Application of a biochemical time–temperature integrator to estimate pasteurisation values in continuous food processes

Abstract The microbiological safety of commercial fruit processes was evaluated using α-amylase time–temperature integrators (TTI) from either a Bacillus amyloliquefaciens or Bacillus licheniformis source. The TTIs were incorporated into silicone particles that were added to batches of fruit preparations to estimate the pasteurisation achieved during two different methods of continuous processing: a tubular heat exchanger and an ohmic column. Pasteurisation values (P-values) estimated with the TTIs represented the integrated thermal process at the core of 12-mm pear cubes for the tubular process of 12-mm strawberries, 12-mm pineapple and 10-mm blackcurrants for the ohmic process. The decimal reduction time at 85.0 °C (D85) for the Bacillus amyloliquefaciens amylase was 6.8 min, with a kinetic factor (z-value) of 9.4±0.3 °C, and for the Bacillus licheniformis amylase the D93 was 8.8 min with a z value of 9.1±0.3 °C. For the high-acid fruit products, the target P-value was equivalent to 5 min at 85 °C (Tref=85 °C, z=10 °C). Amylase activity before and after processing was converted to P-values, with all of the processes showing a substantial safety margin, despite operating conditions that were deliberately set to represent the ‘worst case’ conditions. This method allowed P-value data to be collected under conditions that prevented the use of thermocouples.