Volatile metabolites in various cereal grains

To date, studies on volatile metabolites in cereal grain have focused mainly on a single species. In this paper, results are presented of the analysis of volatile compounds in five cereal grain species (spring wheat, durum wheat, triticale, rye, oats and barley) based on representative sampling of at least 15 cultivars of individual species. Profiles of volatile compounds were determined using solid phase microextraction (SPME) and GC–TOF (time of flight mass spectrometry). Many of the volatile compounds were only present in single samples; however, several dozen were found in over 50% of samples and 46 volatiles were found in all samples. Among them there were six alcohols, 10 aldehydes and ketones, six terpenes, seven hydrocarbons and 11 benzene derivatives. The highest concentrations of these compounds were found in durum wheat, while the lowest were observed in triticale and rye.     

Use of a MS-electronic nose for prediction of early fungal spoilage of bakery products

A MS-based electronic nose was used to detect fungal spoilage (measured as ergosterol concentration) in samples of bakery products. Bakery products were inoculated with different Eurotium, Aspergillus and Penicillium species, incubated in sealed vials and their headspace sampled after 2, 4 and 7 days. Once the headspace was sampled, ergosterol content was determined in each sample. Different electronic nose signals were recorded depending on incubation time. Both the e-nose signals and ergosterol levels were used to build models for prediction of ergosterol content using e-nose measurements. Accuracy on prediction of those models was between 87 and 96%, except for samples inoculated with Penicillium corylophilum where the best predictions only reached 46%.     

Volatiles for mycological quality grading of barley grains: determinations using gas chromatography-mass spectrometry and electronic nose

The possibility of using an electronic nose or gas chromatography combined with mass spectrometry (GC-MS) to quantify ergosterol and colony forming units (CFU) of naturally contaminated barley samples was investigated. Each sample was split into three parts for (i) ergosterol and CFU analysis, (ii) measurements with the electronic nose and (iii) identification of volatiles collected on an adsorbent with a GC-MS system. Forty samples were selected after sensory analysis to obtain 10 samples with normal odour and 30 with some degree of off-odour. The data set of volatile compounds and the data collected from the electronic nose were evaluated by multivariate analyse techniques. SIMCA classification (soft independent modelling of class analogy) was used for objective evaluation of the usefulness of the data from the GC-MS or electronic nose measurements for classification of grain samples as normal or with off-odour. The main volatile compounds of grain with normal odour were 2-hexenal, benzaldehyde and nonanal, while 3-octanone, methylheptanone and trimethylbenzene were the main volatile compounds of grain with off-odours. Using data from the electronic nose three samples of 40 were misclassified, while data analysis of the volatile compounds detected with the GC-MS, led to six misclassified samples. Regression models (partial least-squares, PLS) were built to predict ergosterol- and CFU-levels with data from the GC-MS or electronic nose measurements. PLS models based on both GC-MS and electronic nose data could be used to predict the ergosterol levels with high accuracy and with low root mean square error of prediction (RMSEP). CFU values from naturally infected grain could not be predicted with the same degree of confidence.     

基于统计空间映射和电子鼻的猪肉风味物质检测

为有效地检测并识别不同猪肉样本挥发性风味的差异,利用电子鼻和顶空固相微萃取-气相色谱-质谱联用技术分别对猪肉样本进行检测,针对2 种方法检测物质的相似性,应用系统聚类分析2 种方法的检测数据,建立二者之间的线性回归模型,获得电子鼻检测数据与猪肉挥发性风味物质间的映射关系,并利用映射关系完成电子鼻检测数据的分类。结果显示,猪肉的电子鼻检测数据与挥发性成分间展现了较为一致的聚类结果,回归方程显示2 种检测数据存在显著的线性关系,利用聚类结果进行判别分析,样本识别正确率达到了90%,表明了利用电子鼻检测并识别不同猪肉间挥发性风味物质差异可行。     

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.     

