• The effects of sequential heat treatment on microbial reduction and spore inactivation during milk processing

      Li, Fang; Hunt, Karen; Buggy, Aoife K.; Murphy, Kevin; Ho, Quang Tri; O'Callaghan, Tom; Butler, Francis; Jordan, Kieran; Tobin, John; Department of Agriculture, Food and the Marine; et al. (Elsevier BV, 2020-05)
      Sequential heating processes are commonly applied to milk by the dairy industry as part of their microbiological control strategy. Often pasteurisation at 72 °C is followed by a sequential high heat treatment step of up to 125 °C; however, such severe heat treatment can lead to reduced protein quality. Nine temperature combinations (80–90 °C) were evaluated to assess microbial reduction and whey protein nitrogen index values during pilot scale milk processing. A total of 110 bacterial isolates were identified to species level by 16S rDNA sequencing, with Bacillus licheniformis identified as the dominant species. While the experimental treatments did not achieve microbial reductions comparable with the control heating process, the results of this study provide a benchmark for milk processors relative to the effects of sequential heat treatments on milk and their impact on the survival of both thermally resistant microbial populations and thermally labile milk components during processing.
    • Occurrence and identification of spore-forming bacteria in skim-milk powders

      Li, Fang; Hunt, Karen; Van Hoorde, Koenraad; Butler, Francis; Jordan, Kieran; Tobin, John; Department of Agriculture, Food and the Marine; Enterprise Ireland; 14/F/883; TC 2014 0016 (Elsevier, 2019-05-28)
      The different customer and regulatory specifications for mesophilic and thermophilic aerobic and anaerobic spore numbers in skim-milk powder, in addition to some specifications on specific spore-forming bacteria, such as Bacillus cereus, can be challenging for the industry to meet. Twenty-two samples of medium-heat skim-milk spray-dried powder from eight sources were analysed in triplicate with 16 bacterial and spore enumeration tests to understand the variety of spore-forming bacteria population. Using 16S rDNA sequencing, the species were identified for 269 isolates that were representative of the various tests. Of the isolates identified, 68% were Bacillus licheniformis, a facultative anaerobe that can survive and grow at mesophilic and thermophilic temperatures, making it difficult to eliminate in manufacturing environments. Using whole genome sequencing, 16 of 23 isolates identified as B. licheniformis by 16S sequencing were confirmed as B. licheniformis, four were identified as Bacillus paralicheniformis and three were identified as Bacillus sp. H15-1.