鲜切果蔬酶促褐变关键酶研究进展

机械伤使得鲜切果蔬在生理生化方面出现各种变化,导致果蔬贮藏期间品质下降,其中酶促褐变是导致鲜切果蔬贮藏品质下降的重要原因之一。本文主要介绍了鲜切果蔬酶促褐变过程中4个关键酶,即多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)、脂肪氧合酶(LOX)和过氧化物酶(POD)的特性、作用机理以及影响酶活性的因素,以期为进一步研究鲜切果蔬酶促褐变的机理及酶促褐变的控制方法提供理论基础。     

胡萝卜脆片护色技术研究

果蔬在贮藏加工过程中极易产生褐变,直接影响果蔬品质、食用价值及商业价值。因此控制褐变对保持果蔬品质是十分必要的。以胡萝卜为研究对象,介绍了褐变的原理及相应的抑制褐变方法,期望对研究胡萝卜的护色及脆片加工提供参考。     

果蔬酶促褐变与抑制

果蔬褐变是指水果和蔬菜加工及其制品在贮藏过程中,产生果蔬组织颜色变得晦暗或变成褐色的现象。褐变不仅影响果蔬食品原有的色泽,而且影响其风味和营养价值。随着人们生活水平的不断改善,对食品的感官标准提出了愈来愈高的要求,大多数情况下,褐变是不希望出现的变化,由此,褐变的产生与抑制受到食品加工行业的重视。 果蔬褐变的产生,有因酶的作用而变褐的     

褐变抑制剂对果蔬多酚氧化酶的影响

果蔬贮藏过程中,褐变问题严重影响其经济价值及营养价值,由多酚氧化酶引起的酶促褐变备受关注,寻找合适的抑制方法是国内外研究的热点。一些化学抑制剂对于酶促褐变具有良好的抑制效果,本文综述了果蔬褐变的机理,抗坏血酸、半胱氨酸、柠檬酸抑制剂的作用原理及具体应用,旨在为解决由酶促褐变引起的果蔬生产加工问题提供参考,促进果蔬品质的提升。     

果蔬褐变及其影响因素研究进展

果蔬贮藏、加工过程中的褐变包括酶促褐变和非酶褐变(Maillard反应、焦糖化反应、抗坏血酸氧化变色和多酚类氧化缩合)。发生酶促褐变必须具备酚类物质、酚酶和氧3个条件,影响因素有pH、温度和O2等。非酶褐变的影响因素因褐变类型的不同而存在差异。     

果蔬制品色泽的褐变及其控制

天然果蔬在加工中常失去悦目的色泽，产生酶褐变和非酶褐变，不仅影响外观，更为重要的是其风味和营养价值也受到很大损失。本文较全面地分析了果蔬产生酶褐变和非酶褐变的机理，针对性地提出了控制和预防酶褐变和非酶褐变的各种行之有效的方法。     

影响百合色泽变化因素的研究

百合在采后贮藏过程中会发生明显的褐变和紫红色变。根据影响果蔬色泽变化的主要因素:酶褐变、非酶褐变和色素变化,研究了百合采后贮藏过程中褐变度、还原糖、蛋白质、酸度以及多酚氧化酶(PPO)、过氧化物酶(POD)活性等参数的变化规律及与百合色变的影响关系。研究结果表明:PPO和POD参与了百合酶促褐变过程并起着重要的作用;还原糖和蛋白质发生羰氨反应可能是引起百合的非酶褐变的原因;百合的紫红色变可能是由于无色花色素氧化转变成呈色花色素引起的。     

果蔬酶促褐变机理及酶促褐变抑制研究进展

果蔬在贮藏和加工过程中,会发生酶促褐变现象,主要表现为果蔬颜色的变化,直接导致了营养的损失,对口感、质地也有所影响。果蔬的酶促褐变机理的研究对于褐变抑制具有重要的意义。     

