外源添加单一氨基酸对桑葚酒风味品质的影响

为探究外源添加氨基酸在改善桑葚酒风味品质中的影响,在桑葚果汁中分别添加400 mg/L的异亮氨酸（Ile）、亮氨酸（Leu）、苯丙氨酸（Phe）和缬氨酸（Val）制备桑葚酒,并分析桑葚酒理化指标、挥发性风味物质和感官品质。结果表明,与对照相比,外源添加单一氨基酸可显著增加桑葚酒的挥发性风味物质含量（42.38～84.58 mg/L）（P＜0.05）,添加Ile显著增加活性戊醇、乙酸活性戊酯含量,添加Leu显著增加异戊醇、乙酸异戊酯含量,添加Phe显著增加苯乙醇和乙酸苯乙酯的含量,添加Val显著增加异丁醇和乙酸异丁酯含量,添加四种氨基酸都能增加辛酸乙酯的含量（P＞0.05）;添加Phe可提高桑葚酒花香,添加Ile、Leu或Val提高果香,添加四种氨基酸的桑葚酒的口感评分均显著提高（P＜0.05）。     

灵芝蛋白酶解产物分析及其抗氧化活性的研究

采用商品蛋白酶Alcalase和Protamex对灵芝蛋白进行水解,并对灵芝蛋白水解前后抗氧化活性的变化进行了比较。结果表明:灵芝蛋白经过蛋白酶Alcalase和Protamex水解10 h后,氨基酸态氮含量从酶解前的0.15 mg/mL分别增长到0.61 mg/mL和0.54 mg/mL;Protamex酶解得到的游离氨基酸Lys、Val、Leu、Thr、Phe、Ala、Arg、Ile、Cys、His和Try含量较高,Alcalase酶解得到的游离氨基酸Ala、Val、Glu、Leu、Arg、Try和Thr含量较高;灵芝蛋白经过蛋白酶Alcalase和Protamex水解后,清除羟自由基的能力显著增强,水解前.OH自由基清除率为28.70%,水解后分别为39.10%和33.30%;还原力亦显著增强,水解前OD700值为0.21,水解后分别为0.35和0.34。     

β-乳球蛋白与丙烯酰胺的相互作用研究

为了研究β-乳球蛋白对丙烯酰胺的抑制情况,文章采用液质联用和分子对接手段探究两者相互作用的可能性及其结合位点。研究结果表明,β-乳球蛋白会一定程度上抑制丙烯酰胺的含量,且浓度越大抑制率越高;对接结果表明二者存在相互作用的可能性,其复合物最佳的吉布斯自由能为-3.6 kcal/mol,此时丙烯酰胺结合在β-乳球蛋白内部由氨基酸残基Leu46、Leu54、Ile56、Val92、Val94、Leu103、Phe105和Leu122共同形成的柱状疏水空腔内。上述8个氨基酸残基都对丙烯酰胺均具有疏水作用,进一步实验表明Leu、Val、Ile、Phe都对丙烯酰胺有抑制作用,实验为探究β-乳球蛋白与丙烯酰胺同时被摄入时降低丙烯酰胺对人体负面影响提供了理论基础。     

风鹅现有工艺加工过程中品质的变化规律

通过对风鹅现有工艺加工过程中pH值、色泽、盐分含量、水分含量、硫代巴比妥酸还原物(thiobarbituric acidreactive substance,TBARS)值、总氮含量、非蛋白氮含量、游离氨基酸含量和游离氨基酸态氮含量等指标的测定,研究风鹅肌肉中品质变化规律及脂肪氧化和蛋白质水解可能对风味产生的影响.结果表明,盐分含量在加工过程中不断上升,水分含量不断下降;pH值和TBARS值在一定范围内波动;总氮含量、非蛋白氮含量、游离氨基酸含量、游离氨基酸态氮含量变化差异显著,风干结束后风鹅肌肉中蛋白质水解指数约为3.8％,游离氨基酸含量占非蛋白氮含量的78％以上,含量最多的游离氨基酸含量为Arg、Thr、Glu、Leu和Ala等,而增加较多的游离氨基酸含量是Asp、Leu、Tyr、Val、Ile和Lys等,大部分游离氨基酸的含量都超过其阈值很多倍,可能对风鹅的风味产生重要影响.     

