紫外减菌联合低温对草鱼肉品质及挥发性风味的影响

目的:研究紫外减菌前处理联合低温冷藏对草鱼鱼肉质构品质及挥发性风味物质的影响,并确定最佳的紫外照射时间。方法:以草鱼为试验对象,采用30 W紫外灯照射不同时间(0,30,60,90,150 min)预处理,测定鱼肉冷藏期间(0,3,6,9 d)各品质参数(鱼肉表面细菌总数、汁液流失率、质构参数、色泽、气味感官)及挥发性成分变化。结果:当紫外照射时间为0～150 min时,照射时间越长,草鱼鱼肉表面减菌效果越好,汁液流失率越低,出现腐败气味越晚,但对鱼肉的质构、色泽及冷藏后期(6～9 d)细菌总数影响较小。冷藏期间共检测到90种挥发性风味物质,主要为醛类、酮类、醇类、酯类和酸类,其中辛醛、壬醛、己醛、2,5-辛二酮、1-己醇、1-辛烯-3-醇为紫外处理草鱼肉的主要挥发性成分,且冷藏后期酯类和酸类物质含量逐渐增多。对比控制组,紫外处理可有效延缓冷藏草鱼肉腥味的产生和香味的下降。当紫外照射时间为90 min时,冷藏鱼肉表现出最佳的综合效果,随着照射时间的延长,鱼肉综合得分有所下降。结论:紫外减菌联合低温处理有利于延缓贮藏前期草鱼鱼肉质构品质劣化及风味下降,但对贮藏后期草鱼肉品质影响较小。     

草鱼肌肉风味变化与品质间的关联

为了明晰淡水鱼品质与其气味变化间的关联,利用电子鼻技术研究不同贮藏时间草鱼肌肉挥发性成分的变化,分别对各传感器的响应值进行主成分分析、线性判别分析和传感器区分贡献率分析,并结合同期硫代巴比妥酸值的变化开展气味与腐败间的关联研究。结果发现,电子鼻的10 个传感器均能区分不同贮藏时期的草鱼肌肉。随贮藏时间的延长,氮氧化合物、胺类和脂肪族芳香物质代表的传感器响应剧烈,其中,后两者在常温贮藏12 h后传感器响应变化更为明显,可作为电子鼻检测草鱼肌肉新鲜度的重要依据。硫代巴比妥酸值随贮藏时间延长呈上升趋势。电子鼻及硫代巴比妥酸值检测结果均显示冷藏12 d和常温12 h是草鱼肌肉新鲜度变化的2 个重要时间点。经相关性分析表明,脂肪族-甲烷传感器可作为判定本实验所述2 种不同贮藏条件下草鱼肌肉新鲜度变化的检测手段,为草鱼新鲜度检测及控制提供重要依据。     

电子鼻结合气质联用法分析大菱鲆冷藏过程中挥发性成分变化

通过测定大菱鲆在4℃冷藏过程中的感官品质、菌落总数和TVB-N值等指标的变化,确定贮藏20d时已达腐败阶段。利用电子鼻检测新鲜及腐败鱼肉的气味差异,并对所获数据进行主成分分析,同时结合顶空固相微萃取(HS-SPME)和气质联用技术(GC-MS)对新鲜及腐败鱼肉的挥发性成分进行分析鉴定。结果表明:电子鼻对新鲜及腐败鱼肉整体风味的区分快速、灵敏,其分析结果与常规新鲜度评价指标的变化致;采用GC-MS法在新鲜及腐败鱼肉中分别检测出27及28种挥发性物质,主要为醛类、酮类、醇类、酯类、烃类和胺类化合物等,其中醛类、酮类和醇类物质在新鲜鱼肉中的含量较高,而胺类物质在腐败鱼肉中含量较高。     

