1. IntroductionMeyerozyma (Pichia)

1. Introduction
Meyerozyma (Pichia) guilliermondii belongs to the group of so-called“flavogenic yeasts” (Tanner et al., 1945). Although, it is regarded as acontaminant producing off-flavor compound, i.e. 4-ethylphenol, duringred wine production (Chatonnet et al., 1995; Dias et al., 2003), it is one of the dominant yeasts found in koji and moromi of Japanese and
Chinese fermented soybeans (Kim et al., 2010). Wah et al. (2013)reported that M. guilliermondii EM1Y52 produced volatile phenol compounds and could also enhance the volatile flavor compound production of Zygosaccharomyces rouxii in Thai soy sauce fermentation.
Soy sauce ismade by fermentation of soybean combinedwithwheat flour, rice flour, and brine (Fukushima, 2004; Mongkolwai et al., 1997). Its production involves koji culture using Aspergillus oryzae andmoromi
fermentation by adding brine solution into the koji. During koji culture, A. oryzae mainly secretes protease and amylase to break down protein and carbohydrate in soybean and flour into peptides, amino acids and
sugars, respectively (Mongkolwai et al., 1997). In addition to those enzymes, glutaminase is an important enzyme in soy sauce fermentation that converts L-glutamine originated from soy protein to L-glutamicacid (Fukushima, 2004). Therefore, increasing production of glutaminase during soy sauce fermentation could result in an increase of L-glutamic
acid which imparts so-called “umami” taste and improves the flavor in soy sauce (Ohshita et al., 2000; Yano et al., 1988). L-Glutaminase in soy sauce fermentation has been known to be produced by A. oryzae, however
this fungal enzyme is markedly inhibited by high NaCl concentration of 20–22% (w/v) which is the common condition in moromi fermentation (Yano et al., 1988). Meanwhile, salt-tolerant yeast involving in moromi fermentation, Z. rouxii has been reported for its glutaminase that can tolerate high salt concentration (Iyer and Singhal, 2008). Many
studies on the physiological roles, enzymatic properties, and application of glutaminase from various microorganisms have been conducted, including Micrococcus luteus (Moriguchi et al., 1994), Bacillus pasteurii(Klein et al., 2002), Lactobacillus rhamnosus (Weingand-Ziade et al.,2003), Lactobacillus reuteri KCTC3594 (Jeon et al., 2009), Saccharomyces
cerevisiae (Penninckx and Jaspers, 1985), Cryptococcus albidus (Iwasaet al., 1987) and Debaryomyces sp. (Durá et al., 2002). In this study,the production of glutaminase in salt-tolerant yeast M. guilliermondii isolated from Thai soy sauce moromi is first reported. SinceM. guilliermondii is GRAS (Generally Recognized as Safe) organism
(Sibirny and Boretsky, 2009), understanding of its glutaminase production would be beneficial in the development of the starter culture for soy sauce fermentation. International Journal of Food Microbiology 192 (2015) 7–12
⁎ Corresponding author at: Department of Biotechnology, Faculty of Science, Mahidol University, 272 Rama VI Rd., Rachathevi, Bangkok 10400, Thailand. Tel.: +66 22015300; fax: +66 2 3547160.
E-mail address: apinya.ass@mahidol.ac.th (A. Assavanig).http://dx.doi.org/10.1016/j.ijfoodmicro.2014.09.019
0168-1605/© 2014 Elsevier B.V. All rights reserved.Contents lists available at ScienceDirectInternational Journal of Food Microbiology
journal homepage: www.elsevier.com/ locate/ijfoodmicro