Effect of Chitosan and Temperature on Spore Germination of Aspergillus niger

Inhibition of radial growth and spore germination of Aspergillus niger in media with added chitosan were detected. The highest radial growth inhibition (73%) was determined at 24 h with 3 g · L-1of chitosan, and the percent inhibition of spore germination was 40% after 13 h of inoculation. Further, the CC50, that is, the concentration at which spore germination is inhibited by 50%, was estimated by probit analysis (3.5 g · L-1). The activation energies, EAwere estimated by an Arrhenius model in control and amended chitosan media, obtaining 35.6 and 36.6 kcal · mol-1, respectively. These values were in the same order of magnitude because chitosan as inhibitor was more effective at low temperature (≤ 18°C). Hence synergism of temperature and chitosan were only observed at 12 and 18°C. Therefore, the maximal percentage of germinated spores, Smaxwas also affected by low temperatures in chitosan-amended media with estimated values lower than 70% at temperatures < 37°C whereas in control media Smaxreached values close to 100%. Scanning electron micrographs showed that chitosan produced spore aggregation and morphological anomalies affecting swelling, germ tube emergence, and polarization.