The appearance of 4-ethyl phenol, 4-ethylguaiacol, 2-phenyl ethanol (phenyl ethyl alcohol, floral-rosy), through the action of various yeasts, may also be important to the characteristic flavor profile of soy sauce. The most important role of Candida species and Torulopsis species fermentation is the production of phenolic compounds, such as 4-ethylguaiacol and 4-ethylphenol (79). Investigators proposed that cinnamic acids series compounds, ferulic acid and p-coumaric acids, are the precursors of the two alkylphenols. Wheat and wheat bran incorporated into the koji preparation contribute a series of guaiacol compounds: vanillin, vanillic acid, ferulic acid, and 4-ethyl guaiacol, which are probably derived from lignin and the breakdown of various glycosides during the heat treatment. Nonvolatile components in commercially fermented soy sauce produced from whole soybeans and defatted soybeans were analyzed by reversed phase HPLC (RP-HPLC). Two soy sauce groups were clearly differentiated by soft independent modeling of class analogy (SIMCA), where ferulic acid was identified as one of the key components for the differentiation (80).
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