Nitrogenous Compound Utilization and Production of Volatile Organic Compounds among Commercial Wine Yeasts Highlight Strain-Specific Metabolic Diversity.

William T Scott,David E Block,Eddy J Smid,Richard A Notebaart,Oscar Van Mastrigt,Christina A Cuomo

doi:10.1128/spectrum.00485-21

Abstract

ABSTRACTGenetic background and environmental conditions affect the production of sensory impact compounds by Saccharomyces cerevisiae. The relative importance of the strain-specific metabolic capabilities for the production of volatile organic compounds (VOCs) remains unclear. We investigated which amino acids contribute to VOC production and whether amino acid-VOC relations are conserved among yeast strains. Amino acid consumption and production of VOCs during grape juice fermentation was investigated using four commercial wine yeast strains: Elixir, Opale, R2, and Uvaferm. Principal component analysis of the VOC data demonstrated that Uvaferm correlated with ethyl acetate and ethyl hexanoate production, R2 negatively correlated with the acetate esters, and Opale positively correlated with fusel alcohols. Biomass formation was similar for all strains, pointing to metabolic differences in the utilization of nutrients to form VOCs. Partial least-squares linear regression showed that total aroma production is a function of nitrogen utilization (R2 = 0.87). We found that glycine, tyrosine, leucine, and lysine utilization were positively correlated with fusel alcohols and acetate esters. Mechanistic modeling of the yeast metabolic network via parsimonious flux balance analysis and flux enrichment analysis revealed enzymes with crucial roles, such as transaminases and decarboxylases. Our work provides insights in VOC production in wine yeasts.IMPORTANCE Saccharomyces cerevisiae is widely used in grape juice fermentation to produce wines. Along with the genetic background, the nitrogen in the environment in which S. cerevisiae grows impacts its regulation of metabolism. Also, commercial S. cerevisiae strains exhibit immense diversity in their formation of aromas, and a desirable aroma bouquet is an essential characteristic for wines. Since nitrogen affects aroma formation in wines, it is essential to know the extent of this connection and how it leads to strain-dependent aroma profiles in wines. We evaluated the differences in the production of key aroma compounds among four commercial wine strains. Moreover, we analyzed the role of nitrogen utilization on the formation of various aroma compounds. This work illustrates the unique aroma-producing differences among industrial yeast strains and suggests more intricate, nitrogen-associated routes influencing those aroma-producing differences.

Highlights

IMPORTANCE Saccharomyces cerevisiae is widely used in grape juice fermentation to produce wines
Are yeast cell growth and fermentation completion influenced by the quality and amount of ammonia and amino acids in the grape must, the production of many crucial volatile organic compounds (VOCs) that are associated with desirable wine bouquet are impacted [7,8,9,10,11]
Fermentations were carried out for each of the S. cerevisiae strains in triplicate to evaluate nutrient utilization, i.e., ammonia, amino acids, and sugar consumption, as well as VOC production capabilities across strains growing in the same enological medium

Summary

Introduction

IMPORTANCE Saccharomyces cerevisiae is widely used in grape juice fermentation to produce wines. Are yeast cell growth and fermentation completion influenced by the quality and amount of ammonia and amino acids in the grape must, the production of many crucial volatile organic compounds (VOCs) that are associated with desirable wine bouquet are impacted [7,8,9,10,11]. It has been shown that an inverse correlation exists between initial nitrogen levels (excluding at low initial nitrogen levels) and fusel alcohol concentrations [8, 13,14,15,16] It has been demonstrated in wine fermentations using S. cerevisiae that amino acids are directly involved in the formation of higher alcohols, esters, and fatty acids, and that these volatile organic compounds subsequently influence aroma attributes of wines [12, 17]. These studies were groundbreaking in illustrating strain-dependent behavior for several yeast strains under various environmental conditions, they lacked insight regarding the roles specific nitrogenous compounds play in the

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