Microstructure,free amino acids and free fatty acids in Ras cheese

The physical state of the protein in Ras cheese has been followed by TEM and SEM in parallel with the chemical changes during maturation. The microstructure of young Ras cheese, by TEM, consists of casein micelles joined to form an open network, with some clustering of the micelles that appear, by SEM, as thin fibres aggregated into cross-linked elongated strands. At higher magnification, the casein fibres appear folded to include cavities.With further maturation to 4 months, the cheese matrix changed considerably by dissociation of the casein micelles to form a more homogeneous structure of sub-micelles, as seen by TEM, whilst SEM micrographs indicated that some protein fibres still existed.The protein breakdown, the accumulation of free amino acids and the liberation of free fatty acids in Ras cheese increased during maturation by decomposition of paracasein and cheese fat.Ras cheese is characterized as a compact body but can be viewed as an extensive inter-connection between the casein sheets in a cheese matrix and by a sharp flavour attributed to free glutamic acid and the presence of butyric, caprylic and caproic (free volatile) fatty acids.     

Relative reactivity of amino acids with chlorine in mixtures

The relative reactivity of chlorine with amino acids is an important determinant of the resulting chlorination products in systems where chlorine is the limiting reagent, for example, in the human gastrointestinal tract after consumption of chlorine-containing water, or during food preparation with chlorinated water. Since few direct determinations of the initial reactivity of chlorine with amino acids have been made, 17 amino acids were compared in this study using competitive kinetic principles. The experimental results showed that (1) most amino acids have similar initial reactivities at neutral pH; (2) amino acids with thiol groups such as methionine and cysteine are exceptionally reactive and produce sulfoxides; (3) amino acids without thiol groups primarily undergo monochlorination of the amino nitrogen; and (4) glycine and proline are the least reactive. Dichlorination was estimated to occur with approximately 26% of the amino acid groups when the total amino acid: chlorine concentrations were equal.     

Analysis of free amino acids in cereal products

Free amino acids were extracted from cereal products using 50% ethanol to prevent solubilization of polysaccharides and other viscous polymers and to avoid starch gelatinization. The extracts were analyzed by GC after ion-exchange solid phase extraction and chloroformate derivatization using Ez-Faast technology (Phenomenex). Free amino acids in cereal products could be analyzed within 1 h of extraction and determination, with good separation between peaks and repeatable retention times. Relative correction factor for each amino acid was established. The matrix did not affect the results and the method was repeatable for most of the amino acids (coefficient of variation was in the order of 10%). Different fractions and products of wheat, rye, oats and barely were analyzed. The bran contained more free amino acids than did the other analysed fractions of cereals. Fermentation seemed to consume free asparagine and aspartic acid and to use or release other amino acids.     

Determination of free amino acids in body tissues

The authors describe methods for isolation and assay of free amino acids in body tissues employed today in clinical and experimental studies. Give an account of the main factors affecting the data obtained. Compare the efficacy of different methods for quantitative determination of free amino acids in tissues. Analyse difficulties arising in the option of the deproteinizing agent while preparing tissue samples to be tested. Based on the reported data and their own experience the authors suggest efficacious and less time-consuming research methods for assay of free amino acids in blood plasma, red blood cells, and tissue homogenates.     

同时测定饮料中20种游离氨基酸含量

利用氨基酸分析仪生理体液法测定了茶饮料、凉茶和代茶饮料中的牛磺酸、茶氨酸、天冬氨酸、苏氨酸、丝氨酸、谷氨酸、甘氨酸、丙氨酸、缬氨酸、胱氨酸、蛋氨酸、异亮氨酸、亮氨酸、酪氨酸、苯丙氨酸、赖氨酸、组氨酸、精氨酸、脯氨酸、γ-氨基丁酸共20种游离氨基酸的含量。其中牛磺酸、茶氨酸、γ-氨基丁酸的样品加标平均回收率(n=5)在93.95%～104.20%之间;方法的精密度(RSD,n=5)范围为0.44%～0.93%;脯氨酸的检出限为10nmol/mL,其他氨基酸的检出限均为2nmol/mL。该方法适用于同时测定饮料中的多种氨基酸含量。     

