Polyphasic Analysis of Pectinolytic and Stress-Resistant Yeast Strains Isolated From Ivorian Cocoa Fermentation

Abstract

<p>Microbial preparation containing pectinolytic strains as starter culture should help to standardize cocoa fermentation and reduce the lost due to the variability of cocoa bean. In this study, carbon metabolism, fermentative capacity and effect of environmental conditions on pectinase synthesis were analyzed in four yeast strains previously characterized as highly pectinolytic and stress resistant. The strains showed a restricted carbon metabolism profile with capacity to ferment only glucose and fructose and grown maximally at 5% of these carbon sources. Furthermore, yeasts strains were able to keep round 80% of their relative growth at up to 15% of sugar concentrations and proved to be osmotolerant at 25% glucose. Theses strains expressed their highest fermentative capacity at 35 °C producing up to 10.78 cm<sup>3</sup>of CO<sub>2</sub> and lost more than 50% of this capacity at 40 °C. The isolates studied produced polygacturonase as sole pectinase, optimal production of this enzyme is reached at pH (5-6), at incubation temperature of 30 ºC for strains YS 128, YS 202 and 35 ºC for strains YS 165 and YS 201. However, stress conditions such as 0.5 % acetic acid, 2% lactic acid, 6% citric acid and 6% ethanol repress strongly polygalacturonase production in the strains analyzed. Yeast strains studied present some physiological properties potentially useful for cocoa fermentation but the use of these strains as starter should take into account, the stress conditions susceptible to hinder pectinase production. <strong></strong></p>

Functional role of yeasts, lactic acid bacteria and acetic acid bacteria in cocoa fermentation processes

“…Other screening studies have looked at the tolerance toward acidity, ethanol, heat and osmotic stress and/or the enzymatic potential of candidate yeast strains (Samagaci et al 2014(Samagaci et al , 2015Visintin et al 2016;Koffi et al 2018). For instance, pectinolytic P. kudriavzevii and Candida nitrativorans strains isolated from Ivorian cocoa bean heap fermentation processes have been proposed as candidate yeast starter cultures, solely or in combination (Samagaci et al 2014(Samagaci et al , 2015(Samagaci et al , 2016. It has further been shown that a great genetic and metabolic intraspecies diversity occurs among P. kudriavzevii strains regarding the production of volatile organic compounds during laboratory-scale fermentations (400 g of cocoa pulp-bean mass in 1-L glass bottles) (Pereira et al 2017).…”

Functional yeast starter cultures for cocoa fermentation

“…Many screening experiments to select yeast strains with a high pectinolytic activity have also evidenced this intraspecies variability (see below). Besides polygalacturonases, pectin lyases and pectin esterases have been screened for, although their presence and/or expression in yeasts seem to be improbable (Dzogbefia et al, 1999;Samagaci et al, 2014b;Schwan et al, 1997;C. Díaz-Muñoz, M. Verce, L. De Vuyst, and S. Weckx, unpublished results).…”

Curing of Cocoa Beans: Fine-Scale Monitoring of the Starter Cultures Applied and Metabolomics of the Fermentation and Drying Steps

“…They enabled competitiveness with or inhibition of the background microbiota and improvement of the quality and sensory profiles of the end-products ( Saltini et al, 2013 ; De Vuyst and Weckx, 2016 ; Pereira et al, 2016 ; Ozturk and Young, 2017 ; Castro-Alayo et al, 2019 ; Figueroa-Hernández et al, 2019 ; Mota-Gutierrez et al, 2019 ; De Vuyst and Leroy, 2020 ; Santander Muñoz et al, 2020 ). Therefore, several studies have been performed to select strains of dominant and/or beneficial yeast and bacterial species occurring during spontaneous cocoa fermentation processes to elaborate appropriate inoculation cocktails ( Lefeber et al, 2010 , 2011 ; Pereira et al, 2012 ; Moens et al, 2014 ; Samagaci et al, 2014a , b ; Meersman et al, 2015 ; Visintin et al, 2016 ; Koffi et al, 2018 ). Successful controlled cocoa fermentation processes have been carried out with mixed-strain starter cultures of Saccharomyces cerevisiae , Limosilactobacillus fermentum (formerly known as Lactobacillus fermentum ) and/or Lactiplantibacillus plantarum (formerly known as Lactobacillus plantarum ), and Acetobacter pasteurianus and/or Acetobacter aceti ( Schwan, 1998 ; Lefeber et al, 2012 ; Sandhya et al, 2016 ; Moreira et al, 2017 ; Ho et al, 2018 ).…”