Volatilome changes in brines along the spontaneous fermentation of Spanish-style cv. Chalkidiki green olives under high and low NaCl conditions

Abstract

Abstract Table olives are essential components of the Mediterranean diet and their consumption is constantly spreading worldwide. However, as there are special concerns regarding their contribution to salt intake, there is a trend to reformulate traditional products via safe interventions. The present work systematically examines the profile of volatile organic compounds (VOCs) in brines during spontaneous fermentation of Spanish-style cv. Chalkidiki green table 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 population of the dominant microbial groups, pH and titratable acidity values were also investigated using appropriate methods. A total of 56 VOCs were identified, including acids, alcohols, carbonyls, esters, and phenols. A volatilomic approach through multivariate data analysis allowed to explore 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. Furthermore, a sharply increased content of acetic acid at a late stage of fermentation was typical in low NaCl brines. The comprehensive results aided to systematically evaluate the volatile variation in high/low NaCl content brines throughout spontaneous fermentation of Spanish-style cv. Chalkidiki olives and could be beneficial for marker-assisted monitoring of the fermentation processes in the future.