Characterisation and biofilm screening of the predominant bacteria isolated from whey protein concentrate 80

Abstract

The source of microbiological contamination of whey protein concentrate (WPC), a quality problem for the dairy industry, has not been thoroughly investigated. The objectives of this study were to identify the bacteria isolated from whey protein concentrate containing 80% protein (WPC 80) and determine their ability to form biofilms as a potential source of contamination in a whey processing line. Six Bacillus species including (percentage of isolates in brackets) Bacillus licheniformis (67%), Bacillus cereus (19%), Bacillus thuringensis (4%), Bacillus subtilis (4%), Bacillus pumilus (4%) and Paenibacillus glucanolyticus (2%) were identified based on BLAST databases in six different WPC80 batches. B. licheniformis was the predominant isolate. B. licheniformis are thermo-tolerant bacteria with the ability to form biofilm. This biofilm is a potential source of microbial contamination of product, resulting in microbial specification limits being exceeded. Spoilage of product may result from the metabolic products, such as enzymes, produced by these biofilms.

The Potential Source of B. licheniformis Contamination During Whey Protein Concentrate 80 Manufacture

“…Thirty‐three B. licheniformis strains isolated from Mozzarella WPC80 powder samples, as reported by Zain and others (), were used in this study. The isolates were maintained on nutrient agar slants at 4 °C and in glycerol beads stock at −80 °C.…”

“…Five whey samples from different points in the whey processing plant, preultrafiltration (raw whey balance tank, clarifier, thermalizer; Figure ) were provided by the same whey processing plant reported by (Zain and others ). One milliliter of each sample was diluted in 90 mL of sterile 0.1% peptone water (pH 7.0) and homogenized using a vortex mixer.…”

“…However, they should be able to be controlled with normal cleaning procedures. Zain and others () studied WPC80 samples with high bacterial counts and showed the predominant microflora was the mesophilic bacterium Bacillus licheniformis . B. licheniformis is unable to grow at the low temperatures (10 °C) used in most ultrafiltration membrane plants in the dairy industry.…”

“…Bacteria contaminating dairy manufacturing plant are often growing as a biofilm (Flint and others ; Flint and others ; Tang and others ; Chamberland and others ). Initially, ultrafiltration was thought to be the most likely source of biofilm and product contamination in a WPC manufacturing plant; however, the results from Zain and others () suggest this is unlikely. Other surfaces in the WPC manufacturing plant will now be considered as the site for biofilm growth.…”

“…In the dairy industry, biofilm can cause blockages and reduce heat transfer and passing milk is contaminated with cells and enzymes released from the biofilm. This study is a follow up from research from our earlier publication which determined that B. licheniformis was the predominant bacterial isolate from WPC80 (Zain and others ) and aimed to determine the potential source of B. licheniformis contamination in a WPC80 manufacturing plant, the potential to form biofilm and cause protein damage.…”