Continuous production of antioxidant extracts from olive leaves and branches through twin-screw extrusion: a feasibility study

Abstract

Twin-screw extrusion has recently seen its uses extended to the continuous green extraction of biomolecules. Here, it was successfully used for the extraction of antioxidants using subcritical water from two olive co-products, i.e., leaves (OL), and leaves plus branches (OLB). Extraction yields obtained were 52.5 % and 65.6 %, respectively, in proportion to the initial water-solubles. Total phenolic contents and antioxidant activities in the two freeze-dried extracts were 8.9 and 9.6 g gallic acid eq. per 100 g, and 9.8 and 12.1 g Trolox eq. per 100 g. These are of the same order of magnitude as those obtained in laboratory scale studies in which the extracts were obtained using ethanol rather than water as the extraction solvent, whether by maceration, Soxhlet or ultrasound. Twin-screw extrusion also enabled a high proportion of sugars to be co-extracted and, to a lesser extent, proteins, acetyl groups, and ash. For the future, this continuous industrial-scale technology represents a robust and economical methodology for the green extraction of antioxidants from olive leaves and branches. These extracts could find applications in agriculture or horticulture for plant protection, for food applications, or even in the cosmetics industry.