Analysis of free amino acids in green coffee beans

For the determination of free amino acids in green coffee beans, 9-fluorenylmethylchloroformate was applied successfully as the precolumn derivatization agent. The separation of the 27 free amino acids of green coffee as yet identified or quantitatively determined is almost complete. The paper describes in detail the conditions of extraction, derivatization and resolution and presents reproducible data of standard curves and of quantitative results. It has been demonstrated that by applying the extraction procedure described, 99.8% of the free amino acids detectable by this method are extracted. On principle, Arabica and Robusta coffees contain the same main and minor amino acids. It was possible for the first time to determine the free amino acids ornithine, -alanine and pipecolic acid quantitatively in Arabica and Robusta coffees as well as hydroxyproline in Arabica coffees.

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Bestimmung freier Aminosäuren in grünen Kaffeebohnen. I. Bestimmung der Aminosäuren nach Vorsäulen-Derivatisierung mit 9-Fluorenylmethyloxycarbonylchlorid

Zusammenfassung Zur Bestimmung freier Aminosäuren in Rohkaffees wurde 9-Fluorenylmethyloxycarbonylchlorid als Vorsäulenderivatisierungsreagenz erfolgreich eingesetzt. Die Trennung der 27 in Rohkaffee bisher identifizierten bzw. quantitativ bestimmten freien Aminosäuren gelang weitestgehend vollständig. Extraktions-, Derivatisierungs- und Trennbedingungen sind detailliert beschrieben, Eichung sowie Ergebnisse der quantitativen Aminosäurenanalytik wurden statistisch abgesichert. Es konnte gezeigt werden, daß durch Anwendung des beschriebenen Extraktionsverfahrens 99,8% der mittels dieser Methode erfaßbaren freien Aminosäuren aus Rohkaffees extrahiert werden. Arabica- und Robusta-Rohkaffees weisen prinzipiell gleiche Haupt- und Minoraminosäuren auf. Erstmals wurden die freien Aminosäuren Ornithin, -Alanin und Pipecolinsäure in Arabica- und Robusta-Rohkaffees sowie Hydroxyprolin in Arabica-Rohkaffees quantitativ bestimmt.

     

Analysis of free amino acids in green coffee beans

To investigate amino acid changes in green coffee beans in the post-harvest period, amino acid concentrations were determined in green beans and after modelled drying, fermentation and storage. After the drying at alternating temperatures up to maximally 40°C, considerable changes in the concentrations of individual amino acids were identified. At the beginning of the storage period, significant changes in concentration were found to a minor extent. Under the condition of drying, it was mainly the concentration of glutamic acid that changed considerably. There was an increase in all the samples by 500 mg/kg dry matter on average, which corresponds to an increase of about 50% of the original value. In contrast, the concentration of aspartic acid in most of the samples decreased clearly due to drying. For the predominant part of the coffee samples, there was a significant increase in the hydrophobic amino acids Val, Phe, Ile and Leu. Changes of the quantities of other amino acids were non-uniform and only insignificant. Constant drying at 80°C for most of the amino acids brought about only minor concentration changes compared to those values obtained at 40°C. Modelled fermentation had no significant effect on the concentrations of the individual amino acids. After a 4-week storage of dried beans, amino acid concentrations did not change further. It is very possible that different post-harvest treatment parameters may influence the amount of aroma precursor compounds in the coffee beans.     

野生毛葡萄改良新种NW196中游离氨基酸含量的测定

用氨基酸自动分析仪测定了野生毛葡萄改良新品种NW196中各种游离氨基酸的组成.结果表明:改良毛葡萄新品种中含有苏氨酸,缬氨酸,脯氨酸,丙氨酸,γ-氨基丁酸和精氨酸等多种氨基酸,其中一茬果中人体必需8种氨基酸的含量占总氨基酸含量的17.94%,γ-氨基丁酸的含量占总氨基酸含量的5.76%;二茬果中人体必需8种氨基酸的含量占总氨基酸含量的20.63%,γ-氨基丁酸的含量占总氨基酸含量的8.68%.     

