# Effects of Preharvest Application of Oxalic Acid, γ-Aminobutyric Acid, and Melatonin on the Microbiological and Physicochemical Quality of Dried Figs at Commercial Harvest and During Storage

## TL;DR

This study shows that applying certain substances before harvest can reduce harmful fungi and toxins in dried figs during storage.

## Contribution

The study demonstrates that preharvest elicitors can suppress toxigenic fungi in dried figs without compromising quality.

## Key findings

- Elicitor-treated dried figs showed lower incidence of toxigenic fungi compared to untreated samples.
- Mycotoxin levels were below detection limits in figs treated with 0.5 mM melatonin.
- Moderate concentrations of elicitors provided the best balance between fungal suppression and fruit quality.

## Abstract

The objective of this study was to evaluate the preharvest application of γ-aminobutyric acid (GABA), melatonin (MT), and oxalic acid (OA), at different concentrations and application frequencies, on the physicochemical and microbiological quality of dried figs (cv. Calabacita) at commercial harvest and after 3 and 6 months of refrigerated storage. A further aim was to determine their impact on fungal populations and mycotoxin production. The results showed that untreated dried figs had a higher frequency of Aspergillus welwitschiae, A. tubingensis, and Aspergillus section Flavi, whereas elicitor-treated figs exhibited a lower incidence of toxigenic fungi. A. welwitschiae was the main ochratoxin A (OTA)-associated species detected, although the proportion of OTA-positive figs was lower in elicitor-treated samples than in the control. Aflatoxins (AFs) were detected only sporadically in 2 mM OA treatments, consistent with the limited activity of A. flavus at low storage temperatures. Conversely, Penicillium spp. were widespread but were associated with citrinin (CIT) production only under 2 mM OA treatments. Among the Alternaria toxins, alternariol (AOH) was detected solely in dried figs treated with 1 mM OA. Notably, all investigated mycotoxins were below the limit of detection (<LOD) in dried figs treated with 0.5 mM MT. Moderate elicitor concentrations (e.g., 0.5 mM MT and 50 mM GABA) and multiple preharvest applications generally provided the best balance between fungal suppression and fruit quality, significantly reducing Aspergillus spp. occurrence without promoting the growth of undesirable species. Overall, elicitor treatments decreased the incidence of toxigenic fungi, most likely through direct antifungal effects in senescent dried fruit rather than by inducing host defences. The combined use of preharvest elicitors with appropriate drying and storage conditions is a promising strategy to control fungal contamination and mycotoxin accumulation in dried figs while maintaining quality from preharvest storage. Further research is needed to optimise elicitor concentrations and application timing.