赖丙氨酸特性及检测

赖氨酸是食品中限制性氨基酸,在碱处理和加热时很易与蛋白质分子内其它氨基酸形成交联键,生成某些新氨基酸,如赖丙氨酸等。赖丙氨酸可由赖氨酸残基ε–氨基与脱氢丙氨酰残基缩合而成,后者可能通过胱氨酸残基碱降解、脱硫后生成,也可来自丝氨酸或磷酸丝氨酸残基分解。赖丙氨酸是一种金属螯合剂,因此,可使一些含有金属的酶,如羧肽酶A和羧肽酶B失去活性;且赖丙氨酸对小白鼠具有肾毒性。尽管至今为止,赖丙氨酸对人体毒性尚不明确,但在婴儿食品中,赖丙氨酸含量需严格控制;赖丙氨酸含量可作为蛋白质加工破坏程度和消化性能一个指标。常用的赖丙氨酸分析方法有气相色谱法、液相色谱法、氨基酸分析仪法和薄层层析法等。     

食品加工中赖丙氨酸的产生与控制

食品加工中有害物质的产生与控制对食品安全研究具有重要价值。富含蛋白质的食品在加工过程中易受到温度、pH值、形态、灭菌方式等的影响,产生赖丙氨酸,介绍了赖丙氨酸的性质、危害、产生条件,提出了食品加工中控制赖丙氨酸产生的方法,并对赖丙氨酸的研究趋势做出了展望。     

赖丙氨酸的性质与毒性

<正> 成为加工食品场合发生的毒性因子之一的赖丙酸问题,在十年中引起了众人的关注.现在的核心问题已经缩小到它对人类是否具有毒性?这个疑问的产生是由于它对白鼠具有肾脏毒性而对其他的实验动物又不显示毒性。因而,普遍的看法是赖丙酸的毒性具有特异性。赖丙氨酸对人类是否具有毒性,不能从动物试验的结果来推断,因此,人们对它产生了疑虑。而且,从市售加工食品中检出了赖丙氨酸以及对加工食品依赖程度日益提高的现代人对这个     

焙烤及油炸食品中赖丙氨酸检测方法的建立及监测

为降低焙烤及油炸食品中赖丙氨酸对人体造成危害的可能，文章建立了焙烤和油炸食品中赖丙氨酸的氨基酸分析仪检测方法。该方法将焙烤及油炸食品样品经脱脂、盐酸水解释放出赖丙氨酸，利用氨基酸分析仪，采用阳离子交换色谱柱分离，通过柱后衍生检测分析，外标法定量。结果表明，使用该方法测试时赖丙氨酸在0.50～50.0 mg/L范围内具有良好的线性关系，相关系数为0.9999，定量限为10.0 mg/kg，构建的方法的加标回收率为86.3%～91.3%，相对标准偏差（RSDs）为1.47%～4.26%。该方法简便、准确、稳定，可应用于测定焙烤和油炸食品中赖丙氨酸的含量。     

BTCA交联丝素机制的研究

选用丙氨酸、丝氨酸和桑蚕丝丝素为研究对象,采用热重分析(TG)对BTCA交联丝素的机制进行研究,研究比较了BTCA和丙氨酸、丝氨酸、桑蚕丝丝素系统在100~200℃范围内的TG曲线。结果表明:在次磷酸钠的催化作用下,BTCA和丝氨酸、丝素都可以产生化学反应,而和丙氨酸没有化学反应。由于丝氨酸在化学结构上有羟基存在,而丙氨酸在化学结构上没有羟基存在,因而在普通免烫整理条件下,BTCA交联丝素的主要形式仍然是和羟基反应产生的酯交联。     

