Factors influencing the production of the antioxidant hydroxytyrosol during alcoholic fermentation: Yeast Assimilable Nitrogen and Sugar content.

Abstract

Hydroxytyrosol (HT) is well known for its potent antioxidant activity and anticarcinogenic, antimicrobial, cardioprotective and neuroprotective properties. One possible explanation to its origin in wines is the synthesis from tyrosol, which in turn is produced from the Ehrlich pathway by yeasts.  This work aims to explore the factors that could increase the final content as the initial concentration of yeast assimilable nitrogen (YAN) and sugar. Two different concentrations of YAN were proved between 210mg/L and 300 mg/L. Additionally, two different concentrations of sugar were used: 100g/L and 240 g/L.  Alcoholic fermentations in synthetic must were performed with the strain QA23. Commercial Saccharomyces cerevisiae yeasts QA23 were used, as well as a strain with a specific modification to increase the production of fusel alcohols. Experimental design includes different YAN and sugar concentrations. The analysis was performed in a Thermo Scientific liquid chromatography system consisting of a binary UHPLC Dionex Ultimate 3000RS, connected to a quadrupole orbitrap Qexactive hybrid mass spectrometer (Thermo Fisher Scientific, Bremen, Germany), which was equipped with a heated electrospray ionization probe (HESI-II). The column used was a ZORBAX SB-C18 (2.1 × 100 mm, 1.8-μm particle size) Higher concentrations of hydroxytyrosol were obtained in synthetic must with higher amount of sugar (240g/L) and lesser YAN (210mg/L). Furthermore, the modified yeast presents a higher capacity to produce HT and tyrosol. Selecting the adequate conditions of sugar and YAN can increase the HT and tyrosol content 10 times.These results might explain certain differences between HT content in wines.