Feasibility of utilizing bio-indicators for testing microbial inactivation in sweetpotato purees processed with a continuous flow microwave system

Authors: BRINLEY, TIFFANY - NCSU; DOCK, CHRISTINA - NCSU; Truong, Van Den; CORONEL, PABLO - NCSU; KUMAR, PRABHAT - NCSU; SIMUNOVIC, JOSIP - NCSU; SANDEEP, KP - NCSU; CARTWRIGHT, GARY - NCSU; SWARTZEL, KEN - NCSU; JAYKUS, LEE-ANN - NCSU

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2007
Publication Date: 6/30/2007
Citation: Brinley, T.A., Dock, C.N., Truong, V., Coronel, P., Kumar, P., Simunovic, J., Sandeep, K., Cartwright, G.D., Swartzel, K.R., Jaykus, L. 2007. Feasibility of utilizing bio-indicators for testing microbial inactivation in sweetpotato purees processed with a continuous flow microwave system. Journal of Food Science. 72(5):E235-E242.

Interpretive Summary: Continuous flow microwave is an emerging technology for aseptic processing of various food products, including the purees from sweetpotatoes and other vegetables. Establishing the feasibility of a new processing technology for achieving commercial sterility requires evaluating microbial inactivation. This study aimed to assess the feasibility of using Steriflex® biological indicators containing spores of thermal resistant bacteria for evaluating the degree of microbial inactivation achieved in vegetable purees processed in a continuous flow microwave heating unit. Sweetpotato puree seeded with the bio-indicators was subjected to three levels of processing temperature (126 degrees C, 132 degrees C and 138 degrees C). A set up with two removable tubes connected to a continuous flow microwave system was developed for facilitating the injection of the bio-indicators into unit without interrupting the puree flow. Using this approach, 60% of the indicators injected into the system could be recovered post-process. Spore survival after processing, as evaluated by use of growth indicator dyes and standard plating methods verified inactivation of the spores in sweetpotato puree. This study presents the first report suggesting that bio-indicators such as the Steriflex® pouches can be used for microbial validation of commercial sterilization in aseptic processing of foods using a continuous-flow microwave system.

Technical Abstract: Continuous flow microwave heating has potential in aseptic processing of various food products, including the purees from sweetpotatoes and other vegetables. Establishing the feasibility of a new processing technology for achieving commercial sterility requires evaluating microbial inactivation. This study aimed to assess the feasibility of using commercially available plastic pouches of biological indicators containing spores of Geobacillius stearothermophilus ATCC 7953 and Bacillus subtilis ATCC 35021 for evaluating the degree of microbial inactivation achieved in vegetable purees processed in a continuous flow microwave heating unit. Sweetpotato puree seeded with the bio-indicators was subjected to three levels of processing based on the fastest particles: under-target process (F0~0.65), target process (F0~2.8), and over-target process (F0~10.10). After initial experiments, we found it was necessary to engineer a set up with two removable tubes connected to the continuous flow microwave system to facilitate the injection of indicators into the unit without interrupting the puree flow. Using this approach, 60% of the indicators injected into the system could be recovered post-process. Spore survival after processing, as evaluated by use of growth indicator dyes and standard plating methods verified inactivation of the spores in sweetpotato puree. The log reduction results for B. subtilis were equivalent to the pre-designed degrees of sterilization (F0). This study presents the first report suggesting that bio-indicators such as the flexible, food grade plastic pouches can be used for microbial validation of commercial sterilization in aseptic processing of foods using a continuous-flow microwave system.