Biological Stoichiometric Analysis during Substrate Utilization and Secondary Metabolite Production by Non-Saccharomyces Yeasts Using Grape Pomace Extract as Fermentation Medium

Maxwell Mewa-Ngongang,Neil P Jolly,Boredi S Chidi,Heinrich W Du Plessis,Ucrecia F Hutchinson,Vincent I Okudoh,Seteno K O Ntwampe,Enoch A Akinpelu

doi:10.3390/fermentation7020089

Abstract

The emerging interest in the search for alternatives to synthetic preservatives has led to various successful research studies exploring the use of yeasts as potential biological control agents and producers of biopreservatives. The findings that yeasts could be used as producers of biopreservatives lacked some engineering considerations regarding cost-effective process design for scale-up, although partial process optimization using renewable agro-waste has been achieved. This study investigated the biological stoichiometry and bioenergetic parameters during yeast growth and secondary metabolites production i.e., biopreservatives from non-Saccharomyces yeasts using grape pomace extract (GPE), a type of agro-waste, as a fermentation medium. This was achieved by reconfirming the optimum production conditions previously found for Candida pyralidae Y1117, Pichia kluyveri Y1125, and Pichia kluyveri Y1164 in GPE broth as a fermentation medium, conditions under which a high amount of yeast cells were obtained. High-density cell cultures were produced, from which the yeast cell pellets were harvested, dried, and combusted for the determination of elemental analysis, heat of combustion, biological stoichiometry, and bioenergetic parameters. This work generated biological stoichiometric models and bioenergetics information that could assist in the design of yeast biochemical conversion system when GPE is used as fermentation medium, thereby, addressing the biochemical engineering aspects that were lacking in a previous biopreservative production study using Candida pyralidae Y1117, Pichia kluyveri Y1125, and Pichia kluyveri Y1164.

Highlights

Based on previous research involving the yeasts selected for this work, it was deemed necessary to confirm the growth inhibition activity of the crude biopreservatives produced to ascertain the efficacy of the yeasts as biopreservative producers as previously reported [6]
The growth inhibition activities resulting from the three crude biopreservatives were prominent, with a volumetric zone of inhibition (VZI) of 0.78, 0.40, and 0.35 L VZI.mL−1 BCU for C. pyralidae Y1117, P
The strain P. kluyveri Y1164 was the yeast with the highest carbon and hydrogen content, 44.149% and 6.871%, respectively, while C. pyralidae Y1117 and

Summary

Introduction

The potential of yeasts as biological control agents and as producers of biopreservatives has been established by several independent studies [1,2,3,4,5] Those studies have been carried out in refined media with fewer biochemical engineering aspects for bioreactor designs and performance assessment for high-scale production. The feasibility of a bioprocess engineering system and the related physiological conditions under which bioreactions can occur would only be possible by studying the biological thermodynamics of the process, in particular when considering industrial-scale production.

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Conclusion