Purpose: The objective of this research was to determine the sources of potential “problematic” sporeforming bacteria present throughout a condensed milk processing chain, including sources at the farm level.
Methods: During two seasons, condensed milk samples from a commercial plant and environmental samples from three farms were collected and heat-treated (80°C/12 min) to recover only sporeformers. Samples were spread-plated using Standard Methods Agar (SMA) and incubated at 32°C. Samples were also stored at 7°C and 55°C, to determine which sporeformers had the ability to grow under refrigeration and high temperature conditions. Isolates were identified using molecular techniques (16S or rpoB sequencing).
Results: Molecular typing results showed that Paenibacillus spp. (odorifer, cookii, graminis) were responsible for the fluid milk spoilage due to its ability to grow at low temperatures. Paenibacillus was also found in condensed milk from the plant. Other Bacillus species found in condensed milk include: B. claussi, B. subtilis, Lysinobacillus sp., B. safensis, B. licheniformis, B. sonorensis and Brevibacillus sp. These last three species are capable of growing at thermophilic temperatures. Among the sources of “problematic” strains at the farm, it was found that milking equipment and cow teats contained a variety of psychrotrophic and thermophilic “problematic” strains, suggesting that interventions should be targeting these areas.
Significance: By detecting potential sources of these organisms at the farm level, farmers could design suitable interventions to decrease sporeformers counts in raw milk and ultimately improve the quality of condensed milk.