Effect of cultivar and drying methods on phenolic compounds and antioxidant capacity in olive (<i>Olea europaea</i> L.) leaves

Itxaso Filgueira-Garro; Carolina González-Ferrero; Diego Mendiola; María R. Marín-Arroyo; Itxaso Filgueira-Garro; Carolina González-Ferrero; Diego Mendiola; María R. Marín-Arroyo

doi:10.3934/agrfood.2022016

AIMS Agriculture and Food

2022, Volume 7, Issue 2: 250-264. doi: 10.3934/agrfood.2022016

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Effect of cultivar and drying methods on phenolic compounds and antioxidant capacity in olive (Olea europaea L.) leaves

1.
Department of Research and Development, URZANTE, 31500 Tudela, Spain
2.
Institute on Innovation and Sustainable Development in Food Chain (IS-FOOD), Public University of Navarre (UPNA), Campus Arrosadía, 31006 Pamplona, Spain
3.
National Centre for Food Technology and Safety, CNTA, NA 134, Km. 53, 31570, San Adrián, Spain

Received: 15 October 2021 Revised: 22 March 2022 Accepted: 26 April 2022 Published: 06 May 2022

Up to 5% of the total olive weight arriving at the mill is discarded as leaves. Interest in the possible uses of these residues is growing, because they constitute a potential cheap and abundant source of compounds with high total antioxidant capacity (TAC) associated with total phenolic content (TPC) and biophenols such as hydroxytyrosol (HC) and oleuropein (OC), which could be used as nutraceuticals or as natural substitutes for synthetic antioxidants. However, studies that characterize specific cultivars, interannual variability, and different drying methods are lacking. This work investigates the TAC, TPC, HC and OC in olive (Olea europaea L.) leaves under four drying methods (vacuum-drying, oven-drying, freeze-drying and air-drying). Leaves were collected from cultivars 'Arbequina' grown under organic methods and from 'Arroniz', 'Empeltre', 'Arbosana', 'Picual' and 'Arbequina' grown under conventional systems. Among fresh samples, 'Arbosana' leaves presented the highest TPC (34.0 ± 1.1 mg gallic acid equivalents/g dry weight (DW)) and TAC (146 ± 20 μmol Trolox equivalents/g DW) and the lowest interannual variability of the TPC (3.2%). The four tested drying methods were also compared as the effect on TPC, TAC, HC and OC. Freeze-drying and air-drying best preserved TPC and TAC in olive leaves. However, air-drying maintained greater OC (14–40 mg/g DW) than freeze-drying (3–20 mg/g DW). Air-dried ecological 'Arbequina' leaves exhibited the highest TPC and TAC. Consequently, this cultivar presented more valorization opportunities as a source of nutraceuticals or natural antioxidants.
- olive leaves,
- drying methods,
- oleuropein,
- hydroxytyrosol,
- 'Arroniz',
- 'Empeltre'
Citation: Itxaso Filgueira-Garro, Carolina González-Ferrero, Diego Mendiola, María R. Marín-Arroyo. Effect of cultivar and drying methods on phenolic compounds and antioxidant capacity in olive (Olea europaea L.) leaves[J]. AIMS Agriculture and Food, 2022, 7(2): 250-264. doi: 10.3934/agrfood.2022016

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Abstract

Up to 5% of the total olive weight arriving at the mill is discarded as leaves. Interest in the possible uses of these residues is growing, because they constitute a potential cheap and abundant source of compounds with high total antioxidant capacity (TAC) associated with total phenolic content (TPC) and biophenols such as hydroxytyrosol (HC) and oleuropein (OC), which could be used as nutraceuticals or as natural substitutes for synthetic antioxidants. However, studies that characterize specific cultivars, interannual variability, and different drying methods are lacking. This work investigates the TAC, TPC, HC and OC in olive (Olea europaea L.) leaves under four drying methods (vacuum-drying, oven-drying, freeze-drying and air-drying). Leaves were collected from cultivars 'Arbequina' grown under organic methods and from 'Arroniz', 'Empeltre', 'Arbosana', 'Picual' and 'Arbequina' grown under conventional systems. Among fresh samples, 'Arbosana' leaves presented the highest TPC (34.0 ± 1.1 mg gallic acid equivalents/g dry weight (DW)) and TAC (146 ± 20 μmol Trolox equivalents/g DW) and the lowest interannual variability of the TPC (3.2%). The four tested drying methods were also compared as the effect on TPC, TAC, HC and OC. Freeze-drying and air-drying best preserved TPC and TAC in olive leaves. However, air-drying maintained greater OC (14–40 mg/g DW) than freeze-drying (3–20 mg/g DW). Air-dried ecological 'Arbequina' leaves exhibited the highest TPC and TAC. Consequently, this cultivar presented more valorization opportunities as a source of nutraceuticals or natural antioxidants.

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