Comparison of microbiota and volatile organic compounds in milk from different sheep breeds

In this study, we compared the microbiota and volatile organic compounds (VOC) present in the milk obtained from 3 different sheep breeds, namely Merino, Lacaune, and Assaf. Udder milk was collected from 21 animals, 7 from each breed. Bacterial microflora was determined metagenomically by extracting the DNA from the milk and analyzing the V3-V4 region of the 16S rRNA gene. Headspace solid-phase microextraction gas chromatography-mass spectrometry method was used to analyze VOC. The metagenomic analysis revealed (for Merino, Lacaune, and Assaf milk, respectively) Firmicutes (66.32, 69.36, and 57.08%), Actinobacteria (19.09, 7.67, and 19.40%), Proteobacteria (13.76, 21.06, and 22.19%), and Bacteroidetes (0.84, 1.91, and 1.33%) phyla in the milk samples. Lactobacillus was highly abundant in the milk of 3 breeds (29.64, 43.50, and 18.70%). The genera constituting more than 2% of all bacteria in all groups were Jeotgalicoccus (7.19, 5.34, and 10.77%), Enterococcus (5.18, 9.78, and 3.64%), and Corynebacterium (4.08, 3.00, and 13.44%). A total of 32 different VOC were identified by headspace solid-phase microextration analysis with 9, 30, and 24 different compounds from Merino, Lacaune, and Assaf breeds, respectively. Although ketone was the most abundant compound in Merino milk (71.84%), hydrocarbons were the most detected in Lacaune and Assaf milk (37.18% and 55.42%, respectively). A positive correlation was found between acetone, which was detected at the highest level in all groups, with Salinicoccus, Alloiococcus, Psychrobacter, and Dietzia. In addition, a negative correlation was found between the Lactobacillus genus, detected at the highest level in all groups, with methyl cyclopentane, 3-methylheptane, octane, decane, 3,3-dimethyloctane, and dodecane. Thus, differences were observed in the bacterial microflora and VOC in the sheep milk from different breeds under different feeding and breeding conditions.     

The production characteristics of volatile organic compounds and their relation to growth status of Staphylococcus aureus in milk environment

In our previous research, 3-methyl-butanal and 3-methyl-butanoic acid were identified as representative and specific volatile organic compounds released by Staphylococcus aureus in broth. In this study, we explored the production of the 2 volatiles and their correlation to Staph. aureus growth in milk under different conditions. We found significant correlations between the production of 3-methyl-butanoic acid and cell counts of 5 Staph. aureus strains in sterile milk, and there were no obvious differences for its production among 5 tested strains. The intensities of the 2 volatiles were similar and positively correlated with bacterial counts in cultures at 25°C and 37°C despite delayed production of volatiles at 25°C; however, neither compound could be detected at 4°C. The production of 3-methyl-butanoic acid was strongly correlated with growth of Staph. aureus mixed with Streptococcus agalactiae, Escherichia coli O157:H7, and Shigella flexneri, whereas correlations for 3-methyl-butanal were not statistically significant. Compared with the monoculture of Staph. aureus, in mixed cultures, production of 3-methyl-butanal was decreased and that of 3-methyl-butanoic acid was comparatively higher. In pasteurized and raw milks, production of 3-methyl-butanoic acid was correlated with growth of Staph. aureus, and 3-methyl-butanoic acid could be detected when Staph. aureus populations reached 10⁶ to 10⁷ cfu/mL in pasteurized milk and 10⁵ to 10⁶ cfu/mL in raw milk; the correlations for 3-methyl-butanal were not statistically significant. Our results suggest that 3-methyl-butanoic acid is a more suitable marker for high counts of Staph. aureus in milk, whereas 3-methyl-butanal is a transient metabolite and easily depressed by environmental factors.     

