Potassium Hydroxide Extraction of Polyphenols from Olive Leaves: Effect on Color and Acrylamide Formation in Black Ripe Olives

Olive leaves are generated in large quantities in olive oil and table olive factories. This waste is currently used for multiple purposes, one of them being the extraction of bioactive substances, in particular phenolic compounds. The aims of this study were (i) to obtain a new polyphenolic extract from potassium hydroxide (KOH) -treated olive leaves; and (ii) to reduce acrylamide formation in black olives by using this extract. The results showed that olive leaves and leafless branches of the Manzanilla cultivar treated with 10 g/L KOH provide a solution that, concentrated under vacuum, had >6000 mg/L hydroxytyrosol and >2000 mg/L of hydroxytyrosol 4-glucoside. Moreover, the residual material generated after the treatment with KOH could be used for agronomic purposes, due to its high potassium content. The employment of this non-bitter extract during the darkening step of black ripe olive processing then resulted in darker fruits with higher potassium content. Likewise, the addition of the extract into the packing brine reduced the acrylamide formation by up to 32%, although this effect was batch-dependent. KOH olive extract could be useful for the reduction in acrylamide in black ripe olives along with the enrichment of this product in phenolic compounds and potassium.