Proteolysis of Sorghum Endosperm Proteins when Mashing with Raw Grain Plus Exogenous Protease and Potassium Metabisulphite

With the aim of improving free amino nitrogen (FAN) production when mashing with raw sorghum grain and exogenous enzymes, the effect of mashing with the addition of the reducing agent potassium metabisulphite (KMS) on the sorghum endosperm proteins was studied. When mashing was conducted at low temperature (40°C) over an extended period (7 h) with 0.1% KMS (sorghum basis) in addition to exogenous protease, FAN increased by approx. 6 fold to approx. 91 mg/100 g sorghum, as opposed to 5 fold to approx. 75 mg/100 g sorghum with the exogenous enzyme only. Confocal laser scanning microscopy revealed that the exogenous protease caused the endosperm protein matrix that surrounds the starch granules to break up on cooking. Transmission electron microscopy showed that the exogenous protease predominantly hydrolysed the glutelin matrix protein surrounding the kafirin protein bodies. In the presence of KMS there was also substantial breakdown of the protein bodies. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis indicated that KMS had the effect of reducing kafirin polymers and oligomers into monomers. It appears that the addition of KMS in a sorghum grain mashing system significantly improves the rate of sorghum protein hydrolysis because of the reduction of intermolecular disulphide bonds in the kafirin protein, which allows better access of the protease, resulting in improved FAN production.     

Human Milk Banking: Influence of Different Pasteurization Temperatures on Levels of Protein Sulfur Amino Acids and Some Free Amino Acids

Human milk is frequently heat‐treated in hospitals, particularly milk that is banked, to destroy contaminating bacteria and viruses, but this treatment simultaneously reduces the content of some vitamins, enzymes, and immunological and nutritional factors. This study was performed to find the optimal conditions for heat treatment. The effects of 2 pasteurization temperatures on levels of protein sulfur amino acids (methionine, cystine) and some free amino acids (taurine, glutamine, glutamic acid) in light of the oxidative instability that occurs especially during thermal treatment were examined. These substances in raw human milk and in milk treated at 56.5 °C and 62.5 °C for 30 min were compared. Samples of mature human milk from all feeds over 24 h were obtained from 13 healthy well‐nourished mothers of term infants. Each sample was divided into 3 parts: raw, treated at 56.5 °C for 30 min, treated at 62.5 °C for 30 min. The results showed that the availability of sulfur amino acids and free taurine is the same after heat treatment, whereas milk processing increased positively the levels of free glutamic acid and glutamine, but there is significance only for glutamine. The mean quantities of considered amino acids were similar in milk treated at the recommended pasteurization temperature (30 min at 62.5 °C) and at 56.5 ° for 30 min.     

腌制风干过程中卵形鲳鲹鱼肉性质、蛋白质氧化及游离氨基酸的变化

为探究卵形鲳鲹在腌制风干过程中蛋白质氧化及游离氨基酸的变化规律,对卵形鲳鲹鱼肉含水率、盐含量、质构特性、肌原纤维蛋白二级结构、羰基含量、巯基含量、蛋白质水解指数、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱和游离氨基酸等进行测定分析。结果表明：在腌制风干过程中,卵形鲳鲹鱼肉的盐含量整体呈上升趋势,含水率下降,硬度增加,而弹性则先上升后下降。鱼肉蛋白质在加工过程中发生氧化反应,羰基含量明显增加,而巯基含量明显下降,同时肌原纤维蛋白二级结构中α-螺旋含量减少,而无规卷曲含量增加。在加工过程中肌球蛋白重链条带和肌动蛋白发生明显变化,肌球蛋白重链条带变浅并在风干后消失,表明肌原纤维蛋白发生水解;鱼肉的蛋白质水解指数增加,非蛋白氮含量在腌制后下降而在风干过程中增加;游离氨基酸总量在干制1 d后达到最高,鲜味氨基酸和苦味氨基酸含量整体呈上升趋势。本研究可为腌制水产品加工过程中品质控制提供一定理论参考。     

