Citation: Quartacci, M.F.; Sgherri, C.; Pinzino, C. Impact of Leaf Removal on Phenolics and Antioxidant Activity of Trebbiano Berries (Vitis vinifera L.). Plants 2022, 11, 1303. https://doi.org/10.3390/plants11101303 Academic Editors: Andrei Mocan and Simone Carradori Received: 20 April 2022 Accepted: 10 May 2022 Published: 13 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article Impact of Leaf Removal on Phenolics and Antioxidant Activity of Trebbiano Berries (Vitis vinifera L.) Mike Frank Quartacci 1, * , Cristina Sgherri 1 and Calogero Pinzino 2 1 Department of Agriculture, Food and Environment, University of Pisa, 56124 Pisa, Italy; cristina.sgherri@unipi.it 2 Institute of Chemistry of Organometallic Compounds (ICCOM-CNR), Italian National Research Council, 56124 Pisa, Italy; rino@pi.iccom.cnr.it * Correspondence: mike.frank.quartacci@unipi.it Abstract: Leaf removal is a canopy management practice widely applied in viticulture to enhance the phenol composition and concentration of grapes, which then results in improved wine quality. Many studies were carried out on red berried varieties, but information on white ones is scanty. The aim of the study was to assess the effect of basal leaf defoliation in post fruit set on the phenol composition, ascorbate level and antioxidant activity of Trebbiano grapes. Electron paramagnetic resonance was also employed to monitor the decay kinetics of 1,1-diphenyl-2-picrylhydrazyl which allowed the identification of antioxidants with different action rates. The results show that defoliation caused an increase in the phenolic acid (hydroxycinnamic and hydroxybenzoic acids) and flavonol concentrations of berries without changes in the composition. Both ascorbate and antioxidant activity were also enhanced in the berries from defoliated vines. Besides increasing the number of fast-rate antioxidants, leaf removal resulted in the formation of intermediate-rate ones. In the Trebbiano variety, leaf removal in the post fruit set may represent an effective strategy to enhance the phenolic composition and the antioxidant defense system of berries. Keywords: antioxidant activity; ascorbate; defoliation; electron paramagnetic resonance; flavonols; grape; phenolic acids; phenols; Trebbiano 1. Introduction Among the biologically active metabolites that contribute to the defense against en- vironmental adversities, phenols play a particularly important role. In fact, phenolic compounds represent one of the main constituents of the antioxidative defenses of cells. The antioxidative action of this group of compounds is linked to their ability to avoid the beginning or to slow down the propagation of cell oxidation which causes cell damage due to lipid peroxidation and enzyme inactivation [1]. The phenolic classes detected in grapes are represented by flavonoids (flavonols, anthocyanins, flavan-3-ols and their polymeric form proanthocyanidins) and non-flavonoids (benzoic and hydroxycynnamic acid deriva- tives). The relative amount and distribution of these compounds depend on a variety of factors such as grape variety, vineyard location, climate, soil type, cultivation practices (among which canopy management and irrigation) and harvesting time [2]. Phenolic hydroxycinnamates are commonly accumulated in berry skin and especially in the flesh and are usually the most abundant class of phenolics in white berries, p-coumaric, caffeic and ferulic acids being the main constituents [3]. The hydroxybenzoic acid concentration is lower than that of hydroxycinnamic acids and gallic acid is the most abundant component. Flavonol synthesis occurs primarily during the early stages of fruit development in the outer epidermis of the skin, being sunscreen protectors, and ends at around veraison [4]. The main representatives of this class are kaempferol, quercetin, and myricetin (and its methylated form isorhamnetin). In cells, phenolic compounds may be present in both free and conjugated forms, and their chemical structure has a significant impact on their Plants 2022, 11, 1303. https://doi.org/10.3390/plants11101303 https://www.mdpi.com/journal/plants