Petri dish method to select yeasts able to produce more pigmented table olives

Andrea Caridi

doi:10.4025/actascitechnol.v42i1.48132

Abstract

The study of pigment adsorption of yeasts used for table olive fermentation may allow the protection of olive colour, by excluding those strains adsorbing phenolic compounds responsible for the colour. Fifty-one table olive yeasts were grown on Petri dishes using two olive-based screening media - ‘olive pulp agar’ and ‘olive seed agar’; the red, green, and blue colour components of the yeast’s biomass were measured. Wide and significant differences among the yeasts were observed. Based on the statistical analysis, ten yeasts were selected, excluding all the strains exhibiting a too high pigment adsorption. The research proposes a simple analytical method to characterize yeasts for their pigment adsorption, thus allowing the enhancement of the table olive colour. The two media may be prepared using any olive cultivar, thus allowing a specific screening of the yeasts. The selection of those yeasts unable to adsorb olive pigments may allow the production of more pigmented table olives.

Highlights

IntroductionOne approach considered olive cultivars and their chemical characteristics, in order to implement antioxidant content, fatty acid and sugar profiles that are influenced by cultivar and processing (Issaoui et al, 2011)
In all the selection protocols it is essential to exclude all the harmful yeasts (Arroyo-López et al, 2012): a) the fermentative strains performing a vigorous production of gas (CO2) that may penetrate olives and damage the fruits, producing ‘fish-eye’ spoilage; b) the polysaccharolytic strains, that cause the degradation of the polysaccharides of the olive fruit cell wall; c) the strains possessing polygalacturonase activity, that can grow and form pellicles in olive brines, causing a softening of olives kept in storage; d) the strains affecting sensory attributes of table olives
The main purpose of this research was to demonstrate that is possible to select yeasts for table olive fermentation according to their pigment adsorption activity; Table 8 summarizes the main characteristics of the 10 yeast strains selected on the base of their adsorption activity

Summary

Introduction

One approach considered olive cultivars and their chemical characteristics, in order to implement antioxidant content, fatty acid and sugar profiles that are influenced by cultivar and processing (Issaoui et al, 2011). Another approach considered autochthonous microflora; this was oriented towards the knowledge of the evolution of the microorganisms during table olive fermentation, according to the production technology used (Valenčič et al, 2010). Many studies on yeasts associated with table olives were carried out to identify adjunct cultures able to positively interact with lactic acid bacteria (Tufariello et al, 2019). The colour shelf life of table olives was studied (Sánchez, López‐ López, Beato, Castro, & Montaño, 2017); at present no author has proposed the screening of olive yeasts for their ability to interact in negative or positive way - with olive colour

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Conclusion