非天然磷酰化氨基酸对胰蛋白酶的荧光猝灭效应

作者利用荧光法研究了非天然L-型氨基酸磷酰化前后与胰蛋白酶的相互作用。实验结果表明,L-2-氨基戊酸、庚酸、辛酸及壬酸非天然氨基酸不能使胰蛋白酶的荧光强度减弱,非天然氨基酸磷酰化后能够对胰蛋白酶产生荧光猝灭。同时,浓度不同、侧链长度不同的同系列磷酰化氨基酸对胰蛋白酶的猝灭效应均不同。随着非天然脂肪酸链磷酰化氨基酸侧链的增长及磷酰化庚酸浓度的增大,胰蛋白酶的荧光强度均明显降低,并且其荧光可以被完全猝灭。非天然氨基酸的磷酰化能够影响非天然氨基酸与胰蛋白酶的相互作用。     

基于iTRAQ技术的天然富硒与非富硒水稻差异蛋白分析

为解析不同基因型水稻次生代谢差异成因及其富硒品质形成的蛋白质机制提供参考。采用同位素标记相对和绝对定量(iTRAQ)技术对天然富硒与非富硒水稻进行定量蛋白质组学研究,探讨两种基因型水稻蛋白质组表达水平的差异。结果共鉴定到定量蛋白质有3 161个,差异蛋白为401个,其中上调差异蛋白193个,下调蛋白208个,生物信息学分析得出77个目标差异蛋白,主要分成10类:氧化还原酶、转移酶、异构酶、热休克蛋白、裂解酶、水解酶、连接酶、合成酶、微管蛋白、肌动蛋白。分析表明天然富硒水稻的抗应激、抗氧化、活性氧代谢、碳水化合物和氨基酸代谢较非富硒水稻强,但参与淀粉合成途径作用较非富硒水稻弱。CYS和metE可能是导致两种类型水稻氨基酸差异的2种关键蛋白,OsAPx02、CatC、riPHGPX、HSP70和HSP90可能是调节两种类型水稻抗氧化和抗应激作用的蛋白基因。     

天然植物酚类调控面筋蛋白交联机制的研究进展

小麦面筋品质改良与调控是食品加工过程中的共有经济和技术问题。天然植物酚类具有绿色安全、抗氧化、抑菌等优点,其中有些已被证实具有小麦粉增筋作用,但其交联作用的分子机制尚不明确。本文对归纳总结了天然酚类调控面筋蛋白交联的分子机制,阐述交联体系中共价键连接方式和非共价结合作用,为天然酚类在小麦粉中的开发应用提供了理论依据,为面粉增筋剂的研发开辟了新思路。     

食源性高F值寡肽的制备及护肝功效研究进展

高F值寡肽广泛存在于自然界动植物中,是一种来源丰富、天然环保、无副作用的优质肽源,具有抗疲劳、抗氧化、醒酒、辅助治疗肝病及苯丙酮尿症等多种生物活性。高F值寡肽因其支链氨基酸含量较高,能够逆转肝病患者体内支链氨基酸与芳香族氨基酸比例失衡现象,在辅助治疗慢性肝病及其多种并发症方面起到了重要作用。主要对食源性高F值寡肽的蛋白原料、制备与分离纯化方法、护肝功效及相关作用机制进行了综述,重点介绍植物蛋白、动物蛋白中的水产品蛋白和乳源性蛋白几种原料蛋白,酶解法和微生物发酵法两种高F值寡肽的制备方法,膜分离法、活性炭吸附法和色谱分离法几种分离纯化方法,以及高F值寡肽的护肝功效和发挥护肝功效的三种途径,旨在为提高食源性高F值寡肽开发及其在食品医药领域中的应用提供参考。     

“特鲜调味液”的研制试验

鲜味的来源主要是一些氨基酸,天然蛋白由20多种氨基酸组成,蛋白质经分解后,生成各种氨基酸,如谷氨酰胺、天门冬氨酸、谷氨酸具有鲜味,甘氨酸、丙氨酸、丝氨酸等有甜味,其中谷氨酸的鲜味最突出.为了提高调味液中氨基酸的含量,我们选择一种水解天然植物蛋白的方法.其原料来源十分广泛,价格便宜,比较适合的是豆粕和面筋,其蛋白质中谷氨酸含量可达18.4和32.5.由于面筋价格较高,我们选择了豆粕为水解原料,其水解产物称为“水解植物蛋白”,简称HVP(IIydrolizedvegetable protein).催化蛋白质水解可以用蛋白酶或盐酸,我们对两种水解方法进行实验如下.     

