THE AROMA COMPONENTS PRODUCED BY YEAST IN NITROGEN-FREE SUGAR SOLUTION

In nitrogen-free sugar fermentation yeast produces several other volatile compounds in addition to ethanol. Most of these compounds are distilled over with the ethanol. When the aroma components obtained from the ethanol fraction of a nitrogen-free sugar fermentation were compared with the aroma components of whisky, they showed a qualitatively striking similarity. There was a clear difference in the proportions of the components, however, a fact for which the distillation procedure might be at least partly responsible. The distillate obtained from the fermented sugar solution contained iso-amyl alcohol and β-phenethyl alcohol as well as the ethyl esters of caproic, caprylic, capric, lauric and palmitic acids in considerable amounts. The same acids also appeared as main components among the free acids and, further, isobutyric and isovaleric acid were found quite abundantly. The similarity between the aroma compounds formed in nitrogen-free sugar fermentation and the aroma fraction of alcoholic beverages indicates that the yeast is responsible for the bulk of the aroma compounds produced.     

Impact of starter cultures and fermentation techniques on the volatile aroma and sensory profile of chocolate

The sensory quality of chocolate is widely determined by the qualitative and quantitative composition of volatile compounds resulting from microbial metabolism during fermentation, and Maillard reactions taking place during drying, roasting and conching. The influence of applying mixed starter cultures on the formation of flavour precursors, composition of volatile aroma compounds and sensory profile was investigated in cocoa inoculated with cultures encompassing a highly aromatic strain of Pichia kluyveri or a pectinolytic strain of Kluyveromyces marxianus, and compared to commercially fermented heap and tray cocoa. Although only minor differences in the concentration of free amino acids and reducing sugars was measured, identification and quantification by dynamic headspace gas chromatography–mass spectrometry (HS/GC–MS) revealed pronounced differences in the composition of volatiles in roasted cocoa liquors and finished chocolates. 19 of the 56 volatile compounds identified in the chocolates were found in significantly higher amounts in the tray fermented sample, whilst significantly higher amounts of 2-methoxyphenol was measured in the two inoculated chocolates. The P. kluyveri inoculated chocolate was characterized by a significantly higher concentration of phenylacetaldehyde and the K. marxianus inoculated chocolate by significantly higher amounts of benzyl alcohol, phenethyl alcohol, benzyl acetate and phenethyl acetate compared to a spontaneously fermented control. Sensory profiling described the heap and tray fermented chocolates as sweet with cocoa and caramel flavours, whilst the inoculated chocolates were characterized as fruity, acid and bitter with berry, yoghurt and balsamic flavours. The choice of fermentation technique had the greatest overall impact on the volatile aroma and sensory profile, but whilst the application of starter cultures did affect the volatile aroma profile, differences were too small to significantly change consumer perception of the chocolates as compared to a spontaneously fermented control.     

Pear distillates: influence of the raw material used on final quality

Pear juice from concentrated and natural juices of Blanquilla variety was fermented using Saccharomyces cerevisiae. The pear wines obtained were distilled at two different conditions: distillation in the presence and in the absence of fermented juice lees. The distillates from natural pear juice have a higher amount of most of the volatile compounds compared to the ones from concentrated pear juice. In addition, the distillation of the fermented juice from natural pear juice in the absence of the lees significantly increased the concentration of some of these compounds compared to distillation in the presence of lees. However, most of the compounds whose concentration was higher in the distillates from natural pear juices are negative (furfural, methanol) or become negative in high concentrations (acetaldehyde, ethyl lactate, methyl acetate). Therefore, in terms of the compounds tested, it can be said from our results that using natural pear juice does not offer any benefit when compared to using concentrated pear juice from Blanquilla variety pears.     

