Yeast and volatile evolution in cider co-fermentation with Saccharomyces cerevisiae and Williopsis saturnus

Abstract

This research was conducted to evaluate the impact of co-fermentation with Saccharomyces cerevisiae and Williopsis saturnus var. mrakii on the volatile profile of cider. Cider co-fermentation was carried out by co-inoculating S. cerevisiae and W. saturnus var. mrakii at a ratio of 1:100. Changes in yeast cell population, total soluble solid content (degrees Brix [°Bx]), and pH were monitored. Volatiles were analysed using headspace solid-phase microextraction/gas chromatography–mass spectrometry/flame ionization detector (HS-SPME/GC-MS-FID). A diverse group of volatiles, including fatty acids, alcohols, aldehydes, esters and ketones, were identified, among which alcohols and esters were the predominant compounds. Although most of these compounds showed similar dynamics of change, the final concentrations of some volatiles differed significantly between single-culture and co-culture fermentations. Volatiles that were indigenous to apple juice decreased during fermentation, while production of isoamyl acetate, 2-phenylethyl acetate, ethyl acetate, ethyl decanoate, ethyl dodecanoate and ethyl octanoate varied significantly among the monocultures and co-culture. Co-fermentation by S. cerevisiae and W. saturnus resulted in a more complex volatile profile, which could impact on the aromatic characteristics of cider, thus representing a novel way to modulate flavour.