Effect of acid adaptation on pathogenic bacteria used as challenge organisms for microbial validation of biltong processing
Abstract
Biltong is a South African dried beef product that has grown in popularity in U.S. markets over the last five years. Unlike traditional American beef jerky, biltong is dried at ambient temperature and humidity after marination. However, the United States Department of Agriculture Food Safety and Inspection Service (USDA-FSIS), the regulatory agency that oversees processing of meat and poultry products, requires the use of heat lethality and maintenance of 90% relative humidity in a sealed oven to accomplish adequate reduction of pathogens on dried beef products for consumption [1]. If these parameters are not met, such as is the case with biltong processing, a microbial validation study must be provided to demonstrate that sufficient bacterial reductions of a 'pathogen of concern' can be achieved during processing [2]. The use of acid-adapted cultures during validation studies for acidic foods are 'highly recommended' by USDA-FSIS or they may not consider the process properly validated. Their thinking is that if challenge cultures are not acid-adapted prior to acid dip treatment or subsequent marination, both of which are acidic solutions, the cultures may react by being overly sensitive and result in falsely high microbial reductions of the challenge organisms. They believe that acid-adapting cultures to use for product inoculation and process testing would ensure that the process would need to be sufficiently robust to accomplish a 5-log reduction of the pathogenic and/or surrogate challenge organisms. Communication with USDA-FSIS officials indicate that research data demonstrating the importance of acid-adaptation, if proven, would move USDA-FSIS guidelines to require acid-adapted cultures for industry process validation. Some research publications have insinuated the opposite, that acid-adapted cultures are more sensitive to acid, and contrary to the stance taken by USDA-FSIS. My project is to directly address this issue by performing process validation studies using acid-adapted and non-acid-adapted cultures for biltong processing to determine whether acid-adaptation is a necessary pre-culture treatment prior to microbial validation studies.