Efficient Reduction of Escherichia coli from Apple Cider by Combining Microfiltration with Ultraviolet Treatment

Introduction: Consumption of raw apple juice or cider contaminated with E.coli O157:H7 has resulted in several outbreaks in recent years. Thermal pasteurization can achieve a 5-log reduction of this pathogen, but can negatively affect the nutritional and organoleptic properties of juice. Ultraviolet (UV) treatment is a FDA recognized alternative to thermal processing of apple juice and cider, but the suspended solids in the treated product can limit its efficiency. Microfiltration (MF) can be used to physically remove suspended solids and microorganisms from apple cider, thus enhancing the effectiveness of UV, and allowing a lower UV dose to be used.

Purpose: In this study, the efficiency of a combined UV & MF treatment in the reduction of E.coli from apple cider was investigated.

Methods: Apple cider with pH 3.7 and 12.7 °Brix was used as the raw material. The cider was inoculated with both pathogenic and non-pathogenic strains of E. coli, at more than 10⁷ CFU/ml, and then subjected to the individual or combined treatments. MF was performed with a 0.8 µm ceramic membrane, at 6 °C and 105 kPa transmembrane pressure. The UV treatments were conducted using a CiderSure 3500 reactor, at a low UV dose of 5 mJ/cm². Microbial counts and chemical composition before and after processing were determined.

Results: MF resulted in more than 5-log reduction of E. coli in the permeate, as did UV. The penetration depth of UV was improved by the MF step, and as a result the combined MF & UV treatment led to a cumulative reduction of E. coli of over 7 log. The data also suggests that the UV dose could be further reduced.

Significance: The developed non-thermal hurdle treatment has the potential to significantly reduce pathogens in apple cider, as well as spores, yeasts, molds and protozoa, and thus help juice processors improve the safety and quality of apple juice and cider, as well as other fruit juices.