Characterization and amylolytic activity of yeast and mold strains from Thai sweet rice

ABSTRACT

Aims: The aim of this study was to isolate and identify the yeast and mold strains from the starter and to investigate their amylolytic activity. Methodology and results: Thirty-two yeasts were isolated from ten samples of look-paeng khao-mak, a traditional starter culture in the production of khao-mak (sweet rice) in several places in Thailand. All isolates were identified based on their morphological and biochemical characteristics including the sequencing of D1/D2 domain of large subunit (26S) ribosomal DNA analyses. They were identified as Saccharomycopsis fibuligera (9 isolates), Candida rugosa (2 isolates), C. tropicalis (1 isolate), Clavispora lusitaniae (1 isolate), Wickerhamomyces anomalus (15 isolates) and Meyerozyma guilliermondii (4 isolates). All isolates of S. fibuligera showed high amylolytic activity. One-hundred isolates of mold were isolated from twenty-one samples of look-paeng khao-mak. They were belonged to Amylomyces sp. (42 isolates), Rhizopus sp. (30 isolates), Mucor sp. (12 isolates) and Penicillium sp. (16 isolates) based on their morphological characteristics. Four isolates, LK4-1, LK8-2, LK12-5 and LK17-1 showed amylase activity ranged from 32.24 to 39.74 unit/mL by dinitrosalicylic acid (DNSA) method. The isolates LK4-1, LK8-2 and LK12-5 were identified as Amylomyces rouxii and LK17-1 was Rhizopus microsporus based on their morphological characteristics and the ribosomal RNAencoding DNA (rDNA) internal transcribed spacer (ITS) sequences. Conclusion, significance and impact study The characterization and evaluation of yeast and mold species based on their phenotypic and genetic characteristics including their amylase activity will be useful for the diversity and sweet rice production.