Kenneth R. Swartzel

Continuous flow microwave-assisted processing and aseptic packaging of purple-fleshed sweetpotato purees.

Pumpable purees from purple-flesh sweetpotatoes (PFSP) were subjected to microwave heating using a 60 kW, 915 MHz continuous flow system, followed by aseptic packaging in flexible containers to obtain a shelf-stable product. Initial test runs were conducted using a 5 kW 915 MHz microwave system to measure dielectric in-line properties and examine the puree temperature profiles. The results demonstrated uniformity in heating of the puree at sterilization temperatures (>121 degrees C), and the dielectric constants and loss factors were within the range of published values for orange-fleshed sweetpotato purees. The pilot-scale test runs in a 60 kW microwave unit produced shelf-stable puree packages stable at room temperature. Polyphenolic content of the PFSP purees were evaluated and the results showed that while total phenolics increased (5.9%) and total monomeric anthocyanins slightly decreased (14.5%) with microwave application, antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and oxygen radical absorbance capacity (ORAC) assays did not significantly change as a result of microwave processing. Color values showed that microwave-processed samples differed from fresh puree in saturation and hue angle, but not in overall color change. PFSP purees increased in gel strength when microwave processed, packaged, and stored, but the gel could be easily disrupted into flowable purees. Overall, high-quality retention can be obtained by microwave processing and aseptic packaging of PFSP purees so that they can be used as functional food ingredients.

Design of conservative simulated particles for validation of a multiphase aseptic process.

Simulated food particles with conservative (fast moving and slow heating) properties are required for validation of multiphase aseptic processing for production of shelf-stable low-acid foods. The validation process requires simulated particles to contain residence time tags, thermosensitive implants, and/or bioloads for temperature detection, time-temperature integration, and bactericidal efficacy confirmation. Conservative particle design (CPD) software was used to determine the wall thickness required for conservative behavior of such particles made with polypropylene (PP) and polymethylpentene (PMP) of wall thickness 1 mm (0.0393 inches) and 2 mm (0.0787 inches) containing tube inserts. Thermocouples were inserted in the simulated and real food particles and the particles were heated up to 127 degrees C under pressurized (24 psi) conditions. Based on the heating rates of the real and simulated particles, an appropriate simulated particle was identified for each type of real food particle. This would allow a food processor to use these designed particles with an appropriate tube insert (diameter) to validate an aseptic process for a multiphase food containing any or all the above tested food materials.

Non-Isothermal Kinetic Data Generation for Food Constituents

Two new non-isothermal methods for generating kinetic data for food constituents are examined. The first consists of a stirred batch reactor using linearly increasing temperature. The second employs a continuous flow reactor and a novel thermal evaluation method for defining the thermal treatment. The significance and implications of both methods are examined as related to each other and to classical data generation methods.