茶儿茶素氧化机理

在制茶发酵过程中,儿茶素可发生苯骈环化反应而形成茶黄素,茶黄素还可转化成茶萘酚醒、脱氢茶黄素和高聚合物;同时,儿茶素可发生二聚合反应产生原花青素类以及双黄烷醇类等物质;儿茶素还可能与茶没食子素、杨梅甙、阿福豆素、维生素C、茶氨酸发生聚合反应,形成加合物。体外自由基清除实验表明,儿茶素具有优良的抗氧化特性。儿茶素在清除自由基时,自身氧化产生双黄烷醇,也可发生A环的断裂而产生羧酸类物质。     

火腿微生物研究进展

数千年来,微生物参与的食品发酵为人类保存食物和风味多元化提供了重要的方法。这些可再生且易于操作的发酵食品为研究微生物群落提供了理想的材料。干腌火腿就是传统发酵食品之一,在微生物作用下其加工过程发生了蛋白质和脂肪的水解和氧化反应,产生的一些化合物形成了火腿的独特风味。文中描述了不同地域火腿微生物类群及其对火腿品质形成的作用,为火腿微生物今后的研究提出了参考。     

肠道菌群紊乱所致炎症反应与抑郁症

抑郁症是一种与炎症反应、神经免疫关系密切的神经精神疾病。微生物,尤其是肠道菌群,则与人类免疫调节机制形成、感染和炎症反应息息相关。研究已证实,肠道菌群在炎症性肠病、哮喘等自身免疫性疾病的发生发展过程中起了相当大的作用。这些探讨非感染性疾病与微生物的关系的研究和理论形成了卫生学假说,亦即"老朋友"假说。目前,很多研究正在运用卫生学假说的观念,探索肠道菌群与抑郁症发生、发展、预防和治疗之间的联系,并取得了一些进展。本文重点就肠道菌群失调是否能够促进抑郁症发生及其可能机制做一综述。     

脯氨酸内肽酶研究进展

脯氨酸内肽酶是一类能够特异性水解多肽链中脯氨酸残基羧基端的内切酶,是丝氨酸蛋白酶家族成员之一,其能有效降解小于30个含有脯氨酸残基的多肽链,在对PEP的研究中发现它能特异性地水解许多含脯氨酸的多肽类神经递质和激素,如促甲状腺激素释放激素、P物质(Substance P)等,因此研究认为PEP可能参与一些神经类疾病的发生,如老年性记忆障碍等。本研究经过阅读相关期刊文献,对脯氨酸内肽酶的分布情况、基本理化和酶学性质、分子结构、作用机理以及在食品、医药领域的最新研究和应用进行了综合性评述,以期能对脯氨酸内肽酶相关性质、机理的后续研究以及在食品、医药领域更广泛的应用提供一定的参考。     

P物质拮抗剂及其在P物质作用机理研究中的应用

P物质广泛分布于中枢、外周神经系统和某些组织,与痛觉、内脏传入和传出、炎症反应以及中枢对运动的调节均有密切关系。本文主要介绍P物质拮抗剂的构效关系、与受体结合的特性及其在中枢、外周神经系统 P 物质作用机理研究中的应用。P 物质拮抗剂的研究不仅可以为基础研究提供工具药,推进 P 物质作用机理的研究,而且可能发展成为新型的镇痛药和抗炎药。     

巯基物质在消炎痛诱发大鼠胃粘膜损伤中的作用

本工作研究了巯基物质在消炎痛引起大鼠胃粘膜损伤中的可能作用。在胃粘膜损伤发生过程中、胃粘膜内非蛋白及蛋白结合的巯基物质含量均无明显降低。虽然半胱胺灌胃(132或264μmol)或皮下注射(132μmol)后均明显抑制消炎痛溃疡的发生,其抑制率分别为82％,92％和75％,但同样具有巯基的半胱氨酸却无保护作用。半胱胺(132μmol)皮下注射可使消炎痛大鼠胃酸分泌抑制46％,而灌胃则无此作用。两种途径给予的半胱胺均不影响胃壁结合粘液的分泌。这些结果表明,胃粘膜内巯基物质似不参与消炎痛的致溃疡过程。半胱胺在此种模型上虽有强烈的细胞保护作用,但似乎不是由于其分子上所带的巯基所致。因此,巯基物质在消炎痛引起的胃粘膜损伤模型上没有细胞保护作用。     

