工技术,已被广泛用于食品加工中各个操作单元,如杀菌、灭酶、果汁脱气等。本文首先概括了超声波钝化食品内源酶的机理,随后分析了影响超声波灭酶效果的因素,最后介绍了超声场下酶失活动力学模型及该技术在食品加工中的应用现状,指出其中存在的问题,以期望为超声波灭酶技术在食品加工中的开发与利用提供理论支持。      

Interactions between milk proteins and exopolysaccharides produced by Lactococcus lactis observed by scanning electron microscopy

The interactions between exopolysaccharides produced by Lactococcus lactis ssp. cremoris JFR1 and dairy proteins (caseins and whey proteins) in fermented media (milk permeate and buttermilk) were observed using scanning electron microscopy. An immobilization technique by crosslinking was employed to bind the protein to the observation surface, so that a washing step could be performed to remove noninteracting material. The use of this novel technique allowed us, for the first time, to confirm that the exopolysaccharide molecules interact with dairy proteins. Exopolysaccharides appear as filament strands attached to the protein aggregates and to the bacterial cells. This new sample preparation technique proved to be very valuable for observing molecular interactions in fermented media.     

Thermal inactivation of foot-and-mouth disease virus in milk using high-temperature, short-time pasteurization

Previous studies of laboratory simulation of high temperature, short time pasteurization (HTST) to eliminate foot-and-mouth disease virus (FMDV) in milk have shown that the virus is not completely inactivated at the legal pasteurization minimum (71.7°C/15 s) but is inactivated in a flow apparatus at 148°C with holding times of 2 to 3 s. It was the intent of this study to determine whether HTST pasteurization conducted in a continuous-flow pasteurizer that simulates commercial operation would enhance FMDV inactivation in milk. Cows were inoculated in the mammary gland with the field strain of FMDV (01/UK). Infected raw whole milk and 2% milk were then pasteurized using an Arm-field pilot-scale, continuous-flow HTST pasteurizer equipped with a plate-and-frame heat exchanger and a holding tube. The milk samples, containing FMDV at levels of up to 10⁴ plaque-forming units/mL, were pasteurized at temperatures ranging from 72 to 95°C at holding times of either 18.6 or 36 s. Pasteurization decreased virus infectivity by 4 log₁₀ to undetectable levels in tissue culture. However, residual infectivity was still detectable for selected pasteurized milk samples, as shown by intramuscular and intradermal inoculation of milk into naïve steers. Although HTST pasteurization did not completely inactivate viral infectivity in whole and 2% milk, possibly because a fraction of the virus was protected by the milk fat and the casein proteins, it greatly reduced the risk of natural transmission of FMDV by milk.     

Characterization and association of bacterial communities and nonvolatile components in spontaneously fermented cow milk at different geographical distances

In the ecosystem of spontaneously fermented cow milk, the characteristics and relationship of bacterial communities and nonvolatile components at different scales of geographical distances (provincial, county, and village levels) are unclear. Here, 25 sampling sites from Xin Jiang and Tibet, 2 provinces of China, were selected based on the distribution of spontaneously fermented cow milk and used for metagenomic and metabolomic analysis. At the provincial geographical distance, the same predominant species, Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus, were detected in Xin Jiang and Tibet. Further, the richness of the bacterial composition of samples from Tibet was higher than those from Xin Jiang; specifically, at the species level, 28 species were identified in Tibet samples but only 7 species in Xin Jiang samples. At the provincial geographical level, we detected significant differences in bacterial structure, shown in principal coordinate analysis plots, and significant differences (Simpson index) in bacterial diversity were also detected. However, at the county and village levels, no significant differences were detected in bacterial communities and diversity, but a difference in bacterial compositions was detectable. This indicates that bacterial communities and diversity of spontaneously fermented milk dissimilarity significantly increased with geographic distance. For the nonvolatile component profiles, the partial least squares discriminant analysis plot (R²Y > 0.5 and Q² > 0.5 for the goodness-of-fit and predictive ability parameter, respectively) showed that samples from different geographical distances (provincial, county, and village) were all separated, which indicated that all the discriminations in nonvolatile components profiles were from different geographical distances. Investigating relationships between lactic acid bacteria and discriminatory nonvolatile components at the county level showed that 9 species were positively correlated with 16 discriminatory nonvolatile components, all species with low abundance rather than the predominant species L. delbrueckii ssp. bulgaricus and Strep. thermophilus, which indicates the importance of the selection of autochthonous nonpredominant bacteria.     

