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Evolution of Yeast Consortia during the Fermentation of Kalamata Natural Black Olives upon Two Initial Acidification Treatments.

ABSTRACT: The objective of this study was to elucidate the yeast consortia structure and dynamics during Greek-style processing of Kalamata natural black olives in different brine solutions. Olives were subjected to spontaneous fermentation in 7% (w/v) NaCl brine solution (control treatment) or brine acidified with (a) 0.5% (v/v) vinegar, and (b) 0.1% (v/v) lactic acid at the onset of fermentation. Changes in microbial counts, pH, acidity, organic acids, sugars, and alcohols were analyzed for a period of 187 days. Yeast consortia diversity was evaluated at days 4, 34, 90, 140, and 187 of fermentation. A total of 260 isolates were characterized at sub-species level by rep-PCR genomic fingerprinting with the oligo-nucleotide primer (GTG)₅. The characterization of yeast isolates at species level was performed by sequencing of the D1/D2 domain of 26S rRNA gene. Results showed that yeasts dominated the process presenting a relatively broad range of biodiversity composed of 11 genera and 21 species. No lactic acid bacteria (LAB) or Enterobacteriaceae could be enumerated after 20 and 10 days of fermentation, respectively. The dominant yeast species at the beginning were Aureobasidium pullulans for control and vinegar acidification treatments, and Candida naeodendra for lactic acid treatment. Between 34 and 140 days the dominant species were Candida boidinii, Candida molendinolei and Saccharomyces cerevisiae. In the end of fermentation the dominant species in all processes were C. boidinii and C. molendinolei, followed by Pichia manshurica and S. cerevisiae in lactic acid acidification treatment, P. manshurica in vinegar acidification treatment, and Pichia membranifaciens in control fermentation.

SUBMITTER: Bonatsou S

PROVIDER: S-EPMC5767579 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Evolution of Yeast Consortia during the Fermentation of Kalamata Natural Black Olives upon Two Initial Acidification Treatments.

Bonatsou Stamatoula S Paramithiotis Spiros S Panagou Efstathios Z EZ

Frontiers in microbiology 20180110

The objective of this study was to elucidate the yeast consortia structure and dynamics during Greek-style processing of Kalamata natural black olives in different brine solutions. Olives were subjected to spontaneous fermentation in 7% (w/v) NaCl brine solution (control treatment) or brine acidified with (a) 0.5% (v/v) vinegar, and (b) 0.1% (v/v) lactic acid at the onset of fermentation. Changes in microbial counts, pH, acidity, organic acids, sugars, and alcohols were analyzed for a period of ...[more]

PMID: 29375534

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Project description:The purpose of this study was to explore the inoculated fermentation of cv. Kalamata natural black olives using selected strains of yeast cultures with multifunctional potential. For this purpose, five yeast starters belonging to Candida boidinii (four starters) and Saccharomyces cerevisiae (one starter), previously isolated from table olive fermentation of the same variety and screened for their technological characteristics and probiotic potential, were inoculated in brines at the beginning of fermentation. Microbial populations (lactic acid bacteria, yeasts, and Enterobacteriaceae), pH, titratable acidity, organic acids, and ethanol were monitored during fermentation for a period of 5 months. At the same time, the survival of each starter was assessed by culture-dependent molecular identification at the beginning (0 days), middle (75 days), and final stages (150 days) of fermentation in the brines and olives (at the end of the process only). The results revealed the coexistence of yeasts and lactic acid bacteria (LAB) throughout fermentation in most processes and also the absence of Enterobacteriaceae after the first 20 days of brining. The population of yeasts remained 2 log cycles below LAB counts, except for in the inoculated treatment with C. boidinii Y28, where the yeast starter prevailed from day 60 until the end of the fermentation, as well as in the inoculated treatment with C. boidinii Y30, where no LAB could be detected in the brines after 38 days. At the end of the process, LAB ranged between 4.6 and 6.8 log10 CFU/mL, while yeasts were close to 5.0 log10 CFU/mL, except for the inoculated fermentation with C. boidinii Y27 and spontaneous fermentation (control), in which the yeast counts were close to 3.5 log10 CFU/mL. At the end of fermentation, the recovery percentage of C. boidinii Y27 was 50% in the brines and 45% in the olives. C. boidinii Y28 and S. cerevisiae Y34 could be recovered at 25% and 5% in the brine, respectively, whereas neither starter could be detected in the olives. For C. boidinii Y30, the recovery percentage was 25% in the brine and 10% in the olives. Finally, C. boidinii Y31 could not be detected in the brines and survived at a low percentage (10%) in the olives.

Project description:Nocellara Etnea is one of the main Sicilian cultivars traditionally used to produce both olive oil and naturally fermented table olives. In the present study, the effect of different salt concentrations on physico-chemical, microbiological, sensorial, and volatile organic compounds (VOCs) formation was evaluated in order to obtain functional Nocellara Etnea table olives. The experimental design consisted of 8 treatments as follow: fermentations at 4, 5, 6, and 8% of salt with (E1-E4 samples) and without (C1-C4 samples) the addition of starters. All the trials were carried out at room temperature (18 ± 2°C) and monitored for an overall period of 120 d. In addition, the persistence of the potential probiotic Lactobacillus paracasei N24 at the end of the process was investigated. Microbiological data revealed the dominance of lactic acid bacteria (LAB), starting from the 7th d of fermentation, and the reduction of yeasts and enterobacteria in the final product inoculated with starters. VOCs profile highlighted a high amount of aldehydes at the beginning of fermentation, which significantly decreased through the process and a concomitant increase of alcohols, acids, esters, and phenols. In particular, esters showed an occurrence percentage higher in experimental samples rather than in control ones, contributing to more pleasant flavors. Moreover, acetic acid, ethanol, and phenols, which often generate off-flavors, were negatively correlated with mesophilic bacteria and LAB. It is interesting to note that salt content did not affect the performances of starter cultures and slightly influenced the metabolome of table olives. Sensory data demonstrated significant differences among samples registering the highest overall acceptability in the experimental sample at 5% of NaCl. The persistence of the L. paracasei N24 strain in experimental samples, at the end of the process, revealed its promising perspectives as starter culture for the production of functional table olives with reduced salt content.

Dataset Information

Evolution of Yeast Consortia during the Fermentation of Kalamata Natural Black Olives upon Two Initial Acidification Treatments.

Publications

Evolution of Yeast Consortia during the Fermentation of Kalamata Natural Black Olives upon Two Initial Acidification Treatments.

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