Purpose: To determine if sticks pre-treated with potassium sorbate controlled the proliferation of L. monocytogenes on stem-end inoculated caramel apples during storage.
Methods: Granny Smith apples were stem end-inoculated with 7 log CFU L. monocytogenes per apple, using a cocktail comprised of 3 strains isolated from the caramel apple outbreak, and dried for 2 h. Wood sticks were soaked in 0, 20, 30, 40, or 50% potassium sorbate overnight and dried prior to insertion into the stem end of the apples. Apples were caramel-dipped, dried and packaged into clam-shells. Caramel apples were stored at 25°C for 13 days, and at various timepoints, homogenized with BLEB. Serial dilutions were plated onto PALCAM for enumeration.
Results: Prior to packaging, the L. monocytogenes population in caramel apples made with sticks treated with 50% potassium sorbate was significantly lower (4.33±0.91 log CFU/apple, P<0.05) than all other conditions (approximately 6 log CFU/apple). Populations were also significantly lower in caramel apples made with sticks treated with both 40 and 50% potassium sorbate after 1 and 2 days; however, populations for all treatment conditions increased to 9 log CFU/apple after 6 days. No differences were seen when comparing 0, 20, and 30% treatments at any timepoint.
Significance: This study will help to determine possible stick pre-treatment conditions to diminish L. monocytogenes growth on caramel apples.