食品中有害物赖丙氨酸的检测方法综述

富含蛋白质的食品或食品原料在热或碱加工过程中易产生一种交联氨基酸———赖丙氨酸(LAL),它对某些动物会产生特异的毒性症状,对人体也可能存在潜在的危害,但由于食品基质比较复杂,通常难以准确测定其中的LAL。因此研究食品中LAL的检测方法,对LAL的控制和促进其深入研究以及保障人体健康都具有重要意义。本文首先介绍了LAL的相关理化性质和样品前处理方法,进而综述了国内外测定多种食品中LAL的方法,包括氨基酸分析仪法、气相色谱法、液相色谱法及色谱-质谱联用方法等,分析了各种方法的优缺点,并对其发展趋势进行了展望,可为建立食品中LAL的检测方法提供一定的参考。     

食品防腐剂的制法

食品防腐剂的制法将己二酸与α一氨基酸以一定的比例混合，可制成食品防腐剂。这种防腐剂对食品风味，物理性质毫无不良影响。例如，将己二酸或已二酸化合物与α一氨基酸（以甘氨酸、丙氨酸、丝氨酸、缬氨酸、天门冬氨酸、谷氨酸为优）按１／１０～２／１０的重量比混合而...     

氨基酸对不同pH条件下辛烯基琥珀酸燕麦β-葡聚糖酯自聚集行为的影响

为了揭示食品基质组分对疏水化多糖胶束形成的影响,研究了7种常见氨基酸(谷氨酸、赖氨酸、异亮氨酸、苯丙氨酸、半胱氨酸、丙氨酸和丝氨酸)对辛烯基琥珀酸燕麦β-葡聚糖酯(octenylsuccinated oat β-glucan,OSβG)胶束形成的影响及本质,从而拓宽OSβG胶束在食品工业中的应用范围.该文测定不同pH(...     

丝素的食品化及其功能性

众所周知,丝素除了用作衣服原料外,还被广泛地应用于化妆品、医药、食品和化学工业。基于丝素的结构和成分,丝素完全有可能发展成一种具有特殊功能的新型食品。 丝素的食用功能包括以下方面:营养、品味以及对生理作用和免疫系统这二个力面进行调节。按照丝素的组成和价值,有可能把丝素作为一种高级的有添加功能的食物。 丝素由18种氨基酸组成,其中85％左右为甘氨酸、丙氨酸、丝氨酸和酪氨酸。对氨基酸的很多研究都表明甘氨酸有减少血液中胆固醇含量的作用,丙氨酸能加快酒精的代谢,酪     

Q-Orbitrap高分辨质谱法测定牛奶中赖丙氨酸及其含量随温度变化的规律

建立一种快速、准确测定牛奶中赖丙氨酸的超高效液相色谱-四极杆/静电场轨道阱高分辨率质谱法分析方法。牛奶样品使用盐酸酸解法进行前处理,并选用Ascentis-C8色谱柱(100 mm×4.6 mm,3μm)对待测物进行分离,以0.1%甲酸溶液和乙腈作为流动相进行梯度洗脱,在全扫描-数据依赖二级扫描模式进行检测。结果表明:赖丙氨酸的精确质量数偏差小于1.0×10~(-6),在1～200μg/L范围内线性关系良好,相关系数均大于0.999;牛奶中赖丙氨酸的检出限为0.01 mg/kg,定量限为0.025 mg/kg。加标量分别为0.025、0.1 mg/kg和0.25 mg/kg,样品的回收率为78.7%～117.1%,相对标准偏差为3.64%。同时采用小型模拟加工设备加热液态奶,研究赖丙氨酸在不同加工条件下含量的变化规律。本方法重复性好、准确、灵敏度高,可用于牛奶中赖丙氨酸的定性、定量筛查。     

Relationship between In Vitro Digestibility of Casein and its Content of Lysinoalanine and D-Amino Acids

Alkali and heat induce changes in proteins. These include racemization of L- to D-amino acids and crosslinking via lysinoalanine. Since high-quality proteins are presumably well-digested, possible effects of D-amino acid and lysinoalanine contents on food casein digestibility was examined. The following variables, which were expected to influence all three parameters, were evaluated: (a) pH (8-14); (b) temperature (25-75°C); and (c) time of treatment (10 min to 24 hr). An approximately inverse relationship was observed between D-ammo acid and lysinoalanine content and the extent of proteolysis. Such changes may lower the quality and safety of foods.     