抗菌肽功能特性与作用机制的研究进展

抗菌肽是核糖体合成的天然抗生素,是多细胞生物体免疫系统的一部分。抗菌肽的来源广泛,氨基酸的组成和结构差异很大,具有快速杀伤以及广谱的抗菌活性。随着抗菌肽种类越来越多,对其抗菌机制及构效关系的研究成为学者们关注的热点。文章系统地阐述了抗菌肽的来源和功能特性、抑菌机制以及构效关系。     

牛磺酸降血压作用研究概况

牛磺酸是一种含硫的非蛋白氨基酸,具有多种生理功能。本文概述了牛磺酸对不同类型高血压的影响,并归纳了其主要通过抑制RAAS系统、抑制交感神经的兴奋性、刺激KKS系统、舒张血管而发挥降压作用,为牛磺酸降血压作用机制的深入研究、也为牛磺酸在营养保健食品领域的进一步开发利用提供参考。     

天然鱼翅翅针中氨基酸和脂肪酸组成分析与评价

为客观评价天然鱼翅的营养价值,为消费者做出指导,分析和评价了天然鱼翅的关键食用部位——翅针中的氨基酸和脂肪酸组成。氨基酸测定结果显示:镰状真鲨和大青鲨鱼翅翅针中共检出16种氨基酸,种类齐全,其中包含7种必需氨基酸(EAA);其氨基酸总量(TAA)分别为24.76%和23.32%,高于常见经济鱼类肌肉中TAA含量,但其EAA含量远低于常见经济鱼类肌肉中EAA含量,均为4.44%。氨基酸评分(AAS)结果显示:两种翅针除苯丙氨酸+酪氨酸的AAS评分是FAO/WHO评分标准的1.10和1.25倍之外,其余氨基酸的AAS评分均介于0.3~0.6之间,远低于评分标准;亮氨酸为两种翅针的第一限制性氨基酸。化学评分(CS)结果显示:两种翅针的CS评分均介于0.1~0.5之间,远低于标准蛋白(全鸡蛋蛋白)营养价值,亮氨酸或蛋氨酸+胱氨酸为第一限制性氨基酸;必需氨基酸指数(EAAI)评分结果显示:两种翅针的EAAI评分与标准蛋白(全鸡蛋蛋白)相距甚远,且低于几种常见经济鱼类肌肉的EAAI值。综合AAS、CS和EAAI分析结果认为:镰状真鲨和大青鲨翅针的氨基酸营养价值偏低,非优质蛋白质源,其主要限制性氨基酸为亮氨酸和蛋氨酸+胱氨酸。脂肪酸测定结果显示:两种天然鱼翅翅针中共检出4种饱和脂肪酸(SFA)、5种单不饱和脂肪酸(MUFA)和7种多不饱和脂肪酸(PUFA);其不饱和脂肪酸的含量(MUFA+PUFA)高于饱和脂肪酸(SFA)的含量,且富含花生四烯酸(ARA,分别为9.8%和9.2%)和二十二碳六烯酸(DHA,分别为4.2%和5.9%);两种天然翅针的ΣPUFA(n-3)/ΣPUFA(n-6)比值均明显高于FAO/WHO推荐比值(0.1~0.2),说明两种天然鱼翅翅针的脂肪酸营养价值较高。结论:镰状真鲨与大青鲨鱼翅翅针中氨基酸营养价值偏低,并非优质蛋白质来源;但富含人体必需的不饱和脂肪酸,其脂肪酸营养价值较高。     

牡蛎精氨酸激酶稳定性及同源性分析

目的鉴定从牡蛎中提取的天然蛋白精氨酸激酶(arginine kinase,AK),并了解其基本性质及同源性。方法利用硫酸铵盐析、阴离子交换从牡蛎中分离纯化出蛋白,通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)和圆二色(CD)光谱确定相对分子质量和二级结构,并研究其稳定性;用生物信息学软件对牡蛎AK和其他11种甲壳类、软体类动物过敏原的AK氨基酸序列进行比对,分析它们之间的同源性。结果分离纯化得到的相对分子量为40 kDa的天然蛋白为牡蛎AK,AK既不耐热也不耐强酸。牡蛎AK与软体类动物过敏原AK氨基酸序列的同源性较高,与甲壳类动物氨基酸序列的同源性在55%～60%之间。结论从牡蛎中提取得到天然AK,基本了解牡蛎AK的稳定性和同源性,并为牡蛎AK致敏性和致敏机制的全面研究打下基础。     

