Effect of the combined application of chitosan and carbonate salts on the incidence of anthracnose and on the quality of papaya during storage

The potential of chitosan (1%) alone, or in combination with ammonium carbonate (3%) or sodium bicarbonate (2%), to reduce the incidence of anthracnose (Colletotrichum gloeosporioides) on papaya (Carica papaya L.) and maintain quality was investigated during storage at 13.5 degrees C and 95 % RH for 14 d, and for 2 d under simulated market conditions (25 degrees C, 75% RH). Chitosan alone or in combination with sodium bicarbonate or ammonium carbonate significantly (P < 0.005) reduced the severity of anthracnose in both inoculated and naturally-infected fruit. The effect of chitosan with ammonium carbonate on the incidence and severity of anthracnose was greater than chitosan alone, or chitosan with sodium bicarbonate. Chitosan with ammonium carbonate significantly (P < 0.005) reduced the incidence of anthracnose in, and the recovery of C. gloeosporioides from naturally-infected fruit compared to control fruit. Eating quality was not affected by these post-harvest dip treatments. Chitosan with ammonium carbonate retained high fruit quality, significantly (P < 0.005) retarded colour development of skin and flesh, increased fruit firmness and reduced weight loss. Internal carbon dioxide concentrations increased in chitosan-coated fruit to reach 7% in chitosan and ammonium carbonate-treated fruit. Thus, chitosan combined with ammonium carbonate represents a commercially acceptable, economically viable and effective alternative for post-harvest control of anthracnose during storage of papaya.