Validation protocol for commercial sterility testing methods

Abstract Thermal processing technology has been widely applied for the preservation of food. Initially used for canned foods, thermal processes have since been extended to a large range of foods. Ready-to-eat products processed at Ultra-High Temperature (UHT) and aseptically filled are extensively consumed because of their convenience. Sterilisation and aseptic filling are critical steps, and food business operators have to verify their efficacy by demonstrating commercial sterility. Methods commonly used to demonstrate commercial sterility also originate from the canning industry and are both cumbersome and time consuming. Several alternative methods are available, but they do not have official validation status since standard validation protocols, such as ISO 16140–2 and AOAC guidelines cannot be applied due to differences in the testing procedure. We propose a validation protocol based on inclusivity and limit of detection LOD95 as performance criteria. The traditional direct streaking and six alternative methods were assessed to demonstrate the relevance of the protocol; three methods were based on cellular metabolism during microbial growth (CO2 production, O2 consumption), one was based on cell count by flow cytometer and two methods were based on cellular ATP activity. Nine food items including challenging matrices (high pH, high fat contents) were tested with sporeforming and non-sporeforming microorganims. Inclusivity results show that all the methods could detect a large range of microorganisms provided appropriate culture media were used. The LOD95 results indicated that methods based on cellular metabolisms were very sensitive (LOD95   3 log10 CFU/mL). This is the first study proposing relevant performance criteria to validate alternative commercial sterility methods. The outcomes allow the end user to select a right method according to their requirements.