现代工艺金华火腿中游离氨基酸含量的研究

通过跟踪金华火腿的现代化工艺生产过程,选取原料腿、预腌结束、腌制结束、风干中期、风干结束、成熟前期(成熟1)、成熟中期(成熟2)、成熟结束(成熟3)和后熟结束9 个工艺点对金华火腿股二头肌中游离氨基酸的含量进行测定。结果表明：肌肉中的游离氨基酸(FAA)含量都随金华火腿加工进程逐渐升高;成熟过程中升高最快。FAA 总量比腌制前提高5 倍左右,多数FAA 浓度为腌制前的10 倍,含量较高的FAA 有Glu、Leu、Ala、Arg 等,增加比例较大的有Glu、Thr、Val、Ile 和Pro 等。     

湖北宣恩火腿基本成分分析

以湖北宣恩火腿为原料,测定其股二头肌部位的水分、蛋白质、脂肪、氨基酸、脂肪酸等含量。结果表明:宣恩火腿营养丰富,基本成分含量:水分55.18%、蛋白质22.80%、脂肪21.55%,pH 6.35;宣恩火腿中被检测出的氨基酸17种,必需氨基酸7种,占总氨基酸含量的29.47%;非必需氨基酸10种,占总氨基酸含量的70.53%;含量较高的游离氨基酸有Ala、Pro、Leu、Val、Ile和Phe;含量较高的脂肪酸有棕榈酸(C16∶0)、油酸(C18∶1)和亚油酸(C18∶2)。     

奶牛乳腺对血液游离氨基酸吸收的差异性研究

研究了高、低乳品质奶牛阴外动脉、腹部乳静脉血液游离氨基酸浓度,以及乳腺对氨基酸摄取率的差异性。采用独立样本T检验设计,采集奶牛阴外动脉、腹部乳静脉血液,应用氨基酸全自动分析仪测定17种游离氨基酸浓度,分析高、低乳品质奶牛对氨基酸的差异性利用。结果表明,高乳品质奶牛组阴外动脉必需氨基酸质量浓度显著高于低乳品质奶牛组,非必需氨基酸质量浓度显著高于低乳品质奶牛组。高乳品质奶牛组必需氨基酸Thr,Val,Met,Ile,His,Arg的摄取率显著高于低乳品质奶牛组;非必需氨基酸摄取率除Cys外,其他均显著高于低乳品质奶牛组。     

瓦埠湖产芡实种仁的蛋白质、氨基酸测定

为研究瓦埠湖产芡实种仁中蛋白质、氨基酸的种类和含量,采用凯氏定氮法和氨基酸自动分析法测定瓦埠湖产芡实种仁的粗蛋白质的含量、游离氨基酸和蛋白质氨基酸的种类和含量.结果表明:瓦埠湖产芡实种仁中粗蛋白质含量为95%,含有2种游离氨基酸,即:Cys和His,含量分别为0.52mg/100g、9.26mg/100g;蛋白质氨基酸15种,即:Asp、Ser、Glu、gly、Ala、Val、Met、Ile、Leu、Tyr、Phe、His、Lys、Arg,含量分别为759 mg、1074.44 mg、2 633.88 mg、35.38 mg、70.53 mg、82.58mg、17.59mg、75.39mg、134.35mg、17.21mg、87.90mg、68.85mg、43.24mg、207.78mg/100g,其中Thr含量未能测出.     

