吡咯基丝氨酸乙酯的合成表征及其对大蒜绿变的作用

采用有机合成的方法得到新化合物吡咯基丝氨酸乙酯,验证其是否可以作为大蒜绿变的色素前体,并用核磁共振的方法验证了这种新化合物具有和已报导过的大蒜绿变色素前体-3,4-二甲基吡咯基缬氨酸(PP-Val)和3,4-二甲基吡咯基丙氨酸(PP-Ala)相似的结构,只是R侧链的结构不同.但实验结果表明,吡咯基丝氨酸乙酯不能使新蒜绿变,也不能和丙酮酸发生反应,表明R侧链的结构对这种吡咯基氨基酸是否能作为色素前体起着很重要的作用.     

氧气浓度调控腊八蒜黄色素形成研究

为揭示氧气对腊八蒜黄色素形成的影响,研究了不同比例的氧气对腊八蒜黄色素的形成规律。以绿变大蒜为原料,采用6种不同充气比例氧气进行包装,定期检测腊八蒜色素提取液的色差值和光密度(OD值)。结果表明:随贮藏时间的增加和氧气比例的升高,色素溶液亮度增加,绿色逐渐褪去,溶液变黄。腊八蒜蓝色素在1、3、5 d的OD值均随氧气比例升高而降低,降解速率随氧气比例升高而加快,氧气加快了腊八蒜蓝色素降解。腊八蒜黄色素在0、1、3 d的OD值逐渐升高,第5天时不同处理样品黄色素的OD值有较大差异,40%~60%比例的氧气更易于黄色素的形成,20%和100%比例的氧气处理后黄色素反而下降,可见蓝色素降解形成黄色素的同时,黄色素自身也有一定程度的降解;同时氧气也调控吡咯基氨基酸与丙酮酸反应的黄色素另一形成途径,为黄色腊八蒜的制备提供理论依据及技术参数。     

蒜泥绿变机理的研究

在前人对洋葱泥红变的研究基础上,研究了蒜泥绿变的机理。通过测定休眠与打破休眠的大蒜中γ-谷氨酰转肽酶的活性存在与否,大蒜中γ-谷氨酰转肽酶活性的变化与蒜泥绿变的关系,以及在不能绿变的大蒜中添加γ-谷氨酰转肽酶而使蒜泥变绿,确定了γ-谷氨酰转肽酶对蒜泥绿变的作用。研究了与蒜泥绿色素形成有关的物质:色素中间体、蒜酶、氨基酸、羰基化合物和色素前体,提出了蒜泥绿色素形成的假说。     

吡咯基氨基酸化合物在大蒜绿变中的作用研究

研究了乙酸体系中吡咯基缬氨酸以及吡咯基亮氨酸对"腊八蒜"绿变的影响,发现在醋泡的新蒜浸泡液中添加吡咯基缬氨酸可以导致蒜变绿,吡咯基氨基酸化合物可能是"腊八蒜"绿变的中间体化合物。但吡咯基亮氨酸则不能使蒜变绿,表明"腊八蒜"变绿对吡咯氨基酸中间体有着明显的结构上的要求。在本研究中,吡咯基缬氨酸中间体的发现,非常有助于对于长期悬而未决的"腊八蒜"以及大蒜加工过程的绿变机理的阐明。     

腊八蒜绿变色素的分离提取

通过试验初步确定了提取分离大蒜绿变色素的方法 :体积分数 75 %乙醇提取绿变色素 ,色素经弱阳离子交换树脂CG 5 0 ,sephadexLH 2 0柱层析分离 ,得到了构成绿变色素的蓝色素和黄色素 2条色带 ,两者的最大吸收波长分别为 5 90nm和 440nm。通过试验证明了黄色素为蓝色素转化而来。     