母源物质对重编程作用研究进展

卵母细胞发生过程中会积累大量的物质,即所谓的母源物质(maternal materials),自然状态下,这些母源物质对受精以及之后的发育具有重要的生物学功能。雌雄配子融合后,精子核与卵母细胞中单倍体染色体组均会发生剧烈的表观遗传修饰变化,这个过程也同样发生在体细胞核移植到卵母细胞质之后,这种变化被称之为重编程。重编程奠定了新个体发生发育全部程序的基础,因此是一个备受重视的生物学过程。重编程包括DNA去甲基化、染色质重塑和组蛋白修饰等。受精后,卵母细胞与精子的基因组均会在一定时间和空间范围内经历相应的重编程过程,清除各自基因组在配子形成中保留的表观遗传学修饰,调控基因表达并形成正常发育的全能性胚胎。受精后,卵母细胞成熟中积累的多种母源物质聚集在雄原核周围,调控其基因组的重编程。体细胞核移植胚胎中供体细胞核注到去核卵母细胞后也将在卵母细胞中蛋白质、mRNA、酶类等母源物质的作用下进行重编程。现总结了母源物质对雄原核及供体细胞核重编程作用的研究进展,并探讨了母源物质作用的可能机制。     

锌对盐藻生长与物质积累的调控作用

实验研究了不同浓度的锌对盐藻细胞生长与物质积累的调控作用。结果表明,培养液中供给锌过多或过少都不利于盐藻细胞的生长与物质积累。以培养基中6 mg/L的锌浓度对盐藻细胞生长、蛋白质合成与β-胡萝卜素积累的促进作用最大。这一锌浓度可用于盐藻的生产性培养。当培养液中锌浓度较高(8 mg/L)或较低(2 mg/L)时,单个盐藻细胞中的蛋白质与β-胡萝卜素含量较高。但此时,因培养液中细胞密度较低,盐藻细胞积累的物质总量仍然较少。在锌浓度较高或较低的逆境条件下,盐藻可能通过适应性反应形成了逆境蛋白质与胡萝卜素等。     

血管内微血栓与创伤后脑缺血

脑缺血是继发性颅脑损伤的重要原因之一。但是创伤后脑缺血的发生机制仍不明确。近期一些临床及实验研究认为创伤后血管内微血栓的形成是脑外伤后普遍的反应,在创伤后脑缺血发生中起重要作用。针对微血栓产生的可能机制进行的预防和治疗,可能改善创伤后缺血患者的预后。本文综合近年来有关脑血管内微血栓的研究,时颅脑损伤后脑血管微血栓的形成特点和机制及治疗方面作一综述。     

华东安蕨卵发生的超微结构观察

核心薄囊蕨是蕨类植物中的进化类群,但对受精作用具有显著影响的卵发生研究仍较少,该文利用超微技术对其中蹄盖蕨科的华东安蕨卵发生过程进行了研究,以进一步完善薄囊蕨植物卵发生的科学资料,为理解蕨类植物的有性生殖及演化机制奠定基础。超微结构观察显示:华东安蕨的幼卵和沟细胞在颈卵器中紧密联接;随后,在卵细胞上方出现了分离腔和临时细胞壁,但在卵细胞中间孔区处卵细胞和腹沟细胞始终联接在一起;分离腔中的无定形物质沉积在卵细胞的质膜外形成了1层加厚的卵膜,而在孔区处没有形成卵膜,该位置最后形成了受精孔。在进一步的卵发生过程中,卵细胞核变得高度不规则,形成了大量的核外突和核褶皱。     

Formation of flavour compounds in the Maillard reaction

This paper discusses the importance of the Maillard reaction for food quality and focuses on flavour compound formation. The most important classes of Maillard flavour compounds are indicated and it is shown where they are formed in the Maillard reaction. Some emphasis is given on the kinetics of formation of flavour compounds. It is concluded that the essential elements for predicting the formation of flavour compounds in the Maillard reaction are now established but much more work needs to be done on specific effects such as the amino acid type, the pH, water content and interactions in the food matrix. It is also concluded that most work is done on free amino acids but hardly anything on peptides and proteins, which could generate peptide- or protein-specific flavour compounds.     

