Purpose : This study was conducted to understand the level of inactivation achieved by candying (sugar infusion and consequent air drying) towards bacterial pathogens, HAV and selected surrogates. This will allow better assessment of risks and better management of the microbial safety throughout the berry supply chain.
Methods: Frozen blueberries were thawed and wet inoculated using fresh cultures of Salmonella, Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes, and HAV, as well as the selected surrogates Enterococcus faecium, Escherichia coli P1, Listeria innocua, MS2, and the human Norovirus surrogate, MNV. Inoculated fruits were sugar infused to a final sugar concentration of 34 to 45% using different infusion temperatures (23, 35, 40, 45°C). After infusion samples were air dried, the surviving bacteria and viruses were enumerated and the level of inactivation was calculated.
Results: The sugaring process at 40°C was shown to achieve > seven and > six log CFU/g reduction for Salmonella and the other vegetative microorganisms, respectively. For MS2, 5.75±0.03 log PFU/g reduction were reported. For HAV and MNV, 1.46±0.22 and 3.40±0.17 log PFU/g reductions were reported, respectively, at 45°C. No reportable inactivation was observed at 23°C. The air drying of the sugared berries at 100°C for one hour delivered > five log CFU/g reduction on Salmonella, STEC, E. faecium, and E. coli P1. On HAV, MS2, and MNV, 2.13±0.23, 6.22±0.66, and 3.17±0.03 log PFU/g, respectively, were reported after air drying.
Significance : These data showed that mild processing like sugaring and air drying of blueberries can contribute an acceptable level of inactivation towards bacterial pathogens, HAV, and selected surrogates when specific processing parameters are applied.