Comparative analysis of antioxidant activity and capacity in apple varieties: Insights from stopped flow DPPH• kinetics, mass spectrometry and electrochemistry

The aim of this research was to investigate the antioxidant kinetics of different apple varieties, a red-flesh variety (‘R201’), a non-browning (‘Majda’), and a ‘Golden Delicious’. Kinetic approaches for antioxidant activity provide more detailed information than conventional assays by examining both the quantity and velocity of active molecules in their reaction with radicals. In this study, DPPH• stopped flow method was applied to study the antioxidant activity and capacity of the three apples varieties, allowing the determination of the reaction rates. The results show that the antioxidant activity of ‘R201’ was not significantly different from ‘Golden Delicious’. Instead, the activity of the non-browning variety was 20 times higher than the others according to the DPPH• kinetic approach, despite having the lowest phenolic content. To further understand their reactivity, the antioxidant molecules were identified using HPLC-HRMS/MS coupled with a coulometric array detector, which validated the DPPH• kinetics. This analysis also found differences in the phenolic profile of the three varieties, attributed to the enhanced antioxidant activity of ’Majda’ to its high content of ascorbic acid. Overall, the research highlights that the antioxidant behavior of apples primarily depends on the velocity of the antioxidants rather than the amount of phenolic compound

Effect of Spring Frost Damage on Apple Fruit (Malus domestica Borkh.) Inner Quality at Harvest

In the last few years, spring frosts have become more of a rule than an exception. There are several prevention measures available for growers and numerous are being tested; however, fruitlets are often affected to some extent. One of the more common phenomena is the development of frost rings. The aim of our study was to evaluate how the occurrence of frost rings affects sugar, organic acid, and phenol content in the flesh and phenol content in the peel of cv. ‘Gala’ apples. The results show that the frost damage from spring frost affects compounds in the peel, as well as in the flesh of ripe apples. The flesh of fruits with frost rings contained higher content of fructose and in the flesh directly under the rings there was higher sorbitol and malic acid content. Additionally, the hydroxycinnamic acid and dihydrochalcone content in apple flesh was also altered by frost. The frost-affected peel had a completely different ratio of phenolic compounds content in comparison to healthy apples. While there was a significantly higher content of hydroxycinnamic acids and dihydrochalcones in the corky peel in comparison to the unaffected peel, the flavonol and anthocyanin content was considerably lower

A multifaced approach sheds light on the molecular details underlaying the mechanism preventing enzymatic browning in ‘Majda’ apple cultivar (Malus domestica Borkh.)

Fruit flesh browning is a natural oxidative phenomenon occurring after cutting or processing. This event, manifesting dark-brown coloration, can seriously limit the production and marketability of fresh cut fruit products. Antioxidant compounds can partially prevent this phenomenon, but in turn they can affect the quality and the organoleptic properties of fresh products. In this work we have investigated, through a multidisciplinary approach, the regulation of a natural non-browning phenotype of a particular apple cultivar ‘Majda’ in comparison with the browning reference apple cultivar ‘Golden Delicious’. The results highlight that the non- browning phenotype of ‘Majda’ was controlled by multiple mechanisms, particularly distinguished by a different concentration of chlorogenic acid and the expression of the polyphenol oxidase (MdPPO) gene. The metabolite assessment and gene expression profiling also disclosed the involvement of organic acids and glutathione in the prevention of oxidative browning phenomenon. The peculiar non-browning behavior of ‘Majda’ was also verified by a DPPH•kinetic approach that demonstrated the higher antioxidant activity of this apple cultivar. The results presented in this work proposed ‘Majda’ as a potential parental candidate to be considered for breeding activity oriented to select novel non-browning accessions addressed to ameliorate the sustainability of pre-cut fresh products