Changes in soya bean lipids during tempe fermentation

Abstract Soya beans were fermented with pure cultures of Rhizopus oligosporus and Rhizopus oryzae in perforated petri dishes at 25°, 30° and 37°C for 69 h. During fermentation, samples were taken at different time intervals. Lyophilised samples were analysed for total crude lipid (CL), fatty acids present in glycerides (GFA) and free fatty acids (FFA). With R. oligosporus , the level of GFA decreased from 22·3 to 11·5% (w/w, dry matter) after 69 h fermentation at 37°C. In the final product, only 4·3% (w/w, dry matter) of FFA were found, hence the difference of 6·5% (w/w, dry matter) of fatty acids were lost. This difference was attributed to assimilation of fatty acids by R. oligosporus as a source of carbon. At 25°C the situation was different as the level of FFA was 1·7 times higher than could be explained on the basis of the decrease of GFA. The distribution pattern of GFA showed a slight increase of C18:1 and C18:2 during the fermentation at the expense of C18:3. Similar results were obtained with R. oryzae . With this fungus the strongest effects were observed at 30°C which is close to its optimum temperature for growth. More fatty acids were lost than with R. oligosporus and a more pronounced shift in GFA towards saturated fatty acids was observed.