L-RHAMNOSE - PROGENITOR OF 2,5-DIMETHYL-4-HYDROXY-3[2H]-FURANONE FORMATION BY PICHIA-CAPSULATA

2,5-Dimethyl-4-hydroxy-3 [2H]-furanone (Furaneol, 1), an important aro ma constituent, was detected at concentrations of up to 2 mg/l after 4 days of growth of Pichia capsulata on casein peptone culture medium c ontaining L-(+)-rhamnose (2). Blank samples without yeast contained no 1 after the incubation period. In parallel experiments five samples o f 2 exhibiting different [C-13] abundance were given to P. capsulata. The volatile compounds formed were isolated and analysed for their [C- 13]/[C-12] ratios by on-line gas chromatography/combustion/isotope rat io mass spectrometry (GC/C/IRMS). A positive correlation between the i sotopes in 1 and 2 was observed; thus, 2 served as the carbon source f or 1. However, 1 was formed from a postulated intermediate of 2 genera ted during thermal sterilization, as 1 was neither detected after ster ile filtration of the culture medium nor after separate thermal steril ization of the casein peptone and 2. This observation was confirmed by an experiment investigating the time course of the formation of 1.