HPLC法测定茶树花中可溶性糖、儿茶素和游离氨基酸

采用高效液相色谱法测定茶树(Camellia sinensis)花中可溶性糖、儿茶素和游离氨基酸的含量。结果表明：茶树花中含有216.85mg/g可溶性糖,其花冠、雄蕊群和雌蕊群部分(F-1)及花托、萼片和花梗部分(F-2)的含量分别为250.945mg/g和112.65mg/g;茶树花中总儿茶素含量为37.03mg/g,且F-2中的含量(46.90mg/g)高于F-1(30.88mg/g);茶树花中含有包括茶氨酸在内的16种游离氨基酸,含量为10.87mg/g,虽然F-2中游离氨基酸的种类较少,但其含量(16.47mg/g)显著高于F-1(10.59mg/g)。     

2,4-二硝基氟苯柱前衍生HPLC检测树莓中游离氨基酸

目的：建立一种简单、快速、可同时检测22 种氨基酸的色谱方法,并利用此方法对树莓中的游离氨基酸进行检测和分析,为树莓的开发提供科学依据。方法：以2,4-二硝基氟苯为柱前衍生试剂,Hypersil ODS2色谱柱,流动相A为40 mmol/L pH 6.4乙酸钠溶液,流动相B为体积分数50%乙腈-水溶液,梯度洗脱,反相高效液相色谱,二极管阵列检测器,检测波长360 nm。结果：22 种氨基酸线性方程的相关系数范围为0.993 1～1.000 0,相对标准偏差在0.95%～4.98%之间,加标回收率为97.10%～103.39%,最低检出限为0.39～2.87 μg/mL,定量限为1.29～9.47 μg/mL。利用所建方法检测出树莓中含有14 种游离氨基酸,其中6 种人体必需氨基酸,占总氨基酸含量的29.36%。结论：所建方法操作简便、重复性好,树莓氨基酸含量丰富,有开发价值。     

Study of the effect of using different levels of tahinah (sesame butter) on the protein digestibility‐corrected amino acid score (PDCAAS) of chickpea dip

This study was conducted to investigate the effect of using different proportions of tahinah (0–25%) on the protein digestibility‐corrected amino acid score (PDCAAS) of chickpea dip and to evaluate this parameter when chickpea dip is consumed with wheat bread. Protein quality was evaluated using the methods of amino acid score and true protein digestibility in weanling Sprague–Dawley rats. The levels of tahinah that provided the best true protein digestibility and protein digestibility‐corrected amino acid score were 20 and 25%. Values of true protein digestibility were significantly higher (P ≤ 0.05) than for the other types of chickpea dip (0.87 and 0.88 respectively). The consumption of wheat bread with chickpea dip led to a marked improvement in the true protein digestibility of the protein mixture (0.90); however, the protein digestibility‐corrected amino acid score did not change in the same manner owing to the relatively low amino acid score. It can be concluded that the addition of tahinah to chickpea led to an increase in the protein digestibility‐corrected amino acid score of chickpea dip (based on laboratory rat requirements for essential amino acids) and that the consumption of chickpea dip with bread led to an improvement in the protein digestibility of chickpea dip but not in the protein digestibility‐corrected amino acid score. © 2002 Society of Chemical Industry     

蓝圆鰺腌干工艺中组织蛋白酶与游离氨基酸和滋味形成的关系

为探明传统高盐（traditional high-salted fish,HS）法与低盐乳酸菌（low-salted and lactic acid bacteria fermented fish,LS）法加工过程中鱼类组织蛋白酶与蛋白降解和滋味形成的相关性,以蓝圆鰺（Decapterus maruadsi）为原料,采用以上两种方法进行加工,测定不同加工阶段（鲜鱼、腌制、浸泡脱盐、烘干、成品）蓝圆鰺中组织蛋白酶B、L、H,蛋白降解率（protein degradation rate,PI）,游离氨基酸的变化规律,并利用皮尔逊相关系数对其相关性进行分析。结果表明：2种蓝圆鰺腌干工艺加工过程中组织蛋白酶B、L、H的变化趋势相似,在腌制阶段的组织蛋白酶活力为LS法大于HS法,在烘干阶段及成品中组织蛋白酶B、L活力为HS法大于LS法,HS工艺更利于组织蛋白酶B、L活力的提高;整个加工过程组织蛋白酶H活力为LS法大于HS法;PI值在HS法和LS法中变化趋势相同,PI值、总游离氨基酸（total free amino acid,TFAA）含量、呈味氨基酸含量均在烘干阶段显著增加（P＜0.05）;HS法成品中PI值和TFAA含量较高,但呈味氨基酸为LS法大于HS法。组织蛋白酶B对蛋白降解的作用为HS法大于LS法,组织蛋白酶B、L对蛋白降解及TFAA的生成具有一定的促进作用,其中组织蛋白酶B发挥主要作用。与HS法相比,LS法能够在减少PI值的同时提升制品中呈味氨基酸含量百分比,丰富制品中的滋味物质。     

