Effect of aroma enhancement for dry white wine by selected non-Saccharomyces extracellular enzymes

Abstract: Aroma compounds are mainly produced during brewing, which is involved various yeast flavor enzymes. The potential application of yeast flavoring enzyme in brewing was evaluated through the study on the aroma enhancement of dry white wine treated by extracellular enzymes from two non-saccharomyces strains. Ecolly grape is a kind of white wine with weak flavor. It was used as wine making material in experiment, and the grape juice was fermented by commercial Saccharomyces cerevisiae strain. After 12 hours, the extracellular enzymes from selected Pichia fermentans (PF) and Rhodotorula mucilaginosa (RM) strains were added (10 mU/mL), as well as the commercial almond β-glucosidase (AG). The pure fermentation of Saccharomyces cerevisiae without enzyme treatment was used as the control. During the fermentation, the juice was sampled every 24 h to detect sugar content and aroma compounds. Volatile compounds were extracted by headspace solid-phase microextraction (HS-SPME), and then were desorbed and detected by gas chromatography coupled with mass spectrometry (GC-MS). Grape juice alcohol fermentation was completed when the residue sugar was less than 2 g/L, and the clear wine was racked to a clean bottle and stored at low temperature. In April of the next year,, wine aroma compounds of wine were identified and quantified by HS-SPME-GC-MS, and aroma characteristics were analyzed and quantified by well-trained panelists. Results showed that six flavor enzyme activities were detected in both PF and RM extracellular enzymes. The activities of β-D-glucosidase, α-L-rhamosidase, and β-D-xylosidase in RM enzymes were significantly higher than those in PF enzymes (P < 0.05), while the activities of α-L-arabinosidase and esterases in PF enzymes were significantly higher than those in RM enzymes (P < 0.05). In general, both the treatments of PF and RM extracellular enzymes improved the contents of varietal and fermentative volatiles during fermentation significantly (P < 0.05). Compared with AG treatment, the concentration of terpenes and phenylethyls increased by 41.7% and 31.8%, respectively. Furthermore, the production of most fermentative volatiles was promoted by PF enzymes, particularly fatty acid ethyl esters. The content of fatty acids ethyl esters in PF treatment was almost twice as much as that in the control. It is worth to be noted that the effect of aroma enhancement for dry white wine was different between PF and RM enzymes treatments according to sensory analysis results. Two kinds of extracellular enzymes of non-Saccharomyces showed their respective advantages in aroma improvement. RM enzymes enhanced temperate sour fruits aroma type, while citrus attribute was strengthened by PF enzymes. In summary, the treatment of two sample non-Sacchromyces extracellular enzymes had the clear aroma enhancement effect for dry white wine. The selected PF and RM extracellular enzymes had different flavor enzymes profiles, then their enzymes treatments during wine alcohol fermentation would bring out different improvements of varietal and fermentative aroma compounds. This results led to the different effects of aroma enhancement for dry white wine. This work would give the theoretical and practical guidance to the wine making for aroma enhancement by yeast flavor enzymes.