Integrated control of postharvest decay on sweet orange fruits by hot water and Sodium Carbonate (Na2CO3) applications

Abstract

Integrated control of postharvest decay on sweet orange fruits by hot water and sodium carbonate (Na2CO3) applications during subsequent storage at 28°C was investigated and the effect of such treatment on internal quality attributes of orange fruits determined. Mature sweet orange fruits without bruises were selected and washed in 2% sodium hypochlorite solution for 5 minutes before treatment. For ordinary sodium carbonate treatment (without hot water), selected fruits were separately immersed for 150 seconds in a water bath containing 2% (w/v) and 4% (w/v) sodium carbonate (Na2CO3) solutions. In another experiment, selected fruits were immersed for 150 seconds in a water bath containing hot water and sodium carbonate solution. Sodium carbonate concentrations at 2% (w/v) and 4% (w/v) in 45°C hot water temperature were tested. After treatment, the fruits were rinsed, allowed to air dry and then placed inside plastic buckets and stored at 25°C and 88% relative humidity and assessed weekly for mould infection. Result showed that fruits treated with 4% ordinary Na2CO3 concentration had no incidence of decay during the first week of storage. However, untreated fruits and fruits treated with ordinary 2% Na2CO3 concentration recorded 20.00% disease incidence in the first week of storage. The percentage decay of fruits later increased to 44.16±10.83 in all the fruits treated with 2% Na2Co3 concentration by week two and continued till third week when they were completely diseased, having 100% decay incidence. The causal organisms in the decaying fruits were Penicillium digitatum and Phytophthora palmivora. However, fruits treated with 2% Na2CO3 concentration in 45oC hot water recorded 0% decay incidence throughout storage duration which lasted for 6 weeks and as such implied that all the treated fruits were diseased free.