Termoestabilidade de enzimas dos sucos de graviola e caju

Abstract

The industrialization of fruit into juices aims to maintain its sensorial and nutritional characteristics as similar as possible to in natura produce, besides ensuring the microbiological safety. However, processing and storage of fruit juice triggers a range of complex biochemical reactions that may lead to losses of desirable or development of unpleasant flavors. Enzymes such as peroxidases and pectinases may compromise the quality and shelf-life of juices and therefore should be inactivated. This work´s objective was to evaluate the thermostability of enzymes from cashew apple and soursop juices. Juices were prepared as ripe soursop pulp was homogenized with a domestic blender and diluted in water distilled (1:1) meanwhile, ripe cashew apples were expeller-pressed. The juices were submitted to different thermal treatments (55, 65, 75, 85 and 95 °C) for different periods of times (1, 3, 5, 10, 15, 20 and 30 min) and then, evaluated for activity of enzymes: superoxide dismutase (SOD), catalase (CAT), ascorbate (APX) and guaiacol (G-POD) peroxidases, pectinamethylesterase (PME) and polygalacturonase (PG). For the cashew juice, SOD activity was highly resistant to thermal treatments as the exposure to 95 °C initially decreased its activity followed by a recovery and maintenance of 74% of residual activity, after 30 min. APX residual activity initially declined under all temperatures tested, but then increased, especially at 55 °C. PME from cashew juice was thermoresistant as the 55 °C treatment increased its activity 10-fold and the greater temperatures did not differ from control. PG and PME presented similar thermostability patterns as the lower tested temperatures stimulated their activities and the higher temperatures did not alter them. For the soursop juice, the 85 and 95 °C treatments totally inactivated SOD, after 3 min. The G-POD was inactivated after 1 min, at 65 °C. The PME was thermolabile and treatment at 95 °C caused the greatest reduction in activity, 39%, after 30 min. Treatments at 95 and 85 °C led to the greatest inactivation of PG to 26 and 18%, respectively, after 30min. The enzymes from cashew apple juice were more resistant to heating than those from soursop juice, indicating that characteristics particular to each fruit species and the different preparation methods influenced their thermostability. As a conclusion, the treatment at 75 °C for 30 min was considered optimum for cashew juice enzyme inactivation, whereas 55 °C for 30 min was efficient for the soursop juice in reducing significant amounts of the residual activity of enzymes that would lead to quality loss without compromising the activity of desirable enzymes.