Changes in oxygen radical absorbance capacity during storage of heat-treated fresh-cut broccoli, kale and peppers

Changes in oxygen radical absorbance capacity (ORAC) in fresh-cut broccoli, kale, and green peppers during storage at various temperatures were measured. The effect of prestorage heat treatment on ORAC values in these fresh-cut vegetables was also evaluated. Initially, the ORAC values increased with time in storage in all vegetables. The higher the storage temperature, the greater the increase. These increases also seemed to be associated with yellowing (high b* value and low hue angle) in broccoli. Heat treatment delayed the yellowing of broccoli tissues and retarded the increase of ORAC values at the beginning of storage. However, as storage progressed, the ORAC values in nonheated vegetables declined toward the end of storage while those in heated samples remained elevated. These differences were more pronounced in broccoli and kale than in peppers. The absolute ORAC values were also higher in broccoli and kale than in peppers. The changes in ORAC values of broccoli during storage correlated positively with increases in phenolic compounds. The decline in ORAC values in nonheated vegetables at the end of storage was probably associated with the senescence of tissues, and the retention of high ORAC activity in the heated samples was likely related to the maintenance of quality by the heat treatment.