Fungal diversity in ginger and effect of storage conditions on occurrence of Fusarium and its mycotoxins

Abstract

This study investigated the fungal diversity in ginger from fields and storage and the effects of storage temperature and relative humidity (RH) on fungal and mycotoxin occurrence. A total of 909 isolates from ginger samples (30 from fields and 24 from storages) were identified using a molecular approach. Fusarium (23 species, 82.3%) was dominant in the ginger samples, followed by Aspergillus (16 species, 8.5%), and Penicillium (11 species, 2.1%). Among the Fusarium species, F. oxysporum (28.3%) was predominant, followed by F. asiaticum (14.9%) and F. solani (7.2%). Most isolates of F. oxysporum, F. graminearum, and F. fujikuroi species complex tested produced the respective mycotoxins: beauvericin (15.9–93.4 mg/kg), nivalenol (16.0–611.6 μg/kg), deoxynivalenol (31.3–1605.5 μg/kg), and fumonisins (0.1–101.4 mg/kg) on potato dextrose agar. During six months of ginger storage under three conditions, Fusarium species predominated (64.8%), followed by Aspergillus (3.8%) and Penicillium (0.1%). The frequency of F. oxysporum increased during storage, whereas mycotoxin occurrence varied significantly depending on storage conditions (p < 0.05). At 5 °C/73% RH, F. oxysporum frequency was the lowest (32.8%), while the average concentrations of enniatins were the highest (2030.0 μg/kg). At 14 °C/68% RH, F. oxysporum frequency (71.9%) and beauvericin (725.7 μg/kg) were the highest. At 13 °C/96% RH, F. oxysporum frequency (56.1%) was lower than at 14 °C/68% RH, and beauvericin (56.8 μg/kg) and enniatins (41.3 μg/kg) were the lowest. Aflatoxins and ochratoxin A were not detected in any of the stored samples. These results suggest that 13 °C/96% RH is the most suitable storage condition for ginger to minimize fungal growth and the production of mycotoxins.