Germination and Inactivation of Bacillus amyloliquefaciens Spores Using Moderate High Pressure and Pomegranate Peel Extract

Abstract

The combined effect of two pressure treatments (200 MPa for 20 min and 400 MPa for 10 min at <27 °C) with 0.1% pomegranate peel extract (PPE) on inactivation/germination of Bacillus amyloliquefaciens spores was evaluated. A known quantity of spores (≈108 cfu.ml-1) was suspended in sterile distilled water (DW) or 0.1% PPE. Pressurization was done at 27 °C using a 2 l pressurization vessel. Survival counts were estimated using a spread plate method, and heat shock (80 °C for 15 min) was used as criteria for germination. Results showed that 200 MPa for 20 min induced an inactivation of 0.6 and 0.90-logs of spores suspended in DW and PPE, respectively. Further increasing the high pressure to 400 MPa for 10 min inactivated 2.6 and 2.92-log of spores suspended in DW and PPE. In contrast to inactivation results, germination level was 2.76 and 2.64- logs for 200 MPa and 1.73 and 0.78 logs for 400 MPa in DW and PPE, respectively. Scanning electron microscopic studies indicated that average size of the spores was about 2.2 by 1.2 µ. The control spores were oval in shape with smoother surfaces, but autoclaving and high-pressure treatments caused significant morphological damage. The combination of high pressure and PPE could be further explored for developing a natural method of food preservation.