Systematic studies on the chemical structure and umami enhancing activity of Maillard-modified guanosine 5'-monophosphates

Recent investigations on taste active principles in nucleotide rich yeast extracts led to the discovery of (R)- and (S)-N(2)-(1-carboxyethyl)-guanosine 5'-monophosphate as previously not reported umami enhancing molecules formed upon the Maillard reaction of guanosine 5'-monophosphate (5'-GMP) with dihydroxyacetone and glyceraldehyde, respectively. In the present study, systematic Maillard-type model reactions were performed with 5'-GMP and a homologous series of monosaccharides exhibiting a C(3)- to C(6)-carbon skeleton as well as with the reducing disaccharide maltose in the presence of an amino acid. By preparative RP-HPLC, various (R)- and (S)-N(2)-(1-carboxyalkyl)-guanosine 5'-monophosphates and (R)- and (S)-N(2)-(1-alkylamino)carbonylalkyl)guanosine 5'-monophosphates were isolated and identified by means of LC-MS, LC-TOF-MS, and 1D/2D-NMR spectroscopy. Sensory evaluation of these Maillard products revealed β-values for umami enhancement between 0.06 and 7.0 and identified a strong influence of the stereochemistry as well as the chain length of the N(2)-substituent on the umami enhancing activity. For all of the compounds evaluated, the (S)-configured isomers showed higher taste impact, whereas the (R)-isomers showed only marginal β-values, thus underlining the stereospecifity of the umami taste receptor binding site.     

Evaluation of the umami taste intensity of green tea by a taste sensor

A method for evaluating the umami taste intensity of green tea by a taste sensor system was established. Interference in the measurement from catechins was solved by removing the catechins from sample solutions with poly(vinylpolypyrrolidone). A 5.00 mM aqueous solution of glutamic acid monosodium salt was used as the standard solution. Sensor outputs were converted into EIT uma (estimated intensity of taste concerning umami) values. One unit on the EIT uma scale was defined as the amount of the sensor output corresponding to a difference in 1.2 times the concentration of the standard substance (glutamic acid monosodium salt). The umami taste intensity of green tea was classified into six grades on the EIT uma scale. Sensory tests proved that the EIT uma value had a high correlation to the human gustatory sense.     

适宜氮肥施用量显著提升夏季绿茶品质

  【目的】  我国30%的茶园氮肥施用过量。氮肥过量施用不仅造成能源浪费和茶园土壤质量恶化 (如酸化、板结等)，还使茶叶特别是绿茶增产提质边际效应逐渐下降。夏季绿茶品质 (尤其是香气) 往往低于春茶，但其产量却远大于春茶，因此，研究施氮对夏季绿茶的品质影响，为夏季绿茶提质增效提供理论依据。  【方法】  茶园氮肥长期定位试验位于浙江杭州，始于2005年。氮肥施用水平分别为0、119、285、474、569和712 kg/hm2。采集连续施用12年氮肥的茶树夏季新梢一芽二叶制成绿茶样。采用GB/T 23776—2018茶叶感官审评方法、茚三酮/福林酚-比色法、CN分析仪、氨基酸自动分析仪、顶空固相微萃取法结合气相色谱–质谱联用技术，分别对绿茶感官品质、氨基酸和茶多酚总量、氮含量、氨基酸组分以及香气组分进行检测分析。  【结果】  不同氮肥施用水平对绿茶香气影响较大。在施N 0～474 kg/hm2范围内，绿茶氨基酸总量随着施氮量增加而升高，在施N 474 kg/hm2时达到最高。施氮量提高到569和712 kg/hm2后，绿茶氨基酸总量降低，茶多酚总量升高，对应的酚氨比升高，而绿茶样品氮含量反而低于N 474 kg/hm2处理。在鉴定到的16种氨基酸组分中，大部分氨基酸含量在施氮量285和474 kg/hm2时达到最高，包括决定成品茶鲜爽味的茶氨酸、谷氨酸和天冬氨酸含量，而当施氮量超过474 kg/hm2时，这些氨基酸的含量开始下降。醇类、酮类、烯类、醛类、酯类以及其他香气化合物受氮素供应水平影响存在差异，主导绿茶呈香的醇类物质相对含量在施N 0～285 kg/hm2范围内，随着施氮量的升高而增加，其中以占醇类物质总量比重最高的β-芳樟醇和橙花叔醇变化最为明显。酮类香气化合物在不同氮素供应水平下变化趋势与醇类一致，但受氮素供应水平影响小于醇类。烯类香气物质对氮素供应水平的响应与醇类和酮类则完全相反，总量随着施氮量增加逐渐降低，而醛酯类等其他香气化合物在不同施氮水平下无规律性变化。  【结论】  茶园施氮量在285～474 kg/hm2时，有利于提高茶叶品质，决定成品茶滋味的茶氨酸、谷氨酸等氨基酸组分和主导绿茶呈香的β-芳樟醇和橙花叔醇含量最高。     