饮食与健康

1、氨基酸的最佳来源。中老年人自我保健的要诀之一,就是适当补充氨基酸。氨基酸以苦味食品如苦瓜、苦菜等最为丰富。 2、不饱和脂肪酸的最佳来源。不饱和脂肪酸,既能防止动脉硬化,保护心脏,还有健脑益智作用。据营养学家测定,海鱼、马齿苋等为其最佳来源。 3、核酸的最佳来源。日常食物中鱼类、洋葱、蘑菇等都是含核酸的佳品。但最佳来源当属花粉,其核酸含量为动物素的4倍,猪肉的40倍。 4、微量元素与维生素的最佳来源。每天吃10g干蘑菇,即可获得人体一天对全部微量元素的生理需求。蘑菇也是“天然维生素宝库”。 5、雌激素的来源…     

Non-protein amino acids of plants

Protein forms the major nitrogenous constituent of plants, but other essential nitrogen-containing materials present in all plants include the nucleic acids, chlorophyll and indolylacetic acid. Some plant species produce secondary nitrogenous compounds such as alkaloids, cyanogenetic glucosides and non-protein amino acids. This paper discusses the group of more than 200 non-protein amino acids now characterised as plant products. Emphasis is placed on the variety of chemical structures encountered, upon the occurrence and biosynthesis of representative examples, and upon the toxic nature of certain compounds in relation to their behaviour as metabolic analogues or antagonists.     

Synthesis and characterization of novel sulfur-containing 2-(1H-pyrrolyl) carboxylic acids and their effects on garlic greening

It has been established that protein amino acids are involved in garlic greening by reacting with thiosulfinates to form pigment precursors (PP), a class of 2-(1H-pyrrolyl) carboxylic acids. This opens an interesting question of whether specific sulfur-containing non-protein amino acids naturally occurring in garlic such as derivates of cysteine and their corresponding sulfoxides also play a role in garlic greening through the same way. To answer this question, four new sulfur-containing model compounds having a 2-(1H-pyrrolyl) carboxylic acid moiety were synthesized by reacting four non-protein amino acids with 2,5-dimethoxytetrathydrofuran, respectively, to study their effects on garlic greening, the structures of which are similar to that of a previously proposed pigment precursor for garlic greening. The puree of freshly harvested garlic bulbs turned green after being soaked in solutions of P-methyl, P-allyl and P-propyl, and with both increasing concentrations and incubation time, the green color of the puree became deeper. These results provide evidences that the sulfur-containing non-protein amino acids likewise participate in garlic greening by a similar pathway to their analogues, protein amino acids. Additionally, the three compounds exhibited a good relationship between structure and activity of garlic greening, namely, the larger the size of the R group, the larger the contribution. In contrast, P-methyl-O, P-methyl’s sulfoxide cannot turn the puree of freshly harvested garlic bulbs green within the 13 days time frame of the experiment under the same conditions.     

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.     

L-Theanine: properties, synthesis and isolation from tea

Theanine is a non-protein amino acid that occurs naturally in the tea plant (Camellia sinensis) and contributes to the favourable taste of tea. It is also associated with effects such as the enhancement of relaxation and the improvement of concentration and learning ability. It is also linked with health benefits including the prevention of certain cancers and cardiovascular disease, the promotion of weight loss and enhanced performance of the immune system. Thus, there has been a significant rise in the demand for theanine. While theanine has been chemically and biologically synthesised, techniques to isolate theanine from natural sources remain an important area of research. In this review article, the properties and health benefits of theanine are summarised and the synthesis and isolation of theanine are reviewed and discussed. Future perspectives for the isolation of theanine from natural sources are also outlined.     

Proteolysis of Mahon cheese as affected by acoustic-assisted brining

 Mahon cheeses were brined in the presence of an ultrasonic field and ripened during 75 days at 12  °C and 85% RH. Secondary proteolysis (water-soluble N, non-protein N, and free amino acids) was measured and compared to that obtained for cheeses conventionally brined. There were no differences in water-soluble and non-protein N attributable to the brining treatment. However, cheeses acoustically brined exhibited higher concentrations of free amino acids. The release of total free amino acids was more pronounced during the first 15 days of ripening for both types of brining treatments. The changes in proteolysis (free amino acids) during cheese ripening caused by acoustic-assisted brining are indicative of a higher extent of proteolysis and may also improve cheese flavor. Received: 13 March 2000     