腊八蒜黄色素形成机制及稳定性研究进展

腊八蒜黄色素是打破休眠期的大蒜在加工过程中,通过一系列酶促和非酶促反应产生的一类色素,作为一种天然黄色素,其发展潜力巨大。然而,由于反应物质和色素组成的多样性和复杂性,目前还无法得知其真实反应历程。因此,了解腊八蒜黄色素的形成机制及其稳定性对腊八蒜黄色素的开发与应用极其重要。介绍腊八蒜黄色素的形成途径,归纳近些年腊八蒜黄色素的研究进展和研究手段,探讨影响其稳定性的因素,以期为腊八蒜黄色素的开发利用提供理论基础。     

大蒜中主要含硫非蛋白氨基酸的合成及其与果糖的褐变反应

我们体外合成了大蒜中的主要含硫非蛋白氨基酸:S-甲基-L-半胱氨酸亚砜、S-烯丙基-L-半胱氨酸亚砜以及S-丙基-L-半胱氨酸亚砜。为了阐明大蒜加工和储藏过程中大蒜褐变的机理,我们以非蛋白质氨基酸S-甲基-L-半胱氨酸亚砜和D-果糖为反应物体外研究了它们之间的反应。高效液相色谱和紫外光谱分析表明,反应生成物主要为褐色物质,建议美拉德反应同样可以在非蛋白质氨基酸和还原糖之间进行,这为控制大蒜加工和储藏过程中产生的褐变提供了直接的理论依据。     

香椿芽苗中含硫化合物对其风味物质的影响

通过采用顶空固相微萃取的方法(HS-SPME)对香椿中的香气成分进行富集,并结合气相色谱-质谱(GCMS)法、气相色谱-嗅闻-质谱GC-O-MS对其特征性风味物质进行分析鉴定,从而进一步探究香椿中的香气组成成分。结果表明:在香椿芽苗的生长过程中,第一次得到反式-1-丙烯基双二硫化物,该化合物在一定基础上可以转化为香椿中所含有的1-丙烯基硫醇和3,4-二甲基噻吩。通过对比含硫化合物的结构式发现,香椿与大蒜在很大基础上存在一致性,而导致两者拥有特征性风味的物质在一定基础上也有所相似。     

SIPI-40树脂富集分离大蒜绿变色素的研究

大蒜绿变是一种常见现象,采用适宜手段对绿变色素进行纯化对于深入研究绿变成分具有重要意义。实验中筛选出大孔树脂SIPI-40对大蒜绿变色素进行富集分离和初步纯化,并对分离条件进行了优化,具体操作条件为:以0.5mg/mL的色素提取物水溶液进样,最大进样体积为2BV(柱床体积),进样流速1mL/min,洗脱剂为含0.1%HCl的90%乙醇溶液,洗脱体积为4BV,在此操作条件下测得的洗脱曲线峰形理想;纯化后的色素提取物的色价提高到47.6,达到了对绿变色素富集纯化的目的。大孔树脂成本低,分离高效快速,可用做精确纯化前的预分离,减少杂质对后期纯化的干扰,保证后期层析介质的稳定性和使用寿命。     

含硫风味化合物及其形成原理

含硫风味化合物在食品中含量极少,呈味阈值低,但对加工肉类、加工蔬菜和乳及乳制品的贡献很大。加工肉制品中典型的含硫风味化合物是二甲基二硫,二甲基三硫化物,2-甲基-3-呋喃硫醇,2-糠基硫醇和双(2-甲基-3-呋喃基)二硫化物。乳及乳制品中典型的含硫风味化合物是甲硫醇,二甲基二硫,二甲基硫醚。加工蔬菜中典型的含硫风味化合物是二甲基二硫,硫醇,二烯丙基二硫化物,二甲基硫醚。加工肉制品中的含硫风味化合物主要是通过加工过程中发生的美拉德反应形成,乳及乳制品和加工蔬菜中的含硫风味化合物主要是由前体风味物质经酶促反应转化而来。     

Characterization of a new yellow pigment from model reaction system related to garlic greening

