Short-Term Pre-Harvest UV-B Supplement Enhances the Polyphenol Content and Antioxidant Capacity of Ocimum basilicum Leaves during Storage.

Luana Beatriz Dos S Nascimento,Cecilia Brunetti,Giovanni Agati,Antonella Gori,Francesco Ferrini,Edgardo Giordani,Clara Lo Iacono,Cassandra Detti

doi:10.3390/plants9060797

Abstract

Ocimum basilicum (basil) leaves are rich in polyphenols, conferring them a high antioxidant activity. The application of UV-B can be used to maintain the post-harvest nutraceutical quality of basil leaves. We aimed to investigate the effects of pre-harvest UV-B application on polyphenolic and pigment contents, antioxidant capacity, and the visual quality of basil stored leaves. We also evaluated the applicability of the non-invasive Dualex® for monitoring the accumulation of leaf epidermal phenolics (Flav Index). After exposing plants to white light (control) and to supplemental UV-B radiation for 4 d, the leaves were harvested and stored for 7d (TS7). The UV-B leaves showed both a higher phenolic content and antioxidant capacity than the controls at TS7. In addition, the correlations between the Flav Index and phenolic content demonstrated that Dualex® can reliably assess the content of epidermal phenolics, thus confirming its promising utilization as a non-destructive method for monitoring the phytochemical quality of O. basilicum leaves. In conclusion, a pre-harvesting UV-B application may be a tool for enhancing the content of polyphenols and the antioxidant potential of basil stored leaves without detrimental effects on their visual quality. These results are important considering the nutraceutical value of this plant and its wide commercial distribution.

Highlights

As photosynthetic sessile organisms, plants are naturally exposed to harmful UV-B radiation (280–320 nm) and have developed several morphophysiological and biochemical adaptations for dealing with their possible damages [1]
The aim of this study is to evaluate the changes in the phenolic content and composition, antioxidant capacity, and visual quality of stored leaves by the pre-harvest exposure of O. basilicum potted plants to supplemental UV-B radiation
The UV-B leaves showed significantly higher values of the Total Flav Index than the control leaves at both sampling times, TS0 and TS7 (Figure 1)

Summary

Introduction

Plants are naturally exposed to harmful UV-B radiation (280–320 nm) and have developed several morphophysiological and biochemical adaptations for dealing with their possible damages [1]. Many species have shown an increase in secondary metabolites content, mainly in phenolic compounds, when exposed to UV-B radiation [1,2,4]. UV-B, acting as both radiation screeners and ROS (reactive oxygen species) scavengers [1,2]. These compounds are located in the vacuole of epidermal and subepidermal cells, decreasing the UV-B penetration into the mesophyll [1,5]. They are found in the mesophyll cells, where they perform an antioxidant function [5]

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