碱性和支链氨基酸对啤酒高浓酿造酵母发酵性能的影响

研究分别考察添加三种碱性氨基酸：精氨酸（Arg）、赖氨酸（Lys）、组氨酸（His）与支链氨基酸：缬氨酸（Val）、亮氨酸（Leu）、异亮氨酸（Ile）对24 °P高浓酿造过程中酵母发酵性能及啤酒风味的影响。结果表明,六种氨基酸的添加可促进酵母生长并提高活细胞率,显著提高麦汁发酵度及乙醇产量。其中,添加Val、Leu与Arg的高浓麦汁发酵性能较好,与对照组相比,发酵结束时总CO2失质量分别为92.4 g/L、92.7 g/L与91.2 g/L;发酵度极显著提高（P＜0.01）,分别为83.65%、82.95%和82.93%;乙醇产量极显著提高（P＜0.01）,分别为11.97%（V/V）、11.90%（V/V）和11.83%（V/V）。添加Arg可显著提高酵母总细胞数（1.64×108 cells/mL）（P＜0.05）,His、Val与Leu的添加对风味物质影响较大,可提高啤酒的醇酯比,其中,Val的添加可显著提高异丁醇含量（P＜0.05）,降低总酯含量;Leu的添加则可同时提高异戊醇及乙酸异戊酯的含量。     

贮存温度对巴氏杀菌乳中游离氨基酸组成及品质的影响

在巴氏杀菌乳的贮存过程中,由于其中微生物、酶和各种生化反应的参与,其游离氨基酸含量会不断变化,进而也影响着乳的营养品质和滋味。结合酸度以及滋味的变化,采用反向高效液相色谱法对不同贮存条件下巴氏杀菌乳游离氨基酸的含量进行测定与分析。结果表明,0℃9 d内贮存的巴氏杀菌乳中游离氨基酸含量相对稳定,其游离氨基酸组成也不变。4℃条件贮存的巴氏杀菌乳中,Met、Cys的含量在12 d内保持稳定;Asp、Glu、Tyr、Arg和Ala含量均在4℃贮存3 d后急剧下降,此时巴氏杀菌乳的营养品质大大降低,不能保证人体对氨基酸的摄取。在10℃、15℃、25℃贮存条件下,贮存3 d后,巴氏杀菌乳的游离氨基酸组成由16种氨基酸变为5种,均未检出必需氨基酸Leu、Ile、Val、His。推荐巴氏杀菌乳贮存条件为0℃9 d内、4℃3 d内,不建议10℃、15℃、25℃下贮存。此外,Lys与五种味感均呈现显著相关性,表明Lys是影响巴氏杀菌乳滋味的特征氨基酸。     

马铃薯蛋白的分离及氨基酸组成分析

为了从马铃薯淀粉加工分离汁水中回收具有天然活性的蛋白,以Amberlite XAD7HP树脂作为吸附剂对扩张床吸附进行研究,并分析回收蛋白的氨基酸组成。结果表明：XAD7HP可以实现Patatin蛋白和蛋白酶抑制剂的分离,分离到的马铃薯蛋白酶抑制剂的胰蛋白酶抑制活力为410 mg/g。回收的马铃薯蛋白酶抑制剂Ser、Leu、Glu的含量分别为13.2、9.14、8.14 g/100 g,且必需氨基酸占总氨基酸的40.80%,疏水氨基酸Ile、Leu、Val、Phe和Tyr的含量也比较高。     

Effects of graded levels of duodenal infusions of leucine on mammary uptake and output in lactating dairy cows