应用16S rDNA全序列测序技术鉴定生鲜乳中的细菌种类

采用玻璃珠法提取生鲜乳中分离的34株细菌基因组DNA,用细菌通用引物(27f/1492r)PCR扩增16S r DNA片段并测序,与Gen Bank数据库同源序列比对,系统发育树聚类分析,并结合形态学和生理学特征确定了34株菌的种属地位。结果表明,共鉴定出16个种属。3个生鲜乳样中细菌种类及其分布特点不同。其中1号样有7种细菌,以Acinetobacter sp.(不动杆菌属)为主,2号样有6种细菌,以Klebsiella sp.(克雷贝氏杆菌属)为主,3号样有6种细菌,分布较为分散。从致病性来看,分离菌株主要为条件致病菌或腐败菌,无烈性致病菌。      

Effects of carbon dioxide on bacterial growth parameters in milk as measured by conductivity

Inhibition of bacterial growth by dissolved carbon dioxide (CO2) has been well established in many foods including dairy foods. However, the effects of dissolved CO2 on specific growth parameters such as length of lag phase, time to maximum growth rate, and numbers of organisms at the stationary phase have not been quantified for organisms of concern in milk. The effect of dissolved CO2 concentrations of 0.6 to 61.4 mM on specific bacterial growth parameters in raw or single organism inoculated sterile milk was determined at 15 degrees C by conductance. Commingled raw or sterile milks were amended to a final concentration of 0.5 mg/ml each of urea and arginine HCl. Sterile milks were inoculated singly with one of six different microorganisms to a final concentration of approximately 10(2) to 10(3) cfu/ml; raw milk was adjusted to a final indigenous bacterial population of approximately 10(3) cfu/ml. Conductivity of the milk was recorded every 60 s over 4 to 5 d in a circulating apparatus at 15 degrees C. Conductivity values were fit to Gompertz equations and growth parameters calculated. Conductance correlated with plate counts and was satisfactory for monitoring microbial growth. Data fit the Gompertz equation with high correlation (R2 = 0.96 to 1.00). In all cases, dissolved CO2 significantly inhibited growth of raw milk bacteria, influencing lag, exponential, and stationary growth phases as well as all tested monocultures.     

山羊奶与牛奶和人奶营养成分的比较

对山羊奶、牛奶和人奶中蛋白质、脂肪、维生素、矿物质等主要营养成分进行了比较,分析了3种奶中主要营养成分的差别。通过比较发现,山羊奶在总体营养成分方面优于牛奶,更接近人奶。但山羊奶存在铁、叶酸和维生素B12含量较低以及羊奶膻味的问题,应在营养上对这方面加以重视。     

超声联合酶解法提高豆乳粉溶解性的工艺研究

在湿法制备豆乳粉工艺的基础上,采用超声联合酶解法提高豆乳粉溶解性。在单因素实验基础上,采用响应面分析法对超声联合酶解制备高溶解性豆乳粉工艺进行优化,确定最优超声联合酶解工艺参数为:超声功率350 W,超声时间23 min,酶解温度57℃,酶解时间1.7 h,酶解p H8.6。在最优工艺条件下,蛋白质分散指数为88.79%,比未经超声及酶解处理的豆乳粉提高了近10%,显著提高了豆乳粉的溶解性。      

超高压杀菌效果及机制研究进展

超高压作为一种新型的食品非热加工技术, 处理过程温度低、对食品营养成分破坏小,能在有效杀菌的同时显著提升加工食品品质,是未来食品加工技术发展的热点方向。近年来,超高压技术被广泛应用于食品加工,并在国内外实现了商业化应用。杀菌作为超高压加工食品过程中最重要的环节,是保证食品安全、延长产品货架期的关键点,因此一直是本领域研究的重点。本文介绍了超高压技术的设备和作用原理, 总结了超高压或超高压联合其他手段对微生物营养体、细菌芽孢、真菌孢子及病毒的杀灭效果和杀菌机制, 归纳了超高压杀菌中存在的杀菌机制不清、缺乏杀菌指示菌以及深休眠芽孢等问题, 以期为进一步完善超高压杀菌理论、推动超高压技术在食品加工中的产业化应用指明方向。     

