牦牛乳酪蛋白降血压肽对高血压大鼠体内降压效果研究

目的：观察牦牛乳酪蛋白降血压肽对应激性高血压大鼠（stress induced hypertensive rats,SIHR）和正常Wistar大鼠的降压效果,并与降压药物厄贝沙坦（irbesaran）和卡托普利（Captopril）的作用效果进行比较。方法：采用木瓜蛋白酶、中性蛋白酶水解制备牦牛乳酪蛋白降血压肽,分别以20 mg/kg、40 mg/kg和60 mg/kg剂量的牦牛乳酪蛋白降血压肽一次灌胃,每隔2 h测量SIHR收缩压（SBP）,连续测量8 h;长期实验持续6周,每天60 mg/kg一次灌胃,每隔1周测量SBP一次。结果：SIHR给予牦牛乳酪蛋白降血压肽后,血压均显著下降（P〈0.05）,并均在灌胃后3-6 h达最低,血压下降最大幅度为（27±5.13）mmHg,呈现一定的量效关系;而正常大鼠给予牦牛乳酪蛋白降血压肽后血压无显著变化,服用厄贝沙坦和卡托普利后血压则保持显著下降的趋势。长期灌胃牦牛乳酪蛋白降血压肽可使SIHR血压明显下降（P〈0.05）,并且降压效果稳定。结论：牛乳酪蛋白降血压肽对SIHR有明显的体内降压效果,长期服用可稳定血压,对正常大鼠血压无明显影响。     

龙井茶叶中鞣质含量的测定

用干酪素法对龙井茶叶中鞣质含量进行测定。结果表明,龙井茶叶鞣质含量在2.000-11.000μg/m L范围内呈线性关系（R2=0.999 3）;样品平均加标回收率为84.6%,SD为0.226%,RSD为1.8%（n=6）。该方法准确、可靠、重现性好、精密度好,可用于龙井茶叶中鞣质含量的测定。     

牦牛“曲拉”干酪素凝乳酶的选择及工艺参数优化

以“曲拉”为原料，研究不同酶在凝乳酶干酪素制作中的应用效果，通过L₉(3⁴)正交试验对皱胃酶、木瓜凝乳酶、微小毛霉凝乳酶3种酶最佳工艺参数进行筛选，结合生产成本，优选出微小毛霉凝乳酶为生产凝乳酶干酪素的酶制剂，其最佳工艺条件为酶浓度3.75 mL/g，pH 7，温度55℃，CaCl₂添加量12 g/kg。制品出品率73.49%，感官得分9.49，蛋白质含量85.25%，灰分7.23%，脂肪0.45%，符合QB/T3780-1999标准要求。     

Impact of fermented milk on human health: Cholesterol-lowering and immunomodulatory properties of fermented milk

In this review, we focus on the cholesterol-lowering activity of Lactobacillus gasseri , the immunomodulatory function of casein phosphopeptides (CPPs) and lactic acid bacteria as starters for fermented milk, and the probability and difficulty of creating immunomodulatory fermented milk as a 'food for specified health use'. Among the starter bacteria used for the preparation of fermented milk, L. gasseri SBT0270 could exert a hypocholesterolemic effect in rats fed a diet high in cholesterol through deconjugation of bile salts. On the other hand, CPPs, having a tripeptide sequence consisting of two phosphoserine residues at N- and C-terminal positions, stimulated lymphocyte proliferation and IgA formation via the increase of interleukin-5 and interleukin-6 produced by type 2 helper T cells. The oral ingestion of CPPs enhanced the level of antigen-specific and total intestinal IgA. Moreover, one strain of bifidobacteria ( Bifidobacterium breve YIT4064) and one strain of Lactobacilli ( Lactobacillus casei strain Shirota), used as a starter for fermented milk, activated the humoral and cellular immune system, respectively, and prevented various diseases. It is important to elucidate what components modulate and what mechanisms are responsible for the physiological function of fermented milk in order for it to be accepted as a 'food for specified health use' claiming immunomodulatory activity.     

乳中酪蛋白胶粒的扩散双电层及稳定性

酪蛋白是乳中重要的一种蛋白质,它的结构及其稳定性与乳品工业密切相关。本文详细地阐述了自然状态下乳中酪蛋白胶粒的双电层结构及其组成,並就酪蛋白胶粒的稳定性从理化方面进行了论述,同时对影响酪蛋白胶粒稳定性的各种因素(如乳中盐类的组成、pH、脱水作用、温度以及其它物质等)从理论上进行了探讨和分析。     

Specific role of endopeptidases in modulating the nature of protein digestion products