人常乳与牛常乳中全谱游离氨基酸和水解氨基酸的对比

以产后30～40 d的人常乳和牛常乳为原料,采用同位素标记相对和绝对定量结合高效液相色谱-串联质谱技术对人常乳和牛常乳中全谱游离氨基酸和水解氨基酸的种类及含量进行对比分析。结果表明,人常乳和牛常乳中游离氨基酸质量浓度分别为0.37 g/L和0.16 g/L,水解氨基酸质量浓度分别为2.5 g/L和3.3 g/L。在全谱游离氨基酸中,人常乳和牛常乳均检测到9 种必需氨基酸以及15 种非蛋白质编码氨基酸,分别检测到11 种和7 种非必需氨基酸,其中人常乳9 种必需氨基酸、10 种非必需氨基酸以及7 种非蛋白质编码氨基酸质量浓度显著高于牛常乳（P＜0.05）;在全谱水解氨基酸中,人常乳和牛常乳均检测到8 种必需氨基酸、10 种非必需氨基酸以及12 种非蛋白质编码氨基酸,其中人常乳γ-氨基丁酸、牛磺酸、α-氨基正丁酸和β-丙氨酸质量浓度显著高于牛常乳（P＜0.05）。本研究对比分析人常乳与牛常乳中全谱游离氨基酸和水解氨基酸的种类和含量差异,为配方乳制品以及功能性食品的发展提供一定的参考。     

Kundur [Benincasa hispida (Thunb.) Cogn.]: A potential source for valuable nutrients and functional foods

Kundur [Benincasa hispida (Thunb.) Cogn.], a member of the family Cucurbitaceae, is one of the famous crops that are grown primarily for its fruits and usually recognized with its nutritional and medicinal properties especially in Asian countries. Kundur fruit has been valued as a nutritious vegetable as it provides a good source for natural sugars, amino acids, organic acids, mineral elements and vitamins. A number of medicinal properties such as anti-diarrheal, anti-obesity, anti-ulcer, and antioxidant and diuretic have been ascribed to this fruit of high economic value. As a rich source of functionally important bioactives and therapeutics such as triterpenes, phenolics, sterols, and glycosides, the fruit has been widely used for the treatment of epilepsy, ulcer, and other nervous disorders in the native medicine system of Asia. This review focuses on the cultivation, nutritional and chemical composition, as well as medicinal and therapeutic properties of this multipurpose fruit, as one of the potential sources of bioactives for functional food and nutraceutical applications.     

腊鱼加工过程中微生物及理化特性的变化

以白鲢为原料,采用传统方法制作腊鱼,研究加工过程中微生物及理化特性的变化。腊鱼加工过程中水分含量不断下降,NaCl 含量逐渐增加。腌制阶段各类微生物的生长缓慢,且非蛋白氮和游离氨基酸含量下降。干燥的前10d 各类微生物数量显著上升,干燥的各阶段非蛋白氮和游离氨基酸的含量显著上升,TBA 值也显增
加。乳酸菌、微球菌、葡萄球菌和酵母菌是腊鱼中的优势微生物菌群。腌制和干燥加工改变了鱼肉中游离氨基酸的组成,其中蛋氨酸、谷氨酸、缬氨酸、丝氨酸和苏氨酸的增加对腊鱼风味形成具有重要作用。     

豆酱自然发酵过程中蛋白质和氨基酸的变化规律

为研究豆酱在自然发酵过程中蛋白质、氨基酸组成及含量的变化规律,以按照东北豆酱传统方法制作的自然发酵豆酱为研究对象,在检测蛋白质含量、氨基氮含量、氨基酸含量、非蛋白氮含量和水解指数等指标变化的基础上,对豆酱的氨基酸评分(amino acid score,AAS)、化学评分(chemical score,CS)、必需氨基酸指数(essential amino acid index,EAAI)进行分析。结果表明,豆酱蛋白质含量、非蛋白氮含量、蛋白水解指数先上升后下降;氨基氮含量则先不断增加后减少至稳定。自然发酵豆酱中共含有17种氨基酸,但不同发酵时期豆酱中氨基酸含量差异较大,成品豆酱中氨基酸总量维持在41.00 mg/g左右,明显高于生豆粉(11.42 mg/g)和熟豆粉(11.06 mg/g)中氨基酸总量。不同发酵时期豆酱中必需氨基酸与非必需氨基酸的比值在0.48~0.77之间,提示豆酱中的蛋白质为优质蛋白。分析不同发酵时期豆酱的AAS、CS和EAAI可知,发酵20 d时EAAI最高达29.41,发酵50~75 d豆酱的EAAI保持在16.16~17.40之间。通过比较4种呈味氨基酸的含量可知,甜味氨基酸苦味氨基酸鲜味氨基酸无味氨基酸。     

Amino acid and fatty acid composition of cane molasses.

Cane molasses contain both protein and non-protein amino acids and fatty acids. Gas chromatographic evidence is presented for aspartic and glutamic acids and alanine, being the major acids out of the 18 protein amino acids determined. Two unidentified N-containing free acids, eluting faster than alanine and other protein amino acids on EGA column, are of particular interest. Linoleic (C18:2) is by far the most important fatty acid found. Other major fatty acids are palmitic (C16:0), oleic (C18:1) and arachidic (C20:0).