Identification of the microbiota in olives processed by spontaneous fermentation and production of table green olives via probiotic starter culture

Fermentation is widely applied worldwide to reduce the inherent bitterness of olive fruits; however, olive fermentation remains a complex and poorly standardized process due to the influence of numerous physical, chemical, microbiological, and environmental factors. The aim of this study is to determine the effects of a UV + US pre-treatment applied prior to olive fermentation on reducing the microbial load of the olives, and the effects of adding a probiotic starter culture in conjunction with these pre-treatments on the functional properties of fermented table green olives.The natural microbial load of olive fruits was reduced by combined ultraviolet (UV) and ultrasound (US) treatments, after which Lactobacillus plantarum MF376, Lactobacillus plantarum 299v, and Lactobacillus rhamnosus HA-114 were applied as starter cultures. At the end of fermentation, the pH values of Gemlik green olive brines ranged from 4.20 to 4.84, while titratable acidity values were between 0.266% and 0.452%. Lactic acid bacteria (LAB) counts in the brines ranged from 2.09 to 3.16 log CFU/mL. The total phenolic content of fermented Gemlik green olives varied between 182.91 and 1022.69 mg GAE/100 g. The antioxidant capacities of olive fruits were determined to be 81.23–435.56 µmol TE/100 g (FRAP), 87.78–224.25 µmol TE/100 g (TEAC), and 14.97–21.78 µmol TE/100 g (DPPH). Oleuropein contents ranged from 34.8 to 117.5 ppm. Yeast species isolated from raw green olive and spontaneously fermented control samples were identified as Wickerhamomyces anomalus. The findings demonstrated that the integrated UV + US pretreatment significantly reduced the initial microbial load, enabling improved fermentation control and accelerated brine acidification when combined with probiotic starter cultures. This study is innovative in its integration of non-thermal physical decontamination techniques with probiotic-guided fermentation to achieve both microbial stabilization and functional preservation in green table olives. The proposed approach offers a controlled and reproducible fermentation strategy with clear potential for industrial-scale production of standardized and functionally enhanced probiotic olives.