Lactobacillus pentosus dominates spontaneous fermentation of Italian table olives

Culture-dependent and -independent approaches were applied to identify the bacterial species involved in Italian table olive fermentation. Bacterial identification showed that Lactobacillus pentosus was the dominant species although the presence of Lactobacillus plantarum, Lactobacillus casei, Enterococcus durans, Lactobacillus fermentum and Lactobacillus helveticus was observed. Rep-PCR allowed to obtain strain-specific profiles and to establish a correlation with table olive environment. PCR-DGGE (Denaturing Gradient Gel Electrophoresis) confirmed the heterogeneity of bacterial community structure in fermented table olives as well as the prevalence of L. pentosus. The strains were characterized on the basis of technological properties (NaCl tolerance, β-glucosidase activity and the ability to grow in synthetic brine and in presence of 1 g/100 mL oleuropein). L. pentosus showed a high capacity of adaptation to the different conditions characterizing the olive ecosystem. This species showed the highest percentage of strains able to grow in presence of 10 g/100 mL NaCl, oleuropein and in the synthetic brine. Moreover, all the strains belonging to L. pentosus and L. plantarum species showed a β-glucosidase activity. This study allowed both to identify the main species and strains associated to Italian table olives and to obtain a lactic acid bacteria collection to apply as starter culture in the process of olive fermentation.     

Evaluation of a single and combined inoculation of a Lactobacillus pentosus starter for processing cv. Arbequina natural green olives

The production of Arbequina naturally green olives is a traditional and spontaneous process in which lactic acid bacteria (LAB) and yeasts are present. To better control the fermentation of olives, strains of LAB and yeasts that had been isolated from brines were used in this study.     

Evolution of aroma volatiles during storage of sourdough breads made by mixed cultures of Kluyveromyces marxianus and Lactobacillus delbrueckii ssp. bulgaricus or Lactobacillus helveticus

Two mixed starter cultures were used for sourdough bread making to evaluate their ability to improve quality and increase bread shelf-life: Lactobacillus delbrueckii ssp. bulgaricus or Lactobacillus helveticus mixed with the lactose fermenting yeast Kluyveromyces marxianus as alternative baker’s yeast. Control sourdough breads (K. marxianus) without the addition of bacteria, were also prepared. The changes on the headspace aroma volatiles during storage were assessed using solid-phase microextraction (SPME) GC–MS analysis. The effect of these changes on bread flavour was evaluated by consumer preference evaluations and the results were co-evaluated with those from the GC–MS analysis. The obtained results showed differences in the volatile composition of the different types of breads examined, as well as dramatic decreases of the number and the amount of volatiles after five days of storage. The sourdough breads made with K. marxianus and L. bulgaricus, had a more complex aroma profile, longer shelf-life and achieved the highest scores in the sensory tests.     

Volatile organic compounds from a Tuber melanosporum fermentation system

A total of 59 volatile organic compounds (VOCs) were identified from Tuber melanosporum fermentation: 53 from its fermented mycelia and 32 from the fermentation broth. Alcohol-derived compounds were predominant in both the fermentation mycelia and the broth, although long chain fatty acids and isoprenoids were, for the first time, also found in the mycelia. The intense wine bouquet properties of the broth arose from several specific flavor substances, including sulfur compounds, pyrazines, furans and jasmones. Comparing the VOCs identified in this work with those previously reported, our results are more similar to the composition of the Tuber fruiting-body than previous Tuber fermentations. The composition and accumulation of flavor volatiles (e.g., pyrazines, sulfur compounds, and esters) and major constituents (e.g., 3-methyl-1-butanol and 2-phenylethanol) in this fermentation were significantly influenced by the sucrose concentration in the medium. The obtained information could therefore be useful in applications to convert the flavors of truffle mycelia similar to those of the fruiting-body by optimising the fermentation process.     

