Oleuropein hydrolysis by lactic acid bacteria in natural green olives

Abstract

The presence of phenolic compounds in raw olives, particularly the bitter glucoside oleuropein, requires transforming this substance into other non-bitter to make the fruit palatable. An alkali treatment is currently carried out to hydrolyze the oleuropein but a high volume of wastewater is generated. The aim of this study was to develop a natural product without an alkali treatment and with appropriate organoleptic characteristics similar to those of Spanish-style green olives. Mild heat treatments (60 °C for 10 min) were sufficient to inactivate the β-glucosidase activity which prevented the formation of antimicrobial compounds and thereby the growth of lactic acid bacteria was promoted. By contrast, heating released a high concentration of oleuropein in fruits that remained at a very high level even after 6 months of fermentation. The inoculation of the brines of Manzanilla olives with selected lactic acid bacteria with oleuropeinolytic activity was insufficient for reducing the high concentration of the bitter glucoside. However, favorable results were obtained with varieties such as Gordal and Aloreña, which have lower oleuropein contents. The product obtained showed a very attractive color, similar to that of Spanish-style green olives and lighter than natural green olives, which is a positive aspect for consumer acceptability.