The changes in volatile compounds during papaya juice fermentation with three Williopsis saturnus yeasts were investigated in this study. Time-course papaya juice fermentations were carried out using three Williopsis saturnus yeasts: W. saturnus var. mrakii NCYC2251, W. saturnus var. saturnus NCYC22 and W. saturnus var. sargentensis NCYC2727. Changes in yeast cell population, Brix and pH were similar among the three yeasts, which preferentially utilised glucose over fructose while partially degrading l-malic acid. A range of volatile compounds were produced during fermentation including fatty acids, alcohols and esters with esters being the most abundant volatile compounds produced. Benzyl isothiocyanate, butyric acid, 2-ethylhexanol, benzaldehyde and b-damascenone present in the papaya juice were metabolised to trace levels during fermentation. There were significant variations among the three yeasts in their ability to produce and metabolise volatile compounds during fermentation. The study suggests that papaya juice fermentation with W. saturnus yeasts is able to result in the formation of a more complex aroma compounds.Papaya wine fermented by W. saturnus yeasts P.-R. Lee et al.

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PurposeThe purpose of this study was to characterise the physiochemical properties of selected exotic seasonal tropical fruits available in Singapore.Design/methodology/approachA total of 11 seasonal tropical fruits including cempedak, chiku, custard apple, jackfruit, longkong, mangosteen, red jambu, pearl jambu, rambutan, salak and starfruit were analyzed for their sugars, organic acids and free phenolic acids composition using liquid chromatographic methods. Total phenolic content (free and bound), total soluble solids and pH were determined using Folin‐Ciocalteu method, refractometer and pH meter, respectively.FindingsFructose, glucose and sucrose were the main sugars in all the fruits. Cempedak had the highest sucrose concentration, while custard apple had the highest content of fructose and glucose. Malic and citric acids were the major organic acids in most of the fruits, except for pearl jambu and red jambu where succinic acid was the dominant acid. The total phenolic content varied from 122.94 to 712.20 mg gallic acid equivalent (GAE)/kg fresh weight (FW). Ferulic (0.631 mg/kg) and sinapic acids (1.506 mg/kg) were the predominant free phenolic acids in custard apple, while caffeic acid was the main free phenolic acid in jackfruit, salak and starfruit.Originality/valueThe paper demonstrates that the physiochemical characteristics of the 11 tropical fruits varied markedly, which is responsible for the differential flavour and stability. The findings are useful for epidemiological research and predicting the degree of ripeness, stability and post‐harvest processing required for these fruits.

The findings showed that a more complex flavor could result from fermentation with different non-Saccharomyces yeasts and the typical durian odor would still remain.

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This study investigated the effects of temperature (20 and 30 °C) and pH (pH 3.1, 3.9) on kinetic changes of chemical constituents of the durian wine fermented with Saccharomyces cerevisiae. Temperature significantly affected growth of S. cerevisiae EC-1118 regardless of pH with a higher temperature leading to a faster cell death. The pH had a more significant effect on ethanol production than temperature with higher production at 20 °C (5.95%, v/v) and 30 °C (5.56%, v/v) at pH 3.9, relative to that at pH 3.1 (5.25 and 5.01%, v/v). However, relatively higher levels of isobutyl alcohol and isoamyl alcohol up to 64.52 ± 6.39 and 56.27 ± 3.00 mg/L, respectively, were produced at pH 3.1 than at pH 3.9 regardless of temperature. In contrast, production of esters was more affected by temperature than pH, where levels of ethyl esters (ethyl esters of octanoate, nonanoate, and decanoate) and acetate esters (ethyl acetate and isoamyl acetate) were significantly higher up to 2.13 ± 0.23 and 4.61 ± 0.22 mg/L, respectively, at 20 °C than at 30 °C. On the other hand, higher temperature improved the reduction of volatile sulfur compounds. This study illustrated that temperature control would be a more effective tool than pH in modulating the resulting aroma compound profile of durian wine.

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