Efficacy of chlorine dioxide gas and freezing rate on the microbiological quality of frozen blueberries
2015
Zhang, Lei | Yan, Zhinong | Hanson, Eric J. | Ryser, Elliot T.
Blueberries are prone to microbial contamination, with growth of bacteria, yeasts and molds during bulk freezing negatively impacting quality and marketability. As a follow-up to our previous work, the combined impact of ClO2 gassing and freezing rate on the microbiological quality of frozen blueberries was examined. Sixteen lugs of blueberries (∼9.1 kg/lug) were stacked inside a large plastic container at a commercial blueberry processing facility. In each of four trials, one container was exposed to ClO2 gas (4 ppm) using three 3-kg sachets while one ungassed container remained untarped. Before and after commercial processing, 50-g samples of gassed and ungassed blueberries were quantitatively examined for mesophilic aerobic bacteria (MAB), yeasts, and molds. After processing, additional 50-g samples were placed in a −20 °C freezer under different conditions where the berries reached a temperature of −3 °C after 3 h (quick-frozen), 2 days (intermediate-frozen) and 5 days (slow-frozen). Fruit was sampled periodically during 6 months of frozen storage at −20 °C. MAB yeast and mold populations decreased ∼2 and 1 log CFU/g, respectively, in ClO2-gassed and ungassed fruit, with MAB, yeast and mold populations increasing ∼1 log CFU/g during quick freezing to −3 °C and ∼2 log CFU/g during intermediate and slow freezing to −3 °C. Based on these findings, ClO2 gassing followed by quick freezing provides an effective means for meeting the current microbiological standards being imposed by buyers of frozen blueberries.
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