Inactivation of Aspergillus niger in Small Onions by Ozone Treatment and Process Optimization using RSM

Among the post-harvest diseases of onion, black mould rot caused by Aspergillus niger was the predominant one. Nearly 40% of the onion production is lost during post-harvest handling and sprouting, of which microbial spoilage alone contributes approximately 15–20% of the total loss. The effects of ozone gas concentration (100 to 500 mg/l), flow rate (0.5 to 1.5 l/min), and treatment time (10 to 30 min) on inactivation of Aspergillus niger on CO-3 small onions were studied in this work. The obtained log reduction data were fitted in the classic log linear model and response surface methodology (RSM) was used to find the optimum treatment combinations by minimizing the applied ozone concentration, exposure timeand targeting 3-log reduction asresponse. A 3factor Box-Behnken experimental plan was designed to measure response. The statistical analysis of developed predictive model suggested that ozone gas concentration, treatment time and flow rate influences significantly on the rate of log reduction of A. niger. Among the 3 factors, the effect of ozone gas concentration and treatment time on fungal inactivation was more compared to the effect of flow rate. It is also evident that the model performance (R² = 0.98) of the response surface methodology is accurate in prediction with minimum experimental runs than the full factorial log linear (0.89) model. The study also proved the efficacy of ozone gas treatment as a pre-treatment method before storage to enhance the shelf life of onion.