Abstract
Olive leaves are rich in many compounds precious for human health. Due to this property, the current study was aimed to valorize the extract from this by-product in a cereal-based food, very popular all around the world, the “taralli”. To this aim, ultrasound-assisted extraction was applied to dried olive leaves to obtain the extract, used as “taralli” ingredient, instead of white wine. The “taralli” with and without extract was subjected to in vitro digestion to assess the quantity of polyphenolic compounds released in the gastrointestinal tract to become available for absorption. Total content of phenols and flavonoids, as well as the antioxidant capacity, was measured on both cooked and uncooked samples, before and after digestion. In addition, High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) of the three most abundant polyphenols present in olive leaf extracts, such as oleuropein, hydroxytyrosol, and verbascoside, was carried out at the three stages of the digestion process. The results showed that the substitution of white wine with olive leaf extract increased the total content of polyphenols and flavonoids and the antioxidant capacity. Bio-accessibility of the main phenolic compounds demonstrated that oleuropein resisted slightly after gastric digestion but was almost completely degraded in the intestinal phase, while hydroxytyrosol and verbascoside were not resistant to the digestion process from the gastric phase.
Highlights
Olive leaves are agricultural residues resulting from the pruning of olive trees, as well as from olive mill leavings
The results showed that the substitution of white wine with olive leaf extract increased the total content of polyphenols and flavonoids and the antioxidant capacity
Cedola et al [39] tested a dry, olive paste flour coming from olive oil production process to enrich fish burger and found that a preliminary hydration of the by-products with milk before addition to the rest of the formulation represented a valid technological option to enhance the sensory perception of the processed fish product and a valid shrewdness to reduce the concentration of bitter components
Summary
Olive leaves are agricultural residues resulting from the pruning of olive trees, as well as from olive mill leavings These by-products are around 10% of the total weight of olives arriving to mills [1]. As reported in Silva et al [2], olive leaves contain considerable amounts of phenolic compounds that generally attract remarkable interest in both food and pharmaceutical industry for the properties they possess. Benavente-Garcìa et al [5] identified the main phenolic compounds present in the olive leaf extract obtained from Olea europaea L. of five cultivars, Villalonga, Alfafarenca, Picual, Cornicabra, and Blanqueta, from two south Spain regions (Andalucia and Murcia) and delineated the different antioxidant properties of these active compounds.
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