Analytical, Nutritional and Clinical Methods Comparison of determination method for volatile compounds in Thai soy sauce Pitipong Wanakhachornkrai, Sittiwat Lertsiri* Department of Biotechnology, Faculty of Science, Mahidol University, Rama VI Rd., Payathai, Bangkok 10400, Thailand Received 14 June 2002; received in revised form 1 May 2003; accepted 1 May 2003 Abstract Dynamic headspace (DHS) sampling, direct solvent extraction (DSE) and vacuum simultaneous steam distillation–solvent extraction (V–SDE) were used for sample preparation in volatile compound analysis in Thai soy sauce. The extracts obtained from two brands were then analyzed by gas chromatography-mass spectrometry (GC–MS). A comparative study of volatile compounds obtained from these preparation techniques was performed. Some similarities were observed among different characteristic volatile profiles obtained from each preparation technique. Highly volatile compounds were detected only by DHS whereas DSE and V– SDE gave a wide spectrum of chemical classes of compounds detected. Moreover, differences of volatile compounds detected from both soy sauces were noted. This might be due to the differences of production process employed and strains of microorganism used. # 2003 Elsevier Ltd. All rights reserved. Keywords: Thai soy sauce; Volatile compounds; Dynamic headspace; Direct solvent extraction; Simultaneous steam distillation–solvent extraction 1. Introduction Soy sauce is a fermented soybean food, which is used as a condiment or seasoning sauce worldwide. Its main raw materials are soybeans, wheat, and brine. Soy sauce could be classified into Japanese-type and Chinese-type, base on the amount of wheat used (Nunomura & Sasaki, 1993). In Japanese-type soy sauce, soybeans and wheat are used with the ratio 1:1, whereas less wheat is used in Chinese-type. Thai soy sauce, as one kind of Chinese-type soy sauce, has long history in development of manufacture and is consumed widely in the Southeast Asia (Mongkolwai, Assavanig, Amnajsongsiri, Flegel, & Bhumiratana, 1997; Valyasevi & Rolle, 2002). The characteristic flavor–aroma formation in the soy sauce depends on the manner of production employed, as well as raw materials and strains of microorganism used. The main steps of soy sauce production involved in fla- vor development are heat treatment of raw materials, koji culturing (mold fermentation), moromi fermenta- tion (lactic acid bacteria and yeast fermentation) including aging, and pasteurization (Nunomura & Sasaki, 1993). From this point, variation and complex- ity of soy sauce flavor characteristic from various ori- gins is pronounced. Most of the studies on the volatile flavor compounds in traditional soy sauce made in several regions such as Japan, Korean, including Indonesia have been reported (Apriyantono, Husain, Lie, Jodoamidjojo, & Puspitasari- Nienaber, 1999; Kim, Lee, Shin, Ji, Choi, & Kim, 1996; Kobayashi & Sugawara, 1999; Nunomura, Sasaki, Asao, & Yokosuka, 1976a, 1976b, 1978; Nunomura, Sasaki, & Yokosuka, 1980; Seo et al., 1996). However, the study on volatile flavor compounds in Thai soy sauce has not been well conducted, and there are no such data repor- ted. To cope with the optimization of manufacture and standardization of quality aspects, volatile flavor com- pounds in Thai soy sauce should be identified. To determine the volatile compounds in soy sauce, sample preparation is necessary prior to analysis by gas chromatography–mass spectrometry (GC–MS). The main reason for sample preparation is to obtain a concentrated analytical sample without interfering substances and to improve sensitivity for target analytes (Parliment, 1997). 0308-8146/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0308-8146(03)00256-5 Food Chemistry 83 (2003) 619–629 www.elsevier.com/locate/foodchem * Corresponding author. Tel.: +66-2-210-5300; fax: +66-2-246- 3026. E-mail address: scsls@mahidol.ac.th (S. Lertsiri).