电子鼻应用于猪肉丸子香味预测

为应用电子鼻技术快速、客观地评价猪肉丸子风味,实验设计了4?种肥肉、瘦肉配比（100%瘦、90%瘦、80%瘦和70%瘦）的猪肉丸子,使用电子鼻和顶空固相微萃取和气相色谱-质谱（gas chromatography-mass spectrometry,GC-MS）联用对猪肉丸子的各种挥发性物质进行检测。同时对其进行香味指标感官评定。采用线性判别和神经网络方法对不同猪肉丸子的电子鼻数据进行识别分类;并利用偏最小二乘回归方法对电子鼻传感器和挥发性物质的相关性进行分析。结果表明,4?类丸子在香味评价上差异极显著（P＜0.01）,肥肉比例高的丸子获得了较高的评分。线性判别分析和神经网络方法的分类效果显示,电子鼻对4?类猪肉丸子具有良好的分类能力。GC-MS共检测出了67?种风味化合物,其中主要是醛类、醇类、酮类等物质,挥发性风味物质的差异是造成各类丸子感官评分差异的根本原因。偏最小二乘回归模型显示电子鼻传感器数据与主要挥发性化合物相对含量具有良好的相关性。使用逐步回归建立电子鼻与评价指标数据之间的分值预测回归模型（R2＞0.9,P＜0.01）,表明丸子香味可以使用电子鼻进行预测。     

鸡肉新鲜度电子鼻评价特征值的确定

用电子鼻检测鸡肉在不同试验条件下挥发性成分的变化,用电子鼻输出信号考察了加热温度、时间和样本表面积对鸡肉散发挥发性成分的影响。通过对24份鸡肉样本的试验得出:电子鼻输出信号与采集时间呈线性关系,可以用斜率表示各个样本的特征值;相同加热温度的样本较好的归为一类,不同加热温度的样本区别明显;加热温度较低时,加热时间对样本相聚的影响较小,温度较高时,影响较大;样本的表面积对样本相聚也有影响,但需进一步试验验证。初步试验研究表明,在不同试验条件下,鸡肉挥发性成分发生变化,电子鼻可检测到这些变化。可尝试用电子鼻技术评价鸡肉新鲜度变化的研究。     

Discrimination of Volatiles of Refined and Whole Wheat Bread Containing Red and White Wheat Bran Using an Electronic Nose

Abstract: The principal objective of this study was to evaluate the capability of electronic (E) nose technology to discriminate refined and whole wheat bread made with white or red wheat bran according to their headspace volatiles. Whole wheat flour was formulated with a common refined flour from hard red spring wheat, blended at the 15% replacement level with bran milled from representative samples of one hard red and 2 hard white wheats. A commercial formula was used for breadmaking. Results varied according to the nature of the sample, that is, crust, crumb, or whole slices. Bread crust and crumb were completely discriminated. Crumb of whole wheat bread made with red bran was distinct from other bread types. When misclassified, whole wheat bread crumb with white bran was almost invariably identified as refined flour bread crumb. Using crust as the basis for comparisons, the largest difference in volatiles was between refined flour bread and whole wheat bread as a group. When refined flour bread crust was misclassified, samples tended to be confused with whole white wheat crust. Samples prepared from whole bread slices were poorly discriminated in general. E‐nose results indicated that whole wheat bread formulated with white bran was more similar in volatile makeup to refined flour bread compared to whole wheat bread made with red bran. The E‐nose appears to be very capable to accommodate differentiation of bread volatiles whose composition varies due to differences in flour or bran type. Practical Application: Consumer preference of bread made using refined flour in contrast to whole wheat flour is partly due to the different aroma of whole wheat bread. This study used an electronic nose to analyze bread volatiles, and showed that whole wheat bread incorporating white bran was different from counterpart bread made using red bran, and was closer in volatile makeup to “white” bread made without bran. Commercial millers and bakers can take advantage of these results to formulate whole wheat flour with brans of preferred type in order to foster increased consumption of whole wheat products which confer many favorable health benefits.     

Contribution of enterococci to the volatile profile of slightly-fermented sausages

The volatile profiles of slightly-fermented sausages inoculated with eight different enterococci strains were determined and compared with a fermented sausage manufactured without any inoculation. The volatile profile was determined by solid-phase microextraction (SPME) and gas chromatography coupled to mass spectrometry (GC/MS). A total of 121 volatile and semi-volatile compounds were identified in the samples of the final products (day 21). Terpenes from spices added during manufacture of dry-fermented sausages were the main group of compounds in the volatile profile. Other groups included alcohols (18% of total volatile compounds), aldehydes (16%), alkanes and alkenes (12%), and ketones (10%). These are derived from lipids, proteins or carbohydrates and formed during fermentation and ripening. In terms of global volatile composition, the batches inoculated with enterococci strains were similar to those obtained for non-inoculated batch. However, some quantitative differences in the volatile profiles of different batches were found, mainly in the compounds formed from amino acid catabolism (i.e.: propanol, isoamyl), from free fatty acid oxidation (i.e.: hexanal, hexanol), or from carbohydrate fermentation (i.e.: 2-butanone, acetoin). In comparison with non-inoculated sausages, some batches were more resistant to oxidation; they contained fewer volatile compounds arising from lipid oxidation. The use of different selected enterococci strains did not alter the volatile profile of slightly-fermented sausages. The enterococci strains provide similar volatile compounds to those usually reported in the literature.     