Differences in glutamic acid and 5'-ribonucleotide contents between flesh and pulp of tomatoes and the relationship with umami taste

A difference in taste characteristics between the outer flesh and the inner pulp of tomatoes has been observed; in particular the pulp, which contains the seeds, had more umami taste. Analysis of the free amino acids and 5'-ribonucleotides in the different parts of 13 varieties of tomatoes showed that in all cases the pulp contained higher levels of glutamic acid, 5'-adenosine monophosphate (AMP), 5'-guanosine monophosphate, 5'-uridine monophosphate, and 5'-cytidine monophosphate. The mean concentration of glutamic acid in the flesh was 1.26 g/kg and that in the pulp 4.56 g/kg but in some varieties the difference between pulp and flesh was more than 6-fold. For AMP, the mean concentration in the flesh was 80 mg/kg and that in the pulp was 295 mg/kg with one variety showing an 11-fold difference between pulp and flesh. These differences in concentration of these compounds, which are known to possess umami characteristics, provide an explanation for the perceived difference in umami taste between the flesh and pulp of tomatoes.     

Low molecular weight compounds responsible for savory taste of Indonesian soy sauce

Indonesian soy sauce is made using only soybeans as the nitrogenous source. Moromi obtained from fermentation of yellow soybeans using Aspergillus sojae as the starter was investigated. The fraction with molecular weights of less than 500 Da obtained by stepwise ultrafiltration was then fractionated by several chromatographic procedures, including gel filtration chromatography and RP-HPLC. Several chemical analyses, CE profiles, and taste profiles were performed to obtain the most intense umami fraction. The main components eliciting or enhancing the umami taste present in the fraction were purified and identified by protein sequencing, ESI-MS, and (1)H NMR at 400 MHz. Besides free l-glutamic acid and aspartic acid, free aromatic amino acids such as l-phenylalanine and l-tyrosine may also play an important role in impressing savory or umami taste of Indonesian soy sauce at their subthreshold concentrations and in the presence of salt and free acidic amino acids. This is reported as a new phenomenon of the so-called bitter amino acids.     

Analysis of taste-active compounds in an enzymatic hydrolysate of deamidated wheat gluten

Hydrolyzed plant proteins are widely used as ingredients in culinary products for their glutamate-like ("umami") taste. Three hydrolysates were prepared from wheat gluten using different enzymatic approaches. Comparison of their taste profiles revealed the enzymatic hydrolysate of an acid-deamidated wheat gluten (WGH-3) to be the least bitter of all and to elicit an intense glutamate-like taste. Its umami taste intensity was similar to that of an enzymatic hydrolysate in which glutaminase had been employed to convert free glutamine to glutamic acid and which had a 3-fold higher concentration of free glutamate. Reconstitution studies based on the results of the chemical analysis of WGH-3 and sensory comparison of the model solution and WGH-3 indicated that other components in addition to glutamate and organic acids contribute to its glutamate-like taste. WGH-3 was fractionated by gel permeation chromatography and reversed phase high-performance liquid chromatography, and two fractions with a pronounced glutamate-like taste were obtained. In one of them four pyroglutamyl peptides were tentatively identified: pGlu-Pro-Ser, pGlu-Pro, pGlu-Pro-Glu, and pGlu-Pro-Gln. Apparently, these peptides were formed by cyclization of the N-terminal glutamine residues during the preparation of the hydrolysates.     

