Comparative effect of irradiation and heating on the microbiological properties of licorice (Glycyrrhiza glabra L.) root powders

Purpose : To determine the effect of gamma irradiation, steaming and heating on microbial load and chemical composition of licorice root powder. Materials and methods : Powders were exposed to hot air treatment at 60 degrees C for 24 h, steaming at 1.1 bar and about 121 degrees C for 15 min, and irradiation at 10 kGy using a Co-60 source. Microbial load, moisture, ash, and electrical conductivity (EC) values of licorice root powders were evaluated immediately after treatment, and after 12 months of storage. Results : Total aerobic plate count (TAPC) of licorice roots powder (control sample), including coliform, Escherichia coli, and Klebsiella spp. were relatively high. Irradiation reduced the TAPC by 4 logs and total coliform to negative (less than 1 log 10 colony forming units (CFU) g(-1)) Klebsiella spp., E. coli, and Salmonella spp. were not detected (less than 1 log 10 CFU/g) in irradiated sample. Meanwhile, heating and steaming reduced the total count by 1 and 2 logs with slight effect on reducing the total coliforms counts. Also, irradiated samples were free of coliforms. No considerable changes in the moisture and ash were observed in irradiated powders, but the moisture increased due to steaming, and decreased due to dried heating. Conclusion : Gamma irradiation at 10 kGy was more effective than heating and steaming treatments in their microbial decontamination effect on the licorice root powders.