Olive fruit debittering significantly alters its antioxidant activity as evaluated with multiple free-radical scavenging
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ORIGINAL PAPER
Olive fruit debittering significantly alters its antioxidant activity as evaluated with multiple free‑radical scavenging ability Yoshimi Sueishi1 · Risako Nii1 Received: 10 September 2020 / Accepted: 6 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Raw olive fruits taste bitter and are not edible without debittering. Common debittering process promotes the loss of olive antioxidant activity and the magnitude of loss depends on the debittering reagent used. Antioxidant activity was evaluated as the scavenging ability that was determined with multiple free-radical scavenging (MULTIS) method, where the scavenging abilities against five reactive oxygen species (HO·, O2−·, RO·, t-BuOO·, and 1O2) were determined. Significant change in the scavenging activity of debittered olive was found in four debittering methods, i.e., sodium hydroxide, sodium hydrogen carbonate, ethanol, and sodium chloride treatments. Results indicated that the scavenging activities lowered by 60–90% after most debittering processes. Sodium chloride treatment least affected the scavenging activity. Based on the MULTIS measurements for the antioxidant components and debittering reagents, the rate constants of antioxidant compounds with four ROS were determined and the antioxidant activity that depends on the method of debittering is discussed. Oleuropein, olive-related antioxidant compound, showed high scavenging abilities against HO· (k = 6.70 × 109 M−1 s−1), RO· (k = 4.69 × 106 M−1 s−1), and 1O2 (k = 1.74 × 107 M−1 s−1). This study suggests that functionality and taste do not always come together. MULTIS method is useful in comparative antioxidant capacity studies in foods. Keywords Olive · Debittering treatment · Antioxidant capacity · MULTIS · ESR spin trapping
Introduction Olive (Olea europaea L.) fruits and oil are very popular in the Mediterranean area. Olive oil represents the most used dressing in the Mediterranean diet and many studies report beneficial effects of olives on human health [1, 2]. These benefits are in part associated with the high amounts of nutritionally relevant constituents. Olive fruits and derived products are known as a valuable source of natural compounds with important bioactivity, including antioxidants such as flavonoids and phenolic compounds [3–5]. The importance of olive’s phenolic compounds is due not only to their nutritional properties but also to their free radicalscavenging activity. The dominant antioxidant compounds in fresh olive fruit are oleuropein and hydroxytyrosol, phenolic
* Yoshimi Sueishi ysueishi@okayama‑u.ac.jp 1
Department of Chemistry, Faculty of Science, Okayama University, 3‑1‑1 Tsushima‑naka, Kita‑ku, Okayama 700‑8530, Japan
compounds (Scheme 1) [4, 6]. Oleuropein is very bitter and must be removed to make olive pulp edible [6]. The removal of bitter taste (debittering) in olive fruits is generally achieved through alkaline hydrolysis, resulting in the decomposition of phenolic antioxidant compounds [7, 8]. Alkaline hy
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