Effect of food reductones on the generation of the pyrazine cation radical and on the formation of the mutagens in the reaction of glucose, glycine and creatinine

One of the possible pathways of the formation of mutagens in heated foods is through the pyrazine cation radical generated in the early stage of the Maillard reaction. The aim of the present study was to elucidate how food reductones contribute to the pyrazine cation radical generation in the reaction of glucose (Glc) and glycine (Gly), and to the formation of the mutagens in the reaction of Glc, Gly and creatinine. Electron spin resonance (ESR) studies showed that fragrant reductones, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF), generated in the Maillard reactions, enhanced the generation of the pyrazine cation radical in the reaction of Glc and Gly, and the reaction of DMHF or HEMF with Gly generated a larger amount of the pyrazine cation radical than the reaction of Glc and Gly, indicating that the furanones were intermediates of the pyrazine cation radical. By contrast, food antioxidants, ascorbic acid and erythorbic acid, effectively scavenged the pyrazine cation radical generated in the reaction of Glc and Gly. DMHF and HEMF were not effective to modulate the mutagen formation in the reaction of Glc, Gly and creatinine, and the mutagenicity produced in the reaction of DMHF or HEMF, Gly and creatinine was lower than that produced in the reaction of Glc, Gly and creatinine. On the other hand, ascorbic acid and erythorbic acid were effective to decrease the mutagen formation in the reaction of Glc, Gly and creatinine.     

Pathways of the Maillard reaction under physiological conditions

Initially investigated as a color formation process in thermally treated foods, nowadays, the relevance of the Maillard reaction in vivo is generally accepted. Many chronic and age-related diseases such as diabetes, uremia, atherosclerosis, cataractogenesis and Alzheimer’s disease are associated with Maillard derived advanced glycation endproducts (AGEs) and α-dicarbonyl compounds as their most important precursors in terms of reactivity and abundance. However, the situation in vivo is very challenging, because Maillard chemistry is paralleled by enzymatic reactions which can lead to both, increases and decreases in certain AGEs. In addition, mechanistic findings established under the harsh conditions of food processing might not be valid under physiological conditions. The present review critically discusses the relevant α-dicarbonyl compounds as central intermediates of AGE formation in vivo with a special focus on fragmentation pathways leading to formation of amide-AGEs.     

Effect of Rhamnolipids on Growth of Pseudomonas aeruginosa Mutant Deficient in n-Paraffin-utilizing Ability

Egg white solids freeze-dried with or without the addition of glucose were stored at 50°C under 65 % relative humidity to study the effect of the Maillard reaction on the solubility and heat stability and the formation of aggregates. A stimulative effect on the former properties was observed on the sample with glucose in the initial stage of the Maillard reaction. By comparing the SDS-polyacrylamide gel electrophoretic patterns, solubilities in SDS and SDS/2-mercaptoethanol and the s_20,w values, it was found that glucose, in addition to the effect due to the changes of charged groups in glucose-protein complex occurring in the course of the Maillard reaction, might have a protective effect against aggregate formation through a stable cross-linking, which was not dependent on the SS bond, and through a stable non-covalent bond.     

Participation of the pyrazine cation radical in the formation of mutagens in the reaction of glucose/glycine/creatinine.

Two classes of the free radical Maillard intermediates, the pyrazine cation radical and the carbon-centered radicals, are detected in the reaction of Glc (glucose)/Gly (glycine) by electron spin resonance and spin trapping technique. Profile of the generation of the pyrazine cation radical in the reaction with different ratios of the reactants was found to be similar to that of the formation of mutagens in the subsequent reaction with creatinine. By contrast, profile of the generation of the carbon-centered radicals was not consistent with that of the mutagen formation. Thiol antioxidants and unsaturated fatty acids (or their esters) effectively scavenged the pyrazine cation radical generated in the reaction of Glc/Gly, and inhibited the formation of the mutagens in the reaction of Glc/Gly and creatinine. Ethanol, a sulfide and a saturated fatty acid were not effective to scavenge the pyrazine cation radical and did not inhibit the mutagen formation. The pyrazine cation radical rather than the carbon-centered radicals may play an important role in the mutagen formation. Thiol antioxidants and unsaturated fatty acids can be evaluated as inhibitors of the pyrazine cation radical-derived formation of the mutagens.     