A bacteriocin-like substance produced from Lactobacillus pentosus 39 is a natural antagonist for the control of Aeromonas hydrophila and Listeria monocytogenes in fresh salmon fillets

We studied the ability of Lactobacillus pentosus 39, a BLS (Bacteriocin-like substance)-producing strain, to control the growth of Aeromonas hydrophila ATCC 14715 and Listeria monocytogenes ATCC 19117 artificially added to fresh salmon fillets at refrigeration temperatures and under simulated cold-chain break conditions.At refrigeration temperatures, Lb. pentosus 39 protective culture and its putative bacteriocin significantly reduced A. hydrophila counts compared with the control (2.1 and 1.4 log CFU/g reductions, respectively). Similar behaviour was observed for L. monocytogenes (3.6 and 1.3 log CFU/g reductions, respectively).Under simulated cold-chain break conditions, an increase in temperature (30°C for 12h) produced an evident increase in the development of A. hydrophila, L. monocytogenes, but also of Lb. pentosus 39, with a consequent increase in BLS production. This condition resulted in a greater reduction of both pathogens compared with samples stored at 4°C throughout the experiment (2.8 log CFU/g reduction for A. hydrophila, 5.8 log CFU/g reduction for L. monocytogenes). In samples treated with the putative bacteriocin alone, a less marked decrease was observed.Our study demonstrates the capability of Lb. pentosus 39 to control the growth of psychrotrophic bacteria in an experimental seafood model system. A similar biopreservation technology could provide more prolonged shelf-life during storage of ready-to-eat seafood, ensuring safety, even under extreme conditions.     

基于电子鼻、HS-GC-IMS和HS-SPME-GC-MS 对5种食用植物油挥发性风味成分分析

采用电子鼻、顶空气相色谱-离子迁移谱(HS-GC-IMS)和顶空固相微萃取-气相色谱-质谱联用(HS-SPME-GC-MS)法对5种食用植物油(花生油、大豆油、玉米油、油茶籽油、棕榈油)中挥发性成分进行分析,并采用相对气味活度法确定关键风味物质。结果表明:电子鼻检测发现花生油与油茶籽油气味轮廓相似,但花生油气味浓度大于油茶籽油,大豆油、玉米油和棕榈油整体气味差异相对较小且浓度较低; HS-GC-IMS共检出5种食用植物油56种化合物(其中定性24种),定性的共有风味化合物为戊醛(单体)、己醛(单体)、庚醛、1-戊醇(单体)、1-丙醇、2-丁酮(单体)、辛醛和丁醛(单体),并得到5种食用植物油差异图谱; HS-SPME-GC-MS鉴定出5种食用植物油86种化合物,共有关键风味化合物为己醛、壬醛和庚醛,花生油、大豆油和棕榈油特有关键风味化合物分别为吡嗪类化合物、(E,E)-2,4-庚二烯醛和6-甲基-5-庚烯-2-酮。     

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.     

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。     

鲜白果和熟制白果挥发性成分的分析

采用固相微萃取和气质联用(SPME-GC-MS)技术对鲜白果、微波熟制白果和煮制熟制白果挥发性化合物进行测定,并利用主成分分析法(PCA)对三者的挥发性化合物进行比较分析。结果表明:熟制白果与鲜白果挥发性化合物存在较大差异,从中共检出66种挥发性化合物。鲜白果中检出44种,主要挥发性成分为醛类;微波熟制白果中检测出35种挥发性成分,醇类相对含量较高;煮制熟制白果中有31种挥发性成分被检测出,萜类含量和种类最高。PCA分析发现新鲜白果的挥发性成主要指向醛类,微波和煮制熟制白果的挥发性成分主要指向萜类。     

Temporal gene expression and probiotic attributes of Lactobacillus acidophilus during growth in milk