Umami compounds are a determinant of the flavor of potato (Solanum tuberosum L.)

Vegetable flavor is an important factor in consumer choice but a trait that is difficult to assess quantitatively. The purpose of this study was to assess the levels of the major umami compounds in boiled potato tubers, in cultivars previously assessed for sensory quality. The free levels of the major umami amino acids, glutamate and aspartate, and the 5'-nucleotides, GMP and AMP, were measured in potato samples during the cooking process. Tubers were sampled at several time points during the growing season. The levels of both glutamate and 5'-nucleotides were significantly higher in mature tubers of two Solanum phureja cultivars compared with two Solanum tuberosum cultivars. The equivalent umami concentration was calculated for five cultivars, and there were strong positive correlations with flavor attributes and acceptability scores from a trained evaluation panel, suggesting that umami is an important component of potato flavor.     

不同茶树品种(系)的绿茶滋味分析及评价模型构建

为客观准确地评价不同茶树品种(系)绿茶的滋味品质,该研究系统分析了25个茶树品种(系)绿茶的主要滋味成分含量及其Dot值,利用主成分分析法对不同茶树品种(系)绿茶滋味品质进行综合评价并建立滋味品质评价模型。结果表明:儿茶素、咖啡碱是不同茶树品种(系)绿茶苦涩味强度差异的主要原因,其中表没食子儿茶素没食子酸酯(Epigallocatechingallate,EGCG)是所测样品中涩味的主要贡献物质,EGCG和咖啡碱为所测样品中苦味的主要贡献物质。氨基酸是不同茶树品种(系)绿茶鲜味、甜味差异主要因素,谷氨酸是所测样品中鲜味的主要贡献物质。主成分分析表明:前5个主成分的累计方差贡献率为79.018%,并以前5个主成分的线性回归方程和贡献率构建了滋味品质评价模型,模型评价结果与感官审评结果较为相似,存在极显著相关性(P0.01),相关系数为0.791;利用模型中各主成分的得分,能够较好的区分所测样品的苦、涩、鲜、爽等滋味特征。因此,该研究所建模型能够较好的评价所测样品的滋味品质及其主要滋味特征的差异,为各茶树品种(系)的推广应用提供理论依据,也为不同茶树品种(系)绿茶滋味品质的科学评价提供新的思路和方法。     

贮藏温度对三疣梭子蟹蟹肉风味的影响

为延缓三疣梭子蟹品质劣变,延长其货架期,本试验研究了冰温贮藏、冷藏、冰藏对蟹肉挥发性风味、腺苷三磷酸(ATP)关联物及游离氨基酸含量的影响,并对其呈味物滋味强度值(TAV)及味精当量(EUC)进行分析。结果表明,冰温组蟹肉挥发性风味在贮藏前6 d 无明显变化,而冷藏和冰藏组蟹肉挥发性风味分别在贮藏第2和第4 天开始出现明显变化。冰温组蟹肉肌苷酸(IMP)和腺苷酸(AMP)的滋味强度值、游离氨基酸总量、鲜味氨基酸、甜味氨基酸和甜苦味氨基酸占总游离氨基酸的百分比、EUC均高于同期冰藏、冷藏。组综上所述,冰温贮藏能有效保持蟹肉良好风味,缓解蟹肉风味劣变。本研究结果为冰温贮藏技术在梭子蟹保鲜中的应用提供了一定的理论依据。     

LC-MS study to reduce ion suppression and to identify N-lactoylguanosine 5'-monophosphate in bonito: a new umami molecule?