Inhibiting the color formation by gradient temperature‐elevating Maillard reaction of soybean peptide‐xylose system based on interaction of l‐cysteine and Amadori compounds

Light color and savory flavor enhancer are attractive for consumers and food producers. The effect of addition time of l ‐cysteine on inhibiting color formation was investigated in soybean peptide‐xylose system, and the possible pathway was explored. Once dicarbonyl compounds were formed during the Maillard reaction, the addition of l ‐cysteine had no color‐inhibiting effect; if l ‐cysteine was added immediately after the Amadori compound was formed, the extraordinary color‐inhibiting effect was observed. Therefore, an improved way to inhibit color formation was proposed on the basis of the interaction of l ‐cysteine and Amadori compounds by controlling the addition time of l ‐cysteine through gradient temperature‐elevating Maillard reaction. The system was heated at 80 °C for 60 min to form Amadori compounds, followed by the addition of L‐cysteine, and the temperature was raised to 120 °C and held for 110 min. Compared with traditional products, the lightest color product was found desirable by GC/MS analysis and sensory evaluation. The novel method proposed can be a guide for the industrial preparation of light‐colored products. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Health effects of dietary Maillard reaction products: the results of ICARE and other studies

In food science the Maillard reaction is well known to cause degradation of amino acids and an overall decrease in the nutritional value of foods that have been subjected to heat in processing. There has been evidence more recently of the endogenous formation of some Maillard reaction products (MRPs) in biological systems and their association with pathophysiological conditions including diabetes, renal disease and cardiovascular disease. Several studies have suggested that dietary MRPs increase the in vivo pool of MRPs after intestinal absorption and contribute to the development of diabetes and related complications. This review focuses on the animal and human studies which have assessed the eventual implications of dietary MRPs on human health, highlighting the different diets tested, the experimental designs and the biomarkers selected to estimate the health effects. The results of these studies are compared to those of the recently published ICARE study. In this latter study an accurate determination of the MRP content of the diets was achieved, allowing the calculation of the contribution of individual food groups to daily MRP intakes in a regular western diet.     

The metabolic, nutritional and toxicological consequences of ingested dietary Maillard reaction products: a literature review

The field of Maillard reaction in food has recently re-emerged. This reaction which takes place between carbohydrates and proteins at a high cooking temperatures and causes the formation of flavor and yellow to brown colors was already well documented. Little is known, however, about the formation of other Maillard reaction products (MRPs) which may be toxic: the so-called glycotoxins. It is well recognized that only 10% of these have been identified so far, and improved analytical methods are needed for the discovery of more of the neo-formed contaminants. Only a few studies as yet have focused on the digestion, metabolism and excretion of fructoselysine, carboxymethyllysine, pentosidine, acrylamide, the MRPs which have already been identified. MRPs have been shown to be present at significant amounts in a variety of industrially and domestically heat-treated foodstuffs but their absorption appears to be limited and they are readily excreted. Clinical studies indicate, none the less, that the typical Western diet, which contains a high MRPs content, may have an impact on human health. The main effects are observed on the glucose and lipid metabolisms, and on inflammatory mediators. However, the physiopathological role of the ingested MRPs has yet to be investigated in detail, so no conclusive recommendations can be given at present regarding their possible toxic effects.     

Methylglyoxal-derived β-carbolines formed from tryptophan and its derivates in the Maillard reaction

Summary. Reaction of tryptophan, tryptophan methyl ester and tryptamine with methylglyoxal (a physiological α-oxoaldehyde), which resulted in β-carboline formation, showed that this type of nonenzymatic (Maillard) reaction could spontaneously occur in living organisms or during commercial or domestic food processing and storage.     

Physiological relevance of dietary melanoidins

Melanoidins are the final products of the Maillard reaction. The main dietary sources of melanoidins are coffee, bread crust, bakery products, black beer and cocoa. Although the chemical structures of melanoidins are widely unknown, data from gravimetric techniques allow to roughly estimate a daily intake in the order of 10 g with a Western diet. Melanoidins contribute to the sensorial properties, modulating texture and flavour of foods. Growing evidence also suggests that melanoidins have health beneficial properties, such as chemopreventive, antioxidant and antimicrobial activities, and the ability to chelate different minerals. In the gastrointestinal tract, melanoidins behave not only as antioxidants, but also as dietary fibre by promoting the growth of bifidobacteria. This array of biological activities suggests the need for analytical techniques to identify the melanoidin structures and to control their formation during thermal food processing.