2,5-Dimethyl-4-hydroxy-3(2H)-furanone as a secondary metabolite from D-fructose-1,6-diphosphate metabolism by Zygosaccharomyces rouxii

2, 5-Dimethyl-4-hydroxy-3 (2H)-furanone (DMHF) is an important aroma compou nd found in many fruits such as strawberries and pineapples and it is also produced by the soy-sauce-fermenting yeast Zygosaccharomyces rouxii after t he addition of D-fructose-1,6-diphosphate to yeast-peptone-dextrose nutrien t media. Dilute DMHF solutions exhibit a strawberry-like flavor while DMHF concentrates have a caramel-like aroma. In media containing D-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 D-gluc ose as the sole carbon source, DMHF was only produced when media were suppl emented with D-fructose-1,6-diphosphate. The DMHF concentration always corr elated with the yeast cell count and D-fructose-1,6-diphosphate concentrati on. Addition of CaCl2 (up to 50 g . l(-1) led to a higher DMHF concentratio n. Addition of Na2SO3 reduced the growth of Z. rouxii and inhibited DMHF fo rmation. The amount of DMHF formed by 2. rouxii was not significantly affec ted by the addition of KH2PO4. DMHF concentrations of 5 and 10 g . l(-1) pa rtially and completely inhibited the growth of Z. rouxii cells, respectivel y. Only the singly labeled furanone was formed after the addition of 1-C-13 -D-fructose-1,6-diphosphate to the medium. However, unlabeled DMHF was form ed in the presence of C-13(6)-D-glucose. Therefore, the carbons of the fura none originate exclusively from exogenously supplied D-fructose-1,6-diphosp hate as no exchange with the internal pool of D-fructose-1,6-diphosphate oc curs. This implies that DMHF is a secondary metabolite of Z. rouxii formed from D-fructose-1,6-diphosphate. We assume that at least the first step of the metabolism of D-fructose-1,6-diphosphate takes place in the cell wall o r membrane of the yeast.