Thermal inactivation kinetics of Escherichia coli and Alicyclobacillus acidoterrestris in orange juice

Growing concern about the safety of unpasteurized low-pH foods has changed the view of the microbial loads supported by these products. Recent outbreaks of Salmonella in single-strength unpasteurized orange juice and Escherichia coli O157:H7in apple juice have prompted food processors to seek ways of ensuring the safety of their products without compromising consumer acceptance. Spoilage is also a concern as it relates to the shelf life of fruit juice products. In order to achieve an optimum balance between safety, shelf life, and quality, good estimation of thermal inactivation parameters is essential for designing pasteurization processes that achieve all three goals.; The purpose of this study was to validate a method for estimating thermal inactivation kinetic parameters of specific microorganisms. The method, called the Paired Equivalent Isothermal Exposures (PEIE) method, may be applied to products that are heated under non-isothermal conditions. This method simplifies the estimation of parameters by eliminating the need to perform tedious isothermal bath experiments, while still obtaining accurate estimations. The study was performed in three phases: (1) Estimating thermal kinetic parameters for Escherichia coli in single strength orange juice using traditional analysis of isothermal bath experimental data; (2) Estimating kinetic parameters for thermal inactivation of Escherichia coli in orange juice using the PEIE method with end-point data from continuous high-temperature short-time (HTST) process treatments and validation for each set of kinetic parameters, and (3) Estimating kinetic parameters for thermal inactivation of Alicyclobacillus acidoterrestris using the PEIE method.; Estimating kinetic parameters from isothermal bath and continuous dynamic thermal treatment data gave parameters that were different. To confirm which parameters were more accurate, validation experiments were conducted at higher temperatures. Using the parameters from both methods the number of survivors from each experiment were compared with those predicted by each set of kinetics parameters. Results from validation experiments with Escherichia coli showed that model predictions agreed more closely with experimental data when kinetic parameters used were estimated by the PEIE method rather than the traditional isothermal bath method. The process conditions determined from the kinetic parameters estimated by the PEIE method yielded a 39.7% shorter time than that determined by the isothermal bath method. The PEIE method was used as the preferred method for estimating the kinetic parameters for Alicyclobacillus acidoterrestris in single-strength orange juice.