Four multiparous Holstein cows, each equipped with a duodenal cannula and an ultrasonic mammary blood flow probe, were assigned to a 4x4 Latin square to measure the effects of duodenal infusions of Leu (0, 40, 80 and 120 g/d) on lactational responses and mammary metabolism of nutrients. Cows were fed a diet of 67.0% corn silage, 5.3% grass hay, 14.2% peas, 7.8% maize starch, 1.0% each of molasses, urea, and sodium bicarbonate and 2.4% minerals and vitamins. Requirements of the remaining 9 essential amino acids were met by infusing into the duodenum 323 g/d of a mixture of amino acids including, Ile, Val, Met, Lys, Trp, Phe, His, Thr, Arg, Tyr and Glu. Milk protein content and yield were highest with 40 g/d of Leu and then progressively declined. Milk fat content and yield were significantly decreased over the entire range of Leu infusions. Arterial concentrations of Leu increased linearly and corresponding mammary arterio-venous differences increased to a plateau with 80 g/d of Leu. As Leu infusions increased, extraction rates of Leu decreased linearly, whereas those of Ile, Val, Lys, Arg, Thr and Tyr were significantly increased. Leu was taken up by the mammary gland according to milk output with 0 and 40 g/d of Leu infused and then largely in excess. Based on responses of protein yield and mammary uptake to milk output ratio, Leu concentration in total amino acids absorbed in the small intestine needs to be close to 8.9% for optimal milk protein synthesis.     

Responses to amino acid imbalances and deficiencies in lactating dairy cows

Lactating cows were exposed to large amino acid imbalances and deficiencies by i.v. infusion to characterize responses in milk production and plasma concentrations of metabolites and hormones. Six cows in early lactation were fed a basal diet of 9% CP and infused continuously for 6 d with saline (negative control), 1.1 kg/d of a complete amino acid mix (positive control), or the equivalent mix lacking Met, Lys, His, or all 3 branched-chain amino acids. All cows received all treatments in 6 successive periods in a Latin square design. Infusion of the complete amino acid mix resulted in an increase in the plasma concentrations of several essential amino acids, insulin, and glucagon. Milk protein production was stimulated by 19%, which accounted for 10% of the infused amino acid. Plasma urea, acetate, and β-hydroxybutyrate concentrations were increased. Compared with saline, the amino acid mixtures lacking Met, Lys, or His increased essential amino acids, glucose, insulin, and glucagon concentrations in plasma, and decreased growth hormone. Plasma concentration of the essential amino acid absent from the infusate fell 2-fold but milk protein yield remained within 12% of its basal value. Dry matter intakes were depressed 35% over the first 2 d of infusion of imbalanced mixtures but recovered thereafter. Milk fat yields were increased 258 and 320 g/d by mixtures devoid of Lys and His, respectively. Correction of a Met, Lys, or His deficiency did not affect hormone concentrations in plasma and milk protein yield increased 27% due entirely to increased concentration of the single amino acid in plasma. Although imbalance and deficiency generated similar amino acid profiles in plasma, it was concluded that endocrine responses to total amino acid supply during imbalance can override imperfections in the circulating amino acid profile to maintain milk protein yield at higher levels than expected from deficiency states. Both imbalance and deficiency were characterized by a low protein:fat ratio in milk. Infusion of a mix of amino acids lacking Val, Ile, and Leu, despite a decrease in plasma Leu to 58% of its basal value, increased milk protein and fat yields to the same extent as the complete amino acid mix.     

太门哲罗鲑成熟卵子营养成分分析及评价

以太门哲罗鲑成熟卵子为研究对象,对常规营养成分、氨基酸组成、必需氨基酸营养品质评价和脂肪酸组成进行测定分析。结果表明：太门哲罗鲑成熟卵子（鲜样）中粗蛋白质量分数33.450%、粗脂肪质量分数6.432%、水分质量分数56.683%、灰分质量分数3.418%;17 种氨基酸中人体必需氨基酸7 种,非必需氨基酸10 种,氨基酸总量高达26.823%,必需氨基酸含量11.677%,非必需氨基酸含量15.146%,其中含量最高的为谷氨酸（2.931%）,其次为亮氨酸（2.627%）、丙氨酸（2.370%）、赖氨酸（2.142%）,均高于2.000%;必需氨基酸的构成比例基本符合联合国粮农组织/世界卫生组织的标准,以氨基酸评分来评价,第一限制性氨基酸为缬氨酸,第二限制性氨基酸为蛋氨酸＋半胱氨酸;以化学评分评价,第一限制性氨基酸为蛋氨酸＋半胱氨酸,第二限制性氨基酸为缬氨酸。必需氨基酸指数高达81.905。25 种脂肪酸中含饱和脂肪酸8 种,饱和脂肪酸总量占太门哲罗鲑成熟卵子1.308%,占总脂肪酸为22.497%;不饱和脂肪酸17 种,其中单不饱和脂肪酸6 种、多不饱和脂肪酸11 种,不饱和脂肪酸总量占成熟卵子高达4.483%,占总脂肪酸比例高达77.503%。通过上述分析得出,太门哲罗鲑成熟卵子可作为理想的蛋白质、氨基酸和脂肪酸来源。     

