Purpose: This study determined the effectiveness of various chemical pretreatments for the reduction of L. monocytogenes on wooden sticks and in caramel apples.
Methods: Wooden sticks were soaked, overnight, in solutions of 1, 3, 5, 10, and 20% (w/v) sodium benzoate, Nisaplin, and ascorbic acid and dried for two hours. The sticks were then inoculated with seven log CFU/stick of a L. monocytogenes cocktail composed of three strains isolated from the caramel apples outbreak and dried for another two hours. Sticks were either stored at 25°C for eight days or used in caramel apple production. At timepoints, sticks or apples were homogenized with BLEB for L. monocytogenes recovery by enrichment and enumeration on Brilliance Listeria Agar (Oxoid) plates. Experiments were conducted twice with triplicate samples for each condition.
Results: The L. monocytogenes populations on wooden sticks that received 3% ascorbic acid and 5% sodium benzoate treatments had significant decreases in population compared to controls after two hours drying (4.92±0.21 and 4.27±0.23 log CFU/stick, P<0.05, respectively). After 24 h at 25°C, the L. monocytogenes populations exposed to the 1, 3, and 5% ascorbic acid treatments had decreased below the level of enumeration (two log CFU/stick) and was absent in enrichments. In caramel apples, 10 and 20% ascorbic acid decreased the populations of L. monocytogenes up to 48 hours; however subsequent timepoints revealed no significant differences compared to the controls.
Significance: This study will help to ascertain a functional stick pretreatment that may reduce L. monocytogenes growth on caramel apples.