Volatile composition of raw spirits of different botanical origin

The main purpose of the research was to determine the volatile composition of raw spirits, on the basis of trace compound isolation from their volatile fraction, as well as a comparison of the obtained volatile profiles of agricultural distillates of different botanical origins (maize, wheat, triticale, rye). This approach was chosen to improve methods of quality control and quality assurance in the spirit industry. Volatile composition of all raw spirit samples derived from different raw materials (rye, triticale, maize and wheat) were formed using headspace solid‐phase microextraction (HS‐SPME) and capillary gas chromatography–mass spectrometry (GC‐MS). Performed studies indicated the presence of over 100 compounds in the raw spirit volatile fraction. The richest volatile profile was obtained from samples produced from wheat and the poorest from those produced from corn. Moreover, on the basis of performed discriminant analysis (using the variables 2‐methylbutanol + 3‐methylbutanol, 3‐methylbutyl hexanoate, ethyl dodecanoate, ethyl heptanoate and 3‐methylbutyl octanoate), it was possible to distinguish between agricultural distillates originating from triticale and distillates produced from wheat. Copyright © 2013 The Institute of Brewing & Distilling     

Discrimination of storage shelf-life for mandarin by electronic nose technique

Over the past years, electronic nose technology opened the possibility to exploit information on aroma attribute to assess fruit ripening stage during storage. The objective in this study was to evaluate the capacity of electronic nose in monitoring the change in volatile production of mandarin during different storage treatments, and storage shelf-life of mandarin was evaluated by measuring the change in volatile production of mandarin using electronic nose device (PEN 2). By comparing, storage shelf-life of mandarin was better distinguished using Linear Discriminant Analysis (LDA) than Principal Component Analysis (PCA). PCA and LDA analysis were efficient to classify mandarin with the same storage time in its respective groups; but the methods are not efficient to separate the mandarins by different storage times. The correlation between the measured and predicted values of fruit quality attribute (such as soluble solid content, acidity and compression force) shows poor to reasonable prediction performance by means of electronic nose signals. The results prove that sensors 2, 7 and 9 in the electronic nose PEN 2 for mandarin have a higher influence in the current pattern file. Hence, nearly a subset of few sensors can be chosen to explain all the variance. This result could be used in further studies to optimize the number of sensors and find better performance.     

不同配料及发酵剂对羊肉发酵香肠滋味及香气成分的影响

利用固相微萃取-气质联用(solid phase microextraction-gas chromatography-mass,SPME-GC-MS)结合电子鼻、电子舌技术对四组羊肉发酵香肠样品(对照组、发酵剂组、V_C组、V_C+发酵剂组)的风味进行测定。结果表明,基于电子鼻技术可实现对发酵香肠样品快速区分,而电子舌不能明显区分。利用 SPME-GC/MS技术从四组香肠样品中共鉴定出49种挥发性风味物质,其中对照组、发酵剂组、V_C组及V_C+发酵剂分别检出43、46、48、48种挥发性风味物质,加入发酵剂和V_C能够明显地提高发酵香肠中风味物质含量,尤其是醇类、酮类、酯类物质。结合电子鼻结果分析,V_C+发酵剂组对醇类、醛酮类等物质更灵敏,说明发酵剂和V_C共同作用下为发酵香肠效果更好。相对气味活度值(ROAV)分析结果表明,共有9种挥发性风味物质对香肠整体风味有贡献作用(ROAV>1),分别为己醛、庚醛、辛醛、苯乙醛、壬醛、癸醛、E-癸-2-烯醛、2-十一烯醛和1-辛烯-3-醇。基于对特征挥发性风味物质风味特性的分析,明确发酵香肠的风味特征为淡脂香、青草香味、发酵味。     

Detection of age and insect damage incurred by wheat, with an electronic nose

Wheats of five storage ages and with 15 degrees of insect damage were evaluated and classified by the static-headspace sampling method using an electronic nose (E-nose). A commercial E-nose (PEN2) comprising 10 metal-oxide semiconductor (MOS) sensors was used to generate a typical chemical fingerprint of the volatile compounds present in the samples. Principal-component analysis (PCA) and linear-discriminant analysis (LDA) were applied to the generated patterns to achieve classification into the five groups of different storage-age wheats and the 15 groups of different degrees of insect-damaged wheat. The results obtained indicated that the E-nose could discriminate successfully among wheats of different age and with different degrees of insect damage.     