SPME-GC-MS对不同牛奶香精和稀奶油中的挥发性风味物质比较

利用SPME-GC-MS分析方法,分析比较了稀奶油与不同牛奶香精中挥发性风味组分。稀奶油中共鉴定得到58种挥发性化合物,复配香精A、天然香精B和自制酶解香精C中分别鉴定得到67种、41种和30种挥发性化合物。通过对不同奶油香精与稀奶油风味中挥发性化合物的比较,得到稀奶油中的主要挥发性物质为甲基酮类、醛类化合物,复配香精A中的主要挥发性物质为酯类化合物;天然香精B与自制酶解香精C中的主要挥发性风味组分相似,均为中、短碳链的脂肪酸。     

The diversity of microbial communities in Chinese milk fan and their effects on volatile organic compound profiles

Milk fan is a cheese-like fermented milk product produced in Yunnan Province, China. In this study, we characterized the microbial communities of milk fan from 6 distinct geographical origins and investigated their generation of volatile organic compounds (VOC). The microbial communities found in all milk fan samples were dominated by Lactococcus, Lactobacillus, and Raoultella bacteria and Rhodotorula, Torulaspora, and Candida fungi. Samples from the Kunming and Weishan regions had greater bacterial richness, and samples from Xizhou had greater fungal community richness. Sixty prominent VOC (i.e., those having odor activity values ≥1), including esters, acids, alcohols, aldehydes, ketones, and aromatic compounds, were identified by gas chromatography-mass spectrometry analysis of milk fan samples. Pearson correlation analysis revealed that Lactobacillus, Rhodotorula, Lodderomyces, and Debaryomyces had significant correlations with various VOC, revealing a total of 13 compounds that are characteristic of the odor of milk fan. These bacteria and fungi are therefore identified as functional microorganisms that collectively create the complex VOC profile of milk fan. This study provides a comprehensive overview of the microbial community of milk fan and demonstrates its contribution to the unique aroma profile of this fermented milk product     

Short communication: Volatiles in microfluidized raw and heat-treated milk

As innovative processing equipment is introduced to milk processing, it is essential to determine its effect on milk aroma, a critical factor in consumer acceptance of the final dairy product. Microfluidization is known to cause severe high-pressure homogenization of milk fat and, although severe processing is known to release undesired aromas, no information is available on the levels of the volatile compounds in milk immediately after microfluidization. We hypothesized that microfluidization would alter levels of volatile compounds in milk that may affect aroma. The concentration of 11 selected volatile compounds in raw, thermized, pasteurized, and UHT 3.0% fat milk samples were compared before and after microfluidization at 170 MPa and common 2-stage homogenization at 15 MPa. Overall, the different milk samples had similar trends in response to homogenization, although UHT milk started with lower values of nonanoic acid, and acetone and higher levels of hexanal and heptanol. In many cases, microfluidization did not significantly alter volatile levels compared with the starting milk. Heptanal was the only compound observed to increase in thermized and UHT milk, whereas nonanoic acid and acetone decreased in raw, thermized, and pasteurized milks and octanoic acid decreased in thermized and UHT milks. The highest levels of almost all of the volatiles were found in the 2-stage homogenized milk. Overall, microfluidization had minimal effect on the volatile compound profiles of milk, although sensory evaluation is needed to confirm effects on aroma and flavor.     

Compositional characteristics and volatile organic compounds of traditional PDO Feta cheese made in two different mountainous areas of Greece

The compositional characteristics of Feta cheese manufactured in two mountainous areas from raw milk, from sheep fed by grass, and the forages’ volatile organic compounds (VOC) were studied, to differentiate the Feta cheese. Although the main compositional features did not vary greatly, the proteolysis mode was altered. The VOC profiles of the cheeses varied. While some VOCs were common to both groups of cheeses, others were discriminatory for each production area. There were common terpenes in both the bulk forage and the mature cheeses. Overall, the VOC composition of Feta could provide a basis for identification with regard to its region of origin.     