Lactic acid bacteria have been used as starter strains in the production of fermented dairy products for centuries. Lactobacillus acidophilus is a widely recognized probiotic bacteria commonly added to yogurt and used in dietary supplements. In this study, a whole genome microarray was employed to monitor gene expression of L. acidophilus NCFM cells propagated in 11% skim milk during early, mid and late logarithmic phase, and stationary phase. Approximately 21% of 1,864 open reading frames were differentially expressed at least in one time point. Genes differentially expressed in skim milk included several members of the proteolytic enzyme system. Expression of prtP (proteinase precursor) and prtM (maturase) increased over time as well as several peptidases and transport systems. Expression of Opp1 (oligopeptide transport system 1) was highest at 4 h, whereas gene expression of Opp2 increased over time reaching its highest level at 12 h, suggesting that the 2 systems have different specificities. Expression of a 2-component regulatory system, previously shown to regulate acid tolerance and proteolytic activity, also increased during the early log and early stationary phases of growth. Expression of the genes involved in lactose utilization increased immediately (5 min) upon exposure to milk. The acidification activity, survival under storage conditions, and adhesion to mucin and Caco-2 tissue culture cells of selected mutants containing insertionally inactivated genes differentially expressed in the wild-type strain during growth in milk were examined for any potential links between probiotic properties and bacterial growth and survival in milk. Some of the most interesting genes found to be expressed in milk were correlated with signaling (autoinducer-2) and adherence to mucin and intestinal epithelial cells, in vitro.     

Volatile compounds produced by the probiotic strain Lactobacillus plantarum NCIMB 8826 in cereal-based substrates

The production of volatile compounds by the probiotic strain, Lactobacillus plantarum NCIMB 8826, in cereal-based media (oat, wheat, barley and malt) was investigated. Sixty compounds, including fatty acids and their esters, amides, alcohols, aldehydes, aromatic hydrocarbons, furans, ketones, peroxides and pyrans, were identified. L. plantarum significantly changed the aroma profile of the four cereal broths, and each substrate showed a specific volatiles profile. Oat and barley media were the substrates more influenced by the fermentation process. The most abundant volatiles detected in oat, wheat, barley and malt were oleic acid, linoleic acid, acetic acid, and 5-hydroxymethylfurfural, respectively. Analysis of these products confirmed the heterofermentative pathway of L. plantarum. Maillard compounds were not detected during sterilisation and fermentation. This study is the first to report the volatile composition of probiotic drinks produce with non-supplemented cereal-based media and the results obtained could contribute to the development of new non-dairy probiotic formulations.     

HS-SPME结合GC-MS分析麻婆豆腐中挥发性风味成分

测定麻婆豆腐中挥发性风味成分,对中式菜肴风味稳定及工业化生产有重要贡献。采用顶空固相微萃取（HS-SPME）,结合气质联用技术（GC-MS）分析了实验室自制麻婆豆腐中挥发性风味成分,并对萃取头、预热时间、萃取时间、萃取温度进行了优化。确定了较佳的萃取条件:采用65μm PDMS/DVB的纤维萃取头,60℃预热30 min,萃取30 min。通过GC-MS检测,在麻婆豆腐中一共检测出挥发性风味物质共74种,主要包括烷烯烃类、醇类、醛类、脂类等化合物。含量较多的物质有:萜品油烯、左旋-beta-蒎烯、月桂烯、3-蒈烯、b-侧柏烯、（-）-柠檬烯等。研究表明,顶空固相微萃取技术及气质联用技术能很好的用来分析麻婆豆腐中的挥发性风味物质,且样品萃取条件的不同对麻婆豆腐风味成分的准确测定具有一定影响;不同种类的麻婆豆腐的在感官评鉴上也有所差异。      

基于HS-SPME-GC-MS和电子鼻技术研究不同肉质桃子采后贮藏期的香气成分

以Stony hard型桃子“霞脆”、硬溶质型桃子“霞晖6号”和软溶质型桃子“湖景蜜露”为研究对象,利用顶空固相微萃取-气相色谱-质谱联用（headspace solid-phase microextraction combined with gas chromatography-mass spectrometry,HS-SPME-GC -MS）结合电子鼻技术对3 种不同肉质桃子在采后20 ℃贮藏的挥发性风味物质进行研究。结果表明,3 种不同溶质桃子利用HS-SPME-GC-MS技术共检测出45 种香气物质,主要包括醛类、醇类、酯类、酮类、内酯类、萜烯类和烷类化合物,桃子采后贮藏期内香气物质种类和含量有显著性差异。“霞脆”、“霞晖6号”、“湖景蜜露”桃子贮藏期内分别检测出香气物质40、27、17 种。随着贮藏时间延长,3 种不同肉质桃子的香气物质总含量均呈下降趋势。从主成分分析结果可知,电子鼻技术可以很好地区分不同贮藏期的桃子。载荷分析结果显示,传感器W1S、W5C、W3C、W1C、W1W、W2W对桃子在贮藏期的区分能力最强。HS-SPME-GC-MS结合电子鼻可以很好地评价桃果实在贮藏期的香气品质差异。     

