UHT灭菌和牛乳常见质量问题的原因分析及控制措施

分析了ＵＨＴ灭菌牛乳常见质量问题的主要原因，并提出了相应的预防措施和控制办法。     

牛乳的超高温(UHT)处理

长久以来，通过加热来延长乳制品的货架期已是广为人知的方法。各种不同的巴氏消毒方法被用来杀灭致病微生物，但这种方法仍然需要对产品进行低温贮藏和运输，这是因为产酸细菌并没有被抑制。所以尽管巴氏消毒已经存在许多世纪了，对乳制品进行消毒杀菌依旧是生产长货架期产品的常用方法。产品被灌装入通常为瓶或罐的容器中，然后在１１０～１２０℃下灭菌２０～４０min，这种方法的不利之处在于使产品从白色变为或多或少的褐变颜色，以及由于美拉得反应引起的一种典型的蒸煮气味。在高于１００℃的温度下，缩短乳制品货架期的微生物细菌被…     

UHT灭菌牛乳常见质量问题的原因分析及控制措施

分析了ＵＨＴ灭菌牛乳常见质量问题的主要原因,并提出了相应的预防措施和控制办法     

UHT（超高温灭菌）朱古力牛乳的研制

本文介绍了UHT朱古力牛乳的制作方法及其合理、可行的超高温杀菌生产工艺，其主要由牛乳、朱古力、白砂糖、稳定剂等调制而成，经长时间观察和尝试发现该产品具有稳定性好、口感佳等特点。     

UHT杀菌乳中耐热菌的分离与鉴定

采用2种不同的细菌富集方式对5种不同品牌UHT（Ultra High Temperature）杀菌牛乳中残留的细菌进行了分离，得到18株细菌，并对它们进行了耐热性和细菌学鉴定试验。结果表明，18株细菌全部耐热，初步将其归为3个属。其中，片球菌属10株，均为戊糖片球菌，肠球菌属3株，1株类鸟肠球菌，2株粪肠球菌；微球菌属5株，1株嗜冷微球菌，4株变异微球菌。虽然这些耐热菌均为非致病菌，但是遇到适宜条件，这些耐热菌会生长繁殖，导致乳产品在贮藏和流通过程中发生变质。     

UHT杀菌对绿茶饮料风味的影响研究

研究了UHT杀菌对绿茶饮料风味的影响，通过绿茶饮料在UHT杀菌前、后香气成分的定性．定量分析，说明UHT杀菌在杀死绿茶饮料中的有害及腐败微生物时．不仅可以极大程度地保留产品中的营养成分和风味成分，同时还增加了绿茶饮料的甜香成分．     

牛乳蒸汽热力杀菌技术的发展历程和技术特点

通过对牛乳蒸汽热力杀菌技术的发展历程和各种加热方式进行对比和阐述,使广大读者了解蒸汽热力杀菌方式的特点,以便在无菌牛乳生产过程中进行杀菌方式的工艺设计与相关的运用。     

蒸汽喷射式杀菌对牛乳中热敏性成分的影响研究

采用蒸汽喷射式杀菌方式处理牛乳,对牛乳中常见热敏性成分的变化进行研究。采用蒸汽喷射方式对牛乳直接加热杀菌,处理温度分别为142±2℃、130±2℃、121±2℃,处理时间分别为1s、4s、6s。测定结果表明:在保证杀菌率的前提下,本试验考量不同灭菌条件对原始牛乳及调配牛乳的褐变程度无影响。与原始牛乳中的维生素成分相比,不同温度和时间处理的蒸汽喷射式杀菌方式对蛋白质及脂肪酸的损失率相对较大。对调配牛乳的热敏性成分研究表明:与α-乳白蛋白、β-乳球蛋白相比,不同温度和时间处理的蒸汽喷射式杀菌方式对乳铁蛋白的损失率均较大。142℃喷射1s的条件,蛋白损失率相对较小,高温瞬时杀菌方式有利于降低热敏性蛋白的损失率。与花生四烯酸相比,不同温度和时间的蒸汽喷射条件对DHA的损失率影响较小。121℃喷射4s的蒸汽喷射条件对两种脂肪酸的损失率均较小。142℃喷射6s的条件对四种维生素的影响相对较大,其他处理条件对水溶性维生素的影响不显著。高温长时杀菌条件(142℃喷射6s)对两种脂溶性维生素的损失率影响均较大。     

