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.     

Modified method for the determination of pyruvic acid with dinitrophenylhydrazine in the assessment of onion pungency

Modifications to the commonly used Schwimmer and Weston procedure for determining pyruvic acid in onions are proposed. These modifications involve changes in the concentrations and volumes of the reagents and the use of 515 rather than 420 nm as the wavelength for measurements. These changes improve both the linearity and the sensitivity of the assay and eliminate interference from coloured material found in yellow onions. With these changes, more reliable determinations of pyruvic acid and thus of onion pungency should be possible. Copyright © 2003 Society of Chemical Industry     

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%。     

紫外双波长-pH转换法同时测定混合物中的丙酮酸和乳酸

建立了一种同时测试混合物中乳酸与丙酮酸含量的紫外分光光度方法。在碱性环境下,利用双波长法,测定混合物中的丙酮酸,线性回归方程C=6.75×10-3+0.626A,线性范围为0.0505⁰.505μg/mL;在酸性条件下,利用直接分光光度法,测定混合物中的乳酸,线性回归方程C=1.547+51.76A,线性范围为1.22²44μg/mL。采用本法测量工业样品,其结果与液相色谱法得到的数据基本吻合,但本法实验步骤更加简单、操作更加方便,且容易实现工艺过程的在线检测。      

含硫吡咯基氨基酸化合物的合成表征及其与丙酮酸的反应

通过Paar-Knnor有机合成方法得到一种新的含硫吡咯基氨基酸化合物。此物质的结构类似于可能的大蒜绿变色素前体2-（3,4-dimethyl-1H-pyrrolyl）-3-methylbutanioc acid.（3,4-二甲基-1H-吡咯基）-3-甲基丁酸,简称为含硫吡咯基氨基酸,此物质与丙酮酸反应不能产生黄色素。丙酮酸是大蒜绿变过程中丙烯基半胱氨酸亚砜在蒜酶作用下的产物,先前合成的色素前体类似物与丙酮酸反应大多可以产生黄色素。研究表明,该中间体通过此途径与黄色素的产生无关。      

Investigations on the conversion of onion aroma precursors S‐alk(en)yl‐L‐cysteine sulphoxides in onion juice production

Onion flavour develops when the cells are disrupted, allowing the enzyme alliinase (EC 4.4.1.4) to act upon the aroma precursors S‐alk(en)yl‐L ‐cysteine sulphoxides (ACSOs). For maximum flavour release, optimal cell disintegration and complete enzymatic conversion of ACSOs are desired. To assess an industrial scale onion juice extraction in regard to the extent of cell disintegration and the rate of enzymatic ACSO conversion, samples from all mass flows (ie onion, macerate, juice and pomace) were subjected to ACSO analysis. Applying a modified HPLC method, which allows baseline separation of the aroma precursors, three ACSOs, namely methyl‐, propyl‐ and 1‐propenyl‐L ‐cysteine sulphoxides (MCSO, PCSO and 1‐PeCSO), were determined. Initial ACSO ratios changed in the course of increasing degree of comminution from 17:83 to 100:0 (MCSO/1‐PeCSO). Only negligible amounts of PCSO were detected (<9.2 nmol g^?1 fresh weight (fw)), contributing less than 0.2% to the total ACSO content. For evaluation of the disintegration efficiency a chart was established consisting of an abscissa representing a percentage scale of ruptured cells and ordinates for the development of the marker parameters ACSOs and reaction product pyruvate relative to their initial contents. From this correlation a cell disintegration percentage after grinding of about 70% was deduced according to the determined ACSO contents. On a molar basis, macerate, juice and pomace showed 15, 0.6–2.4 and 0.7–1.0% of initial ACSO contents respectively. Only trace amounts of 1‐PeCSO were found in the juice (<16 nmol g^?1 fw). MCSO was converted to almost 90%, indicating that enzymatic transformation, in a practical sense, goes to completion. Copyright © 2004 Society of Chemical Industry     

响应面分析法优化丙酮酸发酵中维生素水平

报道了几种维生素对光滑球拟酵母(Torulopsis glabrata)TK006以葡萄糖为碳源、硫酸铵为唯一氮源生产丙酮酸的影响。采用Box-Behnken中心组合设计和响应面分析法,并结合SAS统计软件,确定了最优的维生素浓度组合:盐酸硫胺素0.0125mg/L、烟酸9.7mg/L、生物素0.022mg/L、盐酸吡哆醇0.54mg/L,并确证盐酸硫胺素是最重要的影响因素。优化后7L罐中发酵的产量、生产强度和产率分别达到80.51g/L、1.83g/L·h和0.69g/g,比对照提高了44.36%、57.48%和22.78%,达到或高于已报道的同类菌株的国际最佳研究结果。     