In this study a specific taste modulating flavor ingredient, N-lactoylguanosine 5'-monophosphate (N-lactoyl GMP), was determined in bonito (Japanese, Katsuobushi, dried fermented skipjack) and in powdered bonito using liquid chromatography-electrospray ionization (+) mass spectrometry-mass spectrometry (LC-ESI(+)-MS/MS) with a methanol/ammonium acetate or formate gradient. Furthermore, the influence of ion suppression due to sample matrix effect was investigated and was found to substantially influence the total MS response of N-lactoyl GMP; by adjusting the LC conditions the response could be approximately 5-fold-enhanced. The N-lactoyl GMP concentrations in different types of bonito products were between 0.2 and 2.4 microg/g.     

Molecular and sensory studies on the umami taste of Japanese green tea

Aimed at defining the key drivers for the quality-determining umami taste of a high-grade powdered green tea, called mat-cha, a bioactivity-guided fractionation using solvent extraction, solvent precipitation, preparative chromatographic separations, and human psychophysical experiments was applied on freshly prepared mat-cha. Liquid chromatography-tandem mass spectrometry and one-/two-dimensional nuclear magnetic resonance studies on isolated fractions led to the identification of l-theanine, succinic acid, 3,4,5-trihydroxybenzoic acid (gallic acid), and (1R,2R,3R,5S)-5-carboxy-2,3,5-trihydroxycyclohexyl-3,4,5-trihydroxybenzoate (theogallin) as umami-enhancing compounds in the green tea beverage, and it can be shown by sensory studies that these compounds are able to raise the umami intensity of sodium l-glutamate proportionally.     

Production of seafood flavor from red hake (Urophycis chuss) by enzymatic hydrolysis

Protein hydrolysates were prepared as a natural flavor stock from the red hake (Urophycis chuss) headed-gutted (H&G) mince and frame mince using commercial enzymes, Flavourzyme and Savorase, at the natural pH of fish (6.8) and the water/fish ratio of 2:5. The addition of 1.5% NaCl and 0.4% STPP improved the flavor quality of the hydrolysate by masking bitterness and off-flavor. A 6 h hydrolysis of H&G mince with Flavourzyme yielded a hydrolysate of the highest acceptability. Hydrolysis increased the concentration of most free amino acids except Arg and His. Leu, Lys, and Arg were predominant free amino acids in the hydrolysates, whereas Leu and Arg were major ones in the cooking juice. The concentration of Glu responsible for umami taste was increased by 6-9 times upon hydrolysis. Hydrolysates contained higher percentages of free amino acids giving both umami and sweet tastes than did cooking juice.     

滋味物质在不同交联度鱼糜凝胶中的释放动力学分析

为探讨滋味物质在不同交联度鱼糜凝胶中的释放规律并揭示其释放机制,该研究以氯化钠、蔗糖和谷氨酸钠分别为鱼糜凝胶咸味、甜味和鲜味的代表滋味物质,通过感官评价、释放动力学模型拟合和模拟咀嚼释放等方法,分析滋味物质在不同交联度鱼糜凝胶中的释放规律。结果表明,随着交联度的增加,人体对咸味的感知逐渐降低而对鲜味的感知逐渐增强,并当交联度大于42.2%时,咀嚼破碎显著提高了鱼糜凝胶咸味和鲜味的感知（P<0.01）。氯化钠和蔗糖的释放动力学曲线符合准一级动力学模型,而谷氨酸钠的释放则符合准二级动力学模型。随着交联度的增加,鱼糜凝胶在模拟咀嚼过程中氯化钠和蔗糖的释放量先降后升,分别在交联度为42.2%和51.5%时取得最小值（4.54和3.38 mg/g）;而谷氨酸钠的咀嚼释放量则逐渐增加。相关性分析结果表明,氯化钠和蔗糖在鱼糜凝胶中的释放主要与网络结构和化学作用力相关,谷氨酸钠的释放主要与凝胶质地、凝胶持水性和化学作用力相关。综上,滋味物质在鱼糜凝胶中的释放行为受滋味物质种类、凝胶质地以及凝胶与滋味物质的相互作用等多方面的影响,且凝胶在咀嚼过程中较高的破碎程度增强了滋味物质的释放与感知。     

