Fungi associated with the traditional starter cultures used for rice wine in Korea

Abstract

The ‘Nuruk’ starter culture has been used for many years in the fermentation of rice wine in Korea. In present study, mycobiota in Nuruk cultures was identified by performing morphological, physiological, and phylogenetical analyses. Mucorales was the most common mycobiota in Nuruk, followed by yeast and Aspergillus. The composition of fungal species in Nuruk was different among samples and did not correlate with the geographical location from where the Nuruk culture was manufactured. For more detailed identification, 174 filamentous fungal strains were isolated from 39 Nuruk samples. Although the morphological and molecular analyses showed that the strains were identical at the genus level, some discordance was identified between species. Of the 174 strains, 160 showed thermotolerance, and the level of thermotolerance matched the clade generated by phylogenetic analysis. Six genera (Lichtheimia, Aspergillus, Rhizopus, Rhizomucor, Mucor, and Syncephalastrum) and 17 fungal species were identified. Among the genera, the genus Syncephalastrum had not been previously identified in Nuruk cultures, and the isolate was identified as Syncephalastrum racemosum. Two genera, Lichtheimia and Aspergillus, comprised approximately 84% of the filamentous fungal isolates from the Nuruk samples, and Lichtheimia ramosa and Aspergillus oryzae were the most commonly found species. The controversy regarding the presence of mycobiota in Nuruk starter cultures was addressed, and results showed that Nuruk contains unique mycobiota not yet found in other Asian starter cultures.