Volatile composition of partially fermented wines elaborated from sun dried Pedro Ximénez grapes

In this work, we used a cell immobilisation system consisting of Penicillium chrysogenum fungi (GRAS) bound to the osmotolerant yeast strains Saccharomyces cerevisiae X4 and X5 for the partial fermentation of raisin musts. The resulting wines were compared with others obtained by partial fermentation of musts with free yeasts and with a traditionally produced sweet wine (i.e. without fermentation of the must). The analysis of volatile compounds grouped by aroma series showed the partially fermented musts had a more complex aroma than the traditional wine. Specially prominent among aroma series was that of ripe fruit, followed by the milky and chemical series. The volatiles with the greatest impact on wine aroma as assessed in terms of odour activity were ethyl hexanoate, ethyl octanoate, butyrolactone, isoamyl alcohols, acetaldehyde, ethyl acetate, 2,3-butanediol, acetoin and 2,3-butanedione. A cluster analysis according to the Ward method was performed to assess the similarity between the traditional sweet wine and those obtained by partial fermentation with free and immobilised yeasts revealed small differences between the wines obtained with free and immobilised yeasts, and marked differences between partially fermented and traditionally obtained sweet wine. The wines provided by immobilised yeasts were the most appreciated in the sensory analysis (especially those obtained with X4 yeasts).     

自然发酵与接种发酵燕麦醪糟的挥发性成分分析

采用顶空固相微萃取与气相色谱-质谱联用技术分析自然发酵与接种发酵2 种方式燕麦醪糟的挥发性成分,探讨2 种方式下燕麦醪糟挥发性成分的差异性,进而为接种发酵燕麦醪糟工业化生产提供理论依据。结果表明,2 种发酵方式生产燕麦醪糟的挥发性香气成分分别为62、65 种,主要包括酯类、酸类、醇类、醛酮类、杂环类、烃类,主成分分析发现酯类、醇类、杂环类为正影响挥发性物质;接种发酵燕麦醪糟的主要挥发性香气成分为醇类（58.31%）、酯类（20.70%）、酸类（16.75%）,自然发酵燕麦醪糟主要挥发性香气成分为酸类（61.94%）、酯类（18.89%）、醇类（13.58%）;接种发酵燕麦醪糟的酯类、醇类、杂环类成分含量显著高于自然发酵组,酸类成分显著低于自然发酵组。挥发性香气组分分析有助于明确燕麦醪糟接种发酵的可行性,以期为接种发酵燕麦醪糟的品质评价和定向生产提供理论基础。     

Olfactometric characterization of aroma active compounds in fermented fish paste in comparison with fish sauce,fermented soy paste and sauce products

Aroma active compounds in commercial fermented fish meat paste product (fish miso), fermented soy paste (soy miso), fish sauce and soy sauces were characterized by using a dynamic headspace method for volatile isolation and GC olfactometry for odor perception. A total of 123 volatile compounds consisting mainly of aldehydes, alcohols, esters, ketones, furans, sulfur and nitrogen-containing compounds, aromatics and acids were consistently identified. A major 16 odor-active compounds were distinguished to contribute as key aroma compounds for the miso and sauce products. Olfactometric and sensory findings clearly differentiated miso products with caramelic, fruity aroma notes, whereas fish sauce products were characterized by ammoniacal, fishy, nutty and cheesy odor note. Soy sauce products, however, were dominated by nutty and cheese aroma. Use of koji for fish miso production was found effective to enhance sweet aroma to the product with a reduction of nutty, meaty and rancid nuance. Principal component analysis employed for statistical interpretations clearly elucidated the relationship among different types of fermented products.     

顶空固相微萃取- 气相色谱- 质谱法测定苹果渣发酵蒸馏酒的香气成分

以顶空固相微萃取-气相色谱-质谱法测定苹果渣发酵蒸馏酒和酒精浸泡苹果渣蒸馏酒中的香气成分。经过鉴定分析,在苹果渣发酵蒸馏酒中,共测得57种挥发性香气成分,其中酯类物质30种、羧酸类物质5种、醇类物质6种、酮类物质1种、烃类物质14种、其他香气物质1种,相对含量分别占总挥发性香气物质的50.604%、6.322%、22.207%、0.254%、20.542%、0.013%;在酒精浸泡苹果渣蒸馏酒中,共测得37种挥发性香气成分,其中酯类物质22种、羧酸类物质3种、醇类物质2种、烃类物质9种、其他香气物质1种,相对含量分别占总挥发性香气物质的64.272%、2.538%、14.885%、17.437%、0.911%。通过比较分析,苹果渣发酵蒸馏酒中香气成分的种类显著多于酒精浸泡苹果渣蒸馏酒,香气成分分布更加均匀,口感更加醇厚自然,层次感更强。发酵结束后,酒体在保留苹果渣中营养成分的同时,也具有苹果的独特香气。研究说明苹果渣用于生产发酵蒸馏酒是更加利于其综合利用的一种途径。     

