Killer yeasts isolated from olive brines: Technological and probiotic aptitudes

Area of Science:

• Food Microbiology
• Yeast Genetics

Background:

• Table olive fermentation involves complex microbial communities, including yeasts.
• Killer yeasts possess antagonistic properties against other microorganisms.
• Lactic acid bacteria (LAB) starters are commonly used in olive fermentation.

Purpose of the Study:

• To isolate and identify killer yeasts from table olive brines.
• To evaluate the technological and probiotic potential of these killer yeast isolates.
• To investigate the prevalence of killer yeasts during fermentation with different LAB starters and spontaneous fermentation.

Main Methods:

• Isolation of yeasts from table olive brines fermented with six LAB starters and spontaneous fermentation over 120 days.
• Identification of yeast isolates using standard microbiological and molecular techniques.
• Evaluation of killer phenotype, enzymatic activities (β-glucosidase, phytase), growth at low pH and high bile salt concentration, and in vitro digestion viability.

Main Results:

• Killer yeast phenotype was predominantly found in spontaneous fermentations, with numbers decreasing over time.
• Identified killer yeast species include Pichia kluyveri, Zygoascus hellenicus, Wickerhamomyces anomalus, Pichia membranifaciens, Candida boidinii, Candida diddensiae, and Saccharomyces cerevisiae.
• Wickerhamomyces anomalus strains exhibited broad enzymatic activities, high β-glucosidase and phytase levels, and superior tolerance to low pH, bile salts, and simulated digestion.

Conclusions:

• Spontaneous fermentation is a richer source of killer yeasts in table olive brines compared to LAB-inoculated fermentations.
• Wickerhamomyces anomalus strains possess significant technological and probiotic potential, particularly their enzymatic activities and stress tolerance.
• These findings highlight the potential of specific killer yeasts, like W. anomalus, as functional ingredients in food fermentations.