Combined ultraviolet-C and modified atmosphere packaging treatments for reducing microbial growth of fresh processed lettuce

For reducing microbial growth and keeping sensory quality of fresh processed 'Red Oak Leaf' lettuce, combined ultraviolet-C (UV-C) at 254 nm radiation and modified atmosphere packaging (MAP) treatments were applied. Five UV-C doses (0.4, 0.81, 2.44, 4.07, and 8.14 U/m(2)) and passive MAP throughout 10 days of storage at 5degreesC were evaluated. The respiration rates (RR) of unprocessed, fresh processed, and fresh processed and UV-C-treated 'Red Oak Leaf' lettuce were monitored. While minimal processing did not induce significant changes, UV-C radiation increased the RR. Consequently, CO2 level within bags containing radiated lettuce was higher than in control bags. Within packages of radiated product a steady state of about 2-10 kPa O-2 and 5-12 kPa CO2 was established. The combination of UV-C radiation and MAP was effective for reducing the growth of psychrotrophic and coliform bacteria as well as yeast growth. However, lactic acid bacteria growth was not affected or even stimulated. Compared to control, the sensory quality of lettuce pieces was not adversely affected by this combined treatment. As main conclusion, UV-C was effective to reduce growth of most of the microbial groups without adversely affecting sensory quality of 'Red Oak' lettuce. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.