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Distiller-dried grain solid (DDGS), a co-product of alcohol production, contains cereal grain residues, proteins, and yeast metabolites, which make it suitable in poultry feeding. However, high phytate content of DDGS limits its applicability in poultry feed. In this study, Plackett-Burman design was used to improve cell-bound phytase production by Williopsis saturnus NCIM 3298, and we achieved an enzyme activity of 269 IU/g of dry-wet biomass. The effect of this enhanced phytase-displaying yeast strain on hydrolysis of corn phytate and subsequently on ethanol production and DDGS quality was then investigated. Results of saccharification in the presence of phytase showed that reducing sugar content of liquefied mash increased by 11%, which subsequently improved the ethanol production by 18% (w/v) (p < 0.01) compared with the control. Notably, phytase treatment decreased the phytate content of corn by 70% (p < 0.01) compared with the control, thereby improving the availability of free phosphate in fermentation broth and DDGS. Thus, the results obtained suggest that the addition of W. saturnus NCIM 3298 strain has the potential of providing a new source of phytase that would be useful in the feed and ethanol industries.

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This study investigated the effects of sequential inoculation (Seq-I) of Bifidobacterium animalis subsp. lactis or Lactobacillus casei with yeast Williopsis saturnus on durian pulp fermentation. Seq-I of W. saturnus following B. animalis subsp. lactis did not bring about any significant differences compared to the B. animalis subsp. lactis monoculture due to the sharp early death of W. saturnus soon after inoculation. However, Seq-I of W. saturnus significantly enhanced the survival of L. casei and improved the utilization of fructose and glucose compared to L. casei monoculture. In addition, there were significant differences in the metabolism of organic acids especially for lactic acid and succinic acid. Furthermore, Seq-I produced significantly higher levels of volatile compounds including alcohols (ethanol and 2-phenylethyl alcohol) and acetate esters (2-phenylethyl acetate, isoamyl acetate and ethyl acetate), which would positively contribute to the flavour notes. Although the initial volatile sulphur compounds were reduced to trace levels after fermentation, but the durian odour still remained. This study suggests that the use of probiotics and W. saturnus to ferment durian pulp could act as a potential avenue to develop a novel non-dairy durian-based functional beverage to deliver probiotics.

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This work describes cell associated and extracellular synthesis of nanoparticles by the yeast, Williopsis saturnus. The yeast was able to grow in the absence and presence of sodium chloride (NaCl) and form nanoparticles in a cell associated manner. The content of melanin, a stress-associated pigment was found to be progressively greater in the presence of increasing concentrations of NaCl. With higher quantities of melanin (extracted from yeast cells grown in the presence of 4% of NaCl), smaller sized nanoparticles were obtained. This is the first report on understanding the relationship between halotolerance, production of a stress-related pigment (melanin) and synthesis of nanoparticles with antioxidant properties by using W. saturnus as a model system. The cell free extracts derived from cultures grown in the absence of NaCl were able to mediate extracellular synthesis of gold and silver nanoparticles and the biomolecule mediating nanoparticle synthesis was identified to be a glycolipid. Extracellularly synthesized gold nanoparticles displayed good catalytic activity and rapidly mediated the reduction of 4-nitrophenol to 4-aminophenol.

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This study evaluated the effects of three non-Saccharomyces yeasts, namely Torulaspora delbrueckii PRELUDE, Williopsis saturnus NCYC22, and Kluyveromyces lactis KL71 on lychee juice fermentation. The fermentation performance of these non-Saccharomyces yeasts was significantly different. T. delbrueckii PRELUDE had the fastest rate of growth and high sugar consumption. W. saturnus NCYC22 used the lowest amount of sugars, but consumed the highest amount of nitrogen. Correspondingly, strain PRELUDE produced the highest level of ethanol (7.6% v/v), followed by strain KL71 (3.4% v/v) and strain NCYC22 (0.8% v/v). Aroma character-impact terpenes and terpenoids could be partially retained in all lychee wines, with higher odour activity values (OAVs) of geraniol and citronellol in strain KL71. However, strain KL71 and strain NCYC22 over-produced ethyl acetate. Strain PRELUDE had a better ability to generate high levels of ethanol, isoamyl alcohol, 2-phenylethyl alcohol, ethyl octanoate, and ethyl decanoate and retained high OAVs of lychee aroma-character compounds cis-rose oxide (16.5) and linalool (3.5). Thus, it is deemed to be a promising non-Saccharomyces yeast for lychee wine fermentation.

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