Physicochemical and functional properties of goat milk whey protein and casein obtained during different lactation stages

During lactation, goat milk contains colostrum, transitional milk, mature milk, and end milk. The protein present in goat milk during different lactation periods has different characteristics. This study aimed to characterize the protein profile of goat milk samples obtained at different lactation stages and to identify changes in the physicochemical and functional properties of whey protein and casein from goat milk collected at 1, 3, 15, 100, and 200 d after calving. The results demonstrated that the lactation period had a great influence on the physicochemical and functional properties of goat milk whey protein and casein, especially the protein properties of colostrum on the first day after delivery. The denaturation temperature, hydrophobicity, and turbidity of whey protein were significantly higher on the first day postpartum than at other lactation periods. Correspondingly, the colostrum whey protein also had better functional properties, such as emulsification, oil holding capacity, and foaming properties on the first day postpartum than at other lactation periods. For casein, the turbidity, particle size, water holding capacity, and foaming properties on the first day after delivery were significantly higher than those at other lactation periods, whereas the denaturation temperature, oil holding capacity, and emulsification followed the opposite trend. For both whey protein and casein, the 2 indicators of emulsifying properties, namely, emulsifying activity index and the emulsion stability, also followed an opposite trend relative to lactation stage, whereas the changes in foaming capacity with the lactation period were completely consistent with the change of foaming stability. These findings could provide useful information for the use of goat milk whey protein and casein obtained during different lactation stages in the dairy industry.     

Effects of cyclodextrins on the flavor of goat milk and its yogurt

Goat milk fat includes several branched chain fatty acids (BCFAs), like 4-methyloctanoic acid, which when free, are responsible for goaty flavor. This flavor limits the market opportunities for goat milk. Prior research showed that cyclodextrins (CDs) can reduce goaty flavor, presumably by binding free fatty acids. This research extends that observation. In odor ranking trials in citrate buffer at pH 4.8, β-CD concentrations between 0% and 0.35% were increasingly effective in reducing odor intensity due to 4-methyloctanoic acid, but only when present in high molar excess. α-CD was also effective, but γ-CD was not. In lipase-treated goat milk only β-CD was effective but at much lower molar excess, a difference potentially explained by several factors. One was that BCFAs bind to CDs in marked preference to their straight chain isomers. Displacement experiments with phenolphthalein disproved that hypothesis. The ability of β-CD to reduce goaty flavor intensity extended to yogurt. An analytical panel showed that flavor of goat yogurt was reduced by addition of β-CD, but only if added before heating and fermentation. A hedonic trial showed that consumers preferred unsweetened and sweet/vanilla-flavored goat yogurt more when β-CD was included, P = 0.004 and 0.016, respectively. Males liked all yogurts more than females (P < 0.01), but there was a treatment × gender interaction (P = 0.016) for sweet/vanilla yogurt: sweet/vanilla masked the goaty flavor for males but not females. This results parallels previously demonstrated gender effects for sheepmeat flavor caused by BCFAs. PRACTICAL APPLICATION: β-Cyclodextrin masks goaty flavor in yogurt, and with its GRAS status means it could be used in commercial goat yogurts and similar products so the real or perceived nutritional advantages of goat milk are not lost to goaty flavor.     

希腊式酸羊奶的研制

以新鲜羊奶为主要原料,添加羊乳清粉,研究了希腊式酸羊奶的工艺条件。 通过单因素试验和正交试验,以感官评分及酸度 为评价指标,确定希腊式酸羊奶的最佳发酵工艺条件。 结果表明,希腊式酸羊奶的最佳发酵工艺条件为羊乳清粉添加量1.0%,接种 量6%,发酵温度42 ℃,发酵时间8 h。 在此最佳条件下,感官评分达到87分,酸度为97 °T。 希腊式酸羊奶质地均匀,口感细腻浓郁,酸甜 适中,发酵乳香味明显,羊膻味不明显,其理化及微生物指标均符合相关国家标准。     