三种市售牛奶巧克力气味活性化合物的对比及其与感官知觉的关系

应用DHDA和顶空感官鉴评对三种市售牛奶巧克力的主要气味活性化合物进行了鉴定和对比。共有23种主要气味活性化合物被鉴定。定量数据及感官鉴评数据应用主成分分析法（PCA）进行了分析。结果表明,巧克力A除在己醛（青草香）、戊基呋喃（甜香）、三甲基吡嗪（坚果香）有较高浓度水平,其它化合物浓度水平都较其它两种品牌巧克力都要低;巧克力C在2-壬酮（甜香、蜜香）、乙酸（酸香、尖刺）、四甲基吡嗪（烤香,焦香）、苯甲醛（苦杏仁香）、2-甲基丙酸（腐臭）、呋喃甲醇（药香）、3-甲基丁酸（酸臭）、乙酸苯乙酯（花香、蜜香）、苯甲酸异戊酯（甜香、花香）这些化合物浓度指标上都比其它两种品牌巧克力要高且较突出;而B巧克力的呈强烈黑巧克力香的3-甲基丁醛（麦芽香、可可香）含量尤为突出,且具有较高含量的二甲基吡嗪类（爆米花香）、糠醛（土豆香）、苯甲醇（药香）、苯乙醇（玫瑰香）、苯并噻唑（橡胶味）、乙酰基吡咯（坚果香）,其它的一些呈烤香、坚果香的物质含量也较高。结合感官鉴评数据进行相关性分析表明,在牛奶巧克力中,3-甲基丁醛、苯乙醇主要贡献黑巧克力香韵,乙酸、2-甲基丙酸,3-甲基丁酸主要贡献酸香韵,四甲基吡嗪、乙酸苯乙酯主要贡献烤/坚果香韵。另外,清甜香韵和奶香韵与其它香韵有明显负相关作用。      

食源性腐败菌挥发性有机化合物的研究进展

食源性腐败菌是食品腐败的重要原因, 它可通过初级或次级代谢产生具有异味的挥发性有机化合物(volatile organic compounds, VOCs), 加速食品的腐败进程。腐败菌种类及组成会随食品基质和贮藏条件而改变, 导致产生的VOCs也具有多样性和差异性。随挥发性有机物质收集和检测技术的快速发展, 通过分析腐败菌相关的VOCs成分组成可鉴别食源性腐败菌种类和食物腐败进程。本文对常见腐败菌VOCs的产生途径和种类进行归纳, 并重点探讨了VOCs提取分析技术及在食品腐败研究中的具体应用, 为有效进行腐败菌防控, 提升食品质量和安全提供参考。     

Volatile organic compounds profile during milk fermentation by Lactobacillus pentosus and correlations between volatiles flavor and carbohydrate metabolism

Flavor, as one of the most important properties determining the acceptability and preference of fermented milks, is influenced by compositional and processing factors. In this study, we focused on the volatile organic compounds related to flavor during milk fermentation by Lactobacillus pentosus according to electronic nose analysis. Xylose (1% addition) metabolized by Lb. pentosus strongly affects the flavor of yogurt, with the potent volatile organic compounds of ethanol (3.08%), 2,3-butanedione (7.77%), and acetic acid (22.70%) detected using solid-phase microextraction coupled with gas chromatography-mass spectrometry analysis. Sensoryanalysis also showed skimmed yogurt fermented by Lb. pentosus with 1% xylose had the unique scores of sourness (acetic acid) and butter flavor (2,3-butanedione). Furthermore, α-acetolactate synthase and α-acetolactate decarboxylase in carbohydrate metabolism play important roles in milk fermentation. Under preferable conditions (pH 5.5, 42°C) for α-acetolactate synthase and α-acetolactate decarboxylase, the relative content of potent flavor compound 2,3-butanedione was 10.13%, which was 2.55% higher than common culture condition (pH 4.5, 37°C), revealing that xylose metabolized by Lb. pentosus has potential values for the milk product industry, such as the acceptability and preference of fermented milk product.     

Volatile compounds, odor, and aroma of La Serena cheese high-pressure treated at two different stages of ripening

La Serena cheeses made from raw Merino ewe's milk were high-pressure (HP) treated at 300 or 400 MPa for 10 min on d 2 or 50 after manufacture. Ripening of HP-treated and control cheeses proceeded until d 60 at 8°C. Volatile compounds were determined throughout ripening, and analysis of related sensory characteristics was carried out on ripe cheeses. High-pressure treatments on d 2 enhanced the formation of branched-chain aldehydes and of 2-alcohols except 2-butanol, but retarded that of n-aldehydes, 2-methyl ketones, dihydroxy-ketones, n-alcohols, unsaturated alcohols, ethyl esters, propyl esters, and branched-chain esters. Differences between HP-treated and control cheeses in the levels of some volatile compounds tended to disappear during ripening. The odor of ripe cheeses was scarcely affected by HP treatments on d 2, but aroma quality and intensity scores were lowered in comparison with control cheese of the same age. On the other hand, HP treatments on d 50 did not influence either the volatile compound profile or the sensory characteristics of 60-d-old cheese.     

