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.

Microbiota associated with the starter cultures and brewing process of traditional Hong Qu glutinous rice wine

“…They are combinations of mixed cultures including filamentous fungi, yeast, and bacteria grown on a variety of cereal grains. Barley, millet, soybean, and nonwaxy rice are the most popular materials used in Korea, whereas glutinous rice is the most popular cereal used for preparing the starters in China (5). Chinese yellow rice wine can be classified into three main groups: (i) Hong Qu glutinous rice wine (produced mainly in Fujian province), (ii) wheat/yeast rice wine (represented by Shaoxing rice wine produced in Zhejiang province), and (iii) millet yellow wine (symbolized by Jimo old in Shandong province).…”

Concept of Nuruk on Brewing Technology

“…However, as the internal temperature of the mold increases with progression of fermentation, the temperature-sensitive R. oryzae gradually falls out of competition with the high temperature-resistant fungi such as A. oryzae [24]. A. oryzae possesses high glycation ability and secretes α-amylase [25], and is therefore important for glycosylation and liquefaction [8,24]. However, it is difficult to distinguish A. oryzae from aflatoxin-producing A. flavus using conventional taxonomic criteria because of its close relationship with A. flavus; thus, A. oryzae should be tested for its ability to produce aflatoxin [26,27].…”

“…However, as the internal temperature of the mold increases with progression of fermentation, the temperature-sensitive R. oryzae gradually falls out of competition with the high temperature-resistant fungi such as A. oryzae [24]. A. oryzae possesses high glycation ability and secretes α-amylase [25], and is therefore important for glycosylation and liquefaction [8,24].…”

Diversity, Saccharification Capacity, and Toxigenicity Analyses of Fungal Isolates in Nuruk

“…최근의 유전 체 연구에서도 R. oryzae에는 exo-cellulase 유전자, pectin 분해에 필요한 보조유전자, xyloglucan, xylan, inulin 등의 분해에 필요한 유전자가 발견되지 않고 있어서, 단당류나 전분과 같이 쉽게 분해할 수 있는 다당류를 빠르게 점유하 여 다른 곰팡이들과 경쟁에서 이기는 전략을 취하는 것으 로 밝혀졌다 [8]. 누룩에서도 R. oryzae는 발효초기에는 1차 침투자(primary colonizer) 역할을 하며 누룩의 구성성분의 분해역할을 할 것으로 추정되지만, 온도에 민감하기 때문 에 발효가 진행되어 누룩 내부온도가 올라가면 점차적으로 A. oryzae와 같은 고온성 곰팡이와의 경쟁에서 밀려나는 것 으로 생각된다 [2]. 황국균인 A. oryzae는 α-amylase를 분 비·생산하는 높은 당화능을 보이는 곰팡이로서 [9], 누룩에 서도 대표적인 우점균으로서 누룩의 당화 및 액화 기능에 가장 중요한 곰팡이 중 하나이다 [1,2].…”

“…누룩에서도 R. oryzae는 발효초기에는 1차 침투자(primary colonizer) 역할을 하며 누룩의 구성성분의 분해역할을 할 것으로 추정되지만, 온도에 민감하기 때문 에 발효가 진행되어 누룩 내부온도가 올라가면 점차적으로 A. oryzae와 같은 고온성 곰팡이와의 경쟁에서 밀려나는 것 으로 생각된다 [2]. 황국균인 A. oryzae는 α-amylase를 분 비·생산하는 높은 당화능을 보이는 곰팡이로서 [9], 누룩에 서도 대표적인 우점균으로서 누룩의 당화 및 액화 기능에 가장 중요한 곰팡이 중 하나이다 [1,2]. 그러나 A. oryzae는 aflatoxin 생산균인 A. flavus와 전통적인 분류학적 기준으 로는 구분할 수 없을 만큼 유연관계가 가까운 균으로 aflatoxin의 생산 유무를 검증하는 것이 필수적이다 [10,11].…”