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。     

不同杀菌方式对牛乳杀菌效果的比较

牛乳是天然营养品,微生物极易在其中繁殖,病源菌和其他有害菌也常存其中,这些微生物是造成牛乳腐败变质的主要原因。为了探讨不同杀菌方式对牛乳杀菌效果的优劣,对牛乳微波杀菌和热力杀菌进行了对比试验。通过试验表明:微波杀菌不同功率条件下,600W时杀菌效果最好,同时也表明微波杀菌比热力杀菌效果好。     

UHT乳中脂解酶活性的测定

UHT处理不能完全钝化乳中的脂解酶，分解乳及乳制品中的脂肪，从而产生酸败并减弱产品的乳香味。采用琼脂糖扩散法对UHT乳中的脂解酶活性进行测定，发现酶活性大小随产品贮存时间的延长呈现无规律性变化，而且各产品之间差异并不显著。     

奶香风味香肠生产加工工艺

介绍奶香风味香肠的基本配方和对生产加工工艺进行研究,奶香风味香肠具有自然浓郁的奶香、营养丰富、风味独特,产品使用方便,卫生安全。     

Effect of antioxidant (alpha-tocopherol and ascorbic acid) fortification on light-induced flavor of milk

The effectiveness of added antioxidants against oxidation off-flavor development in light-exposed milk was evaluated using sensory and chemical analysis. Sensory testing for similarity showed no perceivable difference between control milk and milk with added (1) 0.05% alpha-tocopherol (TOC) and (2) 0.025% alpha-tocopherol and 0.025% ascorbic acid (TOC/ASC), but did demonstrate a perceivable difference when adding (3) 0.05% ascorbic acid (ASC) alone. Subsequently, sensory testing for difference showed a significant difference in oxidation off-flavor between light-exposed control milk and light-exposed milk with added TOC/ASC, whereas milk fortified with TOC was not different from control. Gas chromatography-olfactometry showed that more aroma-active flavor compounds were observed in light-exposed milk treated with TOC and TOC/ASC than light-exposed milk with no added antioxidants. The thiobarbituric acid reactive substances (TBARS) test verified chemically the extent of oxidation in control and antioxidant-treated milk samples. Milk that was exposed to light for 10 h showed a significantly higher TBARS value (0.92 +/- 0.09 mg/kg) than milk that was protected from light (0.59 +/- 0.184 mg/kg), or milk that was treated with TOC/ASC (0.26 +/- 0.092 mg/kg). Direct addition of low levels of antioxidants (TOC/ASC) to milk protected its flavor over 10 h of light exposed storage.     

乳及其制品中风味物质的研究进展

乳尤其是发酵乳中的风味物质种类繁多,包括非挥发性酸、挥发酸、羰基化合物以及蛋白、脂肪和乳糖等的分解物。由于加工过程中微生物和理化的原因,容易使乳制品产生不良风味。通过加入抗氧化剂等添加剂、加强杀菌措施、控制原料奶的品质和环境条件来控制风味的变化,提高其品质。     

Increasing omega fatty acid content in cow's milk through diet manipulation: Effect on milk flavor

