The patented QMI Stress Test is a proactive method to monitor critical control points (CCP) for post-pasteurization contamination. These CCP would include after high-temperature short time (HTSP), product storage tanks, and distribution valves before the filler.

QMI Stress Test Procedure

  • Select and label the QualiTru TruStream Collection Bag with CCP and date.
  • For tank sampling, aseptically sample while the tank is being offloaded at an elbow near the tank using a QualiTru Collection Bag.
  • For line sampling, aseptically obtain a large product sample using the two or five-liter QualiTru Collection Bag.

NOTE: The QualiTru Collection Bags are oxygen permeable for optimal gram-negative growth and do NOT require adding headspace.

  • Incubate the bagged sample at room temperature for 24 hours (for quick results) and again at 48 hours (for more accurate results).
  • Do a plate count using a gram-negative selective media, such as Violet Red Bile Agar (VRB) or sodium deoxycholate, following the manufacturer’s recommended procedures (both are inhibitory to gram-positive bacteria).
  • Incubate the plates at room temperature for 72 hours, observing for growth every 24 hours.
  • The presence of any growth, Coliform or non-Coliform, indicates post-pasteurization contamination.

Presence of gram-negative bacteria

Gram-negative bacteria do not survive pasteurization, so detecting their presence in process monitoring samples is a warning sign of post-pasteurization contamination that can lead to spoilage and food safety issues. A positive post-pasteurization test requires corrective action.

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Aseptic and representative sampling plays a vital role in monitoring milk quality and in-process monitoring for contamination within the dairy plant. Incorporating the QMI Stress Test as part of your regular quality control process will help identify critical contamination issues early.

Call us at (651) 501-2337 or email sales[@] to learn more and/or to discuss your needs.