纺织品有机挥发物的测定

采用直接顶空进样和顶空-固相微萃取进样的方法，以测定纺织品中有机挥发物的含量，由气相色谱-质谱联用仪进行定性分析，外标法进行定量分析。本方法对目标化合物的检测限低于0．005mg／kg，加标回收率在88％～97％，相对标准偏差小于9％。     

Volatile organic compounds from the interaction between Fusarium verticillioides and maize kernels as a natural repellents of Sitophilus zeamais

Maize kernels are exposed to Sitophilus zeamais attack and Fusarium verticillioides infestation during storage, which can result in product deterioration and economic losses. The objective of this study was to evaluate the involvement of the Volatile Organic Compounds (VOCs) emitted by the fungi-corn system in grain-insect interactions. Volatiles emitted by healthy maize kernels were different from those emitted by fungal infected kernels, with the latter being enriched by alcohols, ketones and sesquiterpenes, which were considered early indicators of fungal contamination. The results demonstrated that the kernels exposed to the fungal VOCs and their pure compounds (1-octen-3-ol and 3-octanol) were less attractive and less damaged by S. zeamais than controls. In addition to compound adsorption, other processes may have caused the protective effect of exposed kernels against insect damage. This is the first contribution of the role of the fungal volatiles on the behavior of S. zeamais, and could provide an important contribution to the conservation of stored grains and pest management and an early indicator of fungal contamination.     

GC/MS法分析烟用接装纸中挥发性有机化合物

建立了顶空-气质联用(HS-GC/MS)法,对烟用接装纸中挥发性有机化合物(VOCs)残留量进行测试.结果表明:(1)该方法检测限为0.001-0.004 mg/mL,回收率为89.35％- 108.96％,相对标准偏差(RSD)＜4％;(2)所有52个被检烟用接装纸榉品均为合格样品,所有样品中均未检出苯、乙苯、二甲苯、乙酸异丙酯、丁酮,YC171-2009《烟用接装纸》标准中规定的5种VOCs成分中只有乙酸正丁酯有个别检出;(3)醇类检出率较高,其中所有样品都有乙醇检出,异丙醇、正丁醇的检出率也比较高;(4)丙二醇甲醚有较高的检出率,且其检出量相对较大.研究结果充分说明,该方法适合于烟用接装纸中VOCs的快速批量检测.     

基于气相-离子迁移谱技术分析不同生长速度肉鸡肌肉中挥发性有机物的差异

基于气相-离子迁移谱(gas chromatography-ion mobility spectroscopy,GC-IMS)技术分析不同生长速度肉鸡品种肌肉中挥发性有机物的差异。试验选取慢速型鸡(狼山鸡)、中速型鸡(3A,花山麻鸡)、快速型鸡(罗斯308),每个品种母鸡6只,取胸大肌同一部位进行GC-IMS测定。根据GC-IMS法测得85种挥发性有机物,已定性物质29种,主要包括醛类、酮类、醇类等化合物。慢速型狼山鸡肉中醛类和醇类含量显著高于其他类型的3个品种(P <0.05),主要特征物质包括反-2-辛烯醛、戊醛、壬醛、己醛、1-丁醇、乙醇、1-戊醇、1-辛烯-3-醇;中速型3A和花山麻鸡特征物质相似,3-羟基-2-丁酮、乙酸乙酯含量极高;快速型罗斯308大部分物质含量较低,主要特征物质为3-戊酮。综上所述,GC-IMS可以对不同生长速度鸡品种肉品质的风味进行差异分析,可直观和快速地看出不同生长速度鸡品种挥发性有机物的特异性、含量差异和相似度,也可明显区分不同生长速度鸡品种。     

Characterization of volatile compounds and organic acids in ultra-high-temperature milk packaged in tetra brik cartons

A study was conducted to evaluate the basic chemical composition, organic acids and volatile compound profiles of ultra-high-temperature milk samples sold in Turkey. The organic acids were determined by reverse-phase high-performance liquid chromatography method, and volatile compounds were analyzed by headspace solid phase micro-extraction/gas chromatography/mass spectrometry technique. A total of 43 volatile compounds including 4 aldehydes, 5 alcohols, 10 ketones, 9 acids, 9 aromatic hydrocarbons, 3 nitrogenous, 2 sulfur containing compounds, and 1 alkane hydrocarbon, were identified in the ultra-high-temperature milk samples. The main compounds were found to be oxime methoxy phenyl, 2-heptanone, 2-mercapto-4-phenylthiazole, 2-amino-5-ethoxycarbonyl benzophenone, acetic acid, 2,6,10,14-tetramethyl pentadecane, and 2-nonanone. The main organic acid in the ultra-high-temperature milk was citric acid a mean value of 133 mg/100 mL, followed by formic, lactic, succinic, oxalic, acetic, orotic, propionic, pyruvic, hippuric, and uric acids.     

