Abstract
Vanillin is valuable and popular flavor used in foods and cosmetics. Many bacteria species have the ability to decarboxylate substituted cinnamic acids in order to form vanillin. However, the phenolic biotransformation including vanillin production in a common fungus, the Aspergillus luchuensis, which is used in distilled beverages, has not yet been clarified. This study focused on elucidating the vanillin production due to phenolic biotransformation in A. luchuensis during fermentation. The phenolic metabolites were extracted by a solid phase column and they were determined using on LC/MS and LC/MS/MS in a selective ion mode. As a result, ferulic acid, vanillin and vanillic acid, were detected in the rice koji fermentationed by A. luchuensis and also fermentated with yeast. In addition, the accurate molecular formula of vanillin glucoside (C14H17O8, 313.0927, (M-H)− and its production ions was also determined by HRESI-mass spectrometry. Based on the results including the phenolic metabolites and related genes found in A. luchuensis genome, this study proposed the vanillin production mechanism due to the side chain cleavage of ferulic acid through Coenzyme A (CoA) and feruloyl-CoA hydratase/lyase, to form vanillin and acetyl-COA. In this study, another possible vanillin production pathway also was proposed due to the neutral hexose hydrolysis of vanillin glucoside. The subsequent dehydrogenation of vanillin produced vanillic acid. In addition, vanillin was detected in the distilled alcohol indicating its contribution to the aroma profile of beverages. It has been unknown that the vanillin in the distilled solution is derived from the vanillin produced during rice-koji and/or moromi mash fermentations.
Highlights
Vanillin is an aromatic flavor compound which is frequently used in foods and cosmetics
Identification of phenolic compounds In this study investigated the phenolic biotransformation including vanillin production due to phenolic biotransformation in A. luchuensis during fermentation together with brewing
The phenolic compounds in A. luchuensis during fermentation were detected by liquid chromatography–mass spectrometry (LC/MS) and LC/ MS/MS (Fig. 1)
Summary
Vanillin is an aromatic flavor compound which is frequently used in foods and cosmetics. One type is catalyzed by nonoxidative decarboxylase, which eliminates one carbon from the ferulic acid side chain, resulting in the formation of 4-vinyl guaiacol. The other type is characterized by the elimination of two carbons from the ferulic acid side chain, and this latter reaction can produce vanillin, a valuable flavor compound. The role of lactic acid bacteria in the conversion of phenolic compounds to vanillin has been elucidated during the brewing of whisky and wine (Rosazza et al 1995; Cavin et al 1993; Bloem et al 2007). The Japanese spirit, shochu, is a traditional distilled beverage that uses a common fungus, the Aspergillus species, with the raw materials, such as rice, Taira et al AMB Expr (2018) 8:40 sweet potato or barley. This study focused on elucidating the biotransformation of phenolic compounds in A. luchuensis during fermentation. The vanillin production mechanism in the Aspergillus species is for the first time proposed based on this study
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