Assessment of Starters of Lactic Acid Bacteria and Killer Yeasts: Selected Strains in Lab-Scale Fermentations of Table Olives (Olea europaea L.) cv. Leccino

Abstract

Olives debittering, organoleptic quality and safety can be improved with yeasts and lactic acid bacteria (LABs) selected strain starters, that allow for better fermentation control with respect to natural fermentation. Two selected killer yeasts (Wickerhamomyces anomalus and Saccharomyces cerevisiae) and Lactobacillus plantarum strains were tested for olive (cv. Leccino) fermentation to compare different starter combinations and strategies; the aim was to assess their potential in avoiding pretreatments and the use of excessive salt in the brines and preservatives. Lactobacilli, yeasts, molds, Enterobacteriaceae and total aerobic bacteria were detected, as well as pH, soluble sugars, alcohols, organic acids, phenolic compounds, and rheological properties of olives. Sugars were rapidly consumed in the brines and olives; the pH dropped quickly, then rose until neutrality after six months. The oleuropein final levels in olives were unaffected by the treatments. The use of starters did not improve the LABs’ growth nor prevent the growth of Enterobacteriaceae and molds. The growth of undesirable microorganisms could have been induced by the availability of selective carbon source such as mannitol, whose concentration in olive trees rise under drought stress. The possible role of climate change on the quality and safety of fermented foods should be furtherly investigated. The improvement of olives’ nutraceutical value can be induced by yeasts and LABs starters due to the higher production of hydroxytyrosol.

Microbial and Chemical Characterization of Natural-Style Green Table Olives from the Gordal, Hojiblanca and Manzanilla Cultivars

“…Finally, a similar trend was observed for verbascoside concentration, but with higher values in Hojiblanca than in the Manzanilla and Gordal brines (final concentration of 346 ± 7 mg/L versus 197 ± 10 and 43 ± 2 mg/L, respectively). The above-mentioned increases in concentrations of hydroxytyrosol, tyrosol and verbascoside in brines during fermentations correspond to the progressive decreases in the content of such phenolic compounds in the olives, as demonstrated by other authors [ 16 , 39 ]. The accumulations of hydroxytyrosol and tyrosol in the brines can be attributed to the hydrolysis of oleuropein, hydroxytyrosol-4-β-glucoside and salidroside in the pulp and then diffusion from the pulp into the brine [ 40 ].…”

Yeast Biotechnology 6.0

“…Bencresciuto et al [42] evaluated starter cultures of lactic acid bacteria (Lactobacillus plantarum strains) and killer yeasts (Wickerhamomyces anomalus and S. cerevisiae) for the fermentation of table olives to debitter olives [43] and improve their organoleptic quality and safety [44,45]. This study aimed to assess their potential to avoid pretreatments and the use of excessive salt in the brines and preservatives.…”

Main Challenges Expected from the Impact of Climate Change on Microbial Biodiversity of Table Olives: Current Status and Trends

“…Generally, the sugar consumption follows a specific sequence. Thus, glucose and fructose are the most easily fermentable sugars and are rapidly consumed by the LAB and yeast [63]. They are converted into lactic acid and ethanol, respectively.…”

“…After the reducing sugars are consumed, sucrose is broken down by microbial sucrases, and the resulting glucose and fructose are then metabolized by LAB and yeast. Maltose, another disaccharide composed of two glucose molecules, can be consumed by some strains able to produce maltases for its breakdown [63]. Other less abundant sugars, such as mannitol and xylose, may be consumed to a lesser extent by certain microorganisms during the fermentation [64][65][66].…”