A challenge for the dairy processing industry is to monitor and control heat-resistant bacteria. These bacteria are significant for the fluid milk industry because they survive pasteurization and grow at refrigeration temperatures, causing product defects.
Heat-resistant psychrotrophic bacteria in milk were first recognized by Mikolajcik in the 1970’s. He and his fellow researchers pointed out that these bacteria are capable of causing product defects in fluid milk products.
Recent changes to the dairy industry have created situations favorable for the growth of heat-resistant psychrotrophs. The dairy industry has improved plant sanitation procedures, improved equipment and continued regulatory involvement and effective quality control and quality assurance programs. These have drastically reduced post-pasteurization contamination in fluid milk processing plants. This has enabled the dairy industry to increase shelf life (code).
With the extended codes and control of post-pasteurization contamination, heat-resistant psychrotrophs are able to grow resulting in product defects. The growth of heat- resistant psychrotrophs result in product defects in 18-21 days.
To determine the presence and effect these bacteria would have on dairy product quality, QMI suggests the following procedures:
To determine the source of heat resistant psychrotrophs, QMI suggests the QMI Heat Resistant Psychrotroph Test. This test involves:
QMI speculates that the primary source of heat-resistant psychrotrophic bacteria is from raw milk handling equipment. Several factors lead us to believe that:
Table 1 shows data collected by DQCI using the QMI Heat-Resistant Psychrotroph Test: