THERMAL-DEGRADATION OF ALL-TRANS-BETA-CAROTENE IN THE PRESENCE OF PHENYLALANINE

Solutions of all-trans-beta-carotene in liquid paraffin were stirred u nder air at 210 degrees C for 15 min in the presence and absence of va rious amino acids. After cooling, the absorbance values at 460 nm of m odel systems containing all-trans-beta-carotene and phenylalanine, cys teine or tryptophan were 34-58 times higher than that obtained on heat ing in the absence of an amino acid. Based on absorbance values at 420 nm, 86% of the coloured material present on heating the all-trans-bet a-carotene-phenylalanine model system at 210 degrees C for 15 min was retained by the liquid paraffin on methanol extraction. The liquid par affin phase remaining after methanol extraction was analysed by revers e-phase HPLC and three major components were identified as all-trans-b eta-carotene and two degradation products of all-trans-beta-carotene, ie 9-cis-beta-carotene and a furanoid diepoxy derivative. None could b e detected on heating all-trans-beta-carotene alone, suggesting that i ts degradation was retarded on heating in the presence of phenylalanin e.