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.
ABSTRACT
Aims: Gram-positive spore forming rod-shaped bacteria from Thai fermented foods were isolated, identified and screened for lipolytic activity. Methodology and results: Bacterial strains were isolated from Thai fermented foods by the standard dilution technique using Tryptic soy agar. Seven isolates which belong to the genus Bacillus and one isolate which belongs to Paenibacillus were characterized based on their phenotypic characteristics and 16S rRNA gene sequence analyses. Isolates NM8-1 (Group 1), PR9-2 (Group 2), PR11-1 (Group 3), KM15-1 and SS49-4 (Group 4), SS48-5 (Group 5) and SS503 (Group 6), were closely related to Bacillus methylotropicus, B. pumilus, B. flexus, B. cereus, B. subtilis and B. anthracis, based on 99.90-100% similarities, respectively. Isolate NM45-3 (Group 7) was closely related to Paenibacillus pasadenensis based on 99.55% similarity. All the isolates were susceptible to amikacin, chloramphenicol, clindamycin, erythromycin, gentamicin, imipenem, kanamycin, levofoxacin, novobiocin, streptomycin, tetracycline and vancomycin. Their lipase production in nutrient broth with Tween 20, Tween 40, Tween 60 or Tween 80 ranged from 0.014±0.129 - 3.231±0.087 U/mL. Bacillus subtilis SS48-5 exhibited highest lipase production when cultured with Tween 80 at pH 7.5 for 24 h. The optimum lipase production of this strain was at 40 °C after incubated for 30 h. Conclusion, significance and impact of study: The characterization and evaluation of the lipolytic activity of Bacillus and Paenibacillus strains isolated from Thai fermented foods will be useful for the species diversity, food fermentation and the lipase production.