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。     

应用顶空固相微萃取-气相色谱质谱技术解析酿造用高粱蒸煮挥发性香气成分

通过比较不同样品前处理方法提取分析蒸熟高粱中香气组分的效果,开发出基于瓶内蒸煮结合顶空固相微萃取-气相色谱质谱联用(headspace solid phase microextraction and gas chromatography mass spectrometry,HSSPME-GC-MS)分析酿造用高粱蒸煮香气组分的方法。采用该方法研究了白酒酿造主要原料高粱蒸煮后挥发性香气特征。在蒸熟的高粱中共鉴定出46种挥发性香气成分,包括醛类化合物16种,有机酸类化合物7种,醇类化合物6种、酯类化合物6种,酚类化合物4种、酮类化合物2种、呋喃类化合物2种、其他类化合物3种。其中峰面积相对含量较高的化合物有苯甲醛(20.21%),己酸(9.00%),壬醛(8.66%),糠醛(8.90%),2-戊基呋喃(6.48%)和萘(5.49%)。同时还检测到一批香气阈值较低的化合物,如壬醛、(E,E)-2,4-癸二烯醛、(E)-2-辛烯醛、(E)-2-癸烯醛、1-辛烯-3-醇、香兰素、4-乙基愈创木酚、4-乙烯基愈创木酚、γ-辛内酯、γ-壬内酯等。这些香气物质可能是构成酿造用高粱蒸煮香气特征的主要香气组分。     

电子鼻和气质联用法分析普洱茶香气成分

为了解不同品牌普洱茶香气成分的特点和差异性,本研究采用电子鼻(electronic nose,E-nose)和顶空固相微萃取(headspace solid phase microextraction,HS-SPME)结合气相色谱-质谱联用(gas chromatography-mass spectrometry,GC-MS)对3个品牌普洱茶香气成分进行分析和鉴定。结果表明,E-nose能够较好区分3个品牌的普洱茶,主成分分析显示不同品牌样品间差异明显,区分度良好。进一步采用HS-SPME-GC-MS对普洱茶香气构成进行分析,结果共检测出74种化合物,共有成分38种,其中大益普洱茶、老同志普洱茶和澜沧古茶分别检测出66、53和48种,主要包括:醛类、醇类、酮类、甲氧基苯类化合物等物质,且物质组成和含量差异显著,主要差异性物质包括2-羟基-6-甲基苯甲醛、藏红花醛、芳樟醇氧化物、4-萜烯醇、甲基庚烯酮、(E,E)-3,5-辛二烯-2-酮、1,4-二甲氧基苯、1-甲氧基-4-(1-丙烯基)-苯、邻异丙基甲苯、α-松油烯、邻苯二甲酸二甲酯、咖啡因。香气活性值(odour active values,OAV)分析表明造成香气差异的物质主要是(E)-2-辛烯醛、(E,E)-2,4-壬二烯醛、壬醛、α-紫罗兰酮、香叶基丙酮。     

Analytical methods for the determination of the geographic origin of Emmental cheese: volatile compounds by GC/MS-FID and electronic nose

The volatile compounds of Emmental cheese of different origins were investigated to check their suitability as markers of geographic origin. A total of 20 Emmental cheese samples from Switzerland, Allgäu (D), Bretagne (F), Savoie (F), Vorarlberg (A) and Finland (produced in winter with a ripening time according to that sold in the corresponding regions) were analysed using dynamic headspace gas chromatography followed by flame ionisation and mass spectrometry. All regions were easily differentiated by using compounds occurring only in the corresponding region or by combining a few compounds by principal component analysis (PCA). Further analyses were carried out using a mass spectrometry-based electronic nose. PCA achieved 90 and 91% of correct classifications for the Emmental from Switzerland and other regions, respectively.     