Simultaneous determination of lysine, lysinoalanine, furosine, and pyridosine in food and feed (author's transl)]

A method for the simultaneous separation and determination of lysinoalanine (LAL), lysine, furosine and pyridosine with an automatic amino acid analyzer using a single Column 4 buffer- and 3 temperature-programme is described. The procedure needs 160 Minutes analysis time and allows a separation and quantitative determination of LAL, when present in amounts of more than 100 ppm (semiquantitative above 10 ppm). All amino acids found in food proteins and all other ninhydrinpositive compounds tested until now do not interfere with the determination.     

D-Lysine,alloisoleucine and lysinoalanine in supplementary proteins with different lysine availabilities

D -Lysine, alloisoleucine and lysinoalanine were determined in 16 commercial protein supplements on which lysine availability had been measured by slope-ratio assay with pigs and by chemical dinitrophenylation. About 2.5% of lysine was racemised by protein hydrolysis in 6 M HCl. Only three of 10 samples with poor lysine availability by slope-ratio assay contained significantly more D -iysine than control proteins (P < 0.01). D -Lysine was not significantly correlated with lysine availability by either method; nor did it improve the poor correlation between the slope-ratio assay and dinitrophenylation. The highest level of alloisoleucine was less than 14% that of isoleucine. In all proteins except skim milk powder lysinoalanine occurred at 0.3% or less of the corresponding lysine level. Neither alloisoleucine nor lysinoalanine was related to lysine availability.     

Effects of Sulfhydryl Compounds,Carbohydrates, Organic Acids,and Sodium Sulfite on the Formation of Lysinoalanine in Preserved Egg

To identify inhibitors for lysinoalanine formation in preserved egg, sulfhydryl compounds (glutathione, L‐cysteine), carbohydrates (sucrose, D‐glucose, maltose), organic acids (L‐ascorbic acid, citric acid, DL‐malic acid, lactic acid), and sodium sulfite were individually added at different concentrations to a pickling solution to prepare preserved eggs. Lysinoalanine formation as an index of these 10 substances was determined. Results indicate that glutathione, D‐glucose, maltose, L‐ascorbic acid, citric acid, lactic acid, and sodium sulfite all effectively diminished lysinoalanine formation in preserved egg albumen and yolk. When 40 and 80 mmol/L of sodium sulfite, citric acid, L‐ascorbic acid, and D‐glucose were individually added into the pickling solution, the inhibition rates of lysinoalanine in the produced preserved egg albumen and yolk were higher. However, the attempt of minimizing lysinoalanine formation was combined with the premise of ensuring preserved eggs quality. Moreover, the addition of 40 and 80 mmol/L of sodium sulfite, 40 and 80 mmol/L of D‐glucose, 40 mmol/L of citric acid, and 40 mmol/L of L‐ascorbic acid was optimal to produce preserved eggs. The corresponding inhibition rates of lysinoalanine in the albumen were approximately 76.3% to 76.5%, 67.6% to 67.8%, 74.6%, and 74.6%, and the corresponding inhibition rates of lysinoalanine in the yolk were about 68.7% to 69.7%, 50.6% to 51.8%, 70.4%, and 57.8%. It was concluded that sodium sulfite, D‐glucose,L‐ascorbic, and citric acid at suitable concentrations can be used to control the formation of lysinoalanine during preserved egg processing.     

Gleichzeitige Bestimmung von Lysin, Lysinoalanin, Furosin und Pyridosin in Lebens- und Futtermitteln

Zusammenfassung Es wird eine Methode zur gleichzeitigen Bestimmung von Lysinoalanin (LAL), Lysin, Furosin und Pyridosin am Aminosäurenanalysator vorgestellt. Im sogenannten Einsäulenverfahren werden die genannten Verbindungen mit Hilfe eines vier-Puffer-und drei-Temperaturen-Programms von allen bisher geprüften weiteren ninhydrinpositiven Substanzen abgetrennt.Störungen im Analysenablauf treten bei Gehalten von über 10 ppm LAL kaum auf. Bei niedrigen LAL-Gehalten muß für die quantitative Bestimmung von Lysin und anderer Aminosäuren allerdings das Hydrolysat stärker verdünnt und noch einmal analysiert werden. Die Analysenzeit beträgt 160 min.