完全发酵与适度发酵苹果醋主要成分的差异性分析

研究苹果醋分别采用适度发酵和完全发酵时主要成分及芳香物质种类和含量的差异性。采用福林-酚法、高效液相色谱法、固相微萃取结合气相色谱-质谱联用分别测定2种发酵方式苹果醋中总酚、有机酸含量和芳香成分。结果表明,适度发酵苹果醋总酚含量比完全发酵高21%;2种果醋的有机酸种类完全一致,但适度发酵法中的酒石酸、柠檬酸和富马酸含量更高,而丙酮酸、苹果酸、α-酮戊二酸、乳酸、乙酸和琥珀酸的含量则略低于完全发酵的醋样。适度发酵苹果醋芳香物质种类更丰富,检测到37种芳香成分,其中保留了不少原果香气,如香茅醇、橙花醇、乙酸丁酯、乙酸-4-甲基-3-己酯和乙酸二甲基丁酯等。适度发酵可减少苹果醋总酚的损失,同时保留了更多的苹果原香物质,是值得探索改善苹果醋品质的途径。     

Characterisation of volatile compounds in an alcoholic beverage produced by whey fermentation

An alcoholic beverage (35.4% v/v ethanol) was produced by distillation of the fermented broth obtained by continuous whey fermentation with a lactose-fermenting yeast Kluyveromyces marxianus. Forty volatile compounds were identified in this drink by gas chromatography. Higher alcohols were the most abundant group of volatile compounds present, with isoamyl, isobutyl, 1-propanol, and isopentyl alcohols being found in highest quantities (887, 542, 266, and 176 mg/l, respectively). Ethyl acetate had the highest concentration (138 mg/l) among the esters. Besides higher alcohols and esters, other components, including aldehydes, acids and terpenes were also identified in the whey spirit. Considering that the quality of an alcoholic beverage can be evaluated by the relation between isoamyl alcohol/2-methyl-1-propanol and 2-methyl-1-propanol/1-propanol, which have to be higher than unity, it was concluded that a novel spirit of acceptable organoleptic characteristics can be produced by cheese whey continuous fermentation with K. marxianus.     

Preparation and aroma analysis of Chinese traditional fermented flour paste

Volatile compounds in Chinese fermented flour paste were extracted using simultaneous distillation and extraction (SDE) and analyzed using gas chromatography-mass spectrometry (GC-MS) with DB-5 and DB-WAX capillary columns. A total of 84 volatile compounds were identified, including 8 aldehydes, 19 esters, 14 acids, 17 hydrocarbons, 7 heterocycles, and 19 other trace compounds. The major volatiles included furfural, 5-methyl-2-phenyl-2-hexenal, 4-ethylguaiacol, 2-phenylacetaldehyde, ethyl hexadecanoate, isovaleraldehyde, palmitic acid, and 5-methylfurfural. Aroma compounds were investigated using gas chromatography-olfactometry (GC-O) and aroma extract dilution analysis (AEDA). A total of 27 olfactory regions were exposed and 18 aroma extracts were located. Altogether, 6 aroma compounds identified using GC-O showed higher flavor dilution factors (FD≥32), including isovaleraldehyde, furfural, pentanoic acid, 2-acetylfuran, 1-octen-3-ol, and 2-phenylacetaldehyde. Compared with soybean sauce, fermented flour paste has more esters and aldehydes, which contribute to the desired fruity, caramel, sweet, and roasted odors.     

