Effect of extended shelf life milk processing on the bacterial composition associated with the nozzles of filling machines
In South Africa extended shelf life (ESL) milk processors are still facing challenges extending the shelf life beyond 14 days. It is hypothesized that post contamination along the milk processing line is responsible of reducing the shelf life of ESL milk. This assumption was investigated through assessing the microorganisms associated with the nozzles of aseptic filling machines post CIP process, this study was designed and divided into two phases. Phase one involved isolation and characterisation of the bacteria associated with the nozzles of aseptic filling machines after CIP process with the aim of determining the diversity of microorganisms attached to the nozzles of aseptic filling machines. Swab samples were collected from a dairy plant processing ESL milk. Twenty swabs were taken from ten different nozzles of aseptic filling machines during 4 visits (n=80) The swab samples were plated on the day of sampling. A total bacterial count ranging from 1.75 1.95 log CFU/cm with an average of 1.81 log CFU/cm (n=80) MALDI TOF revealed a high percentage of Gram positive rods (69% followed by Gram positive cocci (20% and then Gram negative rods (7% The Gram positive rods belonging to genus Bacillus were identified as B. cereus, followed by B. pumilus, B. subtilis and Paenibacillus spp. The Gram positive cocci included S. hominis, S. epidermidis, Micrococcus luteus and Anaerococcus spp. The Gram negative rods were identified as Acinetobacter junii. The prevalence of Bacillus spp. noted in the nozzles of ESL aseptic filling machines is attributed to their ability to resist heat treatment during CIP process and their ability to attach to stainless steel surfaces. There was a degree of similarity in terms of MALDI TOF MS profiles for the strains of B. cereus, Staphylococcus spp. and Paenibacillus spp. originating from the nozzles of aseptic ESL filling machines and the packaged ESL milk product. These bacteria are likely to originate from the nozzles and dispensed into the final ESL milk during filling process.