龙眼干贮藏过程的褐变研究

本文研究了龙眼干在不同的包装形式（抽真空,避光）和不同贮藏温度（4 ℃、25 ℃和37 ℃）下贮藏30 d内龙眼果肉的褐变情况,通过测定贮藏期间的色泽变化,研究了龙眼干的褐变动力学,探讨了不同影响因素对龙眼干贮藏效果的影响,利用通径分析的方法分析了龙眼干贮藏过程中褐变的主要原因。结果表明,对龙眼干色泽变化影响最大的因素为贮藏温度,其次是空气和光照：贮藏温度越高,龙眼干的褐变越快,空气和光照的存在均会不同程度地加速龙眼干褐变;本文推导了龙眼干储藏过程中的颜色变化符合零级动力学方程,定量地描述龙眼干在储藏中的褐变情况;通过分析龙眼干贮藏过程中Vc、总酚、5-羟甲基糠醛（5-HMF）含量的变化表明龙眼干在贮藏过程中色泽变化的主要原因是抗坏血酸降解和美拉德反应。     

淮山褐变机理及其控制技术研究进展

淮山是一种营养价值极高的药食同源食品。褐变是淮山加工贮藏过程中影响其品质的主要问题之一,有效控制淮山褐变,保持其色泽和营养特性,提高其货架贮藏期,对保障淮山品质和提高消费者接受性具有重要意义。在已有研究的基础上,本文阐述了淮山酶促褐变与非酶褐变的相关机理,围绕酚类底物、酶及氧气等酶促褐变三要素阐述了淮山酶促褐变机理,并对淮山加工及贮藏中的美拉德反应和焦糖化非酶褐变机理进行了介绍;综述了不同褐变控制技术对淮山褐变的控制效果,分析现有问题,并对未来前景进行了展望,以期为淮山褐变控制技术的研究和应用发展提供参考。     

CHEMICAL AND ANTIOXIDANT PROPERTIES OF CULTIVATED AND WILD FRAGARIA AND RUBUS BERRIES

ABSTRACT

Content of individual sugars, organic acids, total phenolics (TPH), some important phenolic compounds (kaempferol, myricetin, quercetin, and ellagic acid) and total antioxidant capacity (TAC) in the fruits of strawberry, raspberry and blackberry were studied. A comparison was made between cultivars and wild relatives of each species (Fragaria vesca L., Rubus idaeus L. and Rubus fruticosus L.). The main sugars found were fructose and glucose both in the fruits of wild species and the studied cultivars. Citric acid was determined to be the major organic acid in most of tested berries with the exception of blackberry cultivars, where malic acid was dominant. The content of individual phenolic compounds varied among the wild species, as well as among the studied cultivars. Ellagic acid content was higher in F. vesca, R. idaeus and R. fruticosus (122.5 µg/g FW, 12.71 µg/g FW and 61.7 µg/g FW, respectively) than that obtained in analyzed cultivars. Overall, TPH expressed higher values in the wild strawberry and blackberry species in comparison to the studied cultivars, and consequently, the highest levels of TAC were recorded in F. vesca (5.78 mg asc/g FW), followed by R. fruticosus (4.95 mg asc/g FW).

PRACTICAL APPLICATIONS

In recent years, both wild and cultivated berries have become very attractive for consumers because of potentially beneficial phytochemicals contained in these fruits. Fruit nutritional quality can be described by standard quality parameters (sugars and organic acids), and the analysis of antioxidant capacity influenced by specific related compounds. The importance of flavonoids and other phenolics have been suggested to play a preventive role in the development of cancer and heart disease. A significant positive correlation observed in this study between total phenolics and total antioxidant capacity indicate the need for the use of wild species in the breeding programs of small fruits, especially strawberry and blackberry, in order to increase their nutritive value and the health benefits.     

新合纤及其制造加工技术

说明了日本新合纤(新聚酯)的发展阶段,介绍了国外(日本西欧和美国)新合纤的市场情况,指出了日本在新合纤领域目前处于世界最先进水平。概括了新合纤制造加工技术及1990～1992年间日本各合成纤维厂商推出的新合纤产品。最后指出了新合纤存在的某些缺点。     

BARLEY AND MALT TANNINOGENS AND BEER QUALITY

Anthocyanogen and catechin contents (tanninogen values) were determined for ten two-row and thirteen six-row barleys and for their corresponding malts. Four barley-malts were then selected for brewing, one with high, one with low, and two with intermediate tanninogen contents. The brews were made using bottom-fermenting (lager) as well as top-fermenting (ale) yeasts, both at 50–55° F. and at 68° F. The quality of the beers, as expressed by standard analyses and flavour evaluation, is discussed in the light of the tanninogen contents of the barleys and the different brewing parameters (yeast type and fermentation temperature).     