The impact of various endopeptidases on the nature of protein digestion products was measured with the digestion cell technique. After a 30 min pepsin pre-digestion, casein and rapeseed concentrates were hydrolyzed with various amounts of pancreatin, trypsin and/or chymotrypsin. This hydrolysis was performed in a dialysis tube (molecular weight cut-off 1000) with continuous collection of the digested material. The addition of pure trypsin or chymotrypsin to pancreatin (Enzyme:Substrate 125) did not change the digestibility of casein. Only a higher pancreatin level (Enzyme: Substrate 112.5) increased the total protein digestibility without affecting the amino acid spectra. Rapeseed digestibility was markedly increased by the addition of pure trypsin to pancreatin. Lysine and arginine, target amino acids of trypsin, were favored at the expense of chymotrypsin and elastase target amino acids. Supplementation of pancreatin with, chymotrypsin enhanced rapeseed digestibility without affecting the relative amino acid digestibility. The impact of a higher pancreatin ratio (Enzyme: Substrate 112.5) was similar to that of enriched pancreatin but the rate of amino acid release was modified. The differences between protein sources were mainly attributed to protein structure.     

The effect of beta and kappa casein genes on milk yield and milk composition in different percentages of Holstein in crossbred dairy cattle

The objective of this study was to compare the genotype, and composite genotype frequency, and the association between beta and kappa casein genes and milk yield (MY), percentage of fat (%Fat), protein (%Prot), and solids non‐fat (%SNF) between two groups of crossbred Holstein: G1 ≤ 87.5% Holstein = 89 cows and G2 > 87.5% Holstein = 142 cows. Five genotypes of beta casein gene were observed. A1A2 and A1B were the most and rarest frequency, respectively, in both groups. Five genotypes of kappa casein gene were found. The highest and the lowest frequency were AA, and BB and BE, respectively, in both groups. Composite genotype A1A2AA was the most frequent in both groups. Linkage disequilibrium (LD) between two genes was detected. Significant differences of frequencies between both groups of both genes were not found. The association of the genes and the traits was different between G1 and G2. Negative effects on the traits were found in both groups. In addition, the stronger effect of the beta casein gene was observed in most of the traits. The conclusions were that different %Holstein caused different significant effects of these genes. A study of the association of these genes within each percentage of Holstein is strongly recommended.     

细菌凝乳酶干酪素生产工艺参数优化

以新鲜牛乳为原料、细菌凝乳酶作凝固剂,先采用单因素试验研究了凝乳温度、pH值、CaCl2添加量和凝乳酶添加量4个因素对凝乳效果的影响,然后通过Box-Benhnken设计进一步优化了细菌凝乳酶干酪素生产工艺参数。根据试验结果,采用逐步回归的方法进行二次回归分析,得到相应的回归方程式,模型的R2值为0.98%,说明回归方程的拟合程度良好。采用Design-Expert软件预测得到干酪素得率的最大估计值为3.534%,此时因素X1、X2、X3的对应值分别为0.306、0.216、0.342,3个因素的对应水平为：温度36.53℃、pH值6.216、凝乳酶添加量为0.368 mL。采用上述优化条件进行验证试验时将温度设定为36.5℃、pH值设定为6.2、凝乳酶添加量设定为0.37 mL。验证试验结果表明,在此条件下凝乳酶干酪素的得率为3.527%±0.02%,与理论预测值相比,相对误差为0.19%。分别测定了细菌凝乳酶干酪素和小牛皱胃酶干酪素的水分、灰分和蛋白质等理化指标,结果表明细菌凝乳酶干酪素所含水分、灰分和蛋白质含量比小牛皱胃酶干酪素高,但差异不显著（P>0.05）,而脂肪含量比小牛皱胃酶干酪素低,差异也不显著（P>0.05）。将2种凝乳酶干酪素进行红外光谱扫描,发现小牛皱胃酶干酪素和细菌凝乳酶干酪素的特征峰基本一致。以上结果表明,2种凝乳酶干酪素品质差异不显著,说明细菌凝乳酶可作为小牛皱胃酶的替代品用于凝乳酶干酪素的生产。研究结果可为细菌凝乳酶的应用提供技术依据。     

Comparison of milk protein composition in a Swedish and a Danish dairy herd using reversed phase HPLC

Abstract

The milk composition in a Swedish herd, consisting of Swedish Red and White cows (SRB) and Swedish Holstein cows (SLB), and in a Danish herd, consisting of Danish Holstein-Friesian cows (SDM), was evaluated. Concentrations of the major milk proteins (κ-casein, α_S1-casein, β-casein, β-lactoglobulin A, β-lactoglobulin B and α-lactalbumin) of 134 individual milk samples were determined by reversed phase (RP) HPLC. Other parameters determined included milk fat, urea, lactose, calcium, lactoferrin, somatic cell count and protein degradation (determined as level of free amino-terminals). Analysis of variance was used to compare concentrations of analysed milk variables between SRB and SLB or between SLB and SDM. Concentration of total protein, total casein, β-casein and κ-casein were significantly higher in SRB milk compared with SLB milk. Concentration of α-lactalbumin and calcium were significantly higher in SDM milk than in SLB milk. The concentration of urea was higher in SLB than in SDM milk and is suggested to reflect differences in feeding regimes between the investigated Swedish and Danish herd.