Differentiation of closely related fungi by electronic nose analysis

ABSTRACT:  In this work the potential of electronic nose analysis for differentiation of closely related fungi has been described. A total of 20 isolates of the cheese-associated species Geotrichum candidum, Penicillium camemberti , P. nordicum , and P. roqueforti and its closely related species P. paneum , P. carneum as well as the noncheese-associated P. expansum have been investigated by electronic nose, GC-MS, and LC-MS analysis. The isolates were inoculated on yeast extract sucrose agar in 20-mL headspace flasks and electronic nose analysis was performed daily for a 7-d period. To assess which volatile metabolites the electronic nose potentially responded to, volatile metabolites were collected by diffusive sampling overnight onto tubes containing Tenax TA, between the 7th and 8th day of incubation. Volatiles were analyzed by gas chromatography coupled to mass spectrometry and the results indicated that mainly alcohols (ethanol, 2-methyl-1-propanol, and 3-methyl-1-butanol) and ketones (acetone, 2-butanone, and 2-pentanone) were produced at this stage. The volatile metabolite profile proved to be species specific. Nonvolatile metabolites were collected on the 8th day of incubation and mycotoxin analysis was performed by high pressure liquid chromatography coupled to a diode array detector and a time of flight mass spectrometer. Several mycotoxins were detected in samples from the species P. nordicum , P. roqueforti , P. paneum , P. carneum, and P. expansum . Differentiation of closely related mycotoxin producing fungi incubated on yeast extract sucrose agar has been achieved, indicating that there is a potential for predicting production of mycotoxins on food and feedstuffs by electronic nose analysis.     

Use of wheat,triticale and rye flours in layer cake production

In this study, the capacity of obtaining high quality layer cakes from rye and triticale lines was analysed and compared to wheat lines. The samples were characterised considering grain hardness, flour composition and quality parameters as protein, pentosan, damaged starch, pasting viscosity and functional predictive test – solvent retention capacity test. Cakes were analysed in weight, symmetry, volume, volume index (VI) by measuring the height in different points of the cake, crust and crumb colour, crumb structure and texture. Wheat and triticale cakes showed similar characteristics. Rye cakes showed higher volume and lower weight than those with crumbs darker in colour, higher adhesiveness, springiness and resilience. The multiple regression analysis was used to develop an equation for cake volume index prediction. The best‐fit linear regression model was: VI = 14.75 – 0.14 × protein + 0.93 × water soluble pentosan – 0.27 × total pentosan. Despite the differences, high quality cakes can be elaborated with rye, triticale and soft wheat cultivars.     

基于电子鼻和SPME-GC-MS评价烟熏液对熏鲍挥发性风味物质的影响

运用电子鼻区分不同烟熏液处理鲍鱼的香气差异,固相微萃取结合气质联用(SPME-GC-MS)分析挥发性风味成分的变化情况,进而揭示不同熏液处理鲍鱼主要特征风味的成因。结果表明,电子鼻能够灵敏地检测到不同烟熏液处理鲍鱼的香气变化,通过GC-MS分析表明,经过液熏处理后鲍鱼的挥发性风味物质种类和相对含量发生了明显的变化,经Ⅱ-2001超级烟熏液处理的液熏鲍Ⅰ共检测出72种挥发性物质,经Ⅱ-2008A着色烟熏液处理的液熏鲍Ⅱ共鉴定出98种挥发性物质;酚类物质作为烟熏风味的特征风味物质,液熏鲍Ⅰ共检测出19种,含量为47.52%,液熏鲍Ⅱ共检测出22种,含量高达55.94%;GC-MS数据经PCA分析发现,GC-MS能够有效地区分不同烟熏液处理的鲍鱼样品,样品间风味物质的差异结果与电子鼻结果相吻合。     

Geographical origin identification of propolis using GC–MS and electronic nose combined with principal component analysis

Dynamic headspace sampling (DHS) coupled with gas chromatography–mass spectrometry and olfactometry (GC–MS–O) analysis have been applied for the determination of the characteristic volatile profile of propolis with the aim to differentiate the propolis from different regions of China. Acids, esters, alcohols, terpenes, aromatics represented the most abundant compounds in propolis among the ninety-nine volatile components identified by comparing with mass spectra and retention indices (RI) or from literature. In addition, principal component analysis (PCA) based on the data of DHS–GC–MS and electronic nose was used to study and obtain the important volatile compounds contributed to the differentiation of the propolis samples from different regions. Furthermore, a total of 28 odor-active compounds were detected and characterized by the trained panel of judges in the sniffing port of GC–O by using detection frequency analysis (DFA). In conclusion, GC–MS analysis and electronic nose combining with PCA could successfully distinguish the twelve representative raw propolis samples from 4 different geographical regions of China. The samples have been assigned to four large groups in accordance with their vegetal sampling location and we also have observed the volatile compounds resulting in the odor differentiation.     