Three yellow pigments have been identified from three reaction systems containing pyruvic acid and 2-(1H-pyrrolyl) acetic acid, 1-(2′-methyl-1′-carboxy-propyl) pyrrole, and 1-(2′-methyl-1′-carboxy-butyl) pyrrole (a kind of precursor of garlic green pigment) related to garlic greening in previous paper, respectively. In the present study, another kind of yellow pigment from the same system containing pyruvic acid and 2-(1H-pyrrolyl) acetic acid was identified by liquid chromatography–electrospray ionization mass spectrometry (LC-ESI MS/MS) and high-resolution electrospray ionization mass spectrometry. This kind of pigment made predominant contribution to the production of yellow pigment in this model reaction pathway, which was involved in garlic discoloration. It was observed that there were two more methyl groups located on two conjugated double bonds that bridged two moles of 2-(1H-pyrrolyl) acetic acid compared to the structures of pigments, which was identified in our previous paper. Molecular weight of the pigment is 329.1495 [M+H]⁺, and its molecular formula is C₁₈H₂₀N₂O₄ which has a maximal absorbance at 436.9 nm, due to its conjugated structure.     

Isolation and identification of one kind of yellow pigments from model reaction systems related to garlic greening

It was established that green pigment(s) responsible for garlic greening is composed of yellow and blue species, and pyruvic acid (a product from 1-PeCSO or 2-PeCSO under the action of alliinase) reacted with pigment precursor (PP) model compounds, 2-(1H-pyrrolyl) carboxylic acids to produce yellow pigments. However, the structure of the yellow pigments is unknown. In present paper, we identified three yellow pigments (Y1, Y2 and Y3) from three reaction systems containing pyruvic acid and 2-(1H-pyrrolyl) acetic acid (P-Gly) or 1-(2′-methyl-1′-carboxy-propyl) pyrrole (P-Val) or 1-(2′-methyl-1′-carboxy-butyl) pyrrole (P-Ile), respectively, by LC-ESI MS/MS and IT-TOF mass spectrometry. The three pigments have a UV/visible maximum absorbance between 400 and 434 nm and might be formed by dimerisation of the three corresponding PP under participation of pyruvic acid, molecular formula of which are C₁₆H₁₆N₂O₄ (Y1), C₂₂H₂₈N₂O₄ (Y2) and C₂₄H₃₂N₂O₄ (Y3), respectively.     

Effect of pyruvic acid and ascorbic acid on stability of 3‐deoxyanthocyanidins

BACKGROUND: 3‐Deoxyanthocyanins are a rare class of plant pigments primarily found in sorghum and known to possess distinct chemical and bioactive properties. They have potential as natural food colourants. This work investigates how 3‐deoxyanthocyanin pigments react with pyruvic acid and their stability in the presence of ascorbic acid. RESULTS: Substitution at C‐5 was the major determinant of the mechanism of 3‐deoxyanthocyanidin complexation with pyruvic acid: hydroxyl substitution favoured cyclic condensation, whereas methoxyl substitution favoured oxidative ring contraction. Pure 3‐deoxyanthocyanidins generally showed poor stability in the presence of 500 mg L^?1 ascorbic acid at pH 2.0 and 3.2 but were stable at pH 5.0; pyruvic acid improved their stability at pH 2.0 and 3.2 and enhanced their colour intensity at pH 5.0. Crude sorghum pigment extract was very stable in the presence of ascorbic acid: 31% colour loss at pH 2.0; 1.9‐ and 1.3‐fold increases in colour intensity at pH 3.2 and 5.0 respectively. In contrast, red cabbage pigment lost 30–85% of its colour in the presence of ascorbic acid under the conditions used in the study. CONCLUSION: Crude sorghum pigments are very stable in the presence of ascorbic acid and may be useful as natural food colourants. Copyright © 2008 Society of Chemical Industry     

Underestimation of pyruvic acid concentrations by fructose and cysteine in 2,4-dinitrophenylhydrazine-mediated onion pungency test