不同冷藏期鲳鱼及草鱼气味变化分析

以鲳鱼和草鱼分别作为海水鱼和淡水鱼代表,利用电子鼻评价冷藏条件下不同贮藏期的鱼肉气味,并通过气相色谱-质谱检测挥发性风味成分的变化。结果表明,电子鼻可以较好区分不同贮藏期的鱼肉气味,且草鱼的气味变化较鲳鱼更为显著。贮藏期间鲳鱼和草鱼分别鉴定出22 种和19 种挥发性物质,主要包括醛类、醇类、酯类及腐败性化合物等。新鲜鲳鱼挥发性风味主要以1-戊烯-3醇、己醛、1-辛烯-3醇、庚醛、2-辛烯醛为主,草鱼以己酸甲酯为主。贮藏期间,鲳鱼和草鱼气味成分变化也具有差异性,鲳鱼中和腐败相关的化合物主要为三甲胺和3-甲基丁醇等,且贮藏过程中醛类、醇类均呈下降趋势;草鱼贮藏过程中的第2天及第4天较为相关的化合物为癸醛、1-辛烯-3醇、己醛和壬醛等脂肪氧化的产物,而贮藏后期与腐败相关的化合物较少。上述结果初步说明生长环境、脂肪氧化及微生物腐败影响了海鱼和淡水鱼冷藏期气味形成。     

电子鼻结合气相色谱-质谱联用技术分析贮存条件对马铃薯面包挥发性成分的影响

以常温、冷藏的马铃薯面包为研究对象,采用电子鼻结合顶空固相微萃取-气相色谱-质谱联用技术,分析常温第1天、第6天和冷藏第6天的马铃薯面包样品挥发性成分。结果表明,电子鼻分析结果能够很好地区分常温和冷藏1～9?d马铃薯面包的风味。采用主成分分析和线性判别分析可以量化主成分贡献率和样品间风味的区分度,并利用判别因子分析建立马铃薯面包识别库模型。顶空固相微萃取-气相色谱-质谱联用分析结果表明,3?种马铃薯面包共检测出28?种挥发性风味物质,其中常温第1天17?种,冷藏第6天4?种,常温第6天14?种;经贮藏后,风味物质变化明显,冷藏样品酸类、酯类、酮类和烃类物质消失,常温样品贮藏后醛类和醚类消失,醇类化合物相对含量都显著增加。因此,电子鼻结合气相色谱-质谱联用技术可对贮藏期马铃薯面包的风味进行综合评价。     

牙鲆冷藏过程中肌肉挥发性风味成分的变化

为研究牙鲆不同贮藏阶段挥发性风味物质的组成特征,采用固相微萃取-气质联用技术测定牙鲆4℃冷藏条件下肌肉挥发性风味物质的变化情况,并利用主成分分析法和聚类分析法对挥发性物质的组成差异进行分析。结果表明:在冷藏牙鲆肌肉中共检测出66种主要的挥发性物质,包括醛、醇、酮、烃、酯和胺类化合物等。主成分分析结果表明,不同贮藏时间牙鲆肌肉的特征风味物质组成不同,其中贮藏初期以醛、酮和醇类化合物为主,在第0天和第3天时鱼肉样品的特征风味物质主要是己醛、壬醛、苯甲醛、2-壬酮、2-乙基己醇、1-戊烯-3-醇等;贮藏后期以胺类化合物为主,在贮藏12d时鱼肉样品的特征风味物质主要是甲基乙胺、N-己基甲胺、十九胺等。聚类分析发现,不同贮藏阶段鱼肉样品的风味轮廓可各自聚为一类。     

不同贮藏温度下草鱼内脏鱼油品质变化

为探究草鱼内脏鱼油在不同贮藏温度下的品质变化,以草鱼内脏为原料,采用酶法提取鱼油,将草鱼内脏鱼油分别置于冷藏（4 ℃）、常温（25 ℃）和37 ℃条件下贮藏60 d,定期测定其酸价和过氧化值,并运用指纹特征分析、主成分分析（PCA）、线性判别分析（LDA）和载荷分析等电子鼻技术定期分析其挥发性成分的变化。结果表明:在贮藏期内,低温贮藏时（4 ℃ ）的草鱼内脏粗鱼油酸价、过氧化值和挥发性气味成分变化均不明显;在常温（25 ℃）及37 ℃贮藏温度下草鱼内脏粗鱼油的酸价、过氧化值均明显升高,挥发性气味成分变化较大,尤其37 ℃时变化显著;以酸价和过氧化值作为鱼油是否变质的评判标准,4 ℃时保质期约为55 d,25 ℃时保质期约为40 d,37 ℃时保质期约为30 d;鱼油贮藏过程中的挥发性成分主要为氮氧化合物、硫化物和芳香成分等物质。本研究为草鱼内脏的有效利用提供了理论基础。     

