Inhibitory effect against postharvest diseases in oranges by cassia oil with difference concentration of sodium bicarbonate

Abstract

Penicillium digitatum, the green mold is the most damaging postharvest diseases on citrus fruit such as orange. Continuous used of synthetic fungicide cause the green mold to develop resistant towards the fungicide. Cassia oil and sodium bicarbonate are food additive that shown potential in controlling postharvest disease of fruits and vegetables. In this study, the inhibitory effect of green fungicide by cassia oil alone or in combination with sodium bicarbonate against P.digitatum was investigated in vitro and in vivo on the surface of oranges. Cassia alone and in combination of sodium bicarbonate has shown inhibition towards P.digitatum in vitro and in vivo on the surface of sweet oranges. In antifungal activity study, 0.25 mL/L of cassia oil with 1 % (w/v) of sodium bicarbonate have shown 100 % inhibition. In mode of action study which are spore germination, mycelium dry weight and cell membrane have shown significant effect when treated with cassia oil and sodium bicarbonate. In spore germination study, 0.25 mL/L of cassia oil with 1 % (w/v) of sodium bicarbonate has shown 100 % inhibition towards the conidia. The dry weight of mycelium has significantly reduced from 0.12 g ± 0.01 to 0.05 g ± 0.01 when treated by 0.25 mL/L of cassia oil with 3 % (w/v) of sodium bicarbonate as compare to control. For determination of integrity of cell membrane, the absorbance reading was significantly increases from 0.12 ± 0.01 to 0.35 ± 0.02 in the present of 0.25 mL/L of cassia oil with 3 % (w/v) of sodium bicarbonate as compare to control. For in vivo experiment which have artificially wounded and unwounded oranges. The experiment demonstrated that 0.25 mL/L of cassia oil with 3 % (w/v) of sodium bicarbonate applied to wounded oranges fruits which inoculated with P.digitatum could significantly decrease the disease incidence of green mold from 100 % to 58.33 % for up to 10 days in room temperature compare to control. Meanwhile, the treatment with cassia oil and sodium bicarbonate on unwounded oranges does not affect the quality parameter (colour index, soluble solid content and total acidity) except increase percentage of weight loss from 3.55 % ± 0.85 to 7.43 % ± 1.42 and reduce firmness from 650.12 gf ± 57.25 to 467.23 gf ± 21.12