In plant matrices, folates exist largely as folylpoly-gamma-glutamates requiring deglutamylation to monoglutamates prior to absorption, which might impair dietary folate bioavailability. This study investigated folylpoly-gamma-glutamate stability and conversions in broccoli tissue during thermal (25-90 degrees C, 30 min) and high-pressure treatments (0.1-600 MPa, 25-45 degrees C, 30 min) after vacuum packaging. Folates were analyzed based on poly-gamma-glutamate side chain length by RP-HPLC. During thermal treatments, folates were stable up to 90 degrees C, whereas differences in folyl poly-gamma-glutamate profiles towards higher conjugated folylpoly-gamma-glutamates were observed at elevated temperatures (70-90 degrees C). High-pressure treatments resulted in significant folate losses (48-78%). Depending on the pressure-temperature combinations studied, folylpoly-gamma-glutamates were converted to fiolylmono- and folyldi-gamma-glutamates, which was shown to occur mainly during the initial stages of the high-pressure treatments, i.e. during pressure build-up and subsequent equilibration. Targeted application of high-pressure treatments can hence be applied to obtain broccoli with higher monoglutamates folate content. Implications towards folate bioavailability in relation to the observed folate degradation, however, requires further investigation. (C) 2008 Elsevier Ltd. All rights reserved.