牛初乳IGF-I在常用乳品加工条件下的稳定性研究

目的:探讨常用乳品加工条件对牛初乳IGF-I的稳定性影响。方法:采用加热、调整pH、均质以及乳酸菌发酵等常用的乳品生产加工单元操作处理牛初乳IGF-I,并检测处理前后IGF-I的含量变化。结果:常用的LTLT（65℃30min或72℃20s）或HTST（80℃15s）等巴氏杀菌条件对bc-IGF-I的含量影响不大,但随着温度的升高和时间的延长,IGF-I含量逐渐降低;37℃、30min条件下,pH在2～7的范围内时,IGF-I的保留率较高;当pH在8～12的范围内时,保留率明显下降;55℃、10～20MPa的均质条件对牛初乳IGF-I的含量几乎无影响;酸乳发酵和储存过程对牛初乳IGF-I的含量有一定影响,6h发酵结束时保留率平均为70.61%,4℃储存20d后保留率平均为45.99%。结论:常用的LTLT或HTST巴氏杀菌、均质、调酸对牛初乳IGF-I的含量影响不大,但乳酸菌发酵造成含量明显损失。      

牛初乳IGF-I在模拟胃肠液中的稳定性研究

牛初乳IGF-I的模拟胃肠液稳定性研究表明,分离的牛乳IGF-I在模拟胃液中的稳定性随胃液pH值的升高而增加,0.5～4h内,胃液pH值为2,3,4时的活性保留率变化范围分别为40.25%～0.25%,50.40%～0.60%和93.34%～8.40%;初乳乳清粉中的IGF-I对胃液消化的耐受性远远强于分离的IGF-I,相同条件下,pH值为2,3,4时的活性保留率变化范围分别为67.72%～45.14%,84.59%～58.41%和94.21%～63.35%.分离的牛初SLIGF-I对pH值8的模拟肠液的耐受性相对较差,0.5～4h内活性保留率变化范围为33.20%～0.46%,而初乳乳清粉中的IGF-I活性保留率变化范围为87.80%～24.28%.     

牛初乳原料杀菌和酸奶加工研究

通过添加稳定剂提高牛初乳的热稳定性并将其加工成酸奶。牛初乳中按0.5 g/100g添加Na2HPO4,65℃加热,记录凝固时间及评价杀菌效果;确定葡萄糖和蔗糖的添加比例,将杀菌初乳制成酸奶,进行乳酸菌和杂菌计数。结果表明,添加Na2HPO4的牛初乳加热40 min才开始凝固,而未添加组加热6 min完全凝固。65℃加热15 min,牛初乳菌落总数和大肠菌群均合格;当葡萄糖添加量为3 g/100g,蔗糖添加量为4 g/100g时,牛初乳酸奶口感最佳,乳酸菌数为1.26×106 cfu/mL。因此按0.5 g/100g添加Na2HPO4可以显著提高牛初乳的热稳定性,加工制成的初乳酸奶兼具了牛初乳和酸乳的双重功效。     

牛初乳免疫球蛋白体外稳定性研究

研究了牛初乳中免疫球蛋白的体外稳定性,包括热稳定性、酸碱稳定性、消化系统中的稳定性。牛初乳免疫球蛋白在不高于65℃范围内具有较高的稳定性,随温度升高残存率逐渐降低,当85℃、3min时IgG基本完全失活;牛初乳免疫球蛋白在pH<3.0和pH>11.0时稳定性较差,而在pH4.0～11.0之间具有较好的稳定性;在人工胃液中,pH值的影响最大,牛初乳添加量的影响次之;人工肠液中,胰蛋白酶是影响IgG活力的主要因子,消化时间次之,牛初乳添加量的影响最小。     

牛初乳免疫球蛋白稳定性研究概述

牛初乳富含很多营养成分,其中含有大量的免疫球蛋白,能够抵抗外界病毒侵害,增强机体自身免疫力,但在加工过程中,其活性受到很多因素影响。文中综述了温度、p H值、蛋白酶、超高压等因素对牛初乳免疫球蛋白稳定性的影响,对提高其稳定性的方法如食品添加剂保护法及微胶囊法的研究现状做出总结,为进一步开展牛初乳免疫球蛋白研究提供了参考。     

