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 into the interior of orange fruit and the impact of possible infiltration on achieving a 5-log microbial reduction during fresh juice processing. Fresh orange fruit were treated at the stem end area with dye and either Salmonella Rubislaw or Escherichia coli strains expressing green fluorescent protein. Microscopic images showed that bacterial contaminants localized at the surface or near surface areas that may be sanitized by surface treatments. Dye infiltration was not a reliable indicator of bacterial penetration in citrus fruit. To quantify the reduction of bacterial contamination, orange fruit were inoculated with E. coli and processed with and without hot water treatments. Greater than 5-log reductions were achieved in juice extracted from fruit immersed in hot water for 1 or 2 min at 80 degrees C, in comparison to the E. coli level detected in the control juice obtained by homogenization of inoculated fruit.