Ácido abscísico (ABA) e radiação UV-C na maturação pós-colheita de frutos de morango (Fragaria x ananassa Duch.)

Abstract

Strawberry (Fragaria x ananassa Duch.), a pseudofruit of the Rosaceae family, is highly appreciated for its sensory characteristics, such as its bright red color and flavor, in addition to the presence of antioxidant compounds. As it is a non-climacteric fruit, it is harvested at full maturity, but at this stage it has a fragile texture, which makes it susceptible to mechanical damage, fungal development, resulting in decreased quality and post-harvest losses. One of the alternatives to avoid these problems is to harvest the fruits before being fully ripe; however, in this case, it is necessary to promote the induction of post-harvest ripening. Studies have reported that the phytohormone abscisic acid (ABA) may be involved in the ripening process of strawberry fruits and that the use of ultraviolet radiation (UV-C) can delay the loss of firmness and increase the content of antioxidant compounds. Therefore, the objective of this study was to evaluate the effect of post-harvest treatment of UV-C and ABA on the accumulation of compounds related to the ripening process in strawberry fruits (Fragaria x ananassa Duch.) harvested before full maturation. The fruits were harvested with 75% red surface. Four treatments were performed (Control C – no treatment; UV-C; ABA; ABA+UV-C). The fruits were treated with 1 mmol ABA solution and two doses of 2 kJ m-2 of UV-C radiation (applied on the first and second days) and stored for four days at 20°C and 80% relative humidity; and compared with in vivo ripen (plant-attached) fruits. All post-harvest treatments showed color evolution, but none of them reached the color or the total soluble solids or phenolic compounds content of the fruits ripened in vivo. Storage (control C) did not induce the synthesis of ABA, ABA glycosyl ester (ABA-GE), phaseic acid (PA) or dehydrophaseic acid (DPA) compared to control C 75%, and resulted in reduced fruit firmness in all treatments. The fruits treated with UV-C and ABA+UV-C had a lower a* angle, characterizing a delay in the accumulation of anthocyanins, but there was no difference in the content and profile of anthocyanins between treatments. Unlike expected, firmness was not affected in these UV-C treatments. Despite this, the fruits of these treatments showed values similar to the Lascorbic acid contents of the C 75% and C 100% fruits, suggesting that UV-C radiation toward the preservation of this compound. The treatment with ABA resulted in greater accumulation of ABA, ABA-GE and PA, compared to the other treatments, suggesting that this phytohormone affected the metabolism of the fruits, such as phenolic compounds; ABA, ABA-GE and PA were responsible for separating the ABA and ABA+UV-C treatments from the other treatments in the principal component analysis (PCA). The ABA+UV-C treatment showed an intermediate behavior between the ABA and UVC treatments, being grouped closer to the ABA treatment in the PCA analysis because it presented higher levels of ABA, ABA-GE, PA and DPA than the treatments without ABA application. In conclusion, the postharvest maturation of strawberry fruits is different from the in vivo maturation; the accumulation of ABA and its derivatives in treatments that received exogenous ABA altered fruit metabolism, but did not result in the expected induction of anthocyanins; the application of UV-C may be interesting to maintain the levels of L-ascorbic acid in the fruits; and the combined action of ABA+UVC resulted in combined effects of these two treatments.