牛初乳加工技术研究进展

综述了牛初乳的营养成分、影响牛初乳稳定性的各种因素及目前实验室条件和生产条件下牛初乳及其制品加工工艺条件和各种加工方法的特点,探讨了提高牛初乳加工稳定性的方法,以期为牛初乳产品的开发和生产提供参考。     

牛初乳胰岛素样生长因子的稳定性研究

研究了牛初乳类胰岛素生长因子在不同温度、pH值、添加保护剂条件下对其降糖活性影响,并利用Balb/c3T3成纤维细胞糖代谢测定了IGFs降糖活性。结果表明:细胞培养液的葡萄糖浓度降到对照组的60%,与胰岛素相比同样具有明显降糖活性。IGFs在pH值2～8范围内活性稳定,在温度为4℃时活性最大,30%甘露醇能有效提高IGFs降糖活性。     

益生菌发酵牛初乳对致病菌抑制作用的研究

研究了益生菌发酵牛初乳对致病性大肠杆菌及幽门螺旋杆菌的抑制作用。结果表明,初乳经益生菌发酵,导致初乳pH值降低,初乳IgG活性也相应降低,在pH值为4.6时,IgG活性仅为初乳的25%。不同益生菌发酵初乳在不同pH值对大肠杆菌及幽门螺旋杆菌均有抑制作用,且嗜酸乳杆菌发酵初乳抑制作用最强,对大肠杆菌的抑制率最高达83.2%,对幽门螺旋杆菌抑菌圈直径最大达17.2mm,达到高度敏感,分别较初乳的抑制作用提高47.52%和52.21%。不同益生菌发酵初乳的抑菌作用依次为嗜酸乳杆菌>双歧杆菌>混合乳酸菌>德氏乳杆菌保加利亚亚种>嗜热链球菌。     

两歧双歧杆菌在牛初乳中的发酵特性研究

用经过耐氧驯化后的两歧双歧杆菌发酵牛初乳,研究了其发酵特性。结果表明,两歧双歧杆菌在牛初乳中37℃发酵10h,pH值为4.72,活菌数为3.3×109mL-1,初乳IgG活性、质量浓度基本保持不变。     

发酵法去除牛初乳中酪蛋白提高IgG含量的研究

利用乳酸菌发酵牛初乳从而降低pH达到酪蛋白等电点,通过离心去除酪蛋白,提高免疫球蛋白G（JgG）含量。结果表明,发酵法去除酪蛋白的最适pH为4.65,离心条件为1500×g,30min;随着pH的下降,酪蛋白被去除.初乳中的IgG含量上升,pH由4.70降低到4.65时,IgG含量有显著性变化（P<0.01）。2-7d原料初乳中IgG含量平均为20.09mg/g,经发酵后乳清IgG含量提高约1.5倍,平均达到52.07mg/g。      

牛初乳类胰岛素生长因子-I的降糖作用研究

牛初乳IGF-Ⅰ能够有效地降低糖尿病大鼠的血糖水平，降糖效果呈现明显的剂量效应关系。结果表明，口服IGF-Ⅰ15μg／kg组、10μg／kg组和5μg／kg组大鼠的血糖值平均下降18．21％，14．96％和14．55％；腹腔注射的降糖效果明显好于口服，糖尿病大鼠的血糖值平均下降43．23％。动物实验表明牛初乳IGF-Ⅰ具有持续、稳定的降糖效应。     

Factors affecting insulin-like growth factor-I concentration in bovine milk.

