Oxidative stability of virgin avocado oil enriched with avocado leaves and olive-fruit-processing by-products (leaves, pomace) via ultrasound-assisted maceration

Abstract

Virgin avocado oil (VAO), treasured for its nutritional and sensory properties, is susceptible to oxidation. To improve its oxidative stability, the feasibility of enrichment with antioxidants from avocado or olive-processing by-products via ultrasound-assisted maceration was explored. Dried, milled avocado (AL), olive leaves (OL), or olive pomace (OP) were ultrasound-macerated with laboratory-extracted VAO at 5, 10, and 20% w/w levels. Induction-period (IP) values, determined via Rancimat (110 ◦C, 20 L/h), increased by 1.1–1.6-fold. Maceration with AL and OL added pigments (β-carotene, lutein, α-chlorophyll, and α-pheophytin) but only AL significantly boosted α-tocopherol levels (up to 3.7-fold). Extraction of major polar phenols (chlorogenic acid, oleuropein, and hydroxytyrosol) was poor (<42 mg/kg oil). Oleanolic and maslinic acids, from OL and OP, reached up to 650 and 260 mg/kg. The IP values correlated (r = 0.796, p = 0.002) only with total polar phenol content. Maceration with OP resulted in superior antioxidant activity, extending the predicted shelf-life from 14 to 22.3 months, reaching that of a hydroxytyrosol-rich extra-virgin olive oil (24.9 months). GC-MS revealed the dominance of volatile acids in OL- and OP-VAOs, and estragole in AL-VAO highlighting some organoleptic and safety challenges to be considered, particularly when aiming to exploit these materials for the enhancement of the oxidative stability of VAOs to sustain its production.