乳杆菌发酵剂对酸肉挥发性风味成分的影响

分别采用植物乳杆菌、清酒乳杆菌和类植物乳杆菌作为发酵剂对酸肉发酵过程中挥发性风味成分的影响。 电子鼻分析结果表明,酸肉的整体风味随发酵时间的增加差异显著;利用固相微萃取-气相色谱-质谱技术对酸肉发 酵过程中的挥发性风味物质进行检测,结果表明,酯类物质的相对含量显著增加,且增加的主要是乙酯类物质,发 酵结束时,添加植物乳杆菌、类植物乳杆菌和清酒乳杆菌组酸肉的乙酯类物质相对含量（56%、53%和60%）均显 著高于对照组（47%）,说明乳杆菌发酵剂的添加有利于酸肉中乙酯类物质的形成;通过Heatmap聚类分析发现, 发酵结束时,添加乳杆菌发酵剂的3 组酸肉整体风味比较接近,但与对照组差异较大,说明乳杆菌发酵剂的添加影 响了酸肉的风味品质。此外,发酵过程中添加发酵剂的酸肉中乳酸菌数量增加较快,肠杆菌数量显著降低,这保证 了酸肉的食用安全性。     

植物乳杆菌发酵草鱼肉挥发性成分的变化规律

研究植物乳杆菌发酵草鱼的过程中挥发性成分变化规律。利用电子鼻、顶空固相微萃取和气相色谱-质谱联用技术对草鱼发酵不同时间段的挥发性成分进行分析。结果表明,电子鼻能够较好地区分发酵不同阶段的鱼肉样品的风味,各阶段的成分有显著差异,进一步采用气相色谱-质谱法对不同时间的草鱼发酵样品中的挥发性成分进行分析,鉴定出54 种挥发性物质,在发酵过程中,土腥味的己醛、庚醛等醛类物质逐渐减少;蘑菇香味的1-辛烯-3-醇含量逐渐增多,发酵后期产生了有薄荷香味的丙酮,以及有奶油香味的乙偶姻等增香成分,这和感官评定的结果一致。     

基于电子鼻和SPME/GC-MS技术对勐海县晒青茶的挥发性物质分析

为了解勐海县晒青茶的挥发性物质信息,本试验使用电子鼻和顶空固相微萃取（SPME）与气相色谱-质谱（GC-MS）联用技术对勐海县8份晒青茶样品进行挥发性物质检测。电子鼻检测结果表明:8个茶样可分为4组,其中南糯山（NN）、西定（XD）、布朗山（BL）、格朗和（GL）、章家三队（ZJ）的5份茶样为一组,而巴达（BD）、布朗山边境（BJ）、巴达章朗（ZL）分别为一组;硫化物及烃类化合物是电子鼻富集到的晒青茶样的主要挥发性物质。GC-MS结果显示:8个晒青茶样共检测到55种挥发性物质,主要以醇类（9种）、酯类（7种）、醛类（9种）、酮类（6种）、烯烃类（13种）、烷烃类（5种）、杂环类（4种）为主。醇类物质对晒青茶挥发性物质相对含量影响最大,最高为ZL茶样（64.02%）,最低为BJ茶样（37.14%）,主要表现在芳樟醇和植物醇两种物质上。8个晒青茶样中共有的挥发性物质合计19种,含量较高的10种分别是3种醇（芳樟醇、α-松油醇、香叶醇）、2种醛（苯乙醛、藏花醛）、2种酮（β-紫罗兰酮、植酮）、2种杂环类（顺式芳樟醇氧化物、反式芳樟醇氧化物）和1种酯（二氢猕猴桃内酯）。格朗和乡的晒青茶挥发性物质总相对含量高于南糯山乡和西定乡,主要表现在醛类物质上;布朗山乡的晒青茶优势香气物质为酮类和烷烃类;西定乡的优势香气物质为烯烃类,即不同产地的晒青茶具有不同的优势挥发性物质。