To establish the naturally occurring range of insulin-like growth factor-I concentrations in bovine milk, samples from individual cows (n = 409) managed on five Missouri dairy herds were assayed. Parity, stage of lactation, and farm affected milk insulin-like growth factor-I concentration. Milk insulin-like growth factor-I concentration was higher in early lactation than mid and late lactation with concentrations in multiparous cows exceeding those in primiparous cows. Insulin-like growth factor-I concentration was negatively correlated to milk production the day of sample collection (r = -.15) and not correlated to predicted 305-d milk yields. Unprocessed bulk tank milk samples (n = 100) from a commercial processing plant had a mean concentration of insulin-like growth factor-I in milk of 4.32 ng/ml with a range of 1.27 to 8.10 ng/ml. This distribution was similar to the range detected in samples from individual cows, but values were lower than those reported for human milk. Concentration of insulin-like growth factor-I in milk was not altered by pasteurization (at 79 degrees C for 45 s). However, insulin-like growth factor-I was undetectable in milk heated to temperatures (121 degrees C for 5 min) required for infant formula preparation or in commercially available infant formula. These data indicated that insulin-like growth factor-I is a normal but quantitatively variable component of bovine milk that is not destroyed by pasteurization but is undetectable in infant formula. Concentration of insulin-like growth factor-I in bovine milk is lower than concentrations reported for human milk yet similar to those reported for human saliva.(ABSTRACT TRUNCATED AT 250 WORDS)     

牛初乳多肽酶解条件的研究

近年来，牛初乳多肽越来越受到重视。通过水解多肽时间实验得出，胰蛋白酶〉木瓜蛋白酶〉胃蛋白酶，选用胰蛋白酶采用正交实验得出最佳的水解暑件：酶底浓度比[E／S]5％，水解温度45℃，pH值为8。     

Effect of bovine somatotropin on the distribution of immunoreactive insulin-like growth factor-I in lactating bovine mammary tissue

The distribution pattern of immunoreactive insulin-like growth factor-I in normal lactating bovine mammary tissue and in tissue obtained after bovine somatotropin treatment was determined by indirect immunofluorescence. In normal tissue, insulin-like growth factor-I immunoreactivity was observed almost exclusively associated with stromal elements. Intralobular stromal cells, small blood vessels, and capillaries all expressed moderate to high immunoreactivity. In contrast, mammary epithelial cells displayed only sparse cytoplasmic immunoreactivity. Immunoreactive material was also present in the periductular connective tissue area, possibly associated with the basal plasma membrane of epithelial cells. Somatotropin treatment of animals resulted in elevated serum insulin-like growth factor-I concentrations and altered the distribution of insulin-like growth factor-I-stainable material in mammary tissue. After somatotropin treatment, immunoreactivity was still detected in mammary stroma; however, prominent staining was also observed in the cytoplasm of mammary epithelial cells. Given the possible role of insulin-like growth factor-I in the regulation of bovine mammary epithelial cell growth and function, our findings raise the possibility that somatotropin may induce insulin-like growth factor-I production in mammary tissue, or other tissues, to influence indirectly the growth or function of the epithelial cells. This offers a possible mechanism for bovine somatotropin stimulation of lactation.     

加工方式对羊乳中类胰岛素生长因子I浓度的影响

采用双抗体夹心酶联免疫法测定羊乳中类胰岛素生长因子I(IGF-I)的浓度,主要研究了巴氏杀菌、超高温灭菌、搅拌、均质以及发酵等加工方式对羊乳中IGF-I浓度的影响。研究结果表明,巴氏杀菌可使羊乳中IGF-I的浓度降低,但72℃/15 s巴氏杀菌条件对羊乳中IGF-I浓度的影响相对较小;137℃/2 s超高温灭菌条件对羊乳中IGF-I浓度的影响较大;均质和搅拌对羊乳中IGF-I的浓度基本无影响;发酵会使羊乳中IGF-I的浓度显著降低。因此,在开发富含IGF-I的功能性羊奶产品时,可选择72℃/15 s的巴氏杀菌条件,生产中均质和搅拌2种加工方式均可以采用,但不宜将其发酵成酸奶制品。     

牛初乳多肽的功能性研究

对牛初乳生物学功能进行了研究.结果表明,牛初乳多肽具有显著的抗体力疲劳和增强免疫力的作用.     

