title: Effects of tomato variety, temperature differential, and post-stem removal time on internalization of Salmonella enterica serovar Thompson in tomatoes.
abstract: Tomatoes have been implicated in salmonellosis outbreaks due to possible contamination through bacterial internalization during postharvest handling. This study was conducted to determine the effects of tomato variety, temperature differential between tomato pulp and bacterial suspension, and the time delay between stem removal and immersion in bacterial suspension on internalization of Salmonella enterica serovar Thompson in tomato fruit. Mature green tomatoes at 32.2°C were immersed in water containing approximately 10(6) CFU/ml S. enterica bacteria.  Different tomato varieties (Mountain Spring, Applause, and BHN961), temperature differentials (-10, 0, and 10°F, or -5.6, 0, and 5.6°C, respectively), and post-stem removal times (0, 2, and 16 h) were evaluated for their effects on S. enterica internalization.  The incidence and density of internalized cells were determined by culture enrichment and most-probable-number methods, respectively. Overall, variety and post-stem removal time by variety interaction significantly affected the incidence of S. enterica internalization (P  < 0.0001), while temperature differential had no significant effect (P = 0.36). Mountain Spring tomatoes were less susceptible to S. enterica internalization than were Applause and BHN961. Increasing the time interval between stem removal and immersion greatly reduced pathogen  internalization in BHN961 and Applause, while it had no effect in Mountain Spring tomatoes. The variety and interactions between varieties and post-stem removal times (P = 0.0363) and between temperature differentials and post-stem removal times (P = 0.0257) had significant  effects on the populations of internalized S. enterica. Furthermore, all internalized S. enterica cells were found within the core tissue segments immediately underneath the stem scars.
authors.affiliation: School of Food Science and Engineering, Northwest A&F University, 28 Xinong Road, Yangling, Shaanxi, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Xia
authors.forename: Yaguang
authors.initials: Y
authors.lastname: Luo
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Bryan
authors.initials: B
authors.lastname: Vinyard
authors.forename: Keith
authors.initials: K
authors.lastname: Schneider
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
mesh_terms: D001422:Bacterial Adhesion; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D006801:Humans; D018551:Solanum lycopersicum / Q000145:classification / Q000382:microbiology*; D018547:Plant Stems / Q000382:microbiology; D012478:Salmonella Food Poisoning / Q000517:prevention & control; D019779:Salmonella enterica / Q000472:pathogenicity / Q000502:physiology*; D013045:Species Specificity; D013696:Temperature