A comparison of warmed-over flavour in pork by sensory analysis, GC/MS and the electronic nose

Pork muscle samples (M. longissimus dorsi and M. psoas major) were obtained from pigs given one of 4 dietary treatments, (i) control diet, (ii) supplemental iron (300 mg iron (II) sulphate/kg feed), (iii) supplemental vitamin E (200 mg dl-α-tocopheryl acetate/kg of feed) and (iv) supplemental vitamin E+supplemental iron. Warmed-over flavour (WOF) was evaluated by a trained sensory panel (n=8) for the four treatments cooked and refrigerated at 4?°C for up to 5 days. Gas chromatography mass spectrometry (GC/MS) and Electronic nose analysis was performed on a subset of the full design which included samples of M. longissimus dorsi, treatments (ii) and (iii) and M. psoas major with treatment (i) for 0 days of WOF development. Day 5 of WOF development was included in the subset and represented by samples of M. longissimus dorsi, treatment (iv) and M. psoas major, treatments (ii) and (iii). Bi-linear modeling was used to determine the correlation of GC/MS and electronic nose data to sensory data. Also, the reproducibility and reliability of electronic nose data was evaluated by repeating the analysis of samples in a different laboratory and with a time difference of approximately 11 months. Mean-centring was used to normalise the data from these two different electronic noise data sets. GC/MS data correlated to sensory data with specific compounds (e.g., pentanal, 2-pentylfuran, octanal, nonanal, 1-octen-3-ol and hexanal), proving to be good indices of oxidation in cooked samples of M. longissimus dorsi and M. psoas major. Electronic nose data correlated to sensory data and separated the sensory variation. The reproducibility of this data was high with the second set of samples being predictive of the first set.     

Characterization of flavour and volatile compounds of fermented squid using electronic nose and HPMS in combination with GC-MS

The present study investigated the flavour characteristics and key volatile components of fermented squid (Dosidicus gigas) as well as their formation mechanism by three different starter cultures of lactic acid bacteria (LAB) and natural squid. The sensory assessment, volatile compounds, as well as the amino acids of the mixed fermented squid were detected using pickled brine as samples of fermented squid. A total 88 types of volatile compounds were found in four samples by 0–72 h of fermentation. After fermentation by LAB, the volatile compounds of squid showed that the fermented squid with different started cultures differed mainly in terms of numbers of alcohols, ketones, and esters. Furthermore, the amounts of volatile compounds among three starter cultures were also obviously different. Gas Chromatography-Mass Spectrometer (GC-MS) analysis indicated that the mixed fermentation process contained relatively higher (+)-limonene (11.71%) (lemon scent) and 3-hydroxy-2-butanone (5.72%) (creamy taste). These compounds were not detected in the control group. The main flavour compounds of nonanal and 2, 4-decadienal were gradually reduced. Meanwhile, 2, 3-butanedione, 2-heptanone, 2-pentylfuran, and nonanoic acid are the key flavour components. The total principal component is 94.01%, which were clarified by electronic nose in combination with principal components analysis. After mixed fermentation by LAB, the total amino acid (TAA) content reached 85.36 g/100 g, which was almost twice the amount of the control, especially in aspartate, glutamate, and threonine. Our results indicated that LAB has obvious effects on deodorization and flavour promotion during the fermentation of squid. This study provided an important basis for the further development and utilization of squid.     

Lethality of Salmonella and Listeria innocua in fully cooked chicken breast meat products during postcook in-package pasteurization

The process lethality model was used to predict the thermal kill of Salmonella and Listeria innocua in fully cooked and vacuum-packaged chicken breast meat during hot-water postprocess pasteurization. Time-temperature profiles of the meat samples during treatment and D-values (decimal reduction times) and z-values (change in temperature required to change the D-value) for Salmonella and L. innocua in the same meat product were used in the prediction of lethality. The results of the model prediction were compared with those of the inoculation study for the same meat product at a 95% confidence level of up to 10(7) CFU/g for Salmonella and L. innocua. The thermal lethality predictions obtained with the process lethality model for Salmonella and L. innocua were within the 95% confidence level for the experimental data from the inoculation study, suggesting that the process lethality model was a useful tool for the determination of the kill of Salmonella or L. innocua at up to 10(7) CFU/g in fully cooked chicken breast meat products during postprocess pasteurization with hot water.     

Detection and quantification of ochratoxin A and deoxynivalenol in barley grains by GC-MS and electronic nose

