2018 ASHS Annual Conference

We have found higher bacterial counts on fresh-cut potatoes and apples with wound-induced enzymatic browning tissues than non-browning tissues. Bacterial species isolated only from the browning tissues were identified as Pseudomonas fluorescence on potatoes and Herbaspirillum huttiense on apples. In this study, we investigated the influence of inoculation with P. fluorescence and H. huttiense on the browning response of fresh-cut potatoes and apples, respectively. Surface color, enzymatic activities of polyphenol oxidase (PPO) and peroxidase (POD), amounts of phenolic compounds and lignin, and bacterial counts were determined in sliced potatoes inoculated with P. fluorescence and sliced apples inoculated with H. huttiense (approximately 3 and 6 log CFU/ml) during storage for 3 days at 5°C. Non-inoculated fresh-cuts were used as the controls. When fresh-cut potatoes were initially inoculated with either 3 or 6 log CFU/ml of P. fluorescence and then stored, bacterial counts increased from an initial 3.0 log CFU/g or 5.3 log CFU/g to 5.7 log CFU/g or 8.2 log CFU/g, respectively, after 3 days of storage. However, no differences were found in the surface color, activities of PPO and POD, amounts of phenolics and lignin between non-inoculated and inoculated fresh-cut potatoes regardless of the inoculum levels. With fresh-cut apples, bacterial counts increased to 5.1 log CFU/g following inoculation with 6 log CFU/ml of H. huttiense and the counts were constant during storage for 3 days. In comparison, the bacterial counts of fresh-cut apples either uninoculated or inoculated with 3 log CFU/ml were below the detection level (2.4 log CFU/g) throughout the storage period. Inoculation did not affect surface browning, activities of the enzymes, and amounts of the components during storage, except that the polyphenol content was higher in non-inoculated samples than inoculated samples. These results indicated that artificial inoculation with P. fluorescence and H. huttiense did not enhance browning of fresh-cut potatoes and apples with the accumulation of phenolic compounds and lignification, although we have hypothesized that the bacteria could synthesize bacterial PPO or POD resulting in the browning enhancement.