葡萄酒中游离氨基酸的HPLC测定方法

近年来,人民饮食消费水平日益提高,营养保健意识也不断增强,要求饮食能促进身体健康,吃要注意三低一高食品,喝酒要选择三低三丰富的酒种。所谓三丰富中有丰富的氨基酸一项,而好的葡萄酒中就含有丰富的氨基酸,因此如何准确快速测定葡萄酒中的氨基酸就显得十分重要。氨基酸的分析方法很多,仅液相色谱法就有柱前衍生法,柱后衍生法两种。柱后衍生法需用离子交换柱及多种试剂,且分析时间长,费用较高。本实验采用柱前衍生法进行。该法具有快速、准确、费用低、易于操作等优点。1 材料与方法1.1 仪器及材料仪器:日本岛津LC-6A高效液相色谱仪,SP…     

酱油中游离氨基酸成分分析

采用高效液相色谱柱前衍生法对酱油中氨基酸的组成进行分析,结果表明市售酱油中氨基酸的组成与酿造酱油中氨基酸组成存在一定的差异,这是因为人为添加了鲜味剂,或者是使用植物蛋白水解液所致。经研究表明通过对酱油中氨基酸组成成分分析可以作为酿造酱油品质评价体系提供新思路。     

Microwave-assisted extraction of free amino acids from foods

 A microwave-assisted solvent extraction technique was developed for the extraction of free amino acids from foods. Four different samples were subjected to microwave extraction with varying amounts of extractant at several temperature values, for varying times to determine optimum extraction conditions. The extractions were performed with or without shaking the vessels in order to investigate the effects of mixing on the extraction efficiency and reproducibility. A comparison was made between this method and the traditional 1 h shaking extraction. The experiments indicated that the microwave-assisted extraction is an effective technique for the extraction of free amino acids from samples of plant or animal origin. The extraction yields obtained by the microwave method were about 10% better than by the conventional shaking technique. The times needed for the complete sample preparations were reduced by 66% with the application of microwaves. Received: 10 October 1997 / Revised version: 23 January 1998     

葡萄酒酿造过程中氨基酸含量变化的研究

应用HPLC对我国4个产区多个品种葡萄酒酿造过程样品中氨基酸含量变化趋势进行了研究,结果表明,L-脯氨酸是所有葡萄汁中氨基酸的主体,也是各样品含量差异最大的氨基酸;红葡萄酒中含脯氨酸、苏氨酸、赖氨酸等20种氨基酸,其中以脯氨酸含量最高,发现不同葡萄品种之间游离氨基酸种类和含量有差别,这与葡萄品种、气候、发酵工艺有关。     

6种葡萄籽中水解氨基酸和游离氨基酸含量测定及比较

以异硫氰酸苯酯为柱前衍生试剂,采用Thermo Acclaim~(TM) 120 C_(18)色谱柱(250mm×4.6mm,5μm),流动相A为pH 6.5的乙酸钠缓冲溶液,流动相B为甲醇—乙腈—水(体积比20:60:20),在流速1.0mL/min,梯度洗脱,柱温30℃,检测波长254nm的条件下,建立了高效液相色谱法测定葡萄籽中水解氨基酸和游离氨基酸的含量。结果表明,在试验浓度范围内,17种氨基酸的R~2均0.999 0;水解氨基酸的加样回收率为92.0%～104.6%,RSD为0.83%～4.07%;游离氨基酸的加样回收率为95.2%～102.4%,RSD为1.06%～3.98%。同时,6种葡萄籽中水解氨基酸的含量为130.46～163.24 mg/g,游离氨基酸的含量为2.04～5.13mg/g;用于酿造白葡萄酒的雷司令、赛美容和贵人香3种葡萄籽中游离氨基酸含量较高,用于酿造红葡萄酒的黑皮诺、蛇龙珠和赤霞珠3种葡萄籽中水解氨基酸含量较高。该方法稳定可靠,可用于葡萄籽中水解氨基酸和游离氨基酸的含量测定。     