Onion pungency has been routinely measured by determining pyruvic acid concentration in onion juice by reacting with 2,4-dinitrophenylhydrazine (DNPH) since 1961. However, the absorbency of the color adduct of the reaction rapidly decreased in onion samples as compared to that of the pyruvic acid standards, resulting in underestimations of the pyruvic acid concentrations. By measuring the absorbency at 1 min, we have demonstrated that accuracy could be substantially improved. As a continuation, the causes of degradation of the color adduct after the reaction and pyruvic acid itself before the reaction were examined in this study. Alliinase action in juice (fresh or cooked) and bulb colors did not influence the degradation. Some organic acids indigenously found in onion, such as ascorbic acid, proline, and glutamic acid, did not reduce the absorbency. However, fructose within the onion juice or supplemented caused the degradation of the color adduct, whereas sucrose and glucose had a lesser effect. Degradation rates increased proportionally as fructose concentrations increased up to 70 mg/mL. Cysteine was found to degrade the pyruvic acid itself before the pyruvic acid could react with DNPH. Approximately 90% of the pyruvic acid was degraded after 60 min in samples of 7 mM pyruvic acid supplemented with 10 mg/mL cysteine. Spectral comparisons of onion juice containing fructose naturally and pyruvic acid solution with supplemented fructose indicated identical patterns and confirmed that the color-adduct degradation was caused by fructose. Our study elucidated that fructose, a major sugar in onion juice, caused the degradation of color adduct in the onion pungency test and resulted in underestimation of the pyruvic acid concentration.     

Characterization of yellow pigments formed on reaction of 2-(1H-pyrrolyl)carboxylic acids with pyruvic acid in garlic greening model systems

Two new pyrrole derivatives 2-(1H-pyrrol-1-yl)succinic acid (P-Asp) and 2-(1H-pyrrol-1-yl)pentanedioic acid (P-Glu) were synthesized to study their effect 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 the two compounds. Also, it was found that yellow pigments can be produced by reacting the two model compounds with pyruvic acid at room temperature. Four major new yellow pigments from these two model systems were formed. Two of them named AUP-1 and AUP-2 produced from model system II consisting of P-Asp and pyruvic acid have the same molecular weight 417.1294 [M+H]⁺ but having different retention times in HPLC, suggesting that there are isomers with each other. Likewise, other two isomer compounds GUP-1 and GUP-2 from model system I containing P-Glu and pyruvic acid have molecular weight as 445.1586 [M+H]⁺. The molecular formula for AUP-1 and AUP-2 was C₂₀H₂₀N₂O₈ while the molecular formula for GUP-1 and GUP-2 was C₂₂H₂₄N₂O₈. All these results confirmed previous proposal that pyrrole derivatives acted as PP (pigment precursor) for Allium discoloration.     

A new vinylpyranoanthocyanin pigment occurring in aged red wine

A new pyranoanthocyanin–vinylphenol pigment was detected in an aged Port red wine. The UV–Vis spectrum of this pigment was found to have a λ_max of 538 nm that is bathochromically shifted from that of original anthocyanins, exhibiting a more purple hue in acidic solution. This newly formed pigment was synthesized in model solution through the reaction between malvidin 3-O-glucoside–pyruvic acid adduct and vinylphenol and its structure was assigned by NMR and mass spectrometry. This pigment is reported herein for the first time.     

