Inactivation of Aspergillus flavus on green coffee beans by treatments with organic acid vapor

This study aimed to inactivate Aspergillus flavus on green coffee beans using organic acid vapor treatment. Green coffee beans inoculated with A. flavus spores (approximately 5.2–5.9 log cfu/5 beans) were treated with vapor (100 mg/L) generated from acetic acid, formic acid, or propionic acid at 25 °C or 50 °C and relative humidity (RH) of 43 % or 100 % for up to 6 h. Exposure to acetic acid or propionic acid vapor for 6 h decreased the number of A. flavus on the beans by 1.2–3.1 or 0.5–3.3 log cfu/5 beans, respectively. Treating green coffee beans with formic acid vapor for 6 h reduced number of A. flavus spores to below the detection limit (1.7 log cfu/5 beans), regardless of temperature and RH. Formic acid treatment did not alter the color values (L*, a*, and b* values) of the beans; however, it significantly decreased the pH. Mold did not grow on beans treated with formic acid vapor during storage, whereas untreated beans and those treated with acetic acid or propionic acid showed visible mold after 5 days. The treatment of organic acid vapor significantly reduced A. flavus populations on the beans and high temperatures or RH synergistically enhanced mold inactivation effect of organic acid vapor.