Improving the Berry Quality and Antioxidant Potential of Flame Seedless Grapes by Foliar Application of Chitosan-Phenylalanine Nanocomposites (CS-Phe NCs).

Gholamreza Gohari,Antonio Juárez-Maldonado,José M Lorenzo,Parisa Labib,Roghayeh Mahmoudi,Elnaz Zareei,Gholamreza Mahdavinia,Muhittin Kulak,Hessam Jafari,Sima Panahirad

doi:10.3390/nano11092287

Abstract

The production and sustainability of grape berries with high quality and health-promoting properties is a major goal. In this regard, nano-engineered materials are being used for improving the quality and marketability of berries. In this study, we investigated the potential role of chitosan–phenylalanine nanocomposites (CS–Phe NCs) in improving the quality of Flame Seedless (Vitis vinifera L.) grape berries, such as titratable acidity (TA), pH, total soluble solids (TSS), ascorbic acid, total phenolics, total flavonoids, anthocyanin, 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity, and phenylalanine ammonia-lyase (PAL) activity. In this context, grape berries collected in two growing seasons (2018–2019) were screened. Regarding the experimental design, the treatments included chitosan at a 0.5% concentration (CS 0.5%), phenylalanine at 5 mM and 10 mM concentrations (Phe 5 mM and Phe 10 mM), and chitosan–phenylalanine nanocomposites (CS–Phe NCs) at 5 mM and 10 mM concentrations. The lowest TA was recorded in grape berries treated with CS–Phe NCs with a 10 mM concentration. However, treatments enhanced with TSS, which reached the highest value with 10 mM of CS–Phe NCs, were reflected as the highest ratio of TSS/TA with 10 mM of CS–Phe NC treatment. Nanocomposites (NCs) also increased pH values in both study years compared to the control. Similarly, the ascorbic acid and total phenolic content increased in response to NP treatment, reaching the highest value with 5 mM and 10 mM of CS–Phe NCs in 2018 and 2019, respectively. The highest flavonoid content was observed with 5 mM of CS–Phe NCs in both study years. In addition, the anthocyanin content increased with 5 and 10 mM of CS–Phe NCs. PAL activity was found to be the highest with 5 mM of CS–Phe NCs in both study years. In addition, in accordance with the increase in PAL activity, increased total phenolics and anthocyanin, and higher DPPH radical scavenging activity of the grapes were recorded with the treatments compared to the control. As deduced from the findings, the coating substantially influenced the metabolic pathway, and the subsequent alterations induced by the treatments were notably appreciated due to there being no adverse impacts perceived.

Highlights

Grapevine is a major fruit crop cultivated in all continents and consumed in various forms, such as fresh fruit and other processed products
The higher levels of flavonoids compared to the non-treated groups might be attributed to a reduced conversion of flavonoids to other secondary metabolites or an enhanced oxygen barrier ability playing a significant role in retarding the decline in the flavonoid content [44]. These findings suggest the requirement of deeper research on the bio-conversion of metabolites as a response to chitosan and its conjugation
As a novel and interesting finding, we observed that chitosan coated with phenylalanine as a functional compound triggered the activity of phenylalanine ammonia-lyase (PAL), a significant enzyme in the biosynthesis pathway of phenolics

Summary

Introduction

Grapevine is a major fruit crop cultivated in all continents and consumed in various forms, such as fresh fruit and other processed products (e.g., vines and juice). It is one of the most economically significant sources for the food industry due to the soluble sugars, phenolics, flavonoids, organic acids, and aromatic compounds available [1]. To maintain the high quality of grape berries, especially under changing environmental conditions, chitosan nanomaterials have recently been used [2]. Due to the existence of functional groups, especially amino groups, chitosan plays an important role in the interaction with negatively charged molecules because of the protonation phenomenon [4]. Previous studies have reported that chitosan, combined with other chemicals, has a positive impact on the control of foliar diseases in some crops [6]

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