Chemical and sensory characteristics of low molecular weight fractions obtained from three types of Japanese soy sauce (shoyu) – Koikuchi, tamari and shiro shoyu Hanifah Nuryani Lioe a,1 , Koji Wada a , Takayoshi Aoki b , Masaaki Yasuda a, * a Department of Bioscience and Biotechnology, Faculty of Agriculture, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan b Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan Received 1 August 2005; received in revised form 15 December 2005; accepted 15 December 2005 Abstract Three typical forms of Japanese soy sauce (shoyu), koikuchi, tamari and shiro shoyu, can be differentiated, primarily due to their different compositions of soybeans and wheat used for their productions. To evaluate and compare the chemical characteristics of the low molecular weight (MW) fractions of three types of shoyu with their sensory data, gel filtration fractions of ultrafiltration products with MW less than 500 Da (F-500) were subjected to chemical and sensory analyses. The results showed that salty and umami tastes were characteristic of all F-500 fractions, however, the umami taste intensities of those of koikuchi and tamari shoyu were found to be twice as large as that of shiro shoyu. After separation by gel filtration, it was found that the tastiest fractions of the three types of shoyu were those containing sodium salt, free L-glutamic acid and most other free amino acids, especially sweet taste-eliciting amino acids, at con- centrations above their thresholds. In some umami fractions of koikuchi and shiro shoyu, that predominantly contained salt and phen- ylalanine but had a relatively low free L-glutamic acid content, a potential synergistic effect among free L-glutamic acid, salt and phenylalanine was obvious. This first report offers new insights into soy sauce research. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Ultrafiltration; Gel filtration chromatography; Koikuchi, tamari and shiro shoyu; Soy sauce; Umami taste 1. Introduction Shoyu is a traditional Japanese soy sauce that is made from a mixture of soybeans and wheat using a well-estab- lished two-step fermentation process, which involves koji- mold fermentation to yield koji and brine fermentation to yield moromi. The Japanese people recognize five distinct types of shoyu, based on specific physical and aroma characteristics, that result from differences in the soybean and wheat composition as well as differences in the fer- mentation processes that are used in their production (Fukushima, 1981, 1989). Among these, three typical forms of shoyu – koikuchi, tamari and shiro shoyu – can be differentiated, primarily due to their different raw material compositions. These are thought to contribute to the different types and compositions of breakdown products that are released during fermentation, which consequently impart the characteristic tastes of these three types of shoyu. Koikuchi shoyu, which has a strong aroma and a deep brown colour, is produced from equal amounts of soy- beans and wheat. Tamari shoyu, which is characterized by greater viscosity and less aroma than koikuchi shoyu but has a darker brown colour, is produced using soybeans as the main ingredient with a relatively small amount of wheat. Shiro shoyu is made using a relatively high ratio 0308-8146/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2005.12.047 * Corresponding author. Tel.: +81 98 895 8807; fax: +81 98 895 8734. E-mail address: yasuda@agr.u-ryukyu.ac.jp (M. Yasuda). 1 Present address: Department of Food Science and Technology, Faculty of Agricultural Technology, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16002, Indonesia. www.elsevier.com/locate/foodchem Food Chemistry 100 (2007) 1669–1677 Food Chemistry