Effect of Supercritical CO 2 Modified with Water Cosolvent on the Sterilization of Fungal Spore‐Contaminated Barley Seeds and the Germination of Barley Seeds

We have investigated the effects of supercritical carbon dioxide ( SC ‐ CO 2 ) modified with water as a cosolvent on the inactivation of P enicillium oxalicum spores inoculated on barley grains and also on the germination yield of the SC ‐ CO 2 ‐treated barley grains. After SC ‐ CO 2 treatment at different conditions of temperature, cosolvent (water) content and treatment times, the number of colony‐forming units ( cfu s) of fungal spores and the germination of SC ‐ CO 2 ‐treated barley grains were analyzed. Among the SC ‐ CO 2 treatment parameters, the cosolvent content was the most significant factor affecting the inactivation yields of P . oxalicum spores. When the pressure of SC ‐ CO 2 was fixed at 10  MPa , the optimal conditions obtained by ridge analysis of response surface methodology were cosolvent content of 231  μL , temperature of 44 C and treatment duration of 12 min, which resulted in a 6.8 log 10 reduction of cfu . However, the germination yield of barley grains decreased significantly by treating with SC ‐ CO 2 modified with water. For example, the addition of only 300  μL water in the SC ‐ CO 2 treatment reduced the germination yield from 65.4% to 1.4% at the same SC ‐ CO 2 treatment conditions (40 C , 10  MPa , and 20 min). Practical Applications This study demonstrated the lethal effect of modified supercritical carbon dioxide ( SC ‐ CO 2 ) against plant pathogenic fungal spores in barley grains. Water cosolvent showed significant synergism in inactivating fungal spores with SC ‐ CO 2 . Treatment using SC ‐ CO 2 modified with water cosolvent could be applied in the sterilization step for preservation of barley grains as an alternate for chemical or thermal processes.