Background: The purpose of this study was to achieve rapid improvement of the flavour of soy sauce by increasing the salt stress resistance of Zygosaccharomyces rouxii. Here, we describe genome shuffling to improve the salt tolerance of Z. rouxii while simultaneously enhancing and accelerating flavour formation of soy sauce.
Results: A mutant, S3-2, with a stronger resistance to salt, was selected after three rounds of genome shuffling. S3-2 not only grew well in peptone/yeast extract/dextrose medium containing a high salt content with wide range of pH, but also exhibited stronger stress resistance to potassium chloride and lithium chloride. In high-salt liquid fermentation, S3-2 obviously accelerated flavour formation of soy sauce, thus decreasing the total time required for development of the aroma. In addition, S3-2 gave high amino acid nitrogen and good flavour. In particular, the ethyl acetate content was 2.38 times that in the control. S3-2 distinctly improved the formation of 4-hydroxy-2 (or 5) -ethyl-5 (or 2) -methyl-3 (2H) -furanone by up to 75%. Another important flavour component, 4-ethylguaiacol, was also detected.
Conclusions: Genome shuffling was successfully used to achieve significant improvements in flavour formation. The selected strain improved the main flavour components and amino acid nitrogen, thereby enhancing the quality of soy sauce.
(c) 2009 Society of Chemical Industry.