我国市售奶粉细菌污染情况调查分析

选取代表性的国产市售奶粉为样本,通过检测其细菌总数、嗜热菌总数、耐热菌数、芽孢数以及耐热芽孢数来分析我国市场上奶粉的细菌污染程度及污染菌群的构成特点。     

Combined effect of temperature and pulsed electric fields on soya milk lipoxygenase inactivation

Pulsed electric fields (PEF) were applied to freshly prepared soya milk using a laboratory scale continuous PEF system to study the feasibility of inactivating lipoxygenase (LOX). Square wave PEF using different combinations of pre-treatment temperature, electric field strength and treatment time were evaluated in this study. Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated and modelled. Results showed the highest level of inactivation (84.5%) was obtained using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. Inactivation of LOX activity as a function of treatment time could be described using a first order kinetic model. Calculated D values following pre-heating to 50 °C were 172.9, 141.6 and 126.1 μs at 20, 30 and 40 kV/cm, respectively.     

乳蛋白生物活性肽的药理学作用及应用前景

以乳蛋白生物活性肽中酪蛋白磷酸肽为重点，就乳蛋白生物活性肽的离子载体作用、细胞凋亡诱导作用、细胞免疫调节作用、DNA合成促进作用、抗茵作用、抗高血压作用和抗血栓作用进行了阐述，并对这些药理学作用的研究进展加以介绍，同时展望了乳蛋白生物活性肽在乳品和医药工业中的应用前景：     

微波加热杀菌对牛乳品质的影响

为了掌握微波加热杀菌对牛乳品质的影响,该文以牛乳层厚度和微波功率为试验因素、以营养成分的损失为指标进行了试验研究。研究的结论是：（1）牛乳的微波加热杀菌比水浴加热杀菌对乳中维生素C的影响要小。（2）牛乳层厚度和微波功率对乳脂肪的影响较为显著,而对乳蛋白质的影响均不显著。（3）牛乳层厚度越小,对乳脂肪的影响越小,随着牛乳层厚度的增加乳脂肪的损失增加,但越来越缓慢;微波功率越大,对乳脂肪的影响越小,基本呈直线下降。     

中国荷斯坦牛泌乳早期乳常规成分及乳蛋白组分变化规律的研究

对扬州大学实验农牧场7头中国荷斯坦牛泌乳早期乳常规营养成分、酸度及乳蛋白组分的相对含量进行研究。结果表明，产犊后1h的乳脂率、乳蛋白含量、总固形物含量、滴定酸度、密度最高，而pH值最低，随后乳脂率、乳蛋白率、总固形物含量、滴定酸度密度急剧下降，到60h时接近常乳水平，而pH值逐渐上升，到第7d时接近常乳水平。产犊后1h初乳中免疫球蛋白的相对含量最高，为20．6％，到第5d时接近常乳水平。研究表明，产犊后3d内所产的乳最具有开发价值。     

Comparison of analytical methods and the influence of milk components on milk urea nitrogen recovery

The objectives of this study were to compare analytical instruments used in independent laboratories to measure milk urea nitrogen (MUN) and determine whether any components in milk affect the recovery of MUN. Milk samples were collected from 100 Holstein cows fed one ration in a commercial dairy herd with a rolling herd average of 9500 kg. Half of each sample was spiked with 4 mg/dL of urea N, while the other half was not, to determine recovery. Both milk samples (spiked and not spiked) were sent to 14 independent laboratories involved in the MUN Quality Control Program through National Dairy Herd Improvement Association and analyzed for MUN, fat, protein, lactose, somatic cell count (SCC), and total solids. The laboratories analyzed MUN using CL-10 (n = 3), Skalar (n = 2), Bentley (n = 3), Foss 4000 (n = 3) or Foss 6000 (n = 3) systems. When recovery of MUN was evaluated among the 5 analytical methods, the mean recoveries for the Bentley, Foss 6000, and Skalar systems were 92.1 (SE = 2.76%), 95.4 (SE = 10.1%), and 95.1% (SE = 7.61%), respectively, and did not differ from each other. However, MUN recovery was 85.0% (SE = 2.8%) for the CL-10 system and 47.1% (SE = 9.9%) for the Foss 4000 system, both of which differed from the other 3 systems. Recoveries from Foss 4000, Foss 6000, and Skalar varied among laboratories using the same instrument. As initial MUN concentration increased, recovery decreased using the Bentley and CL-10 systems. Increasing milk fat resulted in a decrease in recovery using the Foss 6000 system. For 4 of the 5 methods, recovery of MUN was not associated with specific milk components. Recovery of MUN was inconsistent for laboratories using the Foss 4000 and the Foss 6000 method and using these systems may result in an overestimation or underestimation of MUN.     