Screening of d-amino acid oxidase inhibitor by a new multi-assay method

This paper describes an investigation of the inhibition of a d-amino acid oxidase (DAAO) activity in several kinds of food additives and fruit. To screen for an inhibitor of DAAO, the method employed checked for two kinds of indicators, namely, pyruvic acid (indicator-1) and hydrogen peroxide (indicator-2), both of which are formed by digestion by DAAO of d-alanine (the standard d-amino acid used in this study). For measurement of pyruvic acid, a reliable and authenticated method was employed: the presence of pyruvic acid was determined by converting it into a chromophore derivative by tagging with 2,4-dinitro phenylhydrazine (DNP), followed by measurement of absorbance at 445 nm. The pyruvic acid thus determined is referred to as “(colorimetric) indicator-1”. To measure hydrogen peroxide, a highly sensitive fluorogenic substrate, 3-(p-hydroxyphenyl)propionic acid (HPPA), was employed in the present study. Hydrogen peroxide was detected by measuring fluorescence intensity (Ex. = 320 nm, Em. = 405 nm) of 2,2′-dihydroxybiphenyl-5,5′-dipropionic acid (oxidize-HPPA), which is produced by horseradish peroxidase (HRP)-catalyzed oxidation of HPPA with hydrogen peroxide. The hydrogen peroxide thus determined is referred to as “(flourometric) indicator-2” After optimizing the multi-assay procedures, the inhibition of DAAO activity against d-alanine (used as the standard d-amino acid) in 11 kinds of food additives and five kinds of fruit was evaluated, first in terms of indicator-1. Then, two substrates, potassium sorbate and apple juice, that were screened by indicator-1, were further evaluated by indicator-2 to conform the inhibition of DAAO activity. This is the first demonstration of the inhibition of DAAO activity by potassium sorbate, which is widely used as a synthetic preservative in food and apple juice.     

响应面法优化丙酮酸发酵培养基

采用响应面法(RSM)对丙酮酸发酵培养基成分葡萄糖、硫酸铵、蛋白胨进行优化,采用多元二次回归方程拟合3种因素与丙酮酸含量间的函数关系,并得到了最佳条件。在优化培养条件下,发酵液中丙酮酸的浓度由35.4g/L提高到41.57g/L,在5L罐的最佳浓度下丙酮酸产量71.23g/L比原产量65.76g/L提高8.3%。     

Transport of lactic acid in Kluyveromyces marxianus: evidence for a monocarboxylate uniport.

Lactic acid-grown cells of a strain of Kluyveromyces marxianus transported D- and L-lactic acid by a saturable mechanism that was partially inducible and subject to glucose repression, with the following kinetic parameters at pH 5.4: Vmax = 1.00 (+/- 0.13) mmol h-1 per g dry weight and Ks = 0.42 (+/- 0.08) mM. Lactic acid transport was competitively inhibited by pyruvic, glycolic, acetic and bromoacetic acids. The latter, a non-metabolizable analogue, was transiently accumulated, the extent depending on the extracellular pH. The pH dependence of the Ks values for undissociated lactic acid and for the lactate anion indicated that the latter was the transported species. Lactate uptake was not accompanied by the simultaneous uptake of protons, potassium ions or sodium ions excluding symport mechanisms. Initial lactic acid uptake led to transient membrane hyperpolarization as measured with a fluorescent dye excluding also an electroneutral anion antiport mechanism. It was concluded that lactate anions use a monocarboxylate uniport and that the counter anion, possibly bicarbonate, uses a separate channel, the coupling being electrical and loose.     

Degradation of pelargonidin 3‐glucoside in the presence of chlorogenic acid and blueberry polyphenol oxidase

Oxidation of both chlorogenic acid (CG) and pelargonidin 3‐glucoside (Pg 3‐glc) as well as their mixture, in the presence of blueberry polyphenol oxidase (PPO) was studied in model solutions. The reactions were monitored by spectrophotometric, polarographic and HPLC methods. In the absence of CG, Pg 3‐glc is not oxidised by blueberry PPO, but pigment degradation is induced by the presence of chlorogenic acid. Kinetic studies showed that Pg 3‐glc was degraded by a mechanism involving a reaction between chlorogenoquinone and/or secondary products of oxidation formed from the quinone and the pigment. Therefore, no coupled oxidation mechanisms occurred with Pg 3‐glc, as expected of its structure. The oxidation of CG by PPO in the presence of Pg 3‐glc involved the consumption of 0.6 μmol of oxygen per μmol of CG oxidised, which is close to the stoichiometry calculated from the oxidation of CG alone (0.63 μmol of oxygen per μmol). The initial phase of the pigment degradation showed a delay which did not correspond to cresolase activity. This phase could be explained by a quinone/anthocyanin reaction which is dependent on the chlorogenoquinone concentration and/or a reaction involving secondary products of oxidation (formed from the chlorogenoquinone) and Pg 3‐glc. © 1999 Society of Chemical Industry