亚临界水提取热稳定脱脂米糠蛋白

利用亚临界水在不同温度（100～200 ℃）和时间（0～30 min）条件下提取热稳定脱脂米糠（heat stable defatted rice bran,HSDRB）中的蛋白质。研究在不同提取条件下提取物中蛋白质含量、总糖含量、氨基酸组成、 分子质量分布以及色差。结果表明：在提取温度175 ℃、提取时间30 min时,提取物中蛋白质及氨基酸的含量最 高,分别为50%和48.6 mg/g HSDRB;在此条件下,氨基酸具有最高的疏水性（1.8 kJ/mol）以及最高的必需氨基酸 含量（14.8 mg/g HSDRB）;温度对提取物颜色具有显著影响,L*值与提取物中蛋白质含量呈负相关关系,而a*值 与提取物中蛋白质含量呈正相关关系;提取物中的疏水性成分主要为小分子物质。     

食物源蛋白高F值寡肽的制备及应用研究进展

寡肽一般由3～9 个氨基酸残基组成,高F值寡肽是指寡肽混合物中支链氨基酸（亮氨酸、异亮氨酸和缬氨酸）与芳香族氨基酸（苯丙氨酸、色氨酸和酪氨酸）的物质的量比值（F值）大于20的肽,研究表明高F值寡肽具有多种生理活性。本文综述了食物源蛋白高F值寡肽制备原料选择、主要制备工艺及其生理活性研究进展,并对其未来研究趋势进行展望。     

Cooling ameliorates decreased milk protein metrics in heat-stressed lactating Holstein cows

Cooling can alleviate the negative consequences of heat stress on multiple milk production metrics in dairy cows. However, it is still controversial whether cooling can increase milk protein content compared with heat-stressed cows. The objective of the present study was to evaluate the relief effect of cooling on the decrease in milk protein concentration during heat stress and elucidate the potential metabolic mechanisms. Thirty lactating multiparous Holstein cows (days in milk = 175 ± 25 d, milk yield = 27.5 ± 2.5 kg/d; mean ± SD) were assigned to 1 of 3 treatments: heat stress (HS; n = 10), cooling (CL; n = 10), and cooling with pair-feeding (PFCL; n = 10). The barns for PFCL and CL cows were equipped with sprinklers and fans, whereas the barn for HS cows were not. The average temperature-humidity index during the experiment ranged from 74 to 83. The spraying was activated automatically 2 times per day (1130–1330 h and 1500–1600 h) with 3 min on and 6 min off during the first 2 wk, and 1.5 min on and 3 min off during the last 2 wk, whereas the fans operated 24 h/d. The experiment lasted for 4 wk in total. Milk, urine, feces, total mixed ration, blood, and rumen fluid samples were collected weekly. Compared with HS, feed efficiency (1.24 and 1.49), milk protein yield (0.82 and 0.94 kg/d), and milk fat yield (0.98 and 1.26 kg/d) were increased in PFCL, whereas the differences between CL and HS were not significant. Compared with HS cows, PFCL and CL cows had a lower respiratory rate (70.6, 59.1, and 60.3 breaths per minute, respectively), rectal temperature (38.95, 38.61, and 38.51°C), and shoulder skin temperature (33.95, 33.25, 33.40°C), and had greater milk protein content (3.41, 3.72, and 3.69%) and milk fat percent (4.08, 4.97, 4.65%). Both the blood activity of catalase (increased by 12.8 and 41.0%) and glutathione peroxidase (12.6 and 40.4%) of PFCL and CL cows were greater than the HS cows. Compared with HS, cooling increased the blood content of glucose, methionine, threonine, and cystathionine by 10.7% and 10.3%, 19.0% and 9.5%, 15.8% and 12.0%, and 9.5% and 23.8% in PFCL and CL, respectively. In conclusion, the results indicated that cooling partially rescued milk protein synthesis induced by heat stress, and the potential mechanism may have been due to increased antioxidant ability, blood glucose, and key AA. Consequently, in addition to modifying the environment, nutritional and physiological strategies designed to influence carbohydrate, AA, and oxidative homeostasis may be an opportunity to maintain or correct low milk protein content during the warm summer months.     