Effects of microwave and ultrasound pretreatments on enzymolysis of milk protein concentrate with different enzymes

Milk protein concentrate was pretreated either by microwave irradiation or by ultrasound before initiation of 3‐h enzymatic hydrolysis. The duration of pretreatment ranged from 1 to 8 min at a power level of 800 W, with the control not being subjected to any pretreatment, and five enzymes (Alcalase, Trypsin, Neutrase, Alkaline Protease and Flavourzyme) were employed. The effects of microwave and ultrasound pretreatments on the kinetics and degree of hydrolysis, protein solubility, bitterness and angiotensin‐converting enzyme inhibitory activity were evaluated. Pretreatments increased the degree of hydrolysis and stabilised the solubility of the hydrolysates but could not significantly reduce bitterness of the hydrolysates The angiotensin‐converting enzyme inhibitory activity of the hydrolysates were improved with 5‐min ultrasound‐pretreated Neutrase hydrolysates giving IC₅₀ value of 0.23 mg mL^?1. Kinetic parameters showed improved catalytic efficiencies. Pretreatments of milk protein concentrates with either microwave or ultrasound significantly improve the bioactivity and functional characteristics of the resulting hydrolysates.     

Noncoagulation of milk in Finnish Ayrshire and Holstein-Friesian cows and effect of herds on milk coagulation ability

The objectives of this study were to compare milk coagulation ability (MCA) and the prevalence of noncoagulation of milk within the main Finnish dairy breeds, Finnish Ayrshire (FA) and Holstein-Friesian (HOL), as well as to study the herd effect on MCA. Data used in the statistical analyses consisted of individual milk samples of 959 FA, 399 HOL, and 50 crossbred cows from 84 herds. Data were collected before the grazing season in the spring 1999. Milk samples were analyzed for the milk coagulation traits (milk renneting time, R and curd firmness, E(30)) and pH. In addition, information on the 305-d milk production traits from the year 1999, and background information about feeding and management regimes of the herds were obtained. Variance components for the random herd and animal effects were estimated using REML methodology and an animal model. Breed, parity, lactation stage (for R, E(30) and pH only), and a measuring unit (for R and E(30) only) were included as fixed effects in the model. When the effects of concentrate feeding frequency and type of concentrate were studied, the random effect of herd was excluded from the model. A relationship matrix included parents, grandparents, and great grandparents of the cows with observations. The HOL cows were superior to FA cows in MCA when both the proportion of poorly coagulating (PC) and noncoagulating (NC) milk, and the differences in curd firmness were considered. About 30% of the FA cows and 12% of the HOL cows produced PC milk. Only 1.3% of the HOL cows and 8.6% of the FA cows produced NC milk. Herd effect explained only a minor part of the variation in MCA (8%) compared with that in 305-d milk production traits (about 43%). Frequent feeding of the concentrate was associated with good MCA as well as for the high milk, protein and fat yields, but it was not associated with the prevalence of the NC milk.     

Effects of ultraviolet light and ultrasound on microbial quality and aroma-active components of milk

BACKGROUND: Heat treatment is the most common way to extend the shelf life of milk. However, alternative technologies such as ultraviolet (UV) light and ultrasound (US), which are non‐thermal methods for processing milk, have been developed to replace heat treatment. These technologies do not have any adverse effects on the quality of milk. The major purpose of this study was to investigate the effects of UV and US on different micro‐organism groups and aroma compounds in milk. RESULTS: Heat pasteurisation at 65 °C for 30 min was used as thermal control treatment. The growth of total coliform group bacteria, Escherichia coli and Staphylococcus spp. was completely reduced by UV treatment. Application of US was not sufficient to reduce the numbers of yeasts and moulds. In neutral/basic fractions, 3‐methylthiophene (plastic), hexanal (grass) and 1‐hexen‐3‐one (floral) were major volatiles in milk samples. CONCLUSION: UV had a major effect on total coliforms, E. coli and Staphylococcus spp., but US was not as effective as UV and heat treatment in reducing certain groups of micro‐organisms. No major differences were observed in terms of aroma‐active compounds and flavour of milk following the different treatments. However, some new volatiles and change in rheological properties were generated by UV and US treatments. Copyright © 2011 Society of Chemical Industry