施氮量对巨胚水稻产量、品质及γ-氨基丁酸含量的影响

  【目的】  巨胚水稻富含对人体具有多种调节功能的γ-氨基丁酸(GABA),明确施氮量对巨胚水稻产量和品质的影响,以期为巨胚水稻合理施用氮肥提供科学依据。  【方法】  于2020—2021年在四川农业大学崇州市现代化农业科研园区进行大田试验,以巨胚水稻J20和常规水稻越光为材料,设置0 (N₀)、90 (N₉₀)、135 (N₁₃₅)、180 (N₁₈₀)、225 (N₂₂₅) kg/hm2 5个施氮水平,测定了不同处理下巨胚水稻产量、加工品质、外观品质、淀粉RVA谱特征值、食味值、蛋白质含量、17种水解氨基酸含量及功能成分γ-氨基丁酸含量。  【结果】  两水稻品种的产量均以N₁₃₅处理最高,这与其具有较高的有效穗数和每穗颖花数有关。随着施氮量增加,稻米的糙米率、精米率、整精米率、GABA含量和胚重量呈先增后降的趋势;垩白粒率、垩白度呈先降后增的趋势,均以N₁₃₅处理最低;米质、功能成分GABA含量和胚重量在施氮量高于135 kg/hm2后均下降。随着施氮量的增加,稻米的峰值黏度显著下降,各施氮处理的平均峰值黏度较N₀处理分别下降了7.44% (J20)和9.74% (越光),崩解值、消减值和糊化温度对施氮量总体上不敏感;J20外观、口感和食味值随着施氮量增加而显著下降,各施氮处理的平均食味值较N₀处理下降了10.73%,越光水稻外观、口感和食味值表现为N₁₃₅>N₀>N₉₀>N₁₈₀>N₂₂₅,但N₁₃₅与N₀处理外观品质差异不显著。随着施氮量增加,两个品种的蛋白质含量均呈增加趋势,N₂₂₅处理达到最大,分别较N₀处理增加了10.29% (J20)和8.62% (越光);各水解氨基酸的含量也整体呈增加趋势,N₂₂₅处理下两个品种的氨基酸总量、必需氨基酸含量、非必需氨基酸含量分别较N₀处理增加了29.25%、23.49%、31.68% (J20)和19.34%、14.88%、21.33% (越光)。根据水稻产量、糙米率、整精米率、垩白粒率、GABA含量与施氮量建立的效应方程计算得出,两品种高产优质的适宜施氮范围为130～140 kg/hm2。与常规水稻越光相比,巨胚水稻J20的产量、整精米率、崩解值和食味值对氮肥更敏感,且相同施氮量下J20的蛋白质含量、水解氨基酸总量及GABA含量均高于越光。  【结论】  合理施用氮肥可有效提高巨胚水稻的产量,改善加工、外观及营养品质,但过量施氮导致稻米蒸煮食味品质变劣;在本试验条件下,实现巨胚水稻J20高产优质、功能特性俱佳的适宜施氮量为130~140 kg/hm2。     

Effect of Glutamate Accumulation During Sourdough Fermentation with Lactobacillus reuteri on the Taste of Bread and Sodium‐Reduced Bread

