Microbiological survey of equipment and wheat‐milled fractions of a milling operation

Abstract

Background and objectives As wheat is milled into flour, there is a substantial risk of cross‐contamination by microorganisms potentially inhabiting the milling equipment. The objectives of this study were designed (a) to assess the levels of microbial contamination associated with the milling equipment and the wheat as it is processed from grain to packaged flour, and (b) to identify equipment that could serve as a source of contamination during processing. Findings Equipment used to clean and temper wheat grain was found to harbor substantial populations of aerobic mesophilic bacteria, Enterobacteriaceae, and molds. Generic E. coli was found in 2 instances on cleaning equipment at an average of 0.4 log CFU/10 cm2. Coliform counts increased markedly in wheat kernels and milled fractions after passing through the different milling steps. Conclusions These data demonstrate that microorganisms, including fecal indicators, were common colonizers of milling equipment and that a consistent cross‐contamination risk existed throughout the processing line. Cleaning and sanitation efforts should focus especially on tempering equipment and prompt removal of buildup of grain/flour residues within the milling equipment. Significance and novelty This study identified critical control areas and equipment where cross‐contamination is likely to occur during milling. Appropriate sanitary measures should, therefore, be implemented in the mill to minimize the risk of microbial contamination during wheat milling.

Significance of wheat milling operations on the distribution of Escherichia coli bacterium into milling fractions

“…The results consistently demonstrated that E. coli was more likely to be transferred in higher amounts into the nonflour fractions (bran, fine bran, middling, shorts) from the initial wheat and that higher initial wheat contamination levels led to increased load oif mill fractions. The results were consistent with published studies in that more wheat microflora (e.g., coliforms, aerobic bacteria) were transferred into the bran, and middling, and shorts fractions compared to the flour fractions after milling (Berghofer et al, 2003; Eglezos, 2010; Sabillón et al, 2020). As for the individual flour fractions, the break, reduction, and straight grade flours had higher E. coli loads compared to the sizing flours.…”

“…The heat generated during the milling process results into moisture condensation within the mill (Berghofer et al, 2003). This generated moisture helps facilitate the accumulation of broken kernel and flour residues inside the mill forming reservoirs for microorganisms (Sabillón et al, 2020). These accumulated residues could then serve as an E. coli contamination source for the subsequent batches of wheat which helps explain the increased counts recovered from the flour fractions as greater quantities of inoculated wheat were milled.…”

Quantifying Escherichia coli contamination in milling equipment during lab‐scale milling operations

“…Hence, their findings indicated that the BK system could have higher amounts of surface contamination and this agrees with the present study as larger microbial loads were observed in the BK mill fractions. Sabillón et al (2020) surveyed the microbial contamination of pilot-scale milling equipment where they reported that for the actual milling equipment, microbial contamination (aerobic counts) was concentrated in the rolls, walls, and sieves of sifter boxes. The results from this study were consistent with Sabillón et al (2020) as E. coli contamination was also higher in the rollers and sifter surfaces.…”

“…Sabillón et al (2020) surveyed the microbial contamination of pilot-scale milling equipment where they reported that for the actual milling equipment, microbial contamination (aerobic counts) was concentrated in the rolls, walls, and sieves of sifter boxes. The results from this study were consistent with Sabillón et al (2020) as E. coli contamination was also higher in the rollers and sifter surfaces. Although the results were relatively consistent with the report on the survey of pilot-scale milling equipment, validations for bigger-scale milling equipment should still be done due to the difference in the operating mechanism of the lab-scale milling equipment used compared to the conventional milling equipment.…”

“…Wheat milling is a series of physical particle size reductions with size‐based separation processes aimed at extracting flour from the wheat kernels. Due to its physical nature, previous studies have demonstrated that milling redistributes the wheat microbiota into the mill fractions produced (Laca et al, 2006; Sabillón et al, 2020).…”