Aqueous ozone sanitization of whole peeled onion: Process optimization and evaluation of keeping quality during refrigerated storage

Fruits and vegetables, especially in their minimally processed form, are highly susceptible to microbial spoilage, highlighting the need of a safe and effective sanitizing agent to extend their shelf-life. This study was carried out to optimize the aqueous ozone sanitization parameters viz. ozone concentration (1-5 mg/L), exposure time (2-8 min), and pH (3-5) for whole peeled onion. Consequently, the keeping quality was investigated for ozonated (optimized conditions), chlorinated (100 mg/L) and water-washed samples packed in tray packs and stored under refrigerated conditions (5 +/- 1 degrees C, 90 +/- 1 % RH). Numerical optimization using the 3 factor, 3 level, Box and Behnken design suggested that aqueous ozone at 4.51 mg/L exposed to the onions for 8 min at a pH of 3 provided optimized sanitization that resulted in the most favorable reductions in microbial load (3.74 log CFU/g), pyruvate content (14.2 % less than fresh untreated) and a good overall acceptability score (8.5). After storage, the microbial shelf life obtained from optimized ozone sanitization was found to be 14.3 % (2 d) higher than waterwashed and 13.04 % lower than chlorinated samples. Ozone-treated onion was observed to retain better quality attributes in terms of pyruvate content, color change and firmness as compared to other treatments studied.