The Core and Seasonal Microbiota of Raw Bovine Milk in Tanker Trucks and the Impact of Transfer to a Milk Processing Facility.

Mary E Kable,Miles Laird,Maria L Marco,Jessie Heidenreich,Jose Zaragoza,Jeremy Mcleod,Yanin Srisengfa,Mark J Bailey

doi:10.1128/mbio.00836-16

Abstract

ABSTRACTCurrently, the bacterial composition of raw milk in tanker trucks and the outcomes of transfer and storage of that milk at commercial processing facilities are not well understood. We set out to identify the bacteria in raw milk collected for large-scale dairy product manufacturing. Raw bovine milk samples from 899 tanker trucks arriving at two dairy processors in San Joaquin Valley of California during three seasons (spring, summer, and fall) were analyzed by community 16S rRNA gene sequencing. This analysis revealed highly diverse bacterial populations, which exhibited seasonal differences. Raw milk collected in the spring contained the most diverse bacterial communities, with the highest total cell numbers and highest proportions being those of Actinobacteria. Even with this complexity, a core microbiota was present, consisting of 29 taxonomic groups and high proportions of Streptococcus and Staphylococcus and unidentified members of Clostridiales. Milk samples were also collected from five large-volume silos and from 13 to 25 tankers whose contents were unloaded into each of them during 2 days in the summer. Transfer of the milk to storage silos resulted in two community types. One group of silos contained a high proportion of Streptococcus spp. and was similar in that respect to the tankers that filled them. The community found in the other group of silos was distinct and dominated by Acinetobacter. Overall, despite highly diverse tanker milk community structures, distinct milk bacterial communities were selected within the processing facility environment. This knowledge can inform the development of new sanitation procedures and process controls to ensure the consistent production of safe and high-quality dairy products on a global scale.

Highlights

Bacteria are essential determinants of the shelf life, organoleptic qualities, and safety of fresh and processed foods
In 354 (39.4%) of the raw milk samples analyzed, taxa detected at less than 1% relative abundance accounted for 50% or more of the bacteria present
The variation in the bacterial populations between the tankers was exemplified by the finding that while some of the trucks contained high (Ͼ30%) proportions of bacteria of certain taxa such as Streptococcus, Pseudomonas, Staphylococcus, and Mycoplasma, these same taxa were detected at very low (Ͻ1%) levels in the milk of the other tankers tested (Fig. 1)

Summary

Introduction

Bacteria are essential determinants of the shelf life, organoleptic qualities, and safety of fresh and (minimally) processed foods. Biota is important for identification of the sources of entry, the bacterial composition of raw milk as it reaches the site of pasteurization and processing is directly relevant to the production of high-quality dairy products with a long shelf life. The microbial community in raw milk samples in California just prior to use for the manufacture of dairy products has not yet, to our knowledge, been comprehensively examined. Given that both the location and transportation of raw milk can affect its microbial contents, we set out to identify the microbiota of raw milk collected for large-scale product manufacturing in California. We measured the consistency of the milk microbiota upon arrival at two processing facilities and determined how that microbiota was affected by large-scale, short-term storage at the manufacturing facility

Methods

Results

Conclusion