NaCl is an important contributor to the taste and texture of bread; therefore, it is challenging to reduce NaCl in bread without compromising quality. This study investigated sensory properties of bread with sourdough fermented with Lactobacillus reuteri accumulating glutamate or γ‐aminobutyrate (GABA). Sourdough was fermented with the GABA‐producing L. reuteri 100‐23 and LTH5448 as well as the glutamate‐accumulating L. reuteri 100‐23ΔgadB and TMW1.106. A consumer panel detected significant differences in the taste of bread with 6% addition of sourdough fermented with glutamate‐ or GABA‐producing L. reuteri. Remarkably, this difference was also detected when GABA‐producing L. reuteri 100‐23 was compared with its glutamate‐producing isogenic mutant L. reuteri 100‐23ΔgadB. The intensity of the salty taste of sourdough bread produced with 1% (flour basis) salt was equivalent to the intensity of the salty taste of reference bread produced with 1.5% salt. A trained panel found that sourdough breads (1 or 2% NaCl flour base) had a higher sour and umami taste intensity when compared with reference bread with the same salt content. Bread produced with sourdough fermented with L. reuteri 100‐23ΔgadB consistently had a higher umami taste intensity when compared with other sourdough breads. Neither sourdough addition nor NaCl level influenced bread volume or texture. In conclusion, the use of sourdough fermented with glutamate‐accumulating lactobacilli allowed reduction of NaCl without adverse effects on the taste or other quality attributes of bread.     

Influenza virus neuraminidase inhibitory activity of phlorotannins from the edible brown alga Ecklonia cava

Influenza A virus infections continue to pose a major threat to humans and several animal species. Neuraminidase (NA) is one of the most promising targets for the development of drugs against influenza viruses because of its critical role in the viral life cycle. During the course of a search for NA inhibitors from edible natural sources, we found that the ethyl acetate layer of ethanol extracts of Ecklonia cava showed extremely high NA-inhibitory activity (72.1% inhibition at 30 μg/mL). Bioactivity-guided fractionation of the ethyl acetate layer yielded five phlorotannins, identified as phloroglucinol (1), eckol (2), 7-phloroeckol (3), phlorofucofuroeckol (4), and dieckol (5). The inhibitory activities of these compounds (1-5) against NAs from group-1 (A/Bervig_Mission/1/18 [H1N1], A/PR/8/34 [H1N1]) and group-2 (A/Hong Kong/8/68 [H3N2], A/Chicken/Korea/MS96/96 [H9N2]) influenza A were evaluated to determine potencies and kinetic behavior. Analyses using various in vitro influenza A virus NA assays showed that all five phlorotannin derivatives were selective NA inhibitors. Of the phlorotannins, phlorofucofuroeckol (4) exhibited the most potent inhibitory activities toward group-1 NAs (IC?? values, 4.5 and 14.7 μM), whereas dieckol (5) potently inhibited group-2 NAs. Kinetic analyses indicated that compounds 1-5 were all noncompetitive. Notably, these noncompetitive inhibitors synergized with oseltamivir to enhance the NA-inhibitory effects of oseltamivir.     

