Effects of Enterococcus faecium and starters on the production of volatile compounds during doenjang fermentation

Bacterial starters Enterococcus faecium and Staphylococcus succinus were introduced into the manufacture of doenjang, a Korean fermented soybean paste, together with a fungal starter to determine the effect of bacterial starters on flavor production during doenjang fermentation. Starters cultured on soybean flakes and rice were mixed with autoclaved soybeans and then refined salt was added to 12% (w/w) to prepare doenjang samples. The doenjang samples were ripened at 20 degrees C and their volatile compounds were analyzed on days 0, 28, 56, and 84. The numbers of bacteria from starter cultures in the samples decreased gradually. The content of amino-type nitrogen in samples decreased as the proportion of bacterial starter culture used in doenjang preparation increased. Nineteen volatile compounds were detected in doenjang samples by gas chromatography-mass spectrometry and were subjected to principal component analysis. Addition of bacterial starters distinctively changed the flavor of doenjang compared with that prepared with a fungal starter alone. Acetic acid, 2-methylbutanoic acid, and 3-methylbutanoic acid were important volatile compounds determining flavor development in the doenjang employing bacterial starters. Starter-specific as well as highly-produced volatile compounds determined the directionality of flavor during doenjang ripening. Raw materials used for the starter culture preparation also affected the flavor.