清香型不同次原酒香气成分分析

采用液液萃取方法提取清香型不同米次原酒中的香气物质,通过气相色谱-闻香技术(GC-O)和气相色谱-质谱法(GC-MS)对香气化合物进行分析。在清香型原酒中共发现FD≥25的香气物质50种,定性47种。闻香结果显示,酯类和芳香族化合物是清香型原酒的重要香气物质。大原酒B和二原酒GC-O分析结果比较接近。酯类香气物质对大原酒A的香气贡献相对较大,芳香族、有机酸、硫化物、内酯类及杂环类化合物对大原酒B和二原酒的香气贡献相对较大,酚类化合物仅在大原酒B中FD值较大。正是这些香气物质的种类、浓度的不同使得次原酒的香气有明显差异。     

Characterisation of volatile compounds in Maotai flavour liquor during fermentation and distillation

Volatile constituents in raw liquor and zaopei during fermentation and distillation were investigated by gas chromatography. Zaopei (steamed grains mixed with Daqu [FG1], stacking fermented grains [FG2], anaerobic fermented grains [FG3] and steamed grains [FG4]) presented changes in physicochemical properties. In all, 72 volatile compounds were identified in zaopei and raw liquor with similarity across 12 zaopei preparations. Principal component analysis and partial least squares discriminant analysis differentiated FG3 from other samples based on content of aroma compounds. FG3 had the highest level of aroma compounds, which increased from the fourth to sixth batches, and was characterised by the presence of 1, 2‐propanediol, acetic acid and linoleic acid, while the others were portrayed by phenylpropionate, ethyl laurate and 4‐ethyl guaiacol. The volatile compounds of raw liquor were dominated by ethyl acetate and ethyl lactate. Correlation analysis illustrated a lack of correlation of volatile compound content between the raw liquors and the zaopei distillation variants. © 2019 The Institute of Brewing & Distilling     

利用D-最优混料设计优化浓香型白酒生物发酵液的配方

以黄水澄清液、酒尾、尾水为主要原料,通过添加生物酶制剂和控制发酵条件得到己酸乙酯含量较高的浓香型白酒生物发酵液。利用D-最优混料设计试验,研究不同黄水澄清液、酒尾和尾水配比对生物发酵液己酸乙酯生成量的影响,建立了配比与生物发酵液中己酸乙酯含量之间的回归模型,探讨了配方中各原料的互作效应,获得了浓香型白酒生物发酵液的最佳配方为：黄水澄清液26.20%、酒尾36.34%、尾水37.46%。在此最佳条件下,生物发酵液己酸乙酯含量达16.32 g/L,总酸含量为152.30 mg/100 mL,总酯（以己酸乙酯计）含量为17.66 g/L。所得生物发酵液风味成分种类丰富,黄色清亮,具有典型的发酵液复合香味。     

Characterisation of wines and distilled spirits from melon (Cucumis melo L.)

Melon fermentation and distillation was studied with a view to produce melon spirits. Three different substrates were obtained from melon (Cucumis melo L.). Sugar concentration was around 60–70 g L^?1 and the pH between 4.6 and 5.2. The substrates were clarified and then fermented at one of two pH levels at 20 °C. A commercial Saccharomyces cerevisiae starter culture was used to obtain melon wines with an alcohol concentration of 3.8–5.8% (v/v). The melon wines were distilled in a distillation column to yield distillates with an alcohol content of 33–60% (v/v). The major volatiles in the melon wines and in the distillates were analysed by gas chromatography (GC). The results demonstrated that melon could be a good substrate of fermentation and distillation but also yielded significant differences in the volatiles analysed in the different melon wines and distillates obtained from the different substrates in the different conditions of the experiment. Fermentation pH greatly affected the methanol, acetaldehyde, and butanol contents and thus the final quality of the spirits produced.     

野生蝉花与发酵菌丝体挥发性化合物分析

为研究不同提取方法对野生蝉花与发酵菌丝体挥发性化合物种类及含量的影响,首先通过ITS基因序列分析、菌落及产孢结构的形态特征对菌株GZU1205241进行鉴定。然后通过顶空固相微萃取（HS-SPME）和水蒸气蒸馏对野生蝉花和发酵菌丝体的挥发性化合物进行提取,并利用气相色谱-质谱（GC-MS）对两者挥发性化合物进行了测定。结果表明,菌株GZU1205241为蝉棒束孢菌。野生蝉花和发酵菌丝体分别含有56和58种挥发性物质,其中25种为共有物质。野生蝉花主要以酸类（90.08%）物质为主,其中油酸的相对含量达到了45.09%,棕榈酸的含量为21.18%,亚油酸的含量为9.44%。发酵菌丝体中主要也以酸类物质（86.57%）物质为主,其中棕榈酸的相对含量达到了38.44%,亚油酸的相对含量达到了18.58%,油酸的相对含量为12.83%。两种方法获得的野生蝉花及发酵菌丝体的挥发性成分种类及相对含量上有明显差别,水蒸气蒸馏法鉴定出的挥发性成分较多,而顶空固相微萃取鉴定出的挥发性成分比较少。但不论是蒸气蒸馏法还是顶空固相微萃取,野生蝉花及发酵菌丝体的挥发性成分都是以脂肪酸为主。      