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Simultaneous determination of lysine, lysinoalanine, furosine, and pyridosine in food and feed

Summary A method for the simultaneous separation and determination of lysinoalanine (LAL), lysine, furosine and pyridosine with an automatic amino acid analyzer using a single Column 4 buffer- and 3 temperature-programme is described. The procedure needs 160 Minutes analysis time and allows a separation and quantitative determination of LAL when present in amounts of more than 100 ppm (semiquantitative above 10 ppm). All amino acids found in food proteins and all other ninhydrinpositive compounds tested until now do not interfere with the determination.

     

The production of lysinoalanine and related substances during processing of proteins

Processing foods may cause unintended changes in their constituent proteins. Bovine milk protein studies have assisted in understanding the formation of lysinoalanine, which has toxic properties, and some phosphoproteins.Protein lysyl residues may enter the Maillard reaction with degradation products of carbohydrates, but losses of lysine can occur in the absence of free carbohydrate. Other alanines have also been detected. The study of bovine milk casein complex, via its four components, has yielded additional understanding of lysinoalanine formation, and has indicated that it corresponded to the lysine loss, but not to the serine loss.The studies report the effect of gentle heat and alkali at neutral pH, but greater heat at the same pH has yielded lysinoalanine. Cyanate, formed from milk urea, may lead to homocitrulline formation.     

Solubilization of wheat gluten with sodium hydroxide

The solubility of wheat gluten may be increased greatly by treatment with 0.25 M sodium hydroxide. At temperatures of 40°C and above, the solubility of the protein exceeds 100 mg/ml in a reaction time of 6 hr or less. The products from the reaction of 60°C and 80°C were darker than the original gluten and had an unpleasant odour of H₂S on dissolution in water. They also contained traces of lysinoalanine. The 40°C reaction product was about the same colour as gluten, and its solutions in water did not smell of H₂S. Reaction of gluten at 20°C also caused a large increase in solubility, but after 24 hr the solubility was only 77 mg/ml. This product was also of the same colour as gluten, and did not smell of H₂S in solution. Neither the 20°C nor the 40°C products contained detectable traces of lysinoalanine. For reasons of flavour, colour, lysinoalanine content and economy of time, the optimum reaction conditions are 6 hr at 40°C.     

Formation of dehydroalanine, lanthionine and lysinoalanine during heat treatment of beta-lactoglobuline A (author's transl)]

Solutions of beta-lactoglobulin A were heated at 97.5 degrees C at pH 6.9 and 9.8 80 min. The formation of dehydroalanine, lanthionine and lysinoalanine as well as changes in the levels of cysteine, cystine and the basic amino acids were recorded. Lanthionine (equal amounts of the 1- and the mesoform) was formed only in small amounts, while the lysinoalanine levels were rather high. Beside this, lysine was converted to unknown compounds. The main sources for the formation of dehydroalanine are the cystine moieties of the protein. Cysteine residues are first oxidized to cystine before beta-elimination occurs.     

Kinetics of Racemization of Amino Acid Residues in Casein

Exposing casein to alkali (0.1N NaOH at 65°C) partly racemized the amino acid residues. A plot of D/L ratios for seven amino acids versus time of treatment shows fast initial racemization rates that decrease after about 1 hr. A linear free energy relationship exists between racemization rates and inductive effects of amino acid side chains or R-substituents (σ*). Kinetic studies over the temperature range 25–75°C yields activation energies (in Kcal/mole) for aspartic acid (20.8), phenylalanine (28.7), glutamic acid (32.5), and alanine (32.4). Racemization rates increase with hydroxide ion concentration but not with protein concentration. Acetylation of amino groups prevents lysinoalanine formation but not racemization, permitting studies which distinguish between effects of these two alkali-induced reactions. Understanding principles that govern racemization should help in designing food processes that minimize undesirable, deteriorative changes in food proteins.