茶游离氨基酸总量测定方法的改进

对国家标准GB/T8314—2002中茶游离氨基酸总量测定方法存在的问题进行探讨,并针对存在问题从方法的原理、标准工作液配制、反应体系缓冲液的选择、加样量、样品分析中参比的选择等方面进行研究并提出改进措施。改进的游离氨基酸总量测定程序为:取茶汤或标准工作液1.0mL于25mL容量瓶中,分别加入pH6.81的1/15mol/L磷酸氢二钠-磷酸二氢钾缓冲液0.5mL和20g/L茚三酮溶液0.5mL,在沸水浴中加热15min,冷却后加水定容至25mL,放置10min后,在570nm处测定吸光度。标准曲线测定以水代替标准工作液按同样操作作为参比,样品分析以水代替茚三酮溶液按同样操作作为参比。改进的方法在谷氨酸浓度为0.1～0.3mg/mL范围内呈现良好线性,精密度高、重复性好。     

自然发酵酸菜游离氨基酸的分析

以自然发酵酸菜为研究对象,利用氨基酸自动分析仪,对酸菜中游离氨基酸的种类及含量进行了测定。结果表明,酸菜中富含17种呈味氨基酸,总含量达635 mg/L。其中,苏氨酸含量最高,其次是谷氨酸、丙氨酸、丝氨酸、缬氨酸和天门冬氨酸等。酸菜中含有7种为人体必需氨基酸,其含量占氨基酸总含量的41.73%。这些呈味氨基酸对酸菜特有风味的形成,具有重要作用。     

Profiles of free amino acids in grapes of grafted Chardonnay grapevines

Chardonnay grapes from a rootstock trial in the Murray Valley region of South Australia were sampled for two seasons and concentrations of free amino acids in grape extract ('juice') were determined. The lowest concentrations of free assimilable amino-N were measured in Chardonnay grapes from vines on 140 Ruggeri and 101–14 rootstocks, and the highest concentrations were in grapes from vines on their own roots, Schwarzmann and K51–40. Free assimilable amino-N concentrations were sufficient to sustain fermentation through to completion. Arginine concentrations were generally too low to expect significant concentrations of urea in the wine. Amino-S concentrations were much lower and varied less than amino-N concentrations. The effect of any particular rootstock on the concentration of total free amino acids in Chardonnay grape 'juice' did not appear to be related to the known effects of those rootstocks on the NO₃-N status of petioles at flowering. The concentrations of leucine, iso-leucine, valine, threonine, tyrosine and phenylalanine were generally higher in Chardonnay grapes grafted onto K51–40 in comparison to grapes from Chardonnay vines grafted on the other rootstocks. Any of these amino acids may be associated with the presence of specific higher alcohols in wine.     

HPLC法测定丙酸菌发酵液中游离氨基酸的含量

建立了一种利用反相高效液相色谱法检测18种氨基酸的方法。以2,4-二硝基氟苯(DNFB)为柱前衍生剂,使用TIANHE Kromasil C18(4.6mm×250mm,5μm)反相色谱柱,采用二元梯度洗脱,流动相A相为0.05mM醋酸钠缓冲液(pH5.3),B相为乙腈-水(v/v=1∶1)。在该条件下,各氨基酸线性回归方程相关系数均大于0.9991,18种氨基酸的加样回收率均在95%103%范围内,该法快速、可靠,并将其应用于丙酸菌发酵液中的氨基酸检测。     

HPLC法测定玉米浆中游离氨基酸的含量

建立测定玉米浆中游离氨基酸的反相高效液相色谱法.Diamonsil C18(2)反相柱(5μm,250mm×4.6mm);梯度洗脱,流动相A相:0.05mol/L醋酸钠缓冲溶液(pH6.50),B相:乙腈-水(v/v=1:1),流速1.0mL/min,检测波长360nm.在该条件下所得各氨基酸的线性回归方程相关系数均在0.999以上.测定17种氨基酸的加样回收率94%～105%,相对标准偏差小于2.0%.