Treatment with high hydrostatic pressure and supercritical carbon dioxide to control Alicyclobacillus acidoterrestris spores in apple juice

• Moderate hydrostatic pressure can induce the germination of Alicyclobacillus acidoterrestris spores.
• SCCD and HHP were varied, and strongly strain and temperature dependent.
• The effectiveness of HHP and SCCD were affected by the soluble solids content.
• The baroprotective effect of increased solute concentration in apple juice on the spores.

Alicyclobacillus acidoterrestris is a thermoacidophilic and spore-forming bacterium that can develop in pasteurized juices. However, there are innovative technologies for food processing and preservation such as high hydrostatic pressure (HHP) and supercritical carbon dioxide (SCCD) that can be used to inactivate these bacteria.The objective of this study was to investigate the effect of SCCD and HHP on inactivation and germination of spores of two A. acidoterrestris strains.Spores were suspended in apple juice (70.7, 35.5, 23.7, 11.2 °Bx) and treated with SCCD: 60 MPa/50–75 °C/20–40 min and HHP: 300 MPa/50–75 °C/5–15 min. The number of surviving population was determined by the plate method on BAT-agar with or without heat treatment (80 °C, 10 min).After 40 min of SCCD treatment at 60 MPa, 75 °C, germination of A. acidoterrestris TO-169/06 spores in apple juice (11.2 °Bx) was 3.9 log of which 3.4 log were inactivated. Under the same process conditions but in the 70.7 °Bx juice much lower degree of germination (0.9 log) and inactivation (0.5 log) was obtained.In the case of A. acidoterrestris TO-169/06 strain HHP processing at 300 MPa, 50 °C, 15 min in apple juice (11.2 °Bx) 4.4 log of spores germinated of which 3.7 log were inactivated.In the contrary, under the same conditions, in apple juice concentrate germination and inactivation of the spores was 1.5 log and 0.9 log resp. The spores of the A. acidoterrestris TO-117/02 strain were significantly more resistant to SCCD and HHP on the used parameters.These results demonstrate that SCCD and HHP combined with moderately elevated temperature may be a useful technique for inactivation of A. acidoterrestris spores in single strength juices.