Abstract
The use of non-Saccharomyces yeast species generally involves sequential or co-inoculation of a Saccharomyces cerevisiae strain to complete fermentation. While most studies have focused on characterising the impact that S. cerevisiae has on the growth and metabolic activity of these non-Saccharomyces species, microbial interactions work reciprocally. Antagonism or competition of non-Saccharomyces species against S. cerevisiae has been shown to impact subsequent fermentation performance. To date, it remains unclear whether these negative interactions are strain specific. Hence, characterisation of strain-specific responses to co-inoculation would enable the identification of specific S. cerevisiae strain/non-Saccharomyces combinations that minimise the negative impacts of sequential fermentation on fermentation performance. The competitive fitness response of 93 S. cerevisiae strains to several non-Saccharomyces species was simultaneously investigated using a barcoded library to address this knowledge gap. Strain-specific fitness differences were observed across non-Saccharomyces treatments. Results obtained from experiments using selected S. cerevisiae strains sequentially inoculated after Metschnikowia pulcherrima and Torulaspora delbrueckii were consistent with the competitive barcoded library observations. The results presented in this study indicate that strain selection will influence fermentation performance when using non-Saccharomyces species, therefore, appropriate strain/yeast combinations are required to optimise fermentation.
Highlights
Inoculation with selected Saccharomyces cerevisiae strains is one way to initiate fermentation efficiently in compositionally and microbiologically diverse grape musts [1].inoculated wines are often considered to lack the complexity of their uninoculated counterparts [2]
The strain-specific effect resulting from preculturing of medium with different nonSaccharomyces species (A. pullulans, H. uvarum, L. thermotolerans, M. pulcherrima and T. delbrueckii) on the growth of S. cerevisiae was investigated
While the majority of these non-Saccharomyces species are associated with beneficial organoleptic effects in wine [12,13,36,37], several studies have reported slower fermentation rates when these species were used in co-culture [11,20,37]
Summary
Inoculation with selected Saccharomyces cerevisiae strains is one way to initiate fermentation efficiently in compositionally and microbiologically diverse grape musts [1].inoculated wines are often considered to lack the complexity of their uninoculated counterparts [2]. Inoculation with selected Saccharomyces cerevisiae strains is one way to initiate fermentation efficiently in compositionally and microbiologically diverse grape musts [1]. This lack of complexity may be attributed to a reduction in non-Saccharomyces metabolic activity To address this perceived shortcoming, several nonSaccharomyces species have been isolated and commercialised with the objective of enhancing the aroma and flavour attributes of wine [3]. Species such as Torulaspora delbrueckii and Metschnikowia pulcherrima are commercially available as starter cultures and represent practical tools that can be used to reduce alcohol and volatile acidity concentrations in wine and to modulate the concentrations of varietal thiols and esters [4]. Due to the variable capacity of these yeasts to complete sugar consumption [5], strains of
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