Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/18832
Title: Kinetic changes of volatile compounds during longan juice fermentation with single and mixed cultures of yeasts
Authors: TRINH THI THANH TAM
Keywords: longan wine, mixed culture, fermentation and flavour, Williopsis, 2-phenylethyl acetate, amyl acetate
Issue Date: 19-Jul-2010
Source: TRINH THI THANH TAM (2010-07-19). Kinetic changes of volatile compounds during longan juice fermentation with single and mixed cultures of yeasts. ScholarBank@NUS Repository.
Abstract: Three yeasts from the genus Williopsis (W. saturnus var. mraki NCYC500, W. saturnus var. saturnus CBS254 and W. californica NCYC2590) were examined for their ability to ferment longan juice and to enhance formation of longan wine aroma compounds. The three yeasts varied with their ability to produce and utilize volatiles. W. saturnus CBS254 was the best producer of ethyl acetate, isobutyl acetate, isoamyl acetate and 2-phenethyl acetate, whereas W. californica NCYC2590 was the highest producer of butyl acetate. W. saturnus CBS254 was subsequently chosen to investigate the impact of two amino acids (L-leucine and L-phenylalanine) on the volatile profiles of longan wine with a view to enhancing longan wine aroma. The results revealed the ability of this yeast to enhance isoamyl alcohol and its ester isoamyl acetate (banana-like aroma), and 2-phenylethanol and its ester 2-phenylethyl acetate (rose-like aroma) with the addition of L-leucine and L-phenylalanine, respectively. The increased production of the targeted acetate esters appeared to be at the expense of other acetate esters, whereas the effects on the biotransformation of other volatiles were minimal. Next, co-fermentation of longan juice by mixed cultures of Saccharomyces cerevisiae var. bayanus EC-1118 and Williopsis saturnus var. saturnus CBS254 at two inoculation ratios (EC-1118 : CBS254= 1 : 100 and 1 : 1000 cfu mL-1) were performed to ascertain their impact on longan wine aroma compound formation. The results showed improved aroma compound profiles in the longan wines fermented with mixed yeasts in comparison with the longan wines fermented with single yeasts in terms of increased production of acetate esters, fatty acid ethyl esters, alcohols and organic acids. The impact of co-fermentation on longan wine aroma formation was affected by the ratio of S. cerevisiae EC-1118 to W. saturnus CBS254 with 1 : 100 cfu mL-1 being more effective. This research suggests that the inoculation ratio of mixedyeasts may be used as an effective means of manipulating longan wine aroma. Again, the addition of L-isoleucine and L-phenylalanine on the volatile profiles of longan wine fermented by this co-culture at a ratio of 1 : 1000 cfu mL-1 with the aim of enhancing longan wine aroma led to significantly higher concentrations of active amyl alcohol (2-methyl-1-butanol), 2-phenylethyl alcohol and their corresponding acetate esters, respectively. These findings suggest that yeasts from the genus Williopsis could be exploited for longan wine aroma enhancement either singly or in co-inoculation with Saccharomyces. Furthermore, the added amino acids play an important role in enhancing targeted aroma compounds in longan wine. Therefore, the combination(s) of a specific amino acid(s) and yeast can be employed as a valuable tool to modulate longan wine aroma.
URI: http://scholarbank.nus.edu.sg/handle/10635/18832
Appears in Collections:Master's Theses (Open)

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