Effect of fusel oil addition on volatile compounds in papaya wine fermented with Williopsis saturnus var. mrakii NCYC 2251

The impact of fusel oil addition on volatile compounds formation in papaya wine fermented with yeast Williopsis saturnus var. mrakii NCYC2251 was studied with a view to enhancing papaya wine aroma production. Time-course papaya juice fermentations were carried out using W. saturnus var. mrakii NCYC2251 with fusel oil added (0, 0.1 and 0.5% v/v). Fermentation characteristics in terms of yeast growth, Brix and pH changes were similar for all fermentations except for those added with 0.5% (v/v) fusel oil. The addition of 0.5% (v/v) fusel oil inhibited yeast growth. A wide range of volatile compounds were produced during fermentation including acids, alcohols, esters and aldehydes with esters being the most abundant volatile compounds produced. The addition of 0.1% (v/v) fusel oil reduced the production of undesirable volatiles such as ethyl acetate and acetic acid, while increasing the desirable volatiles production such as ethanol and acetate esters. This study suggests that papaya juice fermentation with W. saturnus var mrakii NCYC 2251 together with a low concentration of added fusel oil can be another means of modulating papaya wine aroma compound formation.     

Evaluation of an aroma similar to that of sparkling wine: Sensory and gas chromatography analyses of fermented grape musts

The aim of our study was to verify the acceptability and volatile compound composition of grape musts fermented by yeasts commonly found in the natural grape microflora. A consumer panel determined the acceptability of the grape musts, comparing the aromas with that of a corresponding commercial sparkling wine. The volatile compounds were isolated by the purge and trap system. The highest means for acceptability were obtained by the Pinot Noir and Chardonnay musts fermented by Pichia membranaefaciens and by the Chardonnay must fermented by Kloeckera apiculata, with no significant difference amongst them (p<0.05). Pinot Noir and Chardonnay musts fermented by P. membranaefaciens showed similar concentrations of the major fermentation aroma compounds (ethyl acetate, isoamyl acetate, acetaldehyde, ethanol, etc.) suggesting a correlation between the chemical and sensory data. The P. membranaefaciens isolate showed good potential as a producer of aroma similar to that of sparkling wine.     

Volatile compounds in Bacillus‐fermented soybeans

Thua nao, a traditional, proteolytic, fermented soybean condiment of northern Thailand, was prepared from cooked whole soybeans by natural flora fermentation. The microbial flora during the fermentation was dominated by Bacillus species. The formation of volatile compounds during the fermentation was studied. In addition, the volatile compounds of two samples of commercial dried thua nao and two samples of commercial Japanese natto were analysed. Fermentation led to a large increase in the concentration of total volatile compounds, from 35 µg kg^?1 wet weight in cooked soybeans to 3500 µg kg^?1 wet weight in 72 h fermented material. The major volatile compounds in fermented beans were 3‐hydroxybutanone (acetoin), 2‐methlybutanoic acid, pyrazines, dimethyl disulphide and 2‐pentylfuran. Sun drying of 72 h fermented material resulted in the loss of 65% of total volatiles, including important aroma compounds. The commercial dried thua nao samples had low concentrations of total volatile compounds (380 µg kg^?1 wet weight). It is suggested that improved drying/preservation methods are needed to retain aroma compounds in the traditional products. The natto samples were devoid of aldehydes, aliphatic acids and esters, and sulphur compounds, whereas the thua nao samples contained a diversity of these compounds. Previous investigators have reported these compounds in natto and it is not possible to suggest the existence of systematic differences between the volatile compounds in traditional thua nao prepared with an undefined, mixed microbial flora and those in natto fermented with Bacillus subtilis. © 2001 Society of Chemical Industry