Physical properties of yogurt fortified with various commercial whey protein concentrates

The effects of whey protein concentrates on physical and rheological properties of yogurt were studied. Five commercial whey protein concentrates (340 g kg^?1 protein nominal) were used to fortify milk to 45 g protein kg^?1. Fermentation was performed with two different starters (ropy and non‐ropy). Resulting yogurts were compared with a control yogurt enriched with skim milk powder. The water‐holding capacity of the yogurt fortified with skim milk powder was 500 g kg^?1 and ranged from 600 to 638 g kg^?1 when fortified with whey protein concentrates. Significant rheological differences have been noticed between the yogurts fortified with different whey protein concentrates, independent of the starter used. Three whey protein concentrates generated yogurts with a behavior similar to the control. The two others produced yogurt with lower firmness (15 g compared with 17 g), lower Brookfield viscosity (6 Pa s compared with 9 Pa s), lower yield stress (2 Pa compared with 4 Pa), lower complex viscosity (13 Pa s compared with 26 Pa s), and lower apparent viscosity (0.4 Pa s compared with 1 Pa s) than the control, respectively. The yogurts with the lowest firmness and viscosity were produced with concentrates which contained the highest amount of non‐protein nitrogen fraction (160 g kg^?1 versus 126 g kg^?1 of the total nitrogen), and the highest amount of denaturation of the whey protein (262 versus 200 g kg^?1 of the total nitrogen). Copyright © 2004 Society of Chemical Industry     

羊乳与牛乳理化特性比较

以莎能奶山羊羊乳为样品,利用乳样自动分析仪,氨基酸自动分析仪、等离子发射光谱、色谱分析对其基本成分、氨基酸组成及含量进行了分析和检测,并与牛乳理化特性进行比较,为科学合理地利用羊乳,生产具有独特功能的羊乳制品提供了理论依据。     

毛酸浆对酸羊奶感官品质的影响

以毛酸浆水提取物和羊奶为原料,采用Box-Benhnken响应面法对酸羊奶的最佳发酵工艺参数进行了优化,利用电子鼻分析了毛酸浆的添加对产品感官品质的影响。结果提示,毛酸浆对产品的感官品质影响显著,与羊奶可以产生协同增香的效果,与原味酸羊奶相比具有一定的抗氧化性。通过响应面优化所得的毛酸浆酸羊乳最佳发酵工艺参数为:毛酸浆提取物添加量7.5%,发酵剂添加量6.5%,43℃下发酵7 h。经此工艺制备的酸羊乳,提高了产品的营养价值,是一种颇具前途的功能性酸羊奶。      

Effects of different saccharides on the microstructure and functional properties of protein in goat milk during processing

This study investigated the changes in the characteristics of goat milk protein in the presence of trehalose, chitooligosaccharide and pectin during two practical dairy processing operations of pasteurisation and spray drying. The highest denaturation temperature and the largest particle size of milk protein were found in goat milk added with pectin after pasteurisation. And particles with more uniform and compact morphology were observed in goat milk protein with these three saccharides. An elevated emulsifying activity index of 24.37 m/g⁻² was observed in protein after spray drying due to chitooligosaccharide. And the foam stability was also improved significantly in the presence of trehalose and pectin during pasteurisation. During spray drying, saccharides showed the stabilizing effect on goat milk protein. This study revealed a complex interplay between the type of saccharides and the processing operation applied to goat milk, which might be of great significance for the production and processing of goat milk.     

