Microscopic observation and processing validation of fruit sanitizing treatments for the enhanced microbiological safety of fresh orange juice

Studies were conducted to evaluate the infiltration of dye and bacteria int o the interior of orange fruit and the impact of possible infiltration on a chieving a 5-log microbial reduction during fresh juice processing. Fresh o range fruit were treated at the stem end area with dye and either Salmonell a Rubislaw or Escherichia coli strains expressing, green fluorescent protei n. Microscopic images showed that bacterial contaminants localized at the s urface or near surface areas that may be sanitized by surface treatments. D ye infiltration was not a reliable indicator of bacterial penetration in ci trus fruit. To quantify the reduction of bacterial contamination, orange fr uit were inoculated with E. coli and processed with and without hot water t reatments. Greater than 5-log reductions were achieved in juice extracted f rom fruit immersed in hot water for 1 or 2 min at 80 degreesC, in compariso n to the E. coli level detected in the control juice obtained by homogeniza tion of inoculated fruit.