Effect of Temperature, NaCl and Ferulic Acid Concentration on Bioconversion of Ferulic Acid to 4-Vinylguaiacol and 4-Eth
Decarboxylation of ferulic acid (FA) to 4-vinylguaiacol (4-VG) followed metabolized to 4-ethyl guaiacol (4-EG) via yeast metabolism are inherent to soy sauce fermentation process. 4-EG (Smoky-like and sauce flavour) is a representative flavour component i
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1 Introduction 4-EG, more often described as smoky and sauce flavour, is appreciated in Japanese style and Chinese traditional fermented soy sauce [1, 2]. The threshold of 4-EG is reported to be 0.5 mg/L [3], whereas its precursor has a much higher threshold value of *600 mg/L [4]. Moreover, there have been reported that 1–2 mg/L 4-EG could promote aroma and flavor of soy product [5, 6]. Therefore, formation of 4-EG has extremely close relationship with the quality of soy sauce [7]. Chinese soy sauce can be classified into high-salt liquid-state soy sauce and low-salt solid-state soy sauce base on the raw materials, brine, fermentation temperature and fermentation period. The conventional fermentation process of high-salt liquid-state soy sauce starts with koji culturing which a solid-state fermentation of Aspergillus species on a mixture of soybeans and wheat, after that, moromi fermentation which the koji is mixed with saline water (22–23% salt), and resulting brine solution about 17%, furthermore, about 6 month process time for high-salt liquid-state soy sauce at 30 °C [8, 9]. The raw material of low-salt solid-state soy sauce are soy beans and wheat bran. Followed the koji is mixed with saline water (13–14% salt), the resulting brine solution has a lower salt concentration about 11%, about one month fermentation for low-salt solid-state soy sauce at 40 °C [10]. In the cell walls of cereals, ferulic acid monomers as well as dimers are esterified to arabinose residues of arabinoxylans or etherified to lignin surfaces [4]. In the soy sauce fermentation process, of which raw materials, such as soybeans and wheat or
W. Qi W.-T. Zhang F.-P. Lu (&) Key Laboratory of Industrial Fermentation Microbiology, Tianjin University of Science & Technology, Ministry of Education, Tianjin 300457, People’s Republic of China e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2018 H. Liu et al. (eds.), Advances in Applied Biotechnology, Lecture Notes in Electrical Engineering 444, https://doi.org/10.1007/978-981-10-4801-2_29
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wheat bran [11], cell wall of cereal was degraded to small molecular weight substances by degrading enzymes (such as xylanases) secreted by Aspergillus, then feruloyl esterases destroy ester bond between FA and arabinose residues leading to release the FA [12]. FA can be decarboxylated to 4-VG followed metabolized to 4-EG though 4-VG reductase produced by yeast [13, 14]. It has been reported that 4-EG could be yielded by Candida versatilis but not Zygosaccharomyces rouxii [15]. Phenolic compounds are appreciated for their antioxidant activity preventing human from many diseases associated with oxidative stress [16]. Moreover, the flavour and quality of soy sauce are attracting consumer attention, because the condiment has a closely relation with their daily life. Thus, the ability of Candida versatilis biotransform of FA to 4-VG and of 4-VG to 4-EG by several treatments, such as initial FA concentration, NaCl concentration and temperature, have been investigated.
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