Comprehensive analysis of enzymatic browning in hazelnuts (Corylus avellana L.): influence of physical-biochemical, cultivar and agroclimatic parameters on nut development

L.), associated with oxidative processes mediated by polyphenol oxidase (PPO) and peroxidase (POD), whose expression depends on the content of phenolic compounds, the phenological state of the nut, and agroclimatic conditions. The objective of this study was to analyze EB using physical-biochemical parameters, varietal response, and environmental influence, evaluating the incidence of EB, total phenolic content (TPC), and PPO and POD activity in the shell and kernel. The trial was conducted in two consecutive seasons, S1 (2022/2023) and S2 (2023/2024), in two contrasting locations in La Araucanía (Nueva Imperial and Radal), considering four phenological stages of the nut (BBCH 721-89). Industrial parameters showed higher quality in Barcelona, with larger nuts, better yield, and more protective shells. In S2, environmental restrictions limited nut filling and increased the risk of EB, especially in Tonda di Giffoni (TDG). The incidence of EB was low in S1 and increased in S2, mainly in BBCH 85, with increases of up to 392% in TDG in shell and kernel, higher in Radal and towards maturity. Likewise, TPC, PPO, and POD showed more intense responses in S2, with increases of 54-115%, 188%, and 410-529%, respectively, evidencing greater oxidative susceptibility of TDG in Radal. Overall, the results confirm that EB depends on complex multifactorial interactions, providing a basis for optimizing production management and varietal selection under increasing climate variability.