Milk with an increased content of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and conjugated linoleic acid (CLA) was obtained by incorporating fish oil into the feed of cows. The 4 feed treatments used were a control diet of 57% forage and 43% concentrate mix with EnerGII fat supplement at 1.65% of dietary DM, or EnerGII in the basal diet was partially replaced with 1) 0.21% partially ruminally inert calcium salts of 71% fish oil given at 0.41% of DM; 2) 0.41% inert calcium salts of 71% fish oil given at 0.83% of DM; or 3) 0.83% inert calcium salts of 43% fish oil given at 0.83% of DM. The cows were milked after 5 and 8 wk and the EPA, DHA, and CLA contents in the pasteurized whole milk were determined. The presence of off-flavors in the milk was investigated after 3 and 10 d of storage. Twelve judges were trained to evaluate the presence of grassy, fishy, oily, oxidized, and rancid off-flavors. Although levels of EPA, DHA, vaccenic acid, and CLA increased for all 4 treatments, a trained sensory panel detected no difference in milk flavor between treatments and the control, with little or no intensity of off-flavors. Results suggest that feeding fish oil and EnerGII at varying levels enhanced CLA, EPA, DHA, and total n-3 fatty acids in milk over the length of the experiment without negatively affecting milk flavor. This creates the potential for a more marketable and healthful product.     

双酶法制备奶味香精的研究

采用复合蛋白酶ProTamEx1.17L和脂肪酶CR双酶结合可控酶解技术对稀奶油进行酶解,利用GC-MS法和氨基酸自动分析法进行分析检测。结果表明:复合蛋白酶ProTamEx1.17L最佳酶解条件为加酶量0.04%,温度45℃,pH6.0,时间3.5h;脂肪酶CR最佳酶解条件为加酶量0.06%,温度45℃,时间18h,pH6.0。酶解物经GC-MS分析检测,与酶解前相比,短链及中链脂肪酸,如癸酸、辛酸、丁酸等相对含量增加;同时甲基酮类和内酯类物质相比之下含量减少。经氨基酸自动分析仪检测,氨基酸总量达23.80mg/g,相比酶解前增长了约12倍。其中必需氨基酸种类齐全,含量占总氨基酸含量的59.13%。      

The effect of vitamin concentrates on the flavor of pasteurized fluid milk

Fluid milk consumption in the United States continues to decline. As a result, the level of dietary vitamin D provided by fluid milk in the United States diet has also declined. Undesirable flavor(s)/off flavor(s) in fluid milk can negatively affect milk consumption and consumer product acceptability. The objectives of this study were to identify aroma-active compounds in vitamin concentrates used to fortify fluid milk, and to determine the influence of vitamin A and D fortification on the flavor of milk. The aroma profiles of 14 commercial vitamin concentrates (vitamins A and D), in both oil-soluble and water-dispersible forms, were evaluated by sensory and instrumental volatile compound analyses. Orthonasal thresholds were determined for 8 key aroma-active compounds in skim and whole milk. Six representative vitamin concentrates were selected to fortify skim and 2% fat pasteurized milks (vitamin A at 1,500–3,000 IU/qt, vitamin D at 200–1,200 IU/qt, vitamin A and D at 1,000/200–6,000/1,200 IU/qt). Pasteurized milks were evaluated by sensory and instrumental volatile compound analyses and by consumers. Fat content, vitamin content, and fat globule particle size were also determined. The entire experiment was done in duplicate. Water-dispersible vitamin concentrates had overall higher aroma intensities and more detected aroma-active compounds than oil-soluble vitamin concentrates. Trained panelists and consumers were able to detect flavor differences between skim milks fortified with water-dispersible vitamin A or vitamin A and D, and unfortified skim milks. Consumers were unable to detect flavor differences in oil-soluble fortified milks, but trained panelists documented a faint carrot flavor in oil-soluble fortified skim milks at higher vitamin A concentrations (3,000–6,000 IU). No differences were detected in skim milks fortified with vitamin D, and no differences were detected in any 2% milk. These results demonstrate that vitamin concentrates may contribute to off flavor(s) in fluid milk, especially in skim milk fortified with water-dispersible vitamin concentrates.