玉米储藏过程中挥发性成分变化研究

为了研究玉米储藏期间气味变化情况,采用优化的顶空固相微萃取-气质联用法(HS-SPME-GC-MS)分析玉米在常温(25℃)密闭储藏过程中的主要挥发性成分组成。检出的物质主要包括烃类、醛类、酯类、醇类、酮类、酸类和少量杂类物质。结果表明,在储藏过程中烃类物质总相对含量在储藏末期比储藏初期有所增加。酸类物质相对含量呈缓慢上升但含量较低。酮类物质相对含量较低且呈逐渐降低趋势。醇类挥发性成分在储藏120 d前呈现增加趋势,在120 d后有所降低。醛类和酯类物质相对含量呈现先升高后降低,二者相对含量较高,储藏180 d后的相对含量接近于0 d,是玉米风味的主要贡献物质。而烃类和醇类风味阈值较高,不是玉米储藏期间风味的主要贡献物质。25℃下密闭储藏180 d后的玉米其气味与储藏0 d的玉米相比,并未发生人嗅觉可感知的明显异味变化。     

顶空固相微萃取-气质联用法结合电子鼻分析鱼精蛋白对草鱼片挥发性气味的影响

采用5.0 g/L的鱼精蛋白溶液对草鱼片进行浸泡处理,并通过顶空固相微萃取-气质联用(HS-SPMEGC-MS)及电子鼻对4℃贮藏过程中的样品进行挥发性气味检测。结果表明:HS-SPME-GC-MS法共检出挥发性物质132种,其中主要为醛类及醇类物质。在贮藏期内,对照组中醛类及醇类物质含量逐渐增高,酯类物质先增高后降低,酸类及其他类物质呈现较大波动。而处理组中醛类物质不断增加、醇类物质及酯类物质均呈现先降低后增高的趋势,且醇类、醛类及酯类物质的含量均低于对照组。电子鼻检测结果表明,贮藏后期处理组的响应值明显低于对照组。实验结果表明,鱼精蛋白处理能够在一定程度上延缓草鱼的风味劣变。     

顶空固相微萃取-气质联用法研究油麦菜采后香气成分的变化

为探究油麦菜清香风味的化学成分及温度对其风味物质的影响,该研究采用顶空固相微萃取(headspace solid phase micro-extraction,HS-SPME)结合气相色谱-质谱联用技术(gas chromatography-mass spectrometry,GC-MS)鉴定油麦菜的挥发性香气成分,并模拟2种常见的销售贮藏温度条件,研究油麦菜采后香气成分的动态变化。结果表明,油麦菜中挥发性香气成分包括9种醛类、3种醇类、1种酮类、1种酸类,以醛、醇类化合物为主;结合香气活性值(OAV)与绝对含量分析,青叶醛、叶醇、反,反-2,4-庚二烯醛等7种物质是油麦菜的主要特征香气成分,构成了油麦菜的清香、草香、蔬菜香等;油麦菜采后24 h内,冷藏(4℃)和常温(24℃)贮藏条件下主要香气成分种类未发生变化,但各成分含量变化较大,常温条件下香气成分总量显著上升(P 0. 05),而低温条件下香气成分总量显著下降(P 0. 05)。冷藏有助于减缓油麦菜香气的释放,常温贮藏有助于油麦菜香气的合成和释放,这将对叶类蔬菜的香气研究及油麦菜的保鲜有重要参考意义。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

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

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

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.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

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.