甜面酱保温发酵过程中挥发性成分的动态变化

本文采用顶空固相微萃取与气相色谱质谱联用技术（HS-SPME/GC-MS）研究甜面酱在保温发酵过程中不同阶段的风味物质组成情况,并对风味成分的相对含量进行主成分分析。结果表明,在甜面酱保温发酵过程中,主要挥发性风味成分包括醇类9种,酯类20种,醛类10种,酚类2种,酮类1种,呋喃2种,烷烃类2种,其他化合物类3种,共49种,经主成分分析综合评价,发酵7周（49 d）的甜面酱风味最佳。      

固相微萃取-气相色谱-质谱联用法测定传统酸肉发酵过程中特征挥发性成分

通过固相微萃取-气相色谱-质谱联用仪对鲜肉及发酵10、30、50?d酸肉的挥发性物质进行鉴定,探究传统发酵酸肉中挥发性成分种类及含量变化.结果表明:4个时期的肉样中共检出106种挥发性物质,其中酯类32种、酸类2种、醇类11种、醛类16种、酮类3种、碳氢化合物29种及其他类化合物13种;采用主成分分析、偏最小二乘判别分...     

Fermentation characteristics and transit tolerance of probiotic Lactobacillus casei Zhang in soymilk and bovine milk during storage

Lactobacillus casei Zhang is a novel strain that was screened out of koumiss collected in Inner Mongolia, and our previous research showed that L. casei Zhang has health benefits such as cholesterol-reducing and immunomodulating effects. The fermentation characteristics of L. casei Zhang in soymilk and bovine milk and the transit tolerance of L. casei Zhang in fermented milk products during refrigerated storage for 28 d were assessed. A faster decrease in pH and faster growth of L. casei Zhang during fermentation were observed in soymilk compared with bovine milk at various inoculation rates, probably because of the low pH buffering capacity of soymilk. The fermented bovine milk samples had much higher final titratable acidity (TA) values (between 0.80 and 0.93%) than the soymilk samples (between 0.40 and 0.46%). Dramatic increases in TA values in the fermented soymilk samples during storage were observed, and the TA values of the fermented soymilk samples changed from <0.56% to values between 0.86 and 0.98%. On the other hand, only slight increases in TA were observed in the bovine milk samples during the 28 d of storage. The survival rates of freshly prepared cultures of L. casei Zhang in simulated gastric juice at pH 2.0 and 2.5 were 31 and 69%, respectively, and the delivery of L. casei Zhang through fermented soymilk and bovine milk significantly improved the viability of L. casei Zhang in simulated gastric transit. Lactobacillus casei Zhang showed good tolerance to simulated gastric juice and intestinal juice in the fermented soymilk and bovine milk samples, and maintained high viability (>10⁸ cfu/g) during storage at 4°C for 28 d. Our results indicated that both soymilk and bovine milk could serve as vehicles for delivery of probiotic L. casei Zhang, and further research is needed to elucidate the mechanism of the change in pH and TA of L. casei Zhang in fermented milk samples during fermentation and storage and to understand the difference between soy- and milk-based systems.     

GC-MS结合电子鼻分析干燥方式对杏鲍菇挥发性风味成分的影响

为明确干燥方式对杏鲍菇挥发性风味成分的影响,利用电子鼻和顶空固相微萃取结合气相色谱-质谱联用技术对冷冻干燥（freeze drying,FD）、热风干燥（hot air drying,HAD）、中短波红外干燥（short-and mediumwave infrared drying,ID）和微波真空干燥（microwave vacuum drying,MVD）制得的杏鲍菇干燥样品进行挥发性成分分析,并进一步对这4 种干样的挥发性成分进行主成分分析。结果表明：电子鼻对挥发性成分从整体上进行分析,发现线性判别分析能够很好地区分不同干燥方式的杏鲍菇样品。利用HS-SPME-GC-MS从鲜样（fresh sample,FS）及4 种干样中鉴定出99 种挥发性物质,包括醇类、醛类、酮类、酯类、烷烃类和其他类化合物共6 类成分,其中醇类物质（19 种）为FS、FD、HAD和ID样品中的主要挥发性物质,醛类物质（18 种）为MVD样品中的主要挥发性成分,不同干燥方式制得的杏鲍菇主要挥发性成分差异显著。对不同干燥方式制得的杏鲍菇样品挥发性物质进行主成分分析,建立其品质评价模型,得出干样的综合得分顺序依次为ID、FD、HAD及MVD,为杏鲍菇的干燥加工提供了理论依据。     