盐渍藠头发酵过程中乳酸菌的分离及特性研究

对盐渍藠头发酵过程中不同时期的乳酸菌进行了分离、鉴定及特性研究,从中分离出9种菌株。通过菌落形态、培养特征和生化试验等鉴定表明,这9种菌株分别为植物乳球菌、发酵乳杆菌、短乳杆菌、菊糖芽孢杆菌、乳酸链球菌、肠膜明串珠菌葡聚糖亚种、植物乳杆菌、皱膜假丝酵母、膜醭毕赤氏酵母菌。并观察了发酵过程中各个时期的主导菌相,最后得出短乳杆菌、发酵乳杆菌可作为盐渍藠头发酵过程中人工接种的试验菌株。     

新疆洋葱籽挥发油的气相色谱质谱分析

文章采用挥发油提取器对新疆洋葱籽中的挥发油进行了提取,并用气相色谱-质谱联用技术对新疆洋葱籽中的挥发油进行了鉴定,共分离出66种成分,确认了其中的62种成分,占挥发油总离子流的93.94%。采用面积归一化法确定各成分的相对百分含量,其中主要成分为含硫化合物(噻吩类、硫醚类)和含氧有机化合物(醇、酮、醛和酯)。研究为新疆洋葱籽资源的开发利用提供了理论依据。     

洋葱花青素提取物的HPLC特征图谱构建及谱—效关系

采用HPLC方法,检测10个不同地区的洋葱总花青素的指纹图谱,确定其共有峰;并通过Pearson相关分析(PCA)及灰色关联度(GRA)分析探索谱—效关系,即共有峰与含量及其抗氧化活性(清除DPPH、ABTS自由基的能力)、乙酰胆碱酯酶(AChE)抑制活性的相关性。试验结果表明:根据不同批次的洋葱花青素提取物的高效液相色谱图及相对保留时间的特点,建立了洋葱花青素提取物的特征图谱,10个不同地区的洋葱花青素提取物指纹图谱与对照指纹图谱的相似度为0.986～0.997,均0.9;确定了6个共有峰为特征吸收峰,其中1号峰为花青素(矢车菊素-3-O-葡萄糖苷),PCA、GRA分别显示6个共有峰都与含量、抗氧化活性、AChE抑制活性有良好的相关性和较强的关联性,均协同作用于生物活性。     

高效液相色谱法测定糖汁中没食子酸含量的研究

建立准确测定甘蔗糖汁酚类色素没食子酸含量的高效液相色谱法。采用Hypersil BDSC18柱(4.6mm×250mm,5μm),流动相为乙腈-0.05%磷酸(5:95),检测波长是280nm,流动相流速为1.0mL/min。没食子酸线性范围为20～100mg/L,回归方程Y=15960X-4749,相关系数0.9991,检出限0.22mg/L,平均加标回收率为101.45%(RSD为1.13%)。样品清汁、清糖浆配成浓度15°Bx后,过0.45微滤膜,测定滤液中没食子酸含量,分别是21.70、17.06mg/L。结论:高效液相色谱测定方法准确、可靠,可用于甘蔗糖汁色素中没食子酸的检测。     

Study of total fructan and fructooligosaccharide content in different onion tissues

The objective of this work was to determine the fructan and fructooligosaccharide (FOS) content of different onion tissues in order to evaluate the potential use of onion by‐products from the food industry as a source of FOS and fructans. Assays with two methods were carried out to optimise the extraction procedure. The main FOS, namely kestose (GF₂), nystose (GF₃) and fructofuranosylnystose (GF₄), were measured directly using standard sugars. The method for total fructans was based on enzymatic treatment (Novozym 230) of ethanolic/aqueous extract followed by determination of released fructose and glucose by HPLC. Data showed a clear predominance of GF₂ in every onion tissue and no occurrence of highly polymerised fructans. The tissues richest in fructans were the fleshy layers, so that the outer two fleshy layers turn out to be the best onion by‐product as a possible fructan source. © 2000 Society of Chemical Industry     

