Chemical composition, sensorial properties, and aroma-active compounds of ciders fermented with Hanseniaspora osmophila and Torulaspora quercuum in co- and sequential fermentations.

In this study, apple juice was fermented using Hanseniaspora osmophila X25-5 in pure culture as well as mixed culture with Torulaspora quercuum X24-4, which was inoculated simultaneously or sequentially. H. osmophila inhibited the growth of T. quercuum, while T. quercuum had little effect on the growth of H. osmophila. The simultaneous fermentation consumed relatively more sugar and resulted in the highest ethanol content. The production of organic acids varied depending on the yeast species employed and inoculation modality. Esters and alcohols were the main volatile families produced during fermentation, while ethyl esters and terpenes contributed most to the temperate fruity aroma. Gas chromatography-olfactometry (GC-O) showed that 3-methyl-1-butanol, ethyl 2-methylbutanoate, phenylethyl alcohol, β-phenethyl acetate, and β-damascenone were the most potent odorants in all samples. This study suggested that simultaneous fermentation with H. osmophila and T. quercuum might represent a novel strategy for the future production of cider.

Wei J ，Zhang Y ，Qiu Y ，Guo H ，Ju H ，Wang Y ，Yuan Y ，Yue T ... -  《-》

Assessment of chemical composition and sensorial properties of ciders fermented with different non-Saccharomyces yeasts in pure and mixed fermentations.

This work presents the attempt to enhance the flavor complexity of cider fermented by different non-Saccharomyces species. Pichia kluyveri and Hanseniaspora vineae pure cultures were used as reference ciders. Mixed cultures between all 4 species gave 5 fermentations, where Hanseniaspora uvarum or Torulaspora quercuum were included for apple juice fermentation. Chemical composition and sensorial properties of all ciders were studied. The results indicated that the growth of P. kluyveri and H. vineae were interreacted and also affected by H. uvarum and T. quercuum. H. vineae was more capable of consuming sugar than P. kluyveri. Ciders from the single culture fermentation with P. kluyveri (Pk), as well as from mixed fermentation with P. kluyveri and H. uvarum (Pk-Hu), had high residual sugar, sugar/acid ratio, and glucose-fructose consumption ratio. Large shifts in the consumption and production of organic acids and polyphenols among all ciders were observed. The calculation of the relative odor activity value (rOAV) showed that 17 volatile compounds had an rOAV >1 in at least one sample, and acetate esters and ethyl esters were the groups with the highest number of volatile compounds of importance to the cider aroma. Among these 17 compounds, 3-methylbutyl acetate, 2-methylbutyl acetate, ethyl hexanoate, ethyl octanoate, and β-damascenone exhibited high rOAVs in some ciders and might contribute fruity, floral, and sweet features to the cider aroma. Besides, the tropical fruity aroma from 3-methylbutyl acetate was only perceived in Pk and Pk-Hu. The partial least squares regression (PLSR) analysis revealed that acetate esters contributed positively to the roasted and cooked odor of all ciders. This is the first study evaluating simultaneous fermentation of two non-Saccharomyces yeasts to produce cider, which provides new insights into cider production.

Wei J ，Zhang Y ，Wang Y ，Ju H ，Niu C ，Song Z ，Yuan Y ，Yue T ... -  《-》

Chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation.

This work evaluated for the first time the chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation. Compared with the control (yeast only, 5.70% v/v ethanol produced), samples co-inoculated with T. delbrueckii and O. oeni PN4 improved ethanol production (6.06% v/v), which was significantly higher than samples co-inoculated with Viniflora (4.78% v/v) or Enoferm Beta (5.01% v/v). Wines co-fermented with the respective latter two oenococci contained excessive levels of ethyl acetate (>80mg/L) that were likely to affect negatively wine aroma. In addition, they led to significantly higher acetic and lactic acid production relative to PN4. O. oeni PN4 seemed to be the most suitable strain to co-inoculate with T. delbrueckii for simultaneous alcoholic and malolactic fermentation in durian wine by contributing moderately increased concentrations of higher alcohols, acetate esters and ethyl esters that would have positive sensory impacts.

Lu Y ，Chua JY ，Huang D ，Lee PR ，Liu SQ ... -  《-》

Increase of medium-chain fatty acid ethyl ester content in mixed H. uvarum/S. cerevisiae fermentation leads to wine fruity aroma enhancement.

Medium-chain fatty acid (MCFA) ethyl esters, as yeast secondary metabolites, significantly contribute to the fruity aroma of foods and beverages. To improve the MCFA ethyl ester content of wine, mixed fermentations with Hanseniaspora uvarum Yun268 and Saccharomyces cerevisiae were performed. Final volatiles were analyzed by gas solid phase microextraction-chromatography-mass spectrometry, and aroma characteristics were quantitated by sensory analysis. Results showed that mixed fermentation increased MCFA ethyl ester content by 37% in Cabernet Gernischt wine compared to that obtained by pure fermentation. Partial least-squares regression analysis further revealed that the improved MCFA ethyl esters specifically enhanced the temperate fruity aroma of wine. The enhancement of MCFA ethyl esters was attributed to the increased contents of MCFAs that could be induced by the presence of H. uvarum Yun268 in mixed fermentation. Meanwhile, the timing of yeast inoculations significantly affected the involving biomass of each strain and the dynamics of ethanol accumulation.

Hu K ，Jin GJ ，Mei WC ，Li T ，Tao YS ... -  《-》

Enhancing wine ester biosynthesis in mixed Hanseniaspora uvarum/Saccharomyces cerevisiae fermentation by nitrogen nutrient addition.

The dynamic changes of wine ester production during mixed fermentation with Hanseniaspora uvarum Yun268 and Saccharomyces cerevisiae F5 was investigated at different levels and timings of nitrogen nutrient addition. Nitrogen additions were performed by supplementing yeast assimilable nitrogen (YAN) into a synthetic grape must with defined composition. Ester precursors and extracellular metabolites involved in ester synthesis were analyzed throughout the fermentation. Results showed that nitrogen additions covering 50-200 mg/L YAN at the point of yeast inoculation slightly affected yeast competition and ester profiles. Interestingly, when YAN was supplemented in the mid-stage, the survival of H. uvarum Yun268 was enhanced, resulting in more than a 2-fold increase in the levels of higher alcohol acetates compared to that at the initial stage. Furthermore, carbon fluxes may be redistributed in the central pathway, which contributed to the production of medium-chain fatty acids and eventually triggered a 1.2-fold elevation in corresponding ethyl ester levels.

Hu K ，Jin GJ ，Xu YH ，Xue SJ ，Qiao SJ ，Teng YX ，Tao YS ... -  《-》