Time course of l-tryptophan metabolites when fermenting natural grape musts: effect of inoculation treatments and cultivar on the occurrence of melatonin and related indolic compounds

Abstract

Background and Aims:Tryptophan is involved in the formation of bioactive compounds, such as melatonin (MEL) and3-indoleacetic acid (3-IAA), by yeast. Melatonin is a neurohormone whose occurrence in wine has been widely reported inrecent years. The occurrence, however, of MEL and other indolic compounds related to tryptophan metabolism by wineyeast strains has been scarcely reported in grape musts. This work examined the occurrence of these compounds during thealcoholic fermentation (AF) of musts from seven grape cultivars, Corredera, Chardonnay, Moscatel, Palomino Fino, Sau-vignon Blanc, Tempranillo and Vijiriega.Methods and Results:Must was fermented with threeSaccharomyces cerevisiaestrains and then in two cases an additionalsequential inoculation with the non-SaccharomycesyeastTorulaspora delbrueckiiwas carried out. Fermented must samples wereanalysed by UHPLC/HRMS to determine the concentration of:L-tryptophan, 5-hydroxytryptophan, 5-hydroxytryptamine,N-acetyl-5-hydroxytryptamine, MEL, 3-IAA, tryptamine, tryptophol andL-tryptophan ethyl ester. The profile of indoliccompounds during AF with the Aroma White strain depended on the cultivar. The yeast strain did not influence the profile ofindolic compounds; instead, fermentation time was found to be a more influential factor.Conclusions:The production of indolic compounds during the AF depends largely on the cultivar used and the day of fer-mentation on natural grape musts.Significance of the Study:This is thefirst study that quantifies 5-hydroxytryptophan andN-acetyl-5-hydroxytryptamineduring the AF of grape must. The occurrence of compounds with bioactive potential, for example 3-IAA and ML, during fer-mentation with commercial yeast strains is also described.