Mycotoxin contamination of cereal grains can be detected and quantified using complex extraction procedures and analytical techniques. Normally, the grain odour, i.e. the presence of non-grain volatile metabolites, is used for quality classification of grain. We have investigated the possibility of using fungal volatile metabolites as indicators of mycotoxins in grain. Ten barley samples with normal odour, and 30 with some kind of off-odour were selected from Swedish granaries. The samples were evaluated with regard to moisture content, fungal contamination, ergosterol content, and levels of ochratoxin A (OA) and deoxynivalenol (DON). Volatile compounds were also analysed using both an electronic nose and gas chromatography combined with mass spectrometry (GC-MS). Samples with normal odour had no detectable ochratoxin A and average DON contents of 16 microg kg(-1) (range 0-80), while samples with off-odour had average OA contents of 76 microg kg(-1) (range 0-934) and DON contents of 69 microg kg(-1) (range 0-857). Data were evaluated by multivariate data analysis using projection methods such as principal component analysis (PCA) and partial least squares (PLS). The results show that it was possible to classify the OA level as below or above the maximum limit of 5 microg kg(-1) cereal grain established by the Swedish National Food Administration, and that the DON level could be estimated using PLS. Samples with OA levels below 5 microg kg(-1) had higher concentration of aldehydes (nonanal, 2-hexenal) and alcohols (1-penten-3-ol, 1-octanol). Samples with OA levels above 5 microg kg(-1) had higher concentrations of ketones (2-hexanone, 3-octanone). The GC-MS system predicted OA concentrations with a higher accuracy than the electronic nose, since the GC-MS misclassified only 3 of 37 samples and the electronic nose 7 of 37 samples. No correlation was found between odour and OA level, as samples with pronounced or strong off-odours had OA levels both below and above 5 microg kg(-1). We were able to predict DON levels in the naturally contaminated barley samples using the volatile compounds detected and quantified by either GC-MS or the electronic nose. Pentane, methylpyrazine, 3-pentanone, 3-octene-2-ol and isooctylacetate showed a positive correlation with DON, while ethylhexanol, pentadecane, toluene, 1-octanol, 1-nonanol, and 1-heptanol showed a negative correlation with DON. The root mean square error of estimation values for prediction of DON based on GC-MS and electronic nose data were 16 and 25 microg kg(-1), respectively.     

Comparison of volatile components in raw and cooked green beans by GC-MS using dynamic headspace sampling and microwave desorption

 The effects of four culinary treatments (steaming and boiling in a covered pot, a pressure cooker or a microwave oven) on the volatile component profile of green beans were evaluated. Volatile compounds in raw and cooked beans were analysed by means of dynamic headspace sampling onto an adsorbent, followed by microwave desorption into a gas chromatograph equipped with a mass spectrometric detector. Twenty-seven compounds were identified, including alcohols, aldehydes, ketones, esters, terpenes, sulphur compounds and alkenes. All of the thermal treatments caused important changes in the volatile compound profile in particular an increase in carbonyl compounds and a decrease in alcohol compounds, most notably in the case of the covered pot. It is concluded that the change in aroma during the cooking of green beans depends on compounds from lipid oxidation as well as compounds from other types of reactions, for instance the Strecker degradation. Received: 8 March 1999 / Revised version: 23 April 1999     

Changes in the fatty acid composition of dietetic ready-to-cook chicken meat products during frozen storage

A study was made on the fatty acid composition of dietetic ready-to-cook products of boneless chicken legs or breasts prepared by curing using several curing mixtures during frozen storage. Leg muscles were found to be richer in unsaturated fatty acids than breast muscles, substantial differences having been found in the contents of palmitoleic and linolenic acids. During frozen storage, the contents of unsaturated fatty acids were reduced, especially intensively in the leg muscle ready-to-cook products. The fastest changes occurred in linolenic and linolic acids and partly in palmitic acid. The level of oleic acid remained substantially unchanged throughout the storage period. Irrespective of the changes found, the ratio of unsaturated and saturated fatty acids in all the groups studied remained greater than 1 for both types of meat. The application of citrate in the curing mixture had a favourable effect on the changes, in that a minimum alteration in the contents of unsaturated fatty acids was achieved.     

Composition of phospholipid fraction in raw chicken meat and pre-cooked chicken patties: influence of feeding fat sources and processing technology

The effect of dietary lipid sources (animal fat, AF vs. vegetable oil, VO) was investigated on the phospholipid (PL) fraction of raw chicken meat and pre-cooked chicken patties. PL classes were determined on extracted lipids by high-performance liquid chromatography (HPLC) connected with an evaporative light-scattering detector (ELSD). The HPLC-ELSD method showed good intraday repeatability (less than 5% for different PL) and limits of detection ranging from 0.006 mg/mL (phosphatidylethanolamine) to 0.045 mg/mL (sphingomyelin). Diet did not consistently influence PL in chicken breast. A significant difference was assessed in meat batter where total PL were at levels of 349.0 and 388.2 mg/100 g of product in batter from broilers fed AF and VO diet, respectively. Cooking oil absorption caused an important decrease in PL (lower than 300 mg/100 g of product in pre-fried patties). Diet was an effective means to control the PL fatty acid profile in chicken, particularly the levels of polyunsaturated fatty acids (PUFA). In minced breast and thigh and meat batter from birds fed a VO-supplemented diet, the relative amount of PUFA was 46, 81 and 28% higher than that determined in the corresponding samples obtained from broilers fed an AF-based diet.     