姜与人体营养健康

对姜的营养、保健功能及其在日常生活中的应用进行了介绍，更利于推动我国调味品业的进一步研究与开发。     

Tencel机织物的染整加工及所用染化料

Ｔｅｎｃｅｌ纤维易于原纤化和很高的横向膨润性对染整加工设备选型、工序安排、染化料选用提出了很高的要求，关键的助剂是润滑剂、纤维素酶、柔软剂、树脂整理剂、防原纤化助剂，于是详细讨论了Ｔｅｎｃｅｌ机织物的前处理、初级原纤化、酶处理、染色、二次原纤化和柔性、树脂整理及染化料的应用。     

INSTRUMENTAL AND SENSORY TEXTURE ASSESSMENT AND FRACTURE MECHANISMS OF CHEDDAR AND CHESHIRE CHEESES

Textural attributes of Cheddar and Cheshire cheeses, falling within narrow compositional ranges, were assessed by sensory panels, and from force-compression curves generated by compression between two plates, and, for Cheddar cheese only, by penetrometry. Individual sensory measurements did not relate well to any instrumental one, and were better at discriminating between cheeses. Samples of each cheese variety were fractured in different ways and the fracture surfaces were examined in a scanning electron microscope. Fracture surfaces were formed by cutting directly through the matrix, tearing of the matrix along planes high in fat or cracking at grain boundaries. It is suggested that consideration of fracture mechanism may aid the selection and development of useful instrumental methods for texture assessment of cheese.     

AREA- AND PERIMETER-DEPENDENT PROPERTIES AND FAILURE OF MATURE-GREEN AND RED-RIPE TOMATO PERICARP TISSUE

The influence of tomato fruit ripeness on area- and perimeter-dependent properties and dominant failure mechanisms of pericarp tissue were investigated. Tissue discs from mature-green and red-ripe fruit were punctured with a flat-ended cylindrical probe and compressed with a flat plate at a constant rate of deformation. Approximately linear force-deformation curves were obtained to tissue failure by both puncture and flat plate compression, interrupted by a region of pseudoplastic deformation at a relatively low initial bioyield force. Based on estimated area- and perimeter-dependent coefficients and firmness (force/deformation) values, initial bioyielding of tissue appeared to be associated with an abrupt increase in cell-to-cell compaction. Puncture of mature-green tissue led to premature failure induced by shearing or rupture of tissue at the probe perimeter. The contribution to puncture of perimeter-dependent or shear-associated forces and a putative "zone of influence" increased markedly with ripening, while the contribution of area-dependent or compression associated forces generally decreased. A concomitant decrease in failure force and firmness with ripening reflected a general loss of both tissue compression and shear strengths. These results suggested that the dominant mode of tissue failure changed with ripening, from cell relaxation and rupture to cell debonding. The data obtained in this study emphasize the need to exercise caution in the interpretation of force-deformation parameters derived from puncture tests alone.     

THIOLS AND DISULPHIDES IN QUIESCENT AND GERMINATING BARLEY GRAINS,BOTH DORMANT AND MATURE

Reduced and oxidised glutathione, cysteine, cystine and traces (too small to quantify) of γ-glutamyl-cysteine and cysteinylglycine were detected, in about the same amounts, in extracts of the embryos of dormant and mature barleys. During micromalting the levels of the thiols and disulphides altered in various ways, but altered in the same ways in dormant and mature samples of grain until germination began. An early decline in the glutathione content of embryos was mirrored by a rise in the amount in degermed grains. Histochemical tests and analyses of isolated tissues showed that in the quiescent grains thiols were concentrated in the embryo (particularly the scutellum) and in the aleurone layer and isolated embryos released thiols into an incubation medium. We conclude that the endogenous thiols and disulphides are not obviously involved in the regulation of dormancy.