Preharvest Application of Oxalic Acid Improved Pomegranate Fruit Yield, Quality, and Bioactive Compounds at Harvest in a Concentration-Dependent Manner

Pedro J Zapata,Salvador Castillo,Domingo Martínez-Romero,Juan M Valverde,María Serrano,María E García-Pastor,María J Giménez,Daniel Valero,Fabián Guillén

doi:10.3390/agronomy10101522

Abstract

The effects of oxalic acid (OA) applied in preharvest on pomegranate crop yield and quality properties have not yet been investigated. Pomegranate trees were treated with OA at 1, 5, and 10 mM along the developmental growth cycle during 2016, from full blossom until harvest, and the fruit diameter was recorded monthly. The yield was significantly higher in OA-treated pomegranate trees, the on-tree ripening process being promoted in a concentration-dependent manner. With respect to quality traits, OA at 10 mM showed better results in terms of firmness, external color due to a red color enhancement, and respiration rate and sensory attributes. Then, a second-year experiment was performed with OA at 10 mM, and crop yield and fruit quality results were confirmed. In addition, an increase in glucose and total acidity, specifically malic and ascorbic acids, was observed in OA 10 mM-treated pomegranate fruit. Bioactive compounds were also higher in OA-treated fruit than control, the 10 mM concentration being the most effective in increasing total phenolics, total anthocyanins, and total antioxidant activity. Overall, results suggest that OA applied at 10 mM as preharvest treatment could be an effective tool to enhance pomegranate crop and quality and to improve the content of health-related compounds.

Highlights

Pomegranate (Punica granatum L.) is a widely grown horticulture crop in many tropical and subtropical countries
Along the fruit developmental cycle, and results showed that all concentrations of oxalic acid (OA) treatment stimulated fruit growth from the second application (T2; Figure 1), mainly in August, resulting in pomegranate fruit with higher size (p ≤ 0.05) at this developmental stage (≈63 mm for control fruit and 66–68 mm for OA-treated pomegranate fruit), without significant differences (p > 0.05) among the concentrations of OA
Our results show that preharvest treatments with OA, especially applied at 10 mM, increased the total phenolics and total anthocyanins content, as well as ascorbic acid content, as commented above, leading to increases in the hydrophilic total antioxidant activity (H-Total antioxidant activity (TAA))

Summary

Introduction

Pomegranate (Punica granatum L.) is a widely grown horticulture crop in many tropical and subtropical countries. The edible parts of pomegranate fruit represented 52% of the total weight, comprising 78% juice and 22% seeds [1]. Total soluble solids, and anthocyanin content increased continuously during maturation while acidity decreased [3]. Harvest maturity is known to influence quality and could have a negative impact during storage, since early harvest may affect the development of the characteristic color, taste, and aroma of pomegranates, while late-harvested fruit exhibit a reduced shelf life [5]. Proper harvest of pomegranates optimizes the health-promoting compounds in the fruit and juice. Total phenol concentration decreases rapidly in early development and more slowly as the fruit mature. The final concentration can range from 0.90 to 2.10 g kg−1 , depending on cultivar and horticultural practices [3,7,8]

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