鲜切慈菇酶促褐变底物的分析确定

鲜切慈菇在贮藏过程中极易发生酶促褐变。为进一步研究其褐变机理,分析测定了慈菇对不同酚类底物的亲和性,利用薄层层析、紫外吸收光谱及高效液相色谱法鉴定鲜切慈菇酶促褐变的主要底物。结果表明,慈菇中的酚类物质主要为愈创木酚和儿茶酚,慈菇中 POD 对不同底物的结合能力依次为愈创木酚＞焦性没食子酸＞绿原酸＞L-酪氨酸＞儿茶酚,引起酶促褐变的主要底物是愈创木酚。     

鸭梨多酚氧化酶的特性及抑制剂研究

以邻苯二酚为底物，采用分光光度法在420nm处测定鸭梨多酚氧化酶（PPO）的活性，研究了不同底物、温度、pH值和底物浓度对其活性的影响，并建立了酶促褐变反应动力学方程，探讨了柠檬酸、EDTA、亚硫酸氢钠和抗坏血酸四种抑制剂对鸭梨酶促褐变的抑制效果。结果表明，鸭梨多酚氧化酶的最适底物为邻苯二酚，最适温度为30℃，最适pH为6．6；酶促褐变反应动力学符合米氏方程所描述的单底物酶促反应动力学，以邻苯二酚为底物的动力学参数Km=0．333mol／L，Vmax=0．089U／min。相应的动力学方程为v=0．089[S]／（0．333＋[S]；四种物质对该酶均表现出不同的抑制作用，抑制效果为：抗坏血酸〉EDTA〉柠檬酸〉亚硫酸氢钠。     

鲜切甘薯酶促褐变机理的研究

鲜切甘薯中的酚类物质以游离酚(FP)为主,占总酚(TP)的90%左右。贮藏过程中FP和TP均呈先上升后下降的变化规律,且其比值(FP/TP)稍有增加。鲜切甘薯多酚氧化酶(PPO)活性在切分后有所增加至第3d达最大而后下降直到贮藏结束,与TP和FP的变化呈同步性,而过氧化物酶(POD)和过氧化氢酶(CAT)的活性则基本保持不变。鲜切甘薯PPO的最适反应温度为15.2℃,且在该温度下较为稳定,另在50℃处有一肩峰。PPO的最适pH值为4.4,pH4.0以下或者8.5以上PPO活性迅速下降。NaHSO3、CA、EDTA-2Na和VC对鲜切甘薯PPO均有不同程度的抑制效果。甘薯PPO对不同底物的酚类物质亲和力依次为儿茶酚>焦性没食子酸>绿原酸>酪氨酸>苯酚>愈创木酚。鲜切甘薯中主要的酚类物质和酶促褐变底物为绿原酸。     

不同贮藏温度下鲜切紫甘薯褐变相关因素研究

为研究鲜切紫甘薯的褐变条件与机理,本文对不同贮藏温度下(4和12℃)的鲜切紫甘薯的褐变程度、褐变相关酶活力以及褐变底物酚类物质进行分析。结果表明,12℃贮藏组的鲜切紫甘薯褐变度始终显著高于4℃贮藏组(P<0.05)。贮藏期间,褐变重的鲜切紫甘薯多酚氧化酶(Polyphenol oxidase,PPO)和过氧化物酶(Peroxidase,POD)活性更高,丙二醛(Malondialdehyde,MDA)含量更多。2~8 d,不同贮藏温度下鲜切紫甘薯绿原酸和阿魏酸含量显著不同(P<0.05),因此推断褐变相关酶活性、膜脂过氧化程度以及酚类物质含量可能是引起鲜切紫甘薯褐变的关键因素。通过相关性分析,多酚氧化酶(PPO)和过氧化物酶(POD)是引起鲜切紫甘薯褐变的关键酶。绿原酸和阿魏酸是鲜切紫甘薯褐变的主要底物。     

