Alicyclobacillus acidoterrestris Strain Variability in the Inactivation Kinetics of Spores in Orange Juice by Temperature-Assisted High Hydrostatic Pressure

Abstract

In this work, the inactivation kinetics of Alicyclobacillus acidoterrestris spores by temperature-assisted high hydrostatic pressure was assessed by means of the Weibull model. Spores from two A. acidoterrestris strains (a wild-type strain and a reference strain) were inoculated in commercial orange juice and subjected to high pressure levels (500 and 600 MPa) combined with four temperature regimes (25, 45, 60 and 70 °C) for time up to 30 min. Results showed that for a given high-pressure level spore inactivation was higher as temperature progressively increased. Furthermore, the Weibull model consistently produced satisfactory fit to the inactivation data based on the values of the root mean squared error (RMSE < 0.54 log colony-forming units (CFU)/mL) and the coefficient of determination (R2 > 0.90 in most cases). The shape of inactivation curves was concave upward (p < 1) for all temperature/high pressure levels tested, indicating rapid inactivation of the sensitive cells of the bacterium whereas the remaining ones adapted to high hydrostatic pressure (HHP) treatment. The values of the shape (p) and scale (δ) parameters of the Weibull model were dependent on the applied temperature for a given high pressure level and they were further described in a secondary model using first-order fitting curves to provide predictions of the surviving spore population at 55 and 65 °C. Results revealed a systematic over-prediction for the wild-type strain regardless of temperature and high pressure applied, whereas for the reference strain under-prediction was evident after 3 log-cycles reduction of the surviving bacteria spores. Overall, the results obtained indicate that the effectiveness of high hydrostatic pressure against A. acidoterrestris spores is strain-dependent and also underline the need for temperature-assisted HPP for effective spore inactivation during orange juice processing.