Brine Volatilome Changes Along the Spontaneous Fermentation of Spanish-Style cv. Chalkidiki Green Olives Under High and Low NaCl Conditions

Abstract

Table olives are essential components of the Mediterranean diet. Yet, their contribution to salt intake has prompted efforts to reformulate traditional products via safe interventions, mainly focused on the fermentation step. The volatilomics approach is an important tool to assess the complex table olives fermentation. However, extensive data related to monitoring of volatile organic compounds (VOCs) in manufacturing process of Spanish-style cv. Chalkidiki green table olives are scarce in the literature. The present work systematically examines VOCs profile in brines during spontaneous fermentation of cv. Chalkidiki olives under high (8% w/v) and 50% lower NaCl content using selected combinations of chloride salts (NaCl, KCl, CaCl2) in pilot scale for two consecutive periods. VOCs were determined by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. Changes in the population of the dominant microbial groups, pH, and titratable acidity values were also investigated. A total of 56 VOCs were identified, including acids, alcohols, carbonyls, esters, and phenols. Multivariate data analysis explored the links between volatile metabolites, microbial groups, and fermentation stages under different NaCl conditions. The evolution of propanoic acid and 2-butanol was intriguing for monitoring a fermentation dominated by lactic acid bacteria under low NaCl conditions, while 3-methyl-1-butanol was indicative of yeast prevalence arising from seasonal variation and/or high NaCl processing. Τhe important contribution of acetic acid to the overall VOCs profile at a late fermentation stage was typical in low NaCl brines. The complete results could be beneficial for marker-assisted monitoring of the fermentation processes in the future.