Effects of insulin,recombinant bovine somatotropin,and their interaction on insulin-like growth factor-I secretion and milk protein production in dairy cows

This trial was designed to test the effects of insulin, recombinant bovine somatotropin (rbST), and their interaction on milk protein and selected blood parameters in dairy cows. Eight Holstein cows (86 +/- 10 d in milk) were divided in two groups and used in two replicates of a Latin square design with four animals, four periods, and four treatments: 1) intravenous infusion of saline, 2) infusion of saline and subcutaneous administration of 40 mg of rbST per day, 3) intravenous infusion of 12 mg of insulin per day coupled with glucose infusion, and 4) rbST administration combined with insulin and glucose infusion. The glucose infusion rate was adjusted to maintain euglycemia. Each experimental period lasted 14 d: treatments were administered during the first 6 d, and no treatment was administered during the following 8-d resting phase. The average daily amount of glucose infusion needed to avoid hypoglycemia was 2.8 kg/cow when only insulin was infused as opposed to 2.2 kg/cow when both insulin and rbST were administered, indicating that either rbST causes a peripheral resistance to insulin or rbST increased liver gluconeogenesis or both. Data from the last 3 d of infusion were analyzed by using the SAS system for mixed models. Percent protein of milk tended to be lower (2.84 vs. 2.79%) and milk urea content was lower (16.6 vs. 14.8 mg/dl) during rbST administration, regardless of insulin infusion. Insulin infusion increased percent protein (2.78 vs. 2.85%) and percent casein (2.36 vs. 2.46%) and decreased milk urea content (17.1 vs. 14.3 mg/dl) regardless of rbST administration. For milk yield, protein yield, casein yield, lactose percent, and lactose yield, there were significant interactions between insulin and rbST administration. For example, casein yield averaged 1.17, 1.12, 1.20, and 1.28 kg/d for saline, insulin, rbST, and insulin combined with rbST, respectively. Similarly, there was a significant interaction between insulin and rbST on IGF-I levels, which were 122.5, 181.3, 342.3, and 492.2 ng/ml for saline, insulin, rbST, and insulin combined with rbST, respectively. In conclusion, these results clearly demonstrated that insulin interacts with bST in early lactation to improve milk protein synthesis and yield in dairy cows. These effects are probably mediated through a combination of bST nutrient mobilization, bST-induced gluconeogenesis, bST-induced insulin peripheral resistance, and bST/insulin synergism on insulin-like growth factor-I secretion and on mammary epithelial tissue.     

食品添加剂对牛初乳免疫球蛋白(IgG)稳定性的影响

探讨了几种常用食品添加剂对牛初乳免疫球蛋白稳定性的影响,根据食品添加剂对IgG的变性率的影响,选择了几种在食品加工中常用的添加剂进行正交试验,考察其相互综合作用。结果表明:随着柠檬酸、乳酸和磷酸二氢钠浓度的增大,免疫球蛋白的稳定性逐渐降低,变性率逐渐增大;山梨酸钾对免疫球蛋白的稳定性影响较小;磷酸氢二钠、乳酸钙、增稠剂和甜味剂对免疫球蛋白有一定的保护作用。添加剂最佳用量为:乳酸用量为0.3%,乳酸钙用量为0.015%,黄原胶用量为0.5%,蔗糖用量为8%,此时IgG的变性率为14.7%,在4℃的贮藏条件下最佳保存期为30天。     

免疫初乳及过渡乳中类胰岛素生长因子-Ⅰ含量测定及其变化

研究了免疫初乳及过渡乳中类胰岛素生长因子-Ⅰ(IGF-Ⅰ)含量的变化.在制备并收集免疫乳后,用放射免疫法对不同时期收集的免疫乳中IGF-Ⅰ的含量进行测定.结果表明:免疫牛初乳及过渡乳中IGF-Ⅰ含量随产后泌乳的进行急剧下降.泌乳前5d,免疫初乳中的IGF-Ⅰ以游离形态为主,游离IGF-Ⅰ比例由第1d的71.28%下降到第14d的41.44%;5d之后,过渡乳中的IGF-Ⅰ以结合形态为主,结合IGF-Ⅰ比例由第1d的28.72%上升到58.56%,达到常乳水平.