Tempe fermentation: Some aspects of formation of γ-linolenic acid, proteases and vitamins

During a tempe fermentation the concentrations of linoleic, and α-linolenic acids (ALA) decreased while the concentration of oleic acid increased. During fatty acid synthesis Rhizopus sp. produced only γ-linolenic acid (GLA) instead of ALA. The amount of GLA in tempe were influenced by varying external parameters. The proteolytic capacity of 36 strains of the genus Rhizopus isolated from Indonesian tempe or tempe inocula was examined. There was a distinct increase in the amount of free amino acids during tempe fermentation. Fermentations with mixed populations of bacteria and Rhizopus yielded a lower level of free amino acids, but an increase in total amount of amino acids. In comparison to intracellular, and extracellular proteases the proteases of the cell wall fraction are most responsible for proteolytic capacity of the different Rhizopus strains. Two isolated strains of Citrobacter freundii were found to be the best vitamin B 12 producers during the soaking of soybeans. In the solid substrate fermentation the Rhizopus molds formed vitamin B 6, riboflavin, and nicotinic acid. The addition of bacteria to the solid substrate fermentation resulted in a strong increase of active vitamin B 12 in tempe. In the presence of the Rhizopus mold, the vitamin B 12 formation by C. freundii was three times higher than that of a fermentation without the mold.