Antifungal Activity of Chitosan and Its Preservative Effect on Low-Sugar Candied Kumquat

The inhibitory effect of chitosan, a deacetylated form of chitin, on the growth of Aspergillus niger and the aflatoxin production of Aspergillus parasiticus was evaluated. The inhibitory effect of chitosan against A. niger was increased as the chitosan concentration was increased from 0.1 to 5.0 mg/ml (pH 5.4). At concentrations of 4.0 or 5.0 mg/ml, chitosan was less effective than potassium sorbate in inhibiting the growth of A. niger. The greatest inhibitory effect of chitosan against A. parasiticus was found at 3.0-5.0 mg/ml. In addition, chitosan could completely prevent aflatoxin production by A. parasiticus at the concentration of 4.0-5.0 mg/ml. Chitosan (2.0 and 5.0 mg/ml) induced considerable leakage of UV-absorbing and proteinaceous material of A. niger at pH 4.8. Using the response surface methodology, a second order polynomial model was derived and used to predict the number of days to obtain visible mold growth under various combinations of chitosan concentrations and °Brix in candied kumquat. The results showed that there was no significant difference in shelf-life extension of candied kumquat at chitosan concentration of 3.5-6.5 mg/ml. However, °Brix had a significant effect on shelf life. Candied kumquat with 6.0 mg/ml chitosan concentration and 61.9 °Brix had a predicted mold-free shelf life of 65.3 d.