Astringency of bovine milk whey protein

Whey protein solutions at pH 3.5 elicited an astringent taste sensation. The astringency of whey protein isolate (WPI), the process whey protein (PWP) that was prepared by heating WPI at pH 7.0, and the process whey protein prepared at pH 3.5 (aPWP) were adjusted to pH 3.5 and evaluated by 2 sensory analyses (the threshold method and the scalar scoring method) and an instrumental analysis (taste sensor method). The taste-stimulating effects of bovine and porcine gelatin were also evaluated. The threshold value of astringency of WPI, PWP, and aPWP was 1.5, 1.0, and 0.7 mg/mL, respectively, whereas the gelatins did not give definite astringency. It was confirmed by the scalar scoring method that the astringency of these proteins increased with the increase in protein concentration, and these proteins elicited strong astringency at 10 mg/mL under acidic conditions. On the other hand, the astringency was not elicited at pH 3.5 by 2 types of gelatin. A taste sensor gave specific values for whey proteins at pH 3.5, which corresponded well to those obtained by the sensory analysis. Elicitation of astringency induced by whey protein under acidic conditions would be caused by aggregation and precipitation of protein molecules in the mouth.     

Proteomic analysis of differentially expressed whey proteins in Saanen goat milk from different provinces in China using a data-independent acquisition technique

Whey proteins of Saanen goat milk samples from 3 provinces in China (Guangdong, GD; Inner Mongolia, IM; Shaanxi, SX) were characterized and compared using data-independent acquisition quantitative proteomics technique. A total of 550 proteins were quantified in all 3 samples. There were 44, 44, and 33 differentially expressed proteins (DEP) for GD versus IM, GD versus SX, and IM versus SX, respectively. Gene ontology annotation analysis showed that the largest number of DEP for the 3 comparisons were as follows: for biological processes: response to progesterone, glyceraldehyde-3-phosphate metabolic process, and negative regulation of megakaryocyte differentiation; for molecular functions: antioxidant activity, binding, and peroxiredoxin activity; and for cellular components: the same category of extracellular regions for the 3 comparisons, respectively. Pathways for the DEP of 3 comparisons were (1) disease; (2) synthesis and metabolism; and (3) synthesis, degradation, and metabolism. Protein–protein interaction network analysis showed that DEP for GD versus SX had the most interactions.     

牛羊乳蛋白组分比较研究

羊乳被国际营养学界誉为"奶中之王",逐渐被人们列为日常生活的营养保健佳品。该文对羊乳和牛乳的蛋白组分(主要是酪蛋白和乳清蛋白)含量、氨基酸组成及变异体等方面的差异进行了综述,并且对两者酪蛋白胶束的差异进行了比较,为羊乳检验和加工提供理论依据。     

乳成分对酸奶凝胶微观结构和流变学性质的影响

酸奶凝胶的许多宏观的物理特性与其微观结构和流变学性质密切相关。从酸奶的微结构、流变学性质和质地等方面综述了乳脂肪、蛋白质及调节酪蛋白和乳清蛋白比例对酸奶凝胶的影响。     

超滤膜分离技术回收乳清蛋白工艺研究

研究利用超滤膜分离技术,从干酪素乳清废弃液中回收乳清蛋白,通过对不同超滤膜性能的比较,选择最佳的超滤膜材料、工艺流程以及运行参数,并测得分离效果。结果表明:采用PW2540型聚醚砜卷式超滤膜较好,其最佳工艺参数为操作温度35℃,操作压力0.5MPa,且超滤膜透液通量较高,运行稳定。乳清蛋白粉中蛋白质含量72.40%,灰分3.85%。经红外光谱检测证明乳清蛋白粉品质得到较大程度的提高。每吨乳清废弃液中可回收乳清蛋白粉5.13kg,具有较好的经济效益及减排环保效益。     

Effects of fructooligosaccharide and whey protein concentrate on the viability of starter culture in reduced-fat probiotic yogurt during storage

ABSTRACT:  Viability of yogurt starter cultures and Bifidobacterium animalis was assessed during 28 d storage in reduced-fat yogurts containing 1.5% milk fat supplemented with 1.5% fructooligosaccharide or whey protein concentrate. These properties were examined in comparison with control yogurts containing 1.5% and 3% milk fat and no supplement. Although fructooligosaccharide improved the viability of Streptococcus thermophilus , Lactobacillus delbrueckii subs. bulgaricus, and Bifidobacterium animalis , the highest growth was obtained when milk was supplemented with whey protein concentrate in reduced-fat yogurt ( P < 0.05). Supplementation with 1.5% whey protein concentrate in reduced-fat yogurt increased the viable counts of S. thermophilus , L. delbrueckii subs. bulgaricus, and B. animalis by 1 log cycle in the 1st week of storage when compared to control sample. Similar improvement in the growth of both yogurt bacteria and B. animalis was also obtained in the full-fat yogurt containing 3% milk fat and no supplement. Addition of whey protein concentrate also resulted in the highest content of lactic and acetic acids ( P < 0.05). A gradual increase was obtained in organic acid contents during the storage.     

