202: Identifying the Microbial Isolates of Contaminated Maple Syrup and Processing Parameters to Reduce Food Safety Risk

Introduction

A multiple project collaboration worked to identify the cause of floating masses in maple syrup, determine whether certain types of retail containers are more likely to be contaminated, and explore if syrup filling temperature can reduce contamination.

Methods

Fifty-two retail maple syrup samples containing floating masses were collected from syrup producers in the Northeastern US and Canada between 2010-2014. The pH, Brix and water activity levels of the syrups were measured, and subsamples were and plated on agar media to isolate microorganisms. Eight different commercial containers (glass and plastic) were inoculated with a cocktail of Shiga toxin-producing E. coli (STEC), Salmonella and L. monocytogenes, or spores of Penicillium and Aspergillus previously isolated from syrup. Inoculants were dispensed into containers and dried in a biosafety cabinet overnight prior to adding hot syrup (82.2°C or 87.8°C). The controls were unheated syrup poured into inoculated containers. Cooling was monitored in each bottle type and re-isolation of inoculated bacteria and fungi was attempted once syrup reached ambient temperature. ANOVA regressions were performed on data using RStudio, with a confidence level of p < 0.05.

Results

Forty-nine of the 52 maple syrup samples were contaminated with fungi, with the majority being Penicillium, Aspergillus and Wallemia species. Fungi were identified by appearance and DNA sequences. Contaminated samples had Brix of 63-71%, water activity levels from 0.84-0.89, and pH levels from 4.9-7.3 (mostly within normal parameters).

Plastic containers significantly reduced survival of all pathogens compared to glass containers. Fancy glass containers (maple leaf shaped) significantly increased pathogen survival; most likely due to the smaller syrup volume and faster cooling rates than plastic, and the possibility of the inoculants not completely drying at the leaf tips of the bottle. Increases in syrup temperature or volume significantly reduced Salmonella and Listeria, but not STEC survival. For Aspergillus and Penicillium, increases in temperature significantly reduced survival probability for both species.

Significance

This research is considered one of the first steps to help identify the root cause of microbial contamination of maple syrup and develop research-based processing strategies to ensure the microbial safety of maple products.

Authors: BL Calder, SL Annis, JJ Perry, MC Fiore, KM Hopkins