木瓜乳酸发酵饮料的工艺研究

对以木瓜为原料提取的木瓜浆进行乳酸发酵,采用正交试验法优选出最佳发酵条件。结果表明,木瓜浆浓度50％～60％,保加利亚乳杆菌嗜热链球菌最适比例为11,接种量4％,发酵温度42℃,前发酵时间6～8h,研制的木瓜乳酸发酵饮料组织均匀,口感细腻,甜酸适度。     

丙酮酸改性壳聚糖的制备及应用

利用壳聚糖C2位上活泼氨基与丙酮酸进行席夫碱反应,制取丙酮酸改性壳聚糖(简称为PCTS)。实验结果表明其最佳的合成条件为:1.8g溶胀的壳聚糖与1.48g丙酮酸在pH=4～5反应4h后,加入1.7g NaBH4反应1.5h,合成的1.6g PCTS,取代度可达88.14%。结果显示0.1g的PCTS吸附0.1g/L的Cu(Ⅱ)和Zn(Ⅱ),其吸附率分别可达100%和99.29%;PCTS对NO2也有一定的清除作用,11mg/ml的取代度为85.79% PCTS对NO2的清除率可达50.57%。     

反相高效液相色谱法(RP-HPLC)测定麦汁中的草酸

利用反相高效液相色谱法(RP-HPLC)测定麦汁中的草酸含量。对各种色谱条件进行了研究,最终确定色谱柱Hypersil ODS 4.0×125mm,流动相为0.5%KH2PO4-0.5mmol/L TBA(tetrabutylammonium salt,四丁基铵盐)水溶液,pH2.0,紫外检测波长220nm。试验证明该方法能有效地分离麦汁中的草酸和酒石酸,准确灵敏、回收率高、重复性好,并且操作简便,可应用于啤酒生产中草酸含量的检测。     

高效液相色谱法同时测定酵素原液中的乳酸和醋酸

建立了一种利用高效液相色谱法同时测定酵素原液中乳酸和醋酸的方法。通过对检测波长、流动相及其浓度和pH的筛选,建立利用高效液相色谱法同时测定酵素原液中乳酸与醋酸含量方法。结果表明,最优色谱条件为:色谱柱SinoChrom ODS-BP(4.6 mm×150 mm,5 μm),流动相为0.01 mol/L、pH2.88的KH₂PO₄溶液,流速0.8 mL/min,波长215 nm,进样量20 μL,柱温25 ℃。该法可同时测定酵素中乳酸和醋酸,检测速度快,乳酸与醋酸的线性检测范围宽分别为0~2100、0~1800 μg/mL。精密度和重复性好(乳酸和醋酸平行测定的RSD分别为0.99%、1.21%)并得到了良好的回收率(92.31%~102.20%)。     

毛细管气相色谱法测定果汁饮料中对羟基苯甲酸乙酯、对羟基苯甲酸丙酯的含量

建立了果汁饮料中对羟基苯甲酸乙酯、对羟基苯甲酸丙酯含量的毛细管气相色谱测定方法。该法采用WBI进样口、毛细管色谱柱J＆WDBl701（中等极性30mxO．53minx1μm、FID检测器进行检测。进样口温度230℃,载气流速10ml／mim．柱室温度1800℃恒温。检测器温度250℃,样品用盐酸溶液酸化,乙酸乙酯提取后直接进样测定。方法简单、快速、重现性好,平均回收率大于90％,RSD小于3．0％,线性范围为10-200μg／ml。     

An efficient method for production of kynurenic acid by Yarrowia lipolytica

Kynurenic acid (KYNA) is a compound derived from the tryptophan catabolic pathway. Antioxidant and neuroprotective properties have been confirmed for KYNA, which makes it an interesting and important metabolite of biomedical significance. In the present study, the yeast Yarrowia lipolytica was tested for KYNA biosynthesis. The results showed that Y. lipolytica strain S12 is able to produce KYNA in high concentrations (up to 21.38 μg/ml in culture broth and 494.16 μg/g cell dry weight in biomass) in optimized conditions in a medium supplemented with tryptophan. Different conditions of culture growth, including the source of carbon, its concentration and pH value of the medium, as well as the influence of an inhibitor or precursor of KYNA synthesis, were analysed. The obtained data confirmed the presence of KYNA metabolic pathway in the investigated yeast. To our best knowledge, this is the first study that reports KYNA production in the yeast Y. lipolytica in submerged fermentation.