Proteomics and microstructure profiling of goat milk protein after homogenization

This study investigated the protein changes in goat milk during the homogenization process using label-free quantification. We quantified 310 and 315 proteins in the control group (CG) and homogenized group (HG), respectively, and 16 proteins were significantly different between the 2 groups. For HG, the goat milk protein particle sizes were smaller and more evenly distributed and exhibited an increase in the regular arrangement of the secondary structures. Proteomics analysis verified that xanthine dehydrogenase and asparaginase-like 1 expression in CG were higher than in HG, whereas the opposite was observed for fructose-bisphosphate aldolase, κ-casein, and β-casein. Significant changes were found in the homogenization-treated goat milk proteome that were related to goat milk glycolysis/gluconeogenesis metabolism. This work provides updated information on the current proteome characteristics of homogenized goat milk, which may be important for applying the protein component of goat milk to human nutrition and health.     

Effects of protein and fat levels in milk on cheese and whey compositions

Bulk tank milk was standardised to six levels of fat (3·0, 3·2, 3·4, 3·6, 3·8, 4·0%) and similarly to six levels of protein, thus giving a total of 36 combinations in composition. Milk was analyzed for total solids, fat, protein, casein, lactose and somatic cell count and was used to make laboratory-scale cheese. Cheese samples from each batch were assayed for total solids, fat, protein and salt. Losses of milk components in the whey were also determined. Least squares analysis of data indicated that higher protein level in milk was associated with higher protein and lower fat contents in cheese. This was accompanied by lower total solids (higher moisture) in cheese. Inversely, higher fat level in milk gave higher fat and lower protein and moisture contents in cheese. Higher fat level in milk resulted in lower retention of fat in cheese and more fat losses in the whey. Higher protein level in milk gave higher fat retention in cheese and less fat losses in the whey. Regression analysis showed that cheese fat increased by 4·22%, while cheese protein decreased by 2·61% for every percentage increase in milk fat. Cheese protein increased by 2·35%, while cheese fat decreased by 6·14% per percentage increase in milk protein. Milk with protein to fat ratio close to 0·9 would produce a minimum of 50% fat in the dry matter of cheese.     

低膻味酸羊奶加工工艺的研究

对低膻味酸羊奶的加工工艺参数:发酵剂类型、发酵剂添加量、发酵温度、发酵时间和后发酵进行了探究。结果表明:Danisco发酵剂YO-MIX 187是生产低膻味酸羊奶的最适发酵剂,当发酵剂添加量2%,发酵温度40℃,发酵时间4h,在5℃下后发酵24h时,生产的酸羊奶膻味最低,风味最佳。      

酸奶中游离氨基酸含量及乳清蛋白组成分析

用反相高效液相色谱法（RP-HPLC）测定了5种原味发酵型酸奶中游离氨基酸含量，并用十二烷基硫酸钠-聚丙稀酰胺凝胶电泳（SDS-PAGE）分析了酸奶乳清蛋白组成。结果表明：被测酸奶中乳清蛋白含量的范围在5.66-10．45g／L，其主要成分为α-乳清蛋白、β-乳球蛋白及少量酪蛋白。用HPLC在酸奶中检测到17种氨基酸，总游离氨基酸质量浓度范围285．90-1116．21mg／L，其中4个品牌酸奶中精氨酸（她）质量浓度最高，1个品牌酸奶中天冬氨酸（Asp）质量浓度最高。