Effect of Gum Arabic and Sodium Bicarbonate Coating on Disease Development of Red-fleshed Pitaya Fruit (Hylocereus polyrhizus)

Pitaya is a highly perishable fruits that can only last for 5-7 days under room temperature condition. Edible coatings have been used to protect perishable fruit from deterioration by retarding some physiological changes, retain volatile flavour compound as well as reducing microbial growth. In this study, gum Arabic (GA) and sodium bicarbonate (SBC) were used to coat pitaya fruits to evaluate disease development. Firstly, the disease development on fruits coated with 10% GA (w/v), 2% SBC (w/v), 10% GA+2% SBC and control was evaluated by symptomatic observation at 2, 4, 6, and 8 day. Disease incidence and severity was calculated for naturally infected pitaya fruits. Secondly, fungal pathogens on infected fruits were isolated on potato dextrose agar and were identified. To elucidate the infection process on coated pitaya, parameters such as spore germination rate and germ tube length were evaluated. Results showed that coated fruits substantially have reduced development of disease symptoms, decay incidence and severity, germ tube growth and spore germination of Colletotrichum sp. which was the causal pathogen of anthracnose disease being identified. However, fruits coated with only 2% SBC were less inhibitory than 10% GA alone as well as 10% GA+2% SBC in controlling disease incidence and severity although the three treatments were significantly different from control treatment. Pitaya fruits coated with treatments of 10% GA and 10% GA+2% SBC which were artificially inoculated with Colletotrichum sp. resulted in a lower rate of disease progression by 50% as compared with the control.