Influence of a Single Vineyard Yeast Community on Norisoprenoid Release During Pinot Noir Fermentation

Abstract

In the modern wine industry, intense interests have emerged at supplementing the predominant mono-inoculation of Saccharomyces cerevisiae with indigenous yeasts via alternative inoculation schemes, for example, co-inoculation. This study primarily attempts to evaluate the contribution of a single vineyard set of indigenous yeasts to odorants of Pinot noir. This naturally occurring yeast population was sourced from a Marlborough vineyard named MSPC, which were reported in a preceding project to be able to produce more abundant desirable volatiles, such as norisoprenoids, than other yeast populations. The MSPC yeast community, consist of 91 isolates, belonging to three species, including Saccharomyces cerevisiae, Saccharomyces uvarum, and Hanseniaspora uvarum. Volatile analyses, using Headspace Solid-Phase Microextraction (HS-SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS), were conducted to examine the aroma production in the first fermentation trial (Trial 1) using a newly developed formulation of synthetic grape medium plus grape skins (SGMS) to simulate Pinot noir grape must. The impact of two factors, yeasts, and fermentation media, on the wine aroma profile was studied in Trial 1. The fermentation medium was found to be overall more impactful than inoculation treatments on modulating volatile production in Trial 1. The results proved the viability of SGMS, as a fermentation medium formulation, for studying the varietal aroma releases from their grape-derived precursors. In terms of inoculum, the co-inoculation of MSPC yeasts demonstrated high reproducibility in volatile production. Moreover, the MSPC co-inoculum was able to release generally more β-ionone than Saccharomyces cerevisiae EC1118 during fermentation. This work characterized the 19 S. cerevisiae isolates of the MSPC yeast community to the strain level by microsatellite genotyping, indicating they were the same S. cerevisiae CB1 strain. Moreover, this work characterized all 91 yeast isolates in the MSPC collection based on their growth kinetics. For this purpose, an expectation-maximization (EM) algorithm was implemented to estimate Gompertz growth function parameters for each MSPC yeast growth observation dataset. In Trial 2, MSPC yeasts were compared and evaluated for their influence on norisoprenoid (β-damascenone, α-ionone, and β-ionone) aroma profiling of Pinot noir wines in mono-inoculation and co-inoculation schemes. Norisoprenoids were quantified using the same analytical protocol, HS-SPME GC-MS, leading to the following conclusions: - S. cerevisiae CB1 was a poor producer for α-ionone while the H. uvarum yeasts of the MSPC yeast collection released more β-damascenone. - The influence of MSPC yeast metabolism on norisoprenoid release was additive and averaged in co-cultures compared to monocultures.