Effects of high pressure treatment on microbiological and organoleptic quality of fresh-cut vegetables.

Effects of high pressure (HP) treatment on inactivation of various microorganisms in vitro and microbiological and organoleptic quality of fresh-cut vegetables in vivo were determined. For in vitro study, bacteria and bacterial and fungi isolates from indigenous microflora of vegetables were processed at HP ranging from 300 to 700 MPa for 10 min. For in vivo study, fresh-cut and whole vegetables were subjected to 400 MPa for 10 min. and microbial and organoleptic quality determined. With the in vitro study, populations of Pseudomonas fulva, P. mucidolen, Enterobacter kobei, and Lactococcus lactis decreased to below the level of detection with 400 MPa treatment, whereas population of Bacillus cereus decreased by only 1.5 logs at 700 MPa. Populations of indigenous bacteria and fungi isolated from some vegetables decreased to below the detection level at 400 MPa. With the in vivo study, the 400 MPa treatment resulted in reductions of 1.6 to >2.6 logs of bacteria and 3.5 to 5.3 logs of fungi in fresh-cut carrots, cucumber, and lettuce. Fresh-cut carrots and cucumber showed softened appearance and fresh-cut lettuce became brown after pressure treatment. Cut slices of treated whole carrots and cucumber had reduced microbial activity and loss of organoleptic quality. These results indicate that the HP at 400 MPa for 10 min. was effective in decreasing microbial activity in vitro and in vivo, except for spore-former such as Bacillus cereus, but caused deterioration of surface of fresh-cut vegetables, which was less appealing than whole vegetables pressurized and then cut.