HYDROXYTYROSOL PRODUCTION BY DIFFERENT YEAST STRAINS: SACCHAROMYCES AND NON-SACCHAROMYCES AND THE RELATION WITH THE NITROGEN CONSUMPTION

Abstract

Hydroxytyrosol (HT) is a phenolic compound with extensive bioactive properties. It is present in olives, olive oil and wines. Its occurrence in wines is partly due to yeast synthetise tyrosol from tyrosine by the Ehrlich pathway, which is subsequently hydroxylated to .

The aim of the present work is to study how different yeast strains can influence in the HT production and, how the different nitrogen consumption of each strain can interfere the production of bioactive compounds.

A total of six strains were evaluated for the production of HT, four of them were Saccharomyces and two of them were non-Saccharomyces. The Saccharomyces ones were Red Fruit, QA23, Uvaferm and Lalvin Rhone, and the non-Saccharomyces were Torulaspora delbrueckii and Metschnikowia pulcherrima.

In order to know the nitrogen consumption of each yeast, the nitrogen content in the extracellular media was measured at the early days of the fermentation.

The alcoholic fermentation was performed in synthetic must prepared according to the instructions of Riou et al., 1997. Fermentation was carried out in sextuplicate for each strain. lasting 10 days each. A total of 360 samples were collected. The growth of yeast, the weight of the flask, density, and the Baume grade of the must were recorded daily to monitor the fermentation.

Prior to the analyses of the compounds, a cleaning step was performed using a Solid Phase Extraction (SPE). The protocol for the SPE was optimized following the instructions of AOAC, 20212. All the compounds of the Erlich pathway (tyrosine, hydroxyphenylacetic acid, tyrosol, hydroxyphenylacetaldehyde acid, hydroxyphenylpyruvic acid and hydroxytyrosol) were evaluated thanks to a validated method of UHPLC-HRMS. The analysis was carried out in a Waters Acquity UHPLC (Milford, Massachusetts, USA) coupled to a Waters Xevo TQ (Milford, Massachusetts, USA) triple quadrupole mass spectrometer. The MassLynx MS software was used. The column used was an Acquity UPLC BEH C18. The chromatographic conditions consisted of two mobile phases, water with 0.2% acetic acid (A) and acetonitrile (B), with a gradient elution programmed.

The obtained results show that the Saccharomyces strains have a higher production of HT than non-Saccharomyces. Significant differences were observed between strains for the production of HT. The highest production was in day 5 for Uvaferm, reaching a concentration of 4 ng/mL. A different nitrogen consumption was observed for each yeast.