Yield Stress and Microstructure of Set Yogurt Made from High Hydrostatic Pressure-Treated Full Fat Milk

ABSTRACT: Set yogurts were prepared from fortified milk subjected to the following processes: (a) Thermal process (85C,°C,35 min), (b) High hydrostatic pressure process (193 or 676 MPa for 5 or 30 min), and (c) Nonprocessed milk (control). Yogurts from milk treated with 676 MPa for 30 min exhibited similar yield stress and water-holding capacity (WHC) to yogurts from heated milk. Transmission Electron Microscopy (TEM) micrographs exhibited small round casein micelle aggregates without appendages in yogurts from heated milk. Yogurts from milk treated with 193 MPa and untreated milk exhibited low yield stress, low WHC, and large clusters of coalesced micelles. Mechanisms for gel formation are discussed.     

Casein Hydrolysate Fractions Act as Emulsifiers in Process Cheese

ABSTRACT: Degrees of hydrolysis and emulsifying activity of casein hydrolysates were the highest at 4 h hydrolysis. The oil-off values of the mixture of hydrolysate (H) or supernatant (S) and traditional emulsifier (T) were not significantly different from the control made with traditional emulsifier, except for S + T = 3:1. Two other samples made with hydrolysate or supernatant only (H or S) showed higher oil-off value than the others (p < 0.05). In flavor property, no difference was found between samples made with traditional emulsifier and those made with the mixture of hydrolysate or supernatant at the ratio of 3 to 1. Therefore, these results indicated that a mixture of the hydrolysate or supernatant and traditional emulsifier might replace a traditional emulsifier in process cheese manufacturing.     

酪素/蒙脱土插层复合物制备及其耐水性能研究

在十六烷基季胺盐存在下进行蒙脱土插层得到[H4N(CH2)15CH3]+-蒙脱土插层物,酪素加热溶解后与[H4N(CH2)15CH]+-蒙脱土插层物混合,保温复合,然后沉淀分离,得到干酪素/蒙脱土纳米复合物。用XRD,TEM和TGA表征酪素纳米复合物的结构与性能。结果表明,插层复合物中蒙脱土晶片间距扩大,插层复合物耐热性能明显提高,与纯酪素相比,复合物拥有极好的耐水性能,特别适用于制备高速高性能啤酒生产线用贴标胶。     

萃取法制备干酪素

干酪素是一种用途极为广泛的精细化工产品，用萃取法生产工业干酪素，其产品质量优于机械分离法，对生产特级品工业干酪素有一定推动作用。     

干酪素型啤酒标签胶的研究进展

从制备原理及分散体系、交联剂、改性助剂等方面综述了干酪素型啤酒标签胶的研究进展,并对该领域研究进行了展望。     

胰蛋白酶水解酪蛋白进程研究

作者研究了在碱性条件下胰蛋白酶对酪蛋白的水解，用甲醛固定法对蛋白质的水解度进行测定，并用水解度（DH）表征其反应历程。分析了底物浓度（[s]）、酶浓度（[E]）、时间（t）、pH和温度对DH、水解速度的影响。在最适温度50℃、pH=7．0、底物浓度2％、酶浓度1g／L水解30min就可以达到16．19％。最后，根据底物浓度倒数与水解速度倒数关系获得米氏常数Km。     

碱性蛋白酶对酪蛋白水解的最适宜条件

蛋白质酶解是改善蛋白质特性，便于人体吸收的有效途径。我们对富含于乳制品中的酪蛋白，采用碱性蛋白酶进行水解实验。通过对主要影响因素的分析及回归方法，确定碱性蛋白酶对酪蛋白水解的最佳工艺条件：温度55℃，酶—底物比为7％，底物质量分数为6％，pH值为8。     

碱性蛋白酶对酪蛋白水解的最适宜条件

蛋白质酶解是改善蛋白质特性,便于人体吸收的有效途径。我们对富含于乳制品中的酪蛋白,采用碱性蛋白酶进行水解实验。通过对主要影响因素的分析及回归方法,确定碱性蛋白酶对酪蛋白水解的最佳工艺条件:温度55℃,酶-底物比为7%,底物质量分数为6%,pH值为8。     

Interaction of β‐casein with (−)‐epigallocatechin‐3‐gallate assayed by fluorescence quenching: effect of thermal processing temperature

The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λ_max) of up to 8.8 nm. The highest quenching constant (K_q) and the number of binding sites (n) were 0.92 (±0.01) × 10¹³ m ^?1 s^?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.     

The binding of orally dosed hydrophobic active pharmaceutical ingredients to casein micelles in milk

Casein proteins (α_S1-, α_S2-, β- and κ-casein) account for 80% of the total protein content in bovine milk and form casein micelles (average diameter = 130 nm, approximately 10¹⁵ micelles/mL). The affinity of native casein micelles with the 3 hydrophobic active pharmaceutical ingredients (API), meloxicam [351.4 g/mol; log P = 3.43; acid dissociation constant (pK_a) = 4.08], flunixin (296.2 g/mol; log P = 4.1; pK_a = 5.82), and thiabendazole (201.2 g/mol; log P = 2.92; pK_a = 4.64), was evaluated in bovine milk collected from dosed Holstein cows. Native casein micelles were separated from raw bovine milk by mild techniques such as ultracentrifugation, diafiltration, isoelectric point precipitation (pH 4.6), and size exclusion chromatography. Acetonitrile extraction of hydrophobic API was then done, followed by quantification using HPLC-UV. For the API or metabolites meloxicam, 5-hyroxy flunixin and 5-hydroxy thiabendazole, 31 ± 3.90, 31 ± 1.3, and 28 ± 0.5% of the content in milk was associated with casein micelles, respectively. Less than ～5.0% of the recovered hydrophobic API were found in the milk fat fraction, and the remaining ～65% were associated with the whey/serum fraction. A separate in vitro study showed that 66 ± 6.4% of meloxicam, 29 ± 0.58% of flunixin, 34 ± 0.21% of the metabolite 5-hyroxy flunixin, 50 ± 4.5% of thiabendazole, and 33 ± 3.8% of metabolite 5-hydroxy thiabendazole was found partitioned into casein micelles. Our study supports the hypothesis that casein micelles are native carriers for hydrophobic compounds in bovine milk.