Enzymes Characterized From Vanilla

This chapter focuses on particular enzymes catalyzing the chain of reactions beginning from L-phenylalanine and ending with vanillin. The oxidative enzymes, peroxidases, and polyphenoloxidases, are responsible for browning of the pod tissue and for the formation of volatile ketones, aldehydes, and hydrocarbon derivatives, which perhaps may also add to the final vanilla flavor. A non-oxidative chain shortening enzyme, 4-hydroxybenzaldehyde synthase (4HBS), converting 4-coumaric acid to 4-hydroxybenzaldehyde was isolated, purified, and characterized from V. planifolia embryo culture. During the curing process, activity of glycosyl hydrolases liberates vanilla flavor components from their bound glycosidic forms. In vanilla, which is a monocot, both L-phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase activity (TAL) activities were identified. Methylation of the hydroxyl group at position 3 catalyzed by an O-methltransferase (OMT) is considered the final step in the biosynthesis of vanillin (3-methoxy-4-hydroxybenzaldehyde).