The inactivation of Clostridium sporogenes PA 3679 spores by high pressure at high temperatures (HP–HT) in phosphate buffer was investigated in a lab‐scale temperature‐controlled HP system (QFP‐6) with an internal heater to maintain the sample temperature. Some inactivation of spores occurred during the pressurization come‐up time (CUT) and depressurization time. The inactivation of PA 3679 was found to be exponential during the adiabatic holding period of the HP cycle at constant pressures and temperatures. The inactivation rate increased with both pressure and temperature. The kinetic parameters – such as D‐values at tested temperatures and pressures that are necessary for the design of process parameters of HP sterilization process – were determined. Within the pressure range of 600–800 MPa, the calculated D‐values ranged from 270.3 to 357.4 and 49.0 to 67.6 s at 91 and 108C, respectively. These studies provided basic data on the effects of pressure and temperature on the inactivation of PA 3679 spores under conditions applicable to the development of preservation specifications for commercial HP–HT processing of low acid foods. The spore strips of C. sporogenes were used as indicators for microbiological verification of delivered lethality of HP–HT sterilization process at different processing conditions in a pilot scale HP vessel.

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The objective of this study was to validate the performance of a coiled ultraviolet (UV) module with 24 lamps for fresh juice pasteurization. Escherichia coli K12 at an inoculation level of 106 cfu mL–1 was chosen as a target microorganism for biodosimetry. All tested fruit juices highly absorbed UV light, with absorption coefficients ranging from 11 cm–1 to 78 cm–1 for lillikoi and pineapple juice, respectively. Of the juices examined, pineapple juice appeared to be the worst case scenario in terms of UV absorptivity and high viscosity. A caramel model solution was developed to mimic juice absorption properties and was used for inoculation studies. The 5-log10 reduction standard under turbulent flow required by the FDA was achievable in Newtonian liquids with absorption coefficient less than 15 cm–1 after one pass. Turbulent flow was not developed in more viscous orange and pineapple juices at the flow rates tested. A biodosimetry technique that utilizes E. coli as a tracer showed no distribution of UV dose in liquids with absorption coefficient lower than 26 cm–1. The proposed technique may assist in validating the performance of UV reactors and improve efficiency of UV pasteurization. Key words: coiled ultraviolet module, fruit juices, caramel model, E. coli K12, biodosimetry.