确定经济合理施氮量的新方法:基于施氮量与稻米产量效应函数

  【目的】  探究实现水稻高产、优质和氮肥高效的密度与施氮量协同组合。  【方法】  于2018—2019年,在黑龙江省五常市龙凤山乡辉煌村进行田间试验。采用裂区试验方法,以‘五优稻4号’为供试品种。以密度为主区,设置15穴/m2 (D1)和24穴/m2 (D2);以施氮量为副区,设施氮(N）量为0、75、105、135 kg/hm2 4个水平,分别表示为N0、N75、N105、N135处理。在水稻成熟期,测定了植株地上部干物重、稻谷产量、精米产量、精米率、蛋白质含量、直链淀粉含量、食味值等指标;比较了稻谷产量与精米产量确定的施氮量差异。  【结果】  在D1、D2两个密度下,随着施氮量的增加,稻谷产量、地上部干物重、精米产量都呈先升高后降低的趋势,均在N105达到最大值。除D1密度下N105处理的稻谷产量与N135处理差异不显著外,其余均显著高于其他处理,而N135处理的稻谷产量与N75处理无显著差异,但2018年地上部干物重却显著高于N75处理。随着施氮量的提高,精米蛋白质含量呈现增加趋势,精米率和食味值却呈降低趋势。与N0相比,N135处理精米蛋白质含量平均提高了7.58%,精米率和食味值分别平均降低了8.81%和10.24%。N105处理的氮素回收率显著高于N75和N135处理,农学效率、氮肥生理利用率和偏生产力均显著高于N135处理。D2密度下精米蛋白质含量低于D1密度处理,而精米率和食味品质高于D1密度处理,D2密度下的稻谷产量、氮积累量和精米产量均高于D1密度处理,氮积累量和氮肥偏生产力比D1处理平均提高了40.35%和 40.31%,两个密度间氮肥回收率、农学效率和氮肥生理利用率无明显差异。农户直接出售优质米使经济效益提高了7428元/hm2,D2密度使经济效益额外增加了4229元/hm2。施氮量与稻谷产量、精米产量均呈二次曲线关系,依据施氮量与稻谷产量效应函数,确定经济最佳施氮量为96.4～123.7 kg/hm2;依据施氮量与精米产量效应函数,确定的适宜施氮量为76.2～105.9 kg/hm2。  【结论】  适度密植(24穴/m2)有利于稻谷产量、氮素吸收量的提高,而不影响食味值和精米率。在本试验水稻适宜密植条件下,基于施氮量和精米产量效应函数确定的适宜施氮量为76.2～105.9 kg/hm2,该施氮量的确定方法有利于协同实现稻米高产优质和氮肥减施增效。     

Acid- and base-catalyzed hydrolysis of chloroacetamide herbicides

Despite the prevalence of chloroacetamides as herbicides, little is known about the rates or products of acid- or base-catalyzed hydrolysis of these compounds. Mechanisms of acid-catalyzed reactions may parallel those catalyzed by (hydr)oxide minerals, while base-catalyzed processes have as important counterparts reactions with environmental nucleophiles (such as reduced sulfur species). The current study systematically investigates how the structure of nine chloroacetamides affects their reactivity in 2 N NaOH, 2 N HCl, or 6 N HCl at 25 or 85 degrees C. Base-catalyzed hydrolysis proceeds either through an intermolecular SN2 reaction to hydroxy-substituted derivatives or (in a few cases) through amide cleavage, while both amide and ether group cleavages are observed under acidic conditions. Our results reveal that subtle differences in chloroacetamide structure [notably the type of (alkoxy)alkyl substituent] can dramatically influence reactivity and reaction mechanism. Hydroxy-substituted, morpholinone, and secondary aniline derivatives were identified upon reaction for several years in deionized water at circumneutral pH.     

Detection of changes in taste of japonica and indica brown and milled rice (Oryza sativa L.) during storage using physicochemical analyses and a taste sensing system

Changes in the taste of japonica, hybrid, and indica brown and milled rice, stored for 10 months at low (5 degrees C, 65-70% relative humidity) and room temperatures were observed by physicochemical analyses and a novel method using a taste sensing system. During storage, some properties increased or decreased while others were fairly constant. The main taste components of cooked rice such as sweetness (sucrose) and umami tastes (glutamic acid and aspartic acid) were reduced during storage, whereas glucose and fructose increased. The increase of fat acidity and consequent decrease of the pH value of the cooking solution may contribute to the off-taste of cooked stored rice. A taste sensing system with 10 lipid membrane sensors was also used to classify new and old rice samples using principal component analysis. Fresh and room temperature stored japonica and indica rice could be clearly distinguished; however, it was not possible to differentiate the samples stored at low temperature.