Optimizing the initial moromi fermentation conditions to improve the quality of soy sauce Nguyen Xuan Hoang a , Sophia Ferng a , Ching-Hua Ting b , Wei-Hua Huang a , Robin Yih-Yuan Chiou a , Cheng-Kuang Hsu a, * a Department of Food Science, National Chiayi University, Chiayi City 60004, Taiwan, ROC b Department of Mechanical and Energy Engineering, National Chiayi University, Chiayi City 60004, Taiwan, ROC article info Article history: Received 17 April 2016 Received in revised form 9 July 2016 Accepted 21 July 2016 Available online 25 July 2016 Keywords: Soy sauce Optimization Fermentation abstract Soy sauce is a traditional condiment consumed by the people in China, Korea, Japan and Taiwan. The annual production is about 5 million metric tons in China, accounting for over 50% of the world pro- duction. The objective was to optimize the process parameters for preparation of initial moromi fermentation of soy sauce, which was considered as an enzymatic hydrolysis for the further fermentation stage. Temperature (35, 40 and 45  C), fermentation time (1, 3 and 5 days) and brine content (5 and 10% w/w) were studied as independent variables. The responses evaluated for deciding the optimum con- ditions were biochemical properties of total nitrogen, amino nitrogen, reducing sugar and total acid contents, as well as microbial properties of yeast and total bacterial counts. Experimental data were fitted well into second-order polynomial models. The simultaneously optimal conditions were 40.7  C tem- perature, 4.6 days fermentation time and 10% w/w brine content. The optimized response values for total nitrogen, amino nitrogen, reducing sugar and total acid contents and pH were 1.43, 0.65, 2.79, and 1.28% and 5.48, respectively. These conditions could obtain total nitrogen (>1.4%) and amino nitrogen (>0.56%) contents satisfying the requirement of first-grade soy sauce within 5 days fermentation. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Of the many Oriental fermented products, soy sauce is the one most widely consumed in Asiatic countries as a condiment and coloring agent in preparation of foods (Luh, 1995). In the manufacturing process, soy sauce koji is traditionally prepared by a mixture of steam-cooked soybean and roasted wheat with the koji mold such as Aspergillus oryzae or A. sojae. After a couple of days of this so-called solid-state fermentation, the resultant koji is mixed with brine solution and the formed mash, called moromi, is fer- mented to various periods of aging (Zhu & Tramper, 2013). During the aging period, the proteins and polysaccharides of the starting materials are hydrolyzed by the fungal protease and amylase, and the unique soy sauce flavor is artfully developed (Su, Wang, Kwok, & Lee, 2005). However, the fermentation time generally takes from six months to one year (Huang & Teng, 2004; Lee, Rho, Kim, Lee, & Lee, 2013; Zhu & Tramper, 2013), this is a drawback in soy sauce manufacturing. Such a long aging time could be explained by two major reasons, which are fermentation temperature and salt concentration. Fermentation temperature is an important factor in defining the aging period and qualities of soy sauce. However, in regular pro- duction of soy sauce, the fermentation temperature is usually dependent on the outdoors weather (Ko, Ahn, Van Den Berg, Lee, & Hong, 2009; Wu, Kan, Siow, & Palniandy, 2010; Yokotsuka, 1986), thus fluctuated temperature occurs during fermentation period, is one of the attributions to prolongs the time required for the for- mations of taste and flavor components. In order to shorten the fermentation time, as well as improve the qualities of soy sauce, the applications of various range of temperature have been investi- gated. For example, Yong and Wood (1974) indicated that fermentation time of soy sauce would reduce to only 3e4 months if the fermentation temperature was controlled at about 35e40  C. It could be seen that the stability of warm temperature (28e37  C) is suitable for the metabolism of microorganisms in moromi, espe- cially lactic acid bacterial and yeast (Fukushima, 2004; Sugiyama, 1984; Van Der Sluis, Tramper, & Wijffels, 2001; Wu et al., 2010; Yokotsuka, 1986; Yong & Wood, 1974) and thus reduce the * Corresponding author. Department of Food Science, National Chiayi University, No.300 Syuefu Rd., Chiayi City 60004, Taiwan, ROC. E-mail address: ckhsu@mail.ncyu.edu.tw (C.-K. Hsu). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2016.07.049 0023-6438/© 2016 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 74 (2016) 242e250