茶饼病侵染对茶树游离氨基酸组分及含量的影响

为揭示茶饼病菌对茶树叶片中游离氨基酸组分及其含量的影响,以3个不同抗性品种茶树的病、健叶为试验材料,利用高效液相色谱法(HPLC)检测不同抗性品种茶树未感病和感病后鲜叶中氨基酸的组分和含量。结果表明:不同抗性品种未感病叶片中游离氨基酸的的种类和含量有差异,茶氨酸含量最高,其次是γ-氨基丁酸、蛋氨酸、胱氨酸;感病后氨基酸总量上升,高抗品种紫娟叶片中游离氨基酸的种类减少,含量下降,仅γ-氨基丁酸含量增加;中抗品种云抗10号叶片中游离氨基酸的种类增加,含量均增加;感病品种佛香1号叶片中游离氨基酸的种类不变,γ-氨基丁酸、茶氨酸、赖氨酸、色氨酸、精氨酸5种游离氨基酸的含量增加,其余氨基酸的含量下降,因而可以以此分析氨基酸与茶树抗病性的关系。本研究结果可为从生理生化角度探讨茶饼病致病机理提供基础数据。     

菜籽蛋白水解物体外和细胞内抗氧化性评价及氨基酸分析研究

以“双低”油菜籽秦优7号为原料,碱溶酸沉法获得菜籽分离蛋白后进一步用Alcalase2.4L酶解得到菜籽蛋白水解物（rapeseed protein hydrolysates,RPHs）;采用聚丙烯酰胺葡聚糖凝胶柱（Sephacryl S-100HR）对RPHs进行分离纯化,得到3 个组分;采用抗氧化能力指数（oxygen radical absortion capacity,ORAC）方法以及细胞抗氧化活性（cellular antioxidant capacity,CAA）的方法分析筛选得到抗氧化性最好的组分3。结果表明组分3的ORAC值为（1610.38±112.51）μmol TE/g;CAA值为（124.66±2.18）μmol QE/g,EC50值为（57.84±3.38）μg/mL;在此基础之上,对组分3进行氨基酸分析以及电泳分析,表明其抗氧化性与分子质量分布及氨基酸组成可能存在一定关系。     

PITC柱前衍生-反相高效液相色谱法测定黄酒中游离氨基酸和生物胺

建立柱前衍生-反相高效液相色谱,同时测定黄酒中17 种氨基酸及7 种生物胺含量的方法。采用异硫氰酸苯酯柱前衍生试剂,采用Inertsil ODS-SP C18（250 mm×4.6 mm,5 μm）分析,以乙酸钠溶液和乙腈溶液混合液进行梯度洗脱,在254 nm波长处进行氨基酸和生物胺的含量分析。氨基酸和生物胺在2.0～500 mg/L和0.5～125 mg/L范围内具有良好的线性关系,相关系数R2大于0.99,平均回收率在86.44%～99.75%之间,相对标准偏差在0.31%～3.53%之间;检出限为0.02～0.25 mg/L,定量限为0.25～4.50 mg/L。方法线性范围广、准确性高、稳定性好,适用于黄酒中氨基酸及生物胺的检测。     

Cooking does not impair the impact of pulsed electric field on the protein digestion of venison (Cervus elaphus) during in vitro gastrointestinal digestion