普洱茶晒青样游离氨基酸和色泽差异研究

为探讨游离氨基酸和色值在普洱茶晒青样产地及古树茶和台地茶中的差异,分析了来自云南西双版纳州、临沧市普洱茶晒青样中18 种游离氨基酸组分含量,用色差仪测定茶汤色值（L*、a*、b*）,并进行方差分析、主成分分析。结果表明：晒青样中游离氨基酸组分含量在两地间有明显差异,西双版纳样品中茶氨酸、天冬氨酸、谷氨酸、精氨酸等主要鲜味氨基酸含量高于临沧样品。氨基酸主成分分析对西双版纳和临沧晒青样可以很好区分。台地茶游离氨基酸总量、天冬氨酸、谷氨酸、茶氨酸、组氨酸含量均比古树茶高,精氨酸含量比古树茶低,其中氨基酸总量、谷氨酸、精氨酸、组氨酸差异显著,二者也是在主要鲜味氨基酸上存在差异。两地晒青样汤色存在差异,西双版纳样品L*、b*值较临沧大,a*值较小。古树茶与台地茶汤色差异不明显。     

氨基酸分析仪检测牛乳中掺入的大豆蛋白

利用氨基酸分析仪对牛乳和大豆分离蛋白中的17 种氨基酸进行分离测定,氨基酸浓度在0.025～0.350 μmol/mL时,其峰面积和氨基酸浓度的线性相关系数均不小于0.988,重复性较好,牛乳加标回收率范围在94.2%～103.1%,相对标准偏差在0.89%～3.31%。通过对比分析牛乳和大豆的氨基酸图谱找到含量差异较大的6 种氨基酸,并根据模拟掺假实验样品的氨基酸分析6 种氨基酸含量和掺假量的线性关系,相关系数R2达0.889,建立牛乳中大豆蛋白掺假的定性定量检测方法。     

牛乳中体细胞数与脂肪酸含量的相关性分析

目的：研究牛乳中体细胞数（somatic cell count,SCC）对乳脂肪酸含量的影响。方法：采集474 头处于泌乳早期（30～100 d）的中国荷斯坦奶牛乳样,测定乳中SCC及各种脂肪酸单体的含量,分析乳中SCC对脂肪酸相对含量的影响及相关性。结果：SCC极显著影响乳中C4∶0、C16∶1、cis9, trans11-CLA和C18∶3 n3脂肪酸单体的含量（P＜0.01）。同时,随着乳中SCC的升高,多不饱和脂肪酸（polyunsaturated fatty acid,PUFA）的相对含量也显著增加（P＜0.05）。相关性分析显示乳中SCC与PUFA含量呈极显著正相关（P＜0.01）,与短链脂肪酸含量呈显著负相关（P＜0.05）。结论：研究结果初步揭示了乳中SCC与乳脂肪酸相对含量的关系,为进一步揭示SCC对牛乳品质的影响提供了依据。