Molecular characterization and molasses fermentation performance of a wild yeast strain operating in an extremely wide temperature range

abstract Molasses fermentation performance by both a cryotolerant and a thermophilic yeast (strain AXAZ-1) iso-lated from grapes in Greece was evaluated in an extremely wide temperature range (3–40 C). Sequenceanalysis of the 5.8S internal transcribed spacer and the D1/D2 ribosomal DNA (rDNA) regions assignedisolate to Saccharomyces cerevisiae. Restriction fragment length polymorphism of the mitochondrialDNA showed that strain AXAZ-1 is genetically divergent compared to other wild strains of Greek originor commercial yeast starters. Yeast cells growing planktonically were capable of fermentation in a widetemperature spectrum, ranging from 3 Cto38 C. Immobilization of yeast on brewer’s spent grains (BSG)improved the thermo-tolerance of the strain and enabled fermentation at 40 C. Time to complete fer-mentation with the immobilized yeast ranged from 20 days at 3 to 38 h at 40 C. The daily ethanol pro-ductivity reached maximum (58.1 g/L) and minimum (2.5 g/L) levels at 30 and 3 C, respectively. Thearoma-related compounds’ profiles of immobilized cells at different fermentation temperatures wereevaluated by using solid phase microextraction (SPME) gas chromatography–mass spectrometry (GC–MS). Molasses fermentation resulted in a high quality fermentation product due to the low concentra-tions of higher and amyl alcohols at all temperatures tested. Strain AXAZ-1 is very promising for the pro-duction of ethanol from low cost raw materials, as it was capable to perform fermentations of highethanol concentration and productivities in both low and high temperatures. 2009 Elsevier Ltd. All rights reserved.