Bacteriophages – An effective tool to control Salmonella and pathogenic E. coli in milling operation

Introduction

The milling industry does not typically employ targeted antimicrobial intervention believing flour is a low-risk product and subject to heat treatment constituting a kill step in preparation of food products either commercially or in the consumer kitchen. However, recent outbreaks and recalls associated with flour and related products have challenged this paradigm. In 2019, the US Food and Drug Administration (FDA) issued 14 notices for recalls of flour. Of these recalls, 12 were associated with Shiga-toxin producing E. coli (STEC) and 2 were due to presence of Salmonella. Indeed, several studies have now demonstrated that STEC and Salmonella can survive and contaminate the four and flour-products – leading to concerns related to flour-borne outbreak of these pathogens. Recalls of the flour products are costly and may come with a price tag of $5-$10 million per recall and at the same time tarnish the brand and company reputation. The risk of flour associated microbial detection, outbreak and traceability has increased the need for development of intervention strategies.

Recently some millers have started experimenting with various chemical-based antimicrobials. These chemicals reduce the pathogens to varying degrees but may impact the flour functionality and/or organoleptic properties. For example, the use of organic acid at the tempering stage at the concentrations reported to achieve meaningful reductions may impact baking qualities. Another problem associated with the use of acid-based products is corrosion of equipment and other surfaces these chemicals contact. For example, continuous use of chlorine and other antimicrobials is known to corrode steel surfaces. The corrosion results in increased surface roughness which provides niche for bacteria to attach and form biofilms. Biofilms then become a recurrent source of contamination and accelerate the corrosion further damaging the equipment. Biofilms have also been observed on the interior of milling equipment surfaces such as roller mill housings and sifter box interiors. Removal of these biofilms requires higher concentrations of chemicals which then cause further corrosion which may become a downward cycle. Corrosion is also likely to reduce the equipment life. Secondly, certain chemicals can be hazardous to worker and require a rigorous safety procedure to be in place for their use.