title: Influence of moisture content on inactivation of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in powdered red and black pepper spices by radio-frequency heating.
abstract: The influence of moisture content during radio-frequency (RF) heating on heating rate, dielectric properties, and inactivation of foodborne pathogens was investigated. The effect of RF heating on the quality of powdered red and black pepper spices with different moisture ranges was also investigated. Red pepper (12.6%, 15.2%, 19.1%, and 23.3% dry basis, db) and black pepper (10.1%, 17.2%, 23.7%, and 30.5% db) inoculated with Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium were treated in a RF heating system with 27.12 MHz. The heating rate of the sample was dependent on moisture content up to 19.1% (db) of red pepper and 17.2% (db) of black pepper, but there was a significant decrease in the heating rate when the moisture content was increased beyond these levels. The dielectric properties of both samples increased with a rise in moisture content. As the moisture content increased, treatment time required to reduce E. coli O157:H7 and S. Typhimurium by more than 7 log CFU/g (below the detection limit, 1 log CFU/g) decreased and then increased again without affecting product quality when the moisture content exceeded a level corresponding to the peak heating rate. RF treatment significantly (P<0.05) reduced moisture content of both spices. These results suggest that RF heating can be effectively used to not only control pathogens but also reduce moisture levels in spices and that the effect of inactivation is dependent on moisture content.
authors.affiliation: Department of Food and Animal Biotechnology, Department of Agricultural Biotechnology, Center for Food and Bioconvergence, Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Republic of Korea.
authors.forename: Seul-Gi
authors.initials: SG
authors.lastname: Jeong
authors.affiliation: Department of Food and Animal Biotechnology, Department of Agricultural Biotechnology, Center for Food and Bioconvergence, Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Republic of Korea. Electronic address: kang7820@snu.ac.kr.
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Kang
mesh_terms: D002212:Capsicum / Q000382:microbiology; D019453:Escherichia coli O157 / Q000502:physiology / Q000528:radiation effects*; D005516:Food Microbiology / Q000379:methods* / Q000592:standards; D006361:Heating; D050296:Microbial Viability / Q000528:radiation effects*; D029222:Piper nigrum / Q000382:microbiology; D011846:Radio Waves; D012486:Salmonella typhimurium / Q000502:physiology / Q000528:radiation effects*; D017365:Spices / Q000382:microbiology*; D016019:Survival Analysis; D014867:Water
chemical_list: D014867:Water
keywords: Dielectric properties; Foodborne pathogen; Moisture content; Pepper; Radio-frequency heating