Development of a controlled lactic acid fermentation protocol for “Cipolla Bianca di Margherita” using an autochthonous starter

This study aimed to develop a new fermented product based on "Cipolla Bianca di Margherita" PGI (CBM-PGI), a traditional Apulian onion ecotype characterized by high sugar content and low pungency. The experimental work was divided into three phases: i) isolation and phenotypic and technological characterization of autochthonous lactic acid bacteria (LAB) from CBM-PGI; ii) preliminary evaluation of the fermentation capacity of five selected strains in a model formulation; iii) optimization of the fermentation process using a 2k factorial experimental design, modulating the brine/onion ratio, salt concentration, and temperature. Of the 25 isolates, 12 Gram-positive, catalase-negative, and homofermentative strains were characterized for tolerance to extreme pH, temperature, and NaCl. The autochthonous strain L1, identified as Lactococcus lactis, showed high acidifying capacity (Delta pH 1.74 after 48 h) and tolerance to adverse technological conditions. Fermentation trials demonstrated that the optimal combination (1:3 ratio, 5% NaCl, 35 degrees C) allowed the critical safety pH (4.4) to be reached in a short time (0.17 days for L1 vs. 3.53 days for spontaneous fermentation). Electronic nose analysis revealed distinct aroma profiles, with spontaneous fermentation characterized by higher concentrations of volatile compounds compared to inoculated samples. This study demonstrates the technical feasibility of producing a safe and standardized fermented food from CBM-PGI using autochthonous starter cultures, contributing to the valorization of a local agri-food resource and the preservation of crop biodiversity.