The present study was conducted to elucidate whether cooking impairs the positive effect of pulsed electric field (PEF) on the digestibility of venison during in vitro gastrointestinal protein digestion. Previous studies have used fresh uncooked meat to demonstrate the effect of PEF on protein digestibility during gastrointestinal digestion neglecting the effect that cooking could induce during meat preparation process. PEF-treated samples (T₁, 10 kV, 90 Hz, 20 µs) were cooked (core temperature of 75 °C) and subjected to in vitro simulated gastrointestinal protein digestion along with non-treated controls. A 3% increase of in vitro protein digestibility was found in cooked PEF-treated venison (P < 0.05). A positive (P < 0.05) impact of PEF processing was observed on overall protein digestion as measured by soluble protein (%) and SDS-PAGE. PEF did not change (P > 0.05) the release of minerals from cooked venison during digestion. Cooking had no negative influence on the mechanism through which PEF operates in improving the protein digestibility of venison.     

文庆鲤酶解蛋白(EAP)营养成分的分析与评价

文庆鲤酶解蛋白(EAP)是一种高蛋白低脂肪的产品,通过对其氨基酸及无机质的测定分析,知其必需氨基酸和支链氨基酸含量丰富,且与非必需氨基酸的比例合理,同时富含铁、锌等元素.     

控制酶解玉米黄粉蛋白制备富含“条件必需氨基酸”——谷氨酰胺(Gln)活性肽营养液的研究(I)玉米黄粉蛋白水解用酶的筛选研究

研究了醇水体系中酶法水解玉米黄粉蛋白提取Gln活性肽的可行性 ,在 50 %乙醇 (或异丙醇 )水溶液中 ,2h内所筛选酶的活性消失 ,并且 2h内对玉米黄粉蛋白的水解度 (DH)仅有 3 %左右 ,醇浓度越高 ,活性降低越快 ,显然 ,除非对酶进行特殊的固定化处理 ,醇水体系中水解黄粉蛋白是不合适的。文章进而用水解度(DH)、氮溶解指数 (NSI)及Gln得率为指标 ,详细研究了水相中蛋白酶的水解情况 ,结果表明 ,多数酶对酰胺基具有水解作用 ,以中性蛋白酶为最 ,反应 6h ,脱酰胺率高达 4 0 .85% ,碱性蛋白酶和木瓜酶次之 ,复合酶A、风味酶和胃蛋白酶对酰胺基的水解作用较弱。     

高压处理对花生分离蛋白凝胶特性和分子结构的影响

本文研究了质量浓度为5%的花生分离蛋白(PPI)在50-200 MPa压力范围处理5 min后的热凝胶硬度、弹性和粘结力的变化情况,并对处理前后的PPI进行了SDS-PAGE、圆二色谱(CD)、质谱和分子结构模拟分析。SDS-PAGE电泳结果表明,PPI中分子量为61.0 ku的亚基对压力最敏感,对此亚基进行质谱分析,结果表明压力处理后,此亚基的氨基酸序列未发生变化,含580个氨基酸,实际分子量为66.5 ku,为伴花生球蛋白Ⅱ的电泳条带,在此基础上进行分子模拟,发现其空间构象在100 MPa处理后发生了显著变化。CD结果表明,高压处理后,PPI的二级构象发生了显著变化。PPI热凝性结果表明,100 MPa处理后其形成的热凝胶硬度最大,为172 g,比未处理提高了49.6%,弹性和粘结力与未处理相当。以上结果说明压力处理使得PPI热凝胶特性得到了改善。     

高静压处理对芸豆分离蛋白的聚集行为研究

采用排阻色谱-多角度激光光散射-折光联用技术(SEC-MALLS-RI)研究高静压处理(HP)对芸豆分离蛋白分子量分布的影响规律,揭示HP导致KPI聚集-解离行为.根据Debye plot方法,计算出芸豆球蛋白的绝对分子量为161 kDa,200 MPa HP处理解离KPI的可溶性聚集物,而400和600 MPaHP处理诱导不溶性聚集物向可溶性聚集物转化,改善KPI的溶解度(PS).     