乙醇冷藏处理对鲜切马铃薯酶促褐变的抑制及其机理研究

以鲜切马铃薯为原料,研究了乙醇处理对其多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、褐变指数(BI)和丙二醛(MDA)含量的影响,以及酶促褐变底物L-酪氨酸和L-多巴的紫外和红外光谱图的变化来研究乙醇处理对鲜切马铃薯酶促褐变抑制机理。结果表明,分别用4%、5%、6%体积分数的乙醇溶液处理后的鲜切马铃薯在贮藏过程中,PPO活性、POD活性、BI值和MDA含量均低于对照组,且5%体积分数的乙醇溶液处理对酶促褐变的抑制效果最优;通过酶促褐变底物的紫外及红外光谱图可知,乙醇溶液处理对马铃薯酶促褐变的底物的结构没有产生影响,由此可知,乙醇溶液是通过抑制PPO、POD等相关酶的活性来抑制鲜切马铃薯的酶促褐变。     

鲜切莲藕酶促褐变底物的分析确定

鲜切莲藕贮藏期间的酶促褐变及其褐变底物的研究结果表明：切分后莲藕组织中新合成的及与多酚氧化酶（ＰＰＯ）作用的酚主要为ＦＰ，鲜切莲藕贮藏６ｄ后游离酚（ＦＰ）与褐变度（ＢＤ）两者的变化呈显著的负相关（ｒ＝０．９５９），组织中ＰＰＯ活性与ＦＰ、儿茶酚表现为同步的先升后降的变化规律，采用薄层层析和高压液相色谱确定儿茶酚在鲜切莲藕褐变前后发生明显量的变化，由儿茶酚与ＰＰＯ作用后产物的紫外吸收光谱与鲜切莲藕自然褐变产物基本相同的结果，初步认为儿茶酚是鲜切莲藕的主要褐变底物。     

鲜切链藕酶促褐变底物的分析确定

鲜切莲耦贮藏期间的酶促褐变及其褐变底物的研究结果表明：切分后莲藕组织中新合成的及与多酚氧化酶（PPO）作用的酚主要为FP，鲜切莲藕贮藏6d后游离酚（FP）与褐变度（BD）两者的变化呈显著的负相关（r=0.959），组织中PPO活性与FP、儿茶酚表现为同步的先升后降的变化规律，采用薄层层析和高压液相色谱确定儿茶酚在鲜切莲藕褐变前后发生明显量的变化，由儿茶酚与PPO作用后产物的紫外吸收光谱与鲜切莲藕自然褐变产物基本相同的结果，初步认为儿茶酚是鲜切莲藕的主要褐变底物。     

香辛料调味品褐变机理的分析研究

研究了香辛料调味品在贮藏期间褐变度(DB)及有关成分的变化,分析确定了引起褐变的原因及引起酶促褐变的主要底物,并探讨了香辛料调味品中多酚氧化酶(PPO)的部分酶学特性。实验结果表明,香辛料调味品在贮藏过程中PPO活性和褐变度的变化呈显著负相关性(r=-0.9535),即褐变主要是由酚类发生的酶促氧化所致,香辛料调味品PPO的最适反应pH为6.8,PPO与不同底物结合力的大小依次为焦性没食子酸>酪氨酸>儿茶酚>苯酚>愈创木酚;化学抑制剂CA(柠檬酸)、Na2SO3、Vc、Zn(Ac)2、EDTA-2Na、L-cys和植酸对PPO活性均有不同的抑制作用,尤以Na2SO3、L-cys、CA的抑制作用明显。     

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。     

鲜切甘薯不同部位褐变机理差异

以‘渝薯17’甘薯为实验材料,将鲜切甘薯分为皮部、周边以及中心3 个部位。通过对冷藏过程中鲜切甘 薯不同部位褐变情况、褐变底物酚类物质含量、褐变相关酶活力的比较研究,探讨鲜切‘渝薯17’不同部位的褐变 机理及差异。结果表明,绿原酸是甘薯褐变的主要底物,鲜切甘薯不同部位褐变存在差异,皮部褐变最严重,周边 次之,中心最弱。皮部总酚和游离酚含量均显著高于周边和中心组织（P＜0.05）,其中主要底物绿原酸含量为周 边和中心组织的3～4 倍。多酚氧化酶（polyphenoloxidase,PPO）是引起皮部组织褐变的主要酶,苯丙氨酸解氨酶 对酚类物质的积累起促进作用;周边组织褐变由PPO和过氧化物酶（peroxidase,POD）协同作用催化;中心组织 褐变则主要由POD引起。     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