Development of warmed-over flavour in ground turkey, chicken and pork meat during chill storage. A model of the effects of heating temperature and storage time

The susceptibility towards development of warmed-over flavour (WOF) was investigated in meat from turkey and chicken breast and thigh, and from pork longissimus dorsi muscle. Ground meat samples from these five sources were heated for 30 min in a water bath at 60, 70 or 80 °C, and the samples were stored at 5 °C for 0–4 days. During storage, WOF was quantified by measurement of thiobarbituric-acid-reactive substances (TBARS) and by sensory evaluations. The increase in TBARS was modelled for each type of meat at the different heating temperatures by a first-order reaction, and it was shown that a common rate constant could be used for all types of meat. The estimated maximum levels of TBARS in meat samples decreased in the following order: turkey thigh > chicken thigh > turkey breast > chicken breast > pork. For each type of meat, the estimated maximum level of TBARS rose when the heating temperature increased in the range 60–80 °C. This temperature effect was particularly obvious for the chicken samples. Thus thigh and breast meat from chicken heated to 60 °C was almost stable against oxidation during storage. Results obtained by measurement of TBARS were in good agreement with the sensory evaluations.

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Entwicklung von Aufwärmegeschmack in gehacktem Fleisch von Pute, Hähnchen und Schwein während der Kühllagerung. Ein Modell des Effektes der Aufwärmetemperatur und Lagerungzeit

Zusammenfassung Die Entwicklung des Aufwärmegeschmacks (WOF) in Brust und Schenkel von Pute und Hähnchen und im Longissimus dorsi vom Schwein wurde untersucht. Fünf Sorten von gehackten Fleischproben wurden in einem Wasserbad bei 60, 70 oder 80 °C aufgewärmt und 0–4 Tage bei 5 °C aufbewahrt. In der Lagerungzeit wurde WOF über Thiobarbitursäure-reaktive Substanzen (TBARS) und sensorische Beurteilungen bestimmt. Die Erhöhung der Mengen von TBARS für eine Fleischsorte bei einer gegebenen Temperatur wurde mit einer mathematischen Funktion 1. Ordnung beschrieben, und eine gemeinsame Reaktionskonstante für alle Fleischsorten gefunden. Die bestimmten Maximumwerte für TBARS waren in fallender Ordnung: Putenschenkel > Hähnchenschenkel > Putenbrust > Hähnchenbrust > Schwein. Für eine gegebene Fleischsorte stiegen die gemessenen Maximumwerte für TBARS mit erhöhten Aufwärmetemperaturen im Bereich von 60–80 °C. Dieser Temperatureffekt war im besonderen für Hähnchenfleisch anzumerken und äußerte sich bei fast unveränderter Oxidationsstabilität in Schenkel und Brustfleisch von Hähnchen, die bei 60 °C aufgewärmt wurden. Die bei den TBARS bestimmten Resultate waren in guter Übereinstimmung mit den sensorischen Beurteilungen.

     

Salmonella surveillance in raw and cooked meat and meat products in the Republic of Ireland from 2002 to 2004

The food industry, under the regulation of the Department of Agriculture and Food (DAF) in the Republic of Ireland, is required to undertake all microbiological testing in relation to zoonoses control, in laboratories approved by DAF. These laboratories submit a monthly report of all tests undertaken, together with all presumptive Salmonella isolates for confirmation, typing and storage to the Central Veterinary Research Laboratory (CVRL). Details of Salmonella tests on 110,229 raw and 25,189 cooked meat samples from 25 laboratories were recorded over the 3-year period 2002-2004. Salmonella spp. were isolated from 1.0% of the 110,229 raw meat samples and 0.1% of the 25,189 cooked meat samples tested. The percentage of raw meat samples contaminated with Salmonella decreased over the three-year period from 1.2% to 0.9%. There was no seasonal trend in the isolation of Salmonella from any of the meats or meat products. Recoveries of the organism were highest for turkey and chicken meats at 3.1% and 2.8%, respectively, followed by porcine meats at 2.1%. The recoveries were much lower for ovine meats and meat products at 0.2% and bovine meat and meat products at 0.16%.     