环境检测中挥发性有机物检测方法研究

为了使本文所讨论的方向得到有关部门的重视及支持,促进检测技术的进步,本文进行了一系列的检测和试验,介绍了环境中挥发性有机化合物的检测方式,并加强对环境试验中挥发性有机物的分析和总结,为今后的制备方法提供坚实的基础和标准.     

Changes in volatile aroma compounds of organic fragrant rice during storage under different conditions

BACKGROUND: Aroma of fragrant rice greatly affects palatability as well as consumer acceptability. Loss of desirable volatile compounds such as 2‐acetyl‐1‐pyrroline (2‐AP) and increase in volatile lipid oxidation products in aged rice have been reported. The aim of this study was to monitor the changes in key volatile compounds of organic red fragrant rice cv. Hom Daeng during storage. Effects of packaging material, storage temperature and time were evaluated using solid phase microextraction/gas chromatography/mass spectrometry. RESULTS: Thirteen key volatile compounds including ten lipid oxidation products were monitored. For samples vacuum packed in Nylon/LLDPE pouches at ambient temperature, significant increases in hexanal, 2‐pentylfuran, 1‐octanol and 4‐vinyl guaiacol and significant decreases in 2‐AP and geranyl acetone were found after the second month (P?0.05). Vacuum packing in OPP/Al/LLDPE pouches or storage at 15 °C better retarded the formation of volatile lipid oxidation products and greater retained desirable odorants, including 2‐AP. However, accumulation of lipid oxidation products and 4‐vinyl guaiacol was apparent after the sixth month under these storage conditions. CONCLUSION: A greater extent and higher rate of undesirable changes in volatile compounds were found in samples stored under Nylon/LLDPE/ambient temperature condition. Nevertheless, this condition is acceptable for the retail trade of organic rice in Thailand. Storage conditions using reduced temperature or better packaging materials may be more appropriate for exported rice or superior‐grade fragrant rice to better maintain the desirable rice aroma. Copyright © 2010 Society of Chemical Industry     

Volatile organic compounds in human milk: methods and measurements

The present study was conducted to optimize methods for measurement of volatile organic compounds (VOCs) by use of headspace solid-phase microextraction (HS-SPME) and to provide a preliminary assessment of levels in human milk. MTBE (methyl tert-butyl ether), chloroform, benzene, and toluene were measured from two sources of milk: a North Carolina milk bank (n = 5) and multiple samples from three women within nonsmoking households in inner-city Baltimore, MD (n = 8). In Baltimore, indoor air VOC concentrations in the respective households were also measured by active sampling and thermal desorption gas chromatography/mass spectrometry in selective ion monitoring (GC/MS/SIM) over each of the 3 days of milk collection. By application of these optimized methods, we observed median VOC concentrations in Baltimore human milk of 0.09, 0.55, 0.12, and 0.46 ng/mL for MTBE, chloroform, benzene, and toluene, respectively. For benzene, toluene, and MTBE, milk levels trended with observed indoor air concentrations. On the basis of measured concentrations in air and milk, infant average daily dose by inhalation exceeded ingestion rates by 25-135-fold. Thus, VOC exposure from breast milk is vastly exceeded by that from indoor air in nonsmoking households. Accordingly, strategies to mitigate infant VOC exposure should focus on the indoor air inhalation pathway of exposure.     

藻类挥发性物质及其提取方法研究进展

文章介绍了藻中挥发性物质的组成及风味特征,分析了藻中挥发性醛、酮、醇的形成机制,对比了同时蒸馏萃取法、液—液萃取法、动态顶空提取法和固相微萃取技术等几种常用的藻类挥发性物质的提取方法的优缺点,并对藻类挥发性物质今后的研究方向及其提取、分离检测方法进行了展望.