Abstract

2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is an important aroma compound found in many fruits such as strawberries and pineapples and it is also produced by the soy-sauce-fermenting yeast Zygosaccharomyces rouxii after the addition of -fructose-1,6-diphosphate to yeast-peptone-dextrose nutrient media. Dilute DMHF solutions exhibit a strawberry-like flavor while DMHF concentrates have a caramel-like aroma. In media containing -fructose-1,6-diphosphate as the sole carbon source, growth of Z. rouxii and formation of DMHF were not observed. Although Z. rouxii cells grew in media with -glucose as the sole carbon source, DMHF was only produced when media were supplemented with -fructose-1,6-diphosphate. The DMHF concentration always correlated with the yeast cell count and -fructose-1,6-diphosphate concentration. Addition of CaCl₂ (up to 50 g·l⁻¹) led to a higher DMHF concentration. Addition of Na₂SO₃ reduced the growth of Z. rouxii and inhibited DMHF formation. The amount of DMHF formed by Z. rouxii was not significantly affected by the addition of KH₂PO₄. DMHF concentrations of 5 and 10 g·l⁻¹ partially and completely inhibited the growth of Z. rouxii cells, respectively. Only the singly labeled furanone was formed after the addition of 1-¹³C- -fructose-1,6-diphosphate to the medium. However, unlabeled DMHF was formed in the presence of ¹³C₆- -glucose. Therefore, the carbons of the furanone originate exclusively from exogenously supplied -fructose-1,6-diphosphate as no exchange with the internal pool of -fructose-1,6-diphosphate occurs. This implies that DMHF is a secondary metabolite of Z. rouxii formed from -fructose-1,6-diphosphate. We assume that at least the first step of the metabolism of -fructose-1,6-diphosphate takes place in the cell wall or membrane of the yeast.

Author Keywords: Zygosaccharomyces; furanone; flavor; isotope

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