Occurrence of bisphenol-F-diglycidyl ether (BFDGE) in fish canned in oil

The levels of bisphenol-F-diglycidyl ether (BFDGE) were quantified as part of a European survey on the migration of residues of epoxy resins into oil from canned fish. The contents of BFDGE in cans, lids and fish collected from all 15 Member States of the European Union and Switzerland were analysed in 382 samples. Cans and lids were separately extracted with acetonitrile. The extraction from fish was carried out with hexane followed by re-extraction with acetonitrile. The analysis was performed by reverse phase HPL C with fluorescence detection. BFDGE could be detected in 12% of the fish, 24% of the cans and 18% of the lids. Only 3% of the fish contained BFDGE in concentrations considerably above 1mg/kg. In addition to the presented data, a comparison was made with the levels of BADGE (bisphenol-A-diglycidyl ether)analysed in the same products in the context of a previous study.     

Contribution of European research to risk analysis

The European Commission's, Quality of Life Research Programme, Key Action 1—Health, Food & Nutrition is mission-oriented and aims, amongst other things, at providing a healthy, safe and high-quality food supply leading to reinforced consumer confidence in the safety of European food. Its objectives also include the enhancing of the competitiveness of the European food supply. Key Action 1 is currently supporting a number of different types of European collaborative projects in the area of risk analysis. The objectives of these projects range from the development and validation of prevention strategies including the reduction of consumers risks; development and validation of new modelling approaches; harmonization of risk assessment principles, methodologies, and terminology; standardization of methods and systems used for the safety evaluation of transgenic food; providing of tools for the evaluation of human viral contamination of shellfish and quality control; new methodologies for assessing the potential of unintended effects of genetically modified (genetically modified) foods; development of a risk assessment model for Cryptosporidium parvum related to the food and water industries; to the development of a communication platform for genetically modified organism, producers, retailers, regulatory authorities and consumer groups to improve safety assessment procedures, risk management strategies and risk communication; development and validation of new methods for safety testing of transgenic food; evaluation of the safety and efficacy of iron supplementation in pregnant women; evaluation of the potential cancer-preventing activity of pro- and pre-biotic ('synbiotic') combinations in human volunteers. An overview of these projects is presented here.     

低温带皮菜籽粕微粉的不同粒级部分的功能特性

为研究低温带皮菜籽粕微粉的不同粒级部分的功能特性,以经低温脱脂的带皮菜籽粕为原料,经微粉碎后筛分成212~425μm、150~212μm和106~150μm的3个不同粒级的微粉样品,检测这些样品的吸水性、吸油性、乳化性和乳化稳定性、蛋白质体外消化率。结果表明:1 3个不同粒级的微粉样品之间的粗纤维含量存在显著差异,表明三者的结构组成成分有一定差异。23个微粉样品的乳化活性和乳化稳定性随粒度级别的减小而显著增加(P0.01)。33个微粉样品的蛋白质体外消化率随粒度级别的减小而显著增加(P0.01)。4不同粒级带皮菜籽粕微粉样品的吸水性与吸油性受其结构组成物质不同和粒度的双重影响,与粒度的相关性不明显。     

Microbiology of food taints

Fresh and processed foods are often spoilt by the presence of undesirable flavours and odours caused by microbial action. The aim of this paper is to review the current knowledge of microbiologically induced taints that occur in a wide range of foodstuffs, including meats, poultry, fish, crustaceans, milk, dairy products, fruits, vegetables, cereals and cereal products. Examples have been chosen where the compounds responsible for the taint have been identified and sufficient data obtained to demonstrate the involvement of microorganisms. However, in some cases the full identity of the causative organism may not have been elucidated. The types of microorganisms covered by this review include bacteria, fungi, yeasts, actinomycetes and cyanobacteria. Although cyanobacteria do not in general infect foods, their presence in aqueous systems and water supplies can lead to off-flavours in aquatic organisms and processed foodstuffs. Several examples of each of these processes are discussed. Wherever possible, the likely biosynthetic pathway used by the microorganism to produce the offending compound in a foodstuff is indicated.     