Influence of Frozen Storage and Defrosting on the Chemical and Nutritional Quality of Sardine ((Clupea pilchardus)

Studies were carried out on the changes in solubility in SDS+β-mercaptoethanol, the –SH group content, the amino acid and the fatty acid compositions, and nutritional quality of the muscle protein following freezing, storage at −20°C and conventional defrosting of sardines ( Clupea pilchardus ). During the processes, 8% of the total SH– group content was lost and there was a slight drop in solubility in SDS+β-mercaptoethanol. The amino acids which dropped to the greatest extent were the S-amino acids, followed by histidine, tyrosine, leucine, lysine and phenylalanin. The C22:6/C16:0 ratio dropped and this was considered to be related to oxidation phenomena. The digestibility of protein, biological value and net protein utilization (NPU) also dropped as a result of the processes studied.     

Effects of AMP-activated protein kinase (AMPK) signaling and essential amino acids on mammalian target of rapamycin (mTOR) signaling and protein synthesis rates in mammary cells

Regulation of mammary protein synthesis potentially changes the relationships between AA supply and milk protein output represented in current nutrient requirement models. Glucose and AA regulate muscle protein synthesis via cellular signaling pathways involving mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK). The objective of this study was to investigate the effects of essential AA (EAA) and acetate or glucose on mTOR and AMPK signaling pathways and milk protein synthesis rates. A bovine mammary epithelial cell line, MAC-T, was subjected to different media containing 0 or 3.5 mmol/L EAA concentrations with 0 or 5 mmol/L acetate or 0 or 17.5 mmol/L glucose in 2 separate 2 × 2 factorial studies. In a separate set of experiments, lactogenic bovine mammary tissue slices were subjected to the same treatments except that the low EAA treatment contained a low level of EAA (0.18 mmol/L). Supplementation of EAA enhanced phosphorylation of mTOR (Ser2448) and eukaryotic initiation factor 4E binding protein 1 (4EBP1, Thr37/46), and reduced phosphorylation of eukaryotic elongation factor 2 (eEF2, Thr56) in MAC-T cells. Concentration of ATP and phosphorylation of AMPK increased and decreased, respectively, in the presence of EAA in MAC-T cells. Acetate, EAA, or glucose numerically reduced AMPK phosphorylation by about 16% in mammary tissue slices. Provision of EAA increased phosphorylation of mTOR and 4EBP1, intracellular total EAA concentration, and casein synthesis rates in mammary tissue slices, irrespective of the presence of acetate or glucose in the medium. Phosphorylation of mTOR had a marginally negative association with AMPK phosphorylation, which was positively related to eEF2 phosphorylation. Casein synthesis rates were positively and more strongly linked to mTOR phosphorylation than the negative link between eEF2 phosphorylation and casein synthesis rates. A 100% increase in mTOR phosphorylation was associated with an increase in the casein synthesis rate of 0.74%·h⁻¹, whereas a 100% increase in eEF2 phosphorylation was related to a decline in the casein synthesis rate of 0.33%·h⁻¹. Although AMPK phosphorylation was responsive to cellular energy status and had a negative effect on mTOR-mediated signals in bovine mammary epithelial cells, its effect on milk protein synthesis rates appeared to be marginal compared with the mTOR-mediated regulation of milk protein synthesis by EAA.     

氮气及温、湿度条件对锈赤扁谷盗卵发育的影响

在3种氮气浓度（78.8%,83.0%,88.0%）、3种相对湿度（69.6% RH,75.1%RH,83.7%RH）及5种温度（19.9、25.0、29.3、34.7、39.8 ℃）组合条件下,研究了锈赤扁谷盗卵的孵化情况。结果表明：发育历期为2.2～18.9 d,发育起点温度为13.8～14.3 ℃,最高临界发育温度为40.4～43.0 ℃,有效积温为61.6～115.6 日度。发育历期、发育速率与温度之间分别是“指数”型及“S”型曲线关系。氮气及温、湿度因素相互作用影响了卵的孵化,88.0%的氮气对孵化有显著的抑制效应,温度（> 30.0 ℃）及湿度（> 69.6% RH）强化了氮气对孵化的抑制效应。