METABOLISMO DO ÁCIDO ASCÓRBICO DURANTE A MATURAÇÃO DE FRUTOS DA GOIABEIRA ‘PALUMA’ SOB ADUBAÇÃO NITROGENADA

Abstract

Vitamin C is present in many fruits and vegetables as the reduced form, L-ascorbic acid (AA) or in oxidized form, dehydroascorbic acid (DHA). Due to its high antioxidant capacity, the AA has the potential to minimize oxidative stress, reducing lipid peroxidation and degradation of the membrane, acting in defense systems of plants and in the regulation of plant growth. However, the AA content in the fruits may vary according to factors such as pre-harvest fertilization and maturation. Based on the above, this study aimed to evaluate the effect of ripening and nitrogen fertilization in the activity of enzymes related to the oxidation and recycling of ascorbic acid in fruits of guava 'Paluma' produced in Paraíba State coast. Fruits of guava 'Paluma' fertilized with different nitrogen levels (50, 100, 150 and 200 g N.planta-1) were evaluated in four maturation stages (IP - begin of yellow pigmentation, VA - yellowish green, AE - yellow green and TA - fully yellow). The experimental design was randomized block by 4x4 factorial design with five repetitions. The experiment was conducted in the Alhamdra-PB municipality, in a commercial orchard of cv Paluma with 16 months of formation. The application of N (urea) was performed manually in the crown projection, being subdivided in three applications after winter pruning and, at 45 and 75 days. The fruits were harvested and selected according to skin color and absence of defects. Fruits were packed in plastic box and transported to the laboratory of Biologia e Tecnologia Pós-Colheita in the Centro de Ciências Agrárias, on Universidade Federal da Paraíba, in Areia-PB. In the laboratory the fruits were selected by maturity, classified and evaluated. High nitrogen levels in fertilization of guava, reduce the activity of enzymes recycling of ascorbic acid, dehydroascorbic reductase (DHAR) and monodeidroascórbico reductase (MDHAR), providing a reduction in ascorbic acid content of the fruit until the dose of 147 g. plant-1. High levels of nitrogen favored the increased activity of ascorbic acid peroxidase in guava 'Paluma' fruits at the beginning of maturation, which in turn, dropped down the hydrogen peroxide content in the greener fruit. The dose of 170 g N.planta-1 promotes fruit quality of guava 'Paluma' as it keeps the contents of ascorbic acid and reduces oxidative stress, measured from the hydrogen peroxide levels. In guava 'Paluma', fruits the advancing ripening, regardless of nitrogen, promoted increased activity of ascorbic acid peroxidase and recycling enzymes (DHAR and MDHAR) and reduces the activity of ascorbic acid oxidase, increased the content of ascorbic acid.