Study of volatile organic acids in freeze-dried Cheonggukjang formed during fermentation using SPME and stable-isotope dilution assay (SIDA)

Volatile organic acids in freeze-dried Cheonggukjang were quantified using a stable-isotope dilution assay (SIDA) according to the fermentation period. Five organic acids, acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, and 3-methylbutanoic acid, were identified using solid-phase microextraction (SPME) in conjunction with gas chromatography–mass spectrometry (GC–MS). The contents of volatile organic acids in Cheonggukjang were highly dependent on the fermentation period and they increased during fermentation. Moreover, the branched-chained organic acids (namely 2-methylpropanoic acid and 3-methylbutanoic acid) were formed earlier and were present at much higher contents than the corresponding straight-chained organic acids during Cheonggukjang fermentation.     

基于电子鼻与SPME-GC-MS法分析咸鲅鱼加工过程挥发性风味成分变化

本文研究咸鲅鱼加工过程中挥发性风味成分的变化情况。采用电子鼻与固相微萃取-气质联用法(SPME-GC-MS)分别检测鲜鱼、腌制、干制4、10、24、36、48 h 7个不同阶段的风味成分变化。结果表明,腌制和干燥阶段风味变化明显。7个阶段挥发性风味成分种类数分别为27、37、53、42、47、45种以及51种。其中,成品咸鱼中三甲胺、乙二醇单丁醚、己醛、1-戊烯-3-醇、壬醛、正辛醛、庚醛、异戊醛含量较高,相对含量分别为11.05%、7.21%、6.65%、6.35%、5.69%、4.56%、3.52%和3.37%。腌制和干燥是风味产生的主要加工阶段。醛类、醇类、酮类和烃类是主要的挥发性物质的种类,其中己醛、壬醛、正辛醛、庚醛、(Z)-4-庚烯醛、苯甲醛、1-戊烯-3-醇、1-辛烯-3-醇是咸鲅鱼风味的主要成分。因此可通过控制腌制和干燥条件改善咸鲅鱼风味。     

葡萄冷藏时间对贮后货架期芳香物质的影响

为明确冷藏时间对葡萄贮后货架期芳香物质的影响,以‘无核寒香蜜’葡萄为试材,运用顶空固相微萃取-气相色谱-质谱（head space solid-phase microextraction and gas chromatography mass spectrometry,HS-SPME-GCMS）联用技术检测冷藏15、45 d出库后常温货架期间（0、3、6 d）挥发性成分的变化,并采用电子鼻对不同冷藏期（15、30、45、60 d）出库后常温货架的果实进行判别分析。结果表明,葡萄的挥发性成分主要由酯类、醛类和醇类组成,主要挥发性成分为乙酸乙酯、青叶醛、正己醇、叶醇、香茅醇。冷藏45 d后常温货架期间酯类和醇类物质的相对含量均低于冷藏15 d同期果实,醛类物质则较高。电子鼻结果表明,通过线性判别分析可以有效区分不同冷藏期的葡萄,贮后货架期间,除冷藏15 d出库后0、3 d货架重叠外,其余冷藏期货架期间均互不重叠,即随着贮后常温货架的延长,葡萄中挥发性成分变化较大,电子鼻区分效果越加明显;负荷加载分析分析得出,W1W（硫化氢、萜烯类）、W1S（芳香成分）、W2S（乙醇）传感器对挥发性气味的贡献较大,与HS-SPME-GC-MS分析相佐证。因此,HS-SPME-GC-MS结合电子鼻对葡萄冷藏时间及贮后货架期的芳香物质判别具有可行性。