Oxidation-reduction potential affects medium-chain fatty acid ethyl ester production during wine alcohol fermentation.

The medium-chain fatty acid ethyl esters (MCFAEEs) are a group of important aroma compounds generated during wine production. Wine alcohol fermentation involves several redox processes, which are affected by the oxidation-reduction potential (ORP). However, the mechanism via which ORP regulates MCFAEE production remains unclear. To investigate the effect of ORP on MCFAEE production, wine alcohol fermentation was performed using Saccharomyces cerevisiae under different ORPs. The results demonstrated that the ORPs studied (except for 90 mV) did not significantly affect cell growth, sugar consumption, and ethanol production, while the MCFAEE concentration in the simulated wines can be manipulated by ORP operation. MCFAEE levels increased till 96 h, and then decreased. The maximum MCFAEE level of 1222.97 µg/L was obtained after 96 h at 0 mV, which was 45.32% higher than that of the control. During the increase, higher relative expression of ACC1, FAS1, FAA2 and EEB1, elevated external citric acid flux, and moderate intracellular NADP+/NADPH ratio were observed at 0 mV compared to that at other ORPs. During the decrease, lowest relative expression of POX1 was detected at 0 mV. We showed for the first time the relationship between ORP operation and MCFAEE production in winemaking, which will improve the aroma quality of wine.

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.

Evolution of volatile compounds treated with selected non-Saccharomyces extracellular extract during Pinot noir winemaking in monsoon climate.

The dynamic pattern of volatiles during Pinot Noir winemaking in monsoon climate with yeast extracellular extract (EE) treatment was analyzed. EE from selected Pichia fermentans and Rhodotorula mucilaginosa strains, and almond ß-glucosidase were added after 12-h alcohol fermentation, and the volatiles were determined every 24 h by GC-MS. After 6-month storage, wine aroma was evaluated instrumentally as well as by well-trained panelists. Results showed that enzyme treatments improved the contents of both varietal and fermentative volatiles. The levels of C6 compounds, terpenes, and higher alcohols increased constantly during alcohol fermentation, whereas acetates, short and medium chain fatty acid ethyl esters, phenylethyls, and fatty acids increased first, followed by gradual decrease. EE treatment retarded the decrease of fruity ester content in wine. Mathematical regression between wine aroma and volatiles showed that the relatively higher contents of acetates, ethyl esters, and C13-norisoprenoids in 6-month EE-treated wine were responsible for the improvement in floral aroma intensity.

Chemical profiles and aroma contribution of terpene compounds in Meili (Vitis vinifera L.) grape and wine.

The chemical profiles and aroma contribution of terpene compounds in Meili grapes and wine were analyzed. Bound terpene compounds were extracted using methanol, purified using Amberlite XAD-2 resin, concentrated in methanol/ethyl acetate, and enzymatically hydrolyzed to release aglycones. Free terpene compounds were identified using solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Wine aroma characteristics were quantified by a trained sensory panel. Seventeen terpene glycosides were quantified in grapes and wines as pentosyl-glucopyranoside, the content of which ranged from 804 to 836 µg/kg, and from 155 to 192 µg/L, respectively. Eight free terpenes were present in wines with their content ranging from 40.1 to 59.7 µg/L. Linalool was abundant both in bound and free terpenes, and mathematical regression revealed that terpenes, especially linalool (contribution efficient > 0.4), contributed heavily to Meili wine aroma. Finally, a molecular rearrangement scheme based on linalool was proposed in Meili grape and wine.

Wine aroma response to different participation of selected Hanseniaspora uvarum in mixed fermentation with Saccharomyces cerevisiae.

Wine aroma response to a selected Hanseniaspora uvarum Yun268 strain was investigated using different inoculation strategies with commercial Saccharomyces cerevisiae yeast, namely, simultaneous fermentation (SiF), sequential fermentation (SeF), S. cerevisiae fermentation treated with extracellular extract of H. uvarum (EE), and pure S. cerevisiae fermentation (PF). Contributive volatiles in the perception of enhanced aroma traits were uncovered by partial least-squares regression. Results showed that controlled inoculation resulted into different amounts of H. uvarum Yun268, which distinctively affected the chemical and sensory profiles of wines. The concentration of aromatic compounds could be increased by H. uvarum Yun268 yeasts via high levels of ß-glucosidase activity and fatty acids. Terpenes, C13-norisoprenoids, acetate esters, ethyl esters, and fatty acids served as the impact volatiles that contributed to the enhanced aroma traits. SiF specifically increased the contents of C13-norisoprenoids, terpenes, and ethyl esters, while EE enhanced varietal volatile content rather than those of fermentative ones. However, excessive H. uvarum Yun268 in sequential inoculation elevated the concentrations of acetate esters and volatile phenols, triggering nail polish odor in Cabernet Sauvignon red wines.

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.