Analysis for organic residues from aids to polymerization used to make plastics intended for food contact

Polymers intended for food contact use have been analysed for organic residues which could be attributed to a range of substances employed as polymerization aids (e.g. initiators and catalysts). A wide range of polymers was extracted with solvents and the extracts analysed by gas chromatography-mass spectrometry (GC-MS). The overwhelming majority of substances identified were not derived from aids to polymerization but were oligomers, additives and adventitious contaminants. However, a small number of substances were identified as initiator residues. These included tetramethylsuccinonitrile (TMSN) which was observed in two polymers and it derived from recombination of two azobisisobutyronitrile (AIBN) initiator radicals. Methyl benzoate, benzoic acid, biphenyl and phenyl benzoate were detected in one poly(methyl methacrylate) sample and in two polyvinylchlorides and they are thought to be derived from benzoyl peroxide initiator. TMSN was subsequently targeted for analysis of poly-(methyl methacrylate) plastics using proton nuclear magnetic resonance spectrometry (¹     

Tests of potential functional barriers for laminated multilayer food packages. Part II: Medium molecular weight permeants

Experiments were performed to characterize the kinetics of the permeation of different medium molecular weight model permeants: bisphenol A, warfarin and anthracene, from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick orientated polypropylene--OPP) into the food simulants olive oil and 3% (w/v) acetic acid. The characterization of permeation kinetics generally observed the permeation models previously reported to explain the experimental permeation results obtained for a low molecular weight group of model permeants. In general, the model permeants exhibited behaviour consistent with their relative molecular weights with respect to (a) the time taken to attain steady-state permeation into the food simulant in which they were more soluble, (b) their subsequent steady-state permeation rates, and (c) their partition between liquid paraffin and the OPP membrane.     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. I: Interlaboratory studies of methods of analysis

This paper describes the first part of a project undertaken to develop mussel reference materials for Paralytic Shellfish Poisoning (PSP) toxins. Two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin (STX) and decarbamoyl-saxitoxin (dc-STX) in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the second part of the project: the certification exercise. In the first study, 18 laboratories were asked to measure STX and dc-STX in rehydrated lyophilized mussel material and to identify as many other PSP toxins as possible with a method of their choice. In the second interlaboratory study, 15 laboratories were additionally asked to determine quantitatively STX and dc-STX in rehydrated lyophilized mussel and in a saxitoxin-enriched mussel material. The first study revealed that three out of four postcolumn derivatization methods and one pre-column derivatization method sufficed in principle to determine STX and dc-STX. Most participants (13 of 18) obtained acceptable calibration curves and recoveries. Saxitoxin was hardly detected in the rehydrated lyophilized mussels and results obtained for dc-STX yielded a CV of 58% at a mass fraction of 1.86 mg/kg. Most participants (14 out of 18) identified gonyautoxin-5 (GTX-5) in a hydrolysed extract provided. The first study led to provisional criteria for linearity, recovery and separation. The second study revealed that 6 out of 15 laboratories were able to meet these criteria. Results obtained for dc-STX yielded a CV of 19% at a mass fraction of 3.49mg/kg. Results obtained for STX in the saxitoxin-enriched material yielded a CV of 19% at a mass fraction of 0.34mg/kg. Saxitoxin could not be detected in the PSP-positive material. Hydrolysis was useful to confirm the identity of GTX5 and provided indicative information about C1 and C2 toxins in the PSP-positive material. The methods used in the second interlaboratory study showed sufficiently consistent analysis results to undertake a certification exercise to assign certified values for STX and dc-STX in lyophilized mussel.     

The Ministry of Environmental Protection Issued "Feasible Technology Guidelines for Pollution Prevention and Control in Wood Pulping Process of the Paper Industry (Trial)" and Two Other Guiding Technical Documents

On December 27t＂, 2013, the Ministry of Environmenta Protection announced that, in order to implement ＂The Environmental Protection Law of the People＇ s Republic of China＂, improve the working system in environmenta protection technologies, and promote technologica advancement in pollution prevention, the Ministry of Environmental Protection sponsored the formulation of three guiding technical documents including ＂Feasible Technology Guidelines for Pollution Prevention and Contro n Wood Pulping Process of the Paper Industry （Trial）＂     

1~(st) Intelli-Tissue~ EcoEc Tissue Machine Supplied by PMP Group Successfully Put into Operation in China

正On April 29th,2014,Intelli-Tissue EcoEc tissue machine supplied by PMP Group successfully put into operation at Hebei Xuesong Paper Co.,Ltd.,this is the first such kind of paper machine of PMP Group in China.