Contributions of non-volatile and volatile compounds to the umami taste and overall flavour of shiitake mushroom extracts and their application as flavour enhancers in cooked minced meat

Aqueous extracts of dried shiitake mushrooms (Lentinus edodes) were prepared as taste and flavour enhancers for meat formulations. Effects of time and temperature on the chemical and sensory properties of the extracts were examined. Extracts prepared at 70 °C had significantly higher concentrations (p < 0.001) of the savoury tasting 5′-ribonucleotides than those prepared at 22 °C but increasing the extraction time from 30 to 360 min only increased their recovery slightly (p = 0.053). In contrast, higher temperature extracts had considerably smaller concentrations of the major volatile compounds, such as lenthionine, 1-octen-3-ol, 1,3-dithiethane and dimethyl disulfide, because of loss through volatilisation.     

GC-MS法分析金瓜在贮藏过程中挥发性香精油含量及成分的变化

本试验旨在了解金瓜皮中挥发性香精油的含量、主要成分以及贮藏过程中各成分含量的变化,为深入探究此品种的研究价值、综合利用特性提供试验依据。采用水蒸气蒸馏法提取挥发性香精油,并运用GC-MS法对其成分进行分析。贮藏过程中采用膜处理和药剂处理进行保鲜。结果表明:金瓜皮挥发性香精油提取率达1.8%以上,主要成分达70多种,柠檬烯含量最高,在贮藏过程中各成分含量各有变化。     

Odour of cooked silurus (Silurus glanis) flesh: evaluation by sensory analysis and comparison of collection methods to assess the odour representativeness of extracts obtained by dynamic headspace

The odour of silurus (Silurus glanis) coming from two types of rearing environment developed in France was studied. Odour sensory analysis was performed on cooked fillets of silurus. The odour representativeness of extracts obtained by dynamic headspace was assessed. Two methods of extract collection were compared. Rearing environment had an effect on the odour of cooked fillets of silurus. Silurus reared in outdoor ponds for 2 years with no renewal of water had a stronger odour of hay, cut grass and hot milk and a weaker odour of mouldy, hard‐boiled egg and cooked cabbage than silurus reared in indoor concrete ponds for 1 year with renewed geothermal water. Odour extracts collected with the Teflon bag method were more representative of the odour of cooked fillets of silurus than those collected with the glass flask method. Teflon bags showed the relevance of dynamic headspace extraction to analyse the odour of cooked fillets of silurus. Copyright © 2004 Society of Chemical Industry     

Relationship between the solubility,dosage and antioxidant capacity of carnosic acid in raw and cooked ground buffalo meat patties and chicken patties

Antioxidant capacity of oil soluble and water dispersible carnosic acid (CA) extracted from dried rosemary leaves using HPLC was evaluated at two different dosages (22.5 ppm vs 130 ppm) in raw and cooked ground buffalo meat patties and chicken patties. Irrespective of total phenolic content, CA extracts reduced (p < 0.05) the thiobarbituric acid reactive substances (TBARS) by 39%–47% and 37%–40% in cooked buffalo meat and chicken patties at lower dosage (22.5 ppm) relative to control samples. However, at higher dosage (130 ppm) the TBARS values were reduced (p < 0.05) by 86%–96% and 78%–87% in cooked buffalo meat and chicken patties compared to controls. The CA extracts were also effective in inhibiting (p < 0.05) peroxide value and free fatty acids in cooked buffalo meat and chicken patties. The CA extracts when used at higher dosage, were also effective in stabilizing raw buffalo meat color.     

Technical note: Determination of acidity in whole raw milk: comparison of results obtained by two different analytical methods

In Argentina, one analytical method is usually carried out to determine acidity in whole raw milk: the Instituto Nacional de Racionalización de Materiales standard (no. 14005), based on the Dornic method of French origin. In a national and international regulation, the Association of Official Analytical Chemists International method (no. 947.05) is proposed as the standard method of analysis. Although these methods have the same foundation, there is no evidence that results obtained using the 2 methods are equivalent. The presence of some trends and discordant data lead us to perform a statistical study to verify the equivalency of the obtained results. We analyzed 266 samples and the existence of significant differences between the results obtained by both methods was determined.