Lemon trees (Citrus limon (L.) Burm. F) were treated monthly with oxalic acid (OA) at 0.1, 0.5, and 1 mM from initial fruit growth on the tree until harvest in2019. The experiment was repeated in 2020, with the application of OA 1 mM (according to the best results of 2019). In both years, fruit from OA-treated trees and the controls were stored for 35 days at 10 °C. Results showed that all treatments reduced weight loss (WL) and maintained higher firmness, total soluble solids (TSS), and total acidity (TA) than in the controls. Meanwhile, colour (hue angle) did not show significant differences. The activity of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) in the flavedo of the fruit from the OA-treated trees was higher than in the controls at harvest and after 35 days of storage. Similarly, the total phenolic content (TPC) in the flavedo and juice of the fruit from the OA-treated trees were higher than in the controls. The increase in the activity of the antioxidant enzymes and TPC started with the first preharvest OA treatment and were maintained during fruit development on the tree until harvest. Preharvest OA treatments enhanced the antioxidant system of the lemon fruits, reducing the postharvest incidence of decay. Thus, OA could be a useful tool to increase the quality and functional properties of lemon fruits.

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.

The main aim of this study was to evaluate the effect of salicylic acid (SA) as a preharvest treatment on crop yield throughout the crop cycle of green pepper fruit as well as on its quality parameters, including functional quality, at harvest and during 21 days of storage at 7 °C. Thus, ‘Herminio’ pepper plants were treated with SA at 0.5, 1 and 5 mM, and higher crop yield (kg per plant, number of fruits per plant and average fruit weight) and quality parameters (firmness, green color and total acidity) at harvest were obtained with the 0.5 mM dose, as well as greater phenolic compounds content and total antioxidant activity. These quality traits and functional quality were also maintained at higher levels for this treatment than in controls during postharvest storage, leading to a delay of fruit quality losses. In addition, the decay incidence for 0.5 mM SA-treated pepper fruits reached a ca. value of 2% at the end of the storage, which was lower than untreated fruits (16.6%). These results suggest that preharvest application of SA at low doses tested on pepper plants could be a useful tool to increase crop yield and fruit quality parameters at harvest and maintain them during storage, delaying quality losses and decay incidence.

Green pepper fruit is often consumed before it is completely ripe. However, the influence of the phenological stage in which the green pepper is consumed as a potential influencing factor in its bioactive compounds content and antioxidant capacity remains unknown. In addition, no literature is available concerning the bioactive compounds changes in ‘Lamuyo’ green peppers along its developmental and growth cycle. For this, two different approaches have been carried out, one using twelve different phenological stages (S1 to S12), and in the other, seven different harvest dates (from 27 February to 20 April). Moreover, bioactive compounds changes during 21 days of postharvest storage at 8 °C were investigated. In this study, bioactive compounds (ascorbic acid, dehydroascorbic acid, and total phenolic content) and the total hydrophilic and lipophilic (TAA-H and TAA-L) antioxidant activity were analysed. In addition, total soluble solids, total acidity, individual sugars, and organic acids were determined. Vitamin C levels increased along the phenological stages and harvest dates due to significant increases in ascorbic and dehydroascorbic acid levels. Our results show that the total phenol content decreases as vegetables develop and subsequently increases both as ripening begins and by the last harvest date. Furthermore, TAA-H was also greater by the phenological stage S12 and the 20 April harvest date. In conclusion, the phenological stage and harvest date are key factors that significantly influence the bioactive compounds of green peppers, and those that appear by S12 and 20 April could be more beneficial to health.

Lemon postharvest losses are mainly due to the presence of fungal diseases. Current postharvest decay strategies rely on synthetic chemical fungicides; however, consumers are demanding that fruit is free of any chemical residue. The use of new natural alternatives, including essential oils, is emerging due to their potential antimicrobial activity. Therefore, the aim of this work is the elucidation of the effect of carvacrol, eugenol, and thymol, individually and in combination, applied in preharvest. Three different concentrations (100, 500, and 1000 µL/mL) of carvacrol, eugenol, and thymol were individually applied and in combination in ‘Fino’ and ‘Verna’ lemon cultivars. The fungal incidence (mainly Penicillium digitatum and P. italicum) was evaluated weekly for 35 days. Moreover, the main different quality parameters (weight loss, firmness, colour, total soluble solids, titratable acidity, and total phenolic content) of lemons were evaluated at harvest and after 35 days of cold storage. The results showed that carvacrol at the lowest concentration (100 µL/L) provided the lowest fungal incidence with a non-negative effect on the lemon quality parameters during storage, while the highest concentrations and the combination of essential oils resulted in the opposite effect. Therefore, carvacrol applied at 100 µL/L in preharvest could be an eco-friendly alternative to the current fungicides to control lemon decay, while maintaining their optimal quality.

Currently, approximately one third of food is wasted; to counteract this, several novel packaging technologies have been developed to extend its shelf life, among which active packaging stands out. In this research, filmogenic solutions of pectin and beeswax with the addition of bioactive compounds as anthocyanins were developed and characterized to evaluate their potential application as active coatings. The antioxidant and antifungal activity of anthocyanins and coatings were determined, and the rheological properties, pH, color, SEM and FT-IR of the coatings were evaluated. The antioxidant activity of the anthocyanins had IC50 values of 79.52 and 56.14 μg/mL for DPPH^• and ABTS^•+, respectively, and 0.25% (w/v) for the antifungal activity against Colletotrichum siamense, which was inhibited by 32.16% and had morphological affectations in the fungus. The best formulation for coating was obtained with 3% (w/v) pectin, 1% (w/v) wax, and 1% (w/v) Tween 80, and 0.1, 0.25, and 0.5% anthocyanins were added. The rheological properties showed adequate viscosity values (0.08–0.12 Pa·s), and the pH values were acidic (3.05–3.78) and showed reddish tones. FT-IR analysis showed that the interactions between the components included the C=O stretching band being shifted due to intermolecular interactions and SEM micrographs showed that the film coatings presented continuous areas of pectin with embedded wax crystals. Promising results were obtained for antioxidant and antifungal activity for the coatings. The formulations presented suitable characteristics for their use as active coating in food.