Effect of chitosan with different molecular weights on the antifungal activity against Colletotrichum gloeosporioides and activation of the non-enzymatic antioxidant system on infected papaya.

Chitosan (Ch) is a biopolymer with excellent antimicrobial and antioxidant properties, capable of maintaining the organoleptic quality of fruits. These properties have been related to its molecular weight. However, the effect of different molecular weights on the non-enzymatic antioxidant system and postharvest quality of anthracnose-infected papaya is still unknown. Therefore, this study evaluated the effect of different Ch molecular weights (13, 25, and 55 kDa) on anthracnose development, antioxidant capacity, and postharvest quality of papaya. The Ch-55, Ch-25, and 13 kDa inhibited the development of Colletotrichum gloeosporioides. In comparison with thiabendazole, Ch with different molecular weights showed fungicidal effects. Ch-55 kDa reduced anthracnose incidence and severity and maintained postharvest quality parameters of papaya. In addition, Ch-55 and Ch-13 kDa favored synthesis of ascorbic acid, total phenolics, and antioxidant capacity. Therefore, Ch-55 kDa is an alternative to the protection against C. gloeosporioides and a stimulant of the non-enzymatic antioxidant system in papaya fruits during its postharvest storage. PRACTICAL APPLICATION: Ch with different molecular weights have different effects over anthracnose control and postharvest quality in papaya. In addition, they have different stimulation levels on the non-enzymatic antioxidant system of papaya fruits, in a higher level than the chemical fungicide TBZ, by regulating the growth of the fungus and the degradative processes that are generated in fungal infection. In this sense, we believe that our findings could be of interest for producers and farmers to take advantage of this biopolymer to control anthracnose, preserve the postharvest quality, and stimulate the non-enzymatic antioxidant system of papaya fruit.

Impact of hot water-calcium on the activity of cell wall degrading and antioxidant system enzymes in mango stored at chilling temperature.

Mango can develop symptoms of chilling injury (CI) during storage at low temperatures. The application of a hot water treatment (HWT) prior to cold storage can prevent this disorder; however, prolonged exposure to heat may cause accelerated softening of the fruit. Calcium salts allow the formation of pectates delaying softening and in combination with HWT can reduce the susceptibility to CI. This study evaluated the effect of the quarantine HWT (46.1°C, 75-90 min), calcium lactate (CaLac, 0.05%), and their combination (HWT-CaLac) on the activity of cell wall and antioxidant system enzymes in "Keitt" mango stored for 20 days (5°C) and during ripening (21°C). HWT and HWT-CaLac reduced CI sensitivity while the combination was more effective to reduce cell wall enzymatic activity and to increase the activity of the antioxidant system enzymes in mango, this demonstrated the usefulness of a HWT-CaLac combination to extend mango storage life by inducing CI tolerance. PRACTICAL APPLICATIONS: Simultaneous application of treatments in diverse crops is significant for prevention of rapid deterioration. In this study, the application of calcium lactate in an established quarantine hot water treatment for mango fruit fly reduced chilling injury presence and stimulated the antioxidant defense mechanism. In this sense, producers and packers can take advantage of this procedure to prolong the storage period of the fruit preserving its postharvest quality and minimizing the risk of chilling injury presence.

Effect of the Combination Hot Water - Calcium Chloride on the In Vitro Growth of Colletotrichum gloeosporioides and the Postharvest Quality of Infected Papaya.

Anthracnose of papaya fruit caused by the fungus Colletotrichum gloeosporioides is one of the most economically important postharvest diseases. Hot water immersion (HW) and calcium chloride (Ca) treatments have been used to control papaya postharvest diseases; however, the effect of the combination HW-Ca on the pathogen growth and the development of the disease in infected papaya fruit has been scarcely studied. The aim of this study was to evaluate the effect of the HW-Ca treatment on the in vitro growth of C. gloesporioides conidia and the quality of infected papaya. In vitro, the HW-Ca treated conidia showed reduced mycelial growth and germination. In vivo, the HW-Ca treatment of infected papaya delayed for 5 days the onset of the anthracnose symptoms and improved the papaya postharvest quality. The combined treatment HW-Ca was better than any of the individual treatments to inhibit the in vitro development of C. gloeosporioides and to reduce the negative effects of papaya anthracnose.