Impact of postharvest treatments, chlorine and ozone, coupled with low-temperature frozen storage on the antimicrobial quality of lowbush blueberries (Vaccinium angustifolium)

The additive antimicrobial influence of low-temperature frozen storage and oxidation treatments was investigated using 100 mg/L chlorine or 1 mg/L aqueous ozone sprays applied to lowbush blueberries (Vaccinium angustifolium) destined for individually quick frozen (IQF) markets. Following a 60 s contact time with either oxidant, treated berries were blast frozen at -30 degrees C and stored at -18 +/- 2 degrees C for up to 12 months. Significant differences (p <= 0.05) between treatment effectiveness at time 0 were not observed among all populations evaluated (mesophilic bacteria, yeast, and mold), although ozone treatments resulted in the greatest log reductions in each population. In contrast, after 12-months of frozen storage, the greatest microbial reductions in all populations were observed on chlorine-treated berries. Results suggest a significant impact (p <= 0.05) of low-temperature frozen storage on microbial counts of both treated and non-treated blueberries yet, chlorine-treated berries stored for up to 12 months exhibited significantly greater reductions (p <= 0.05) in bacterial and yeast counts compared to non-treated controls and ozone-treated berries. Study results suggest an additive effect between freezing and chlorine pre-treatments in altering microbial integrity and survival on blueberries. (C) 2012 Elsevier Ltd. All rights reserved.