On the non-enzymatic liberation of limonin and C17-epilimonin from limonin-17-β-D-glucopyranoside in orange juice

Limonin is well-known to induce the so-called "delayed" bitterness which is developing during standing and/or processing of orange juice. The objective of this study was to investigate the hydrolytic liberation of limonin from its precursor limonin-17-beta-D-glucopyranoside in aqueous model solutions and orange juice samples. Quantitative model studies on the degradation of limonin-17-beta-D-glucopyranoside under acidic conditions as well as during storage of orange juice revealed the formation of limonin besides a second hydrolysis product of yet unknown structure. After isolation, the structure of that compound was unequivocally determined for the first time as the C-17-epimer of limonin, named C-17-epilimonin. In order to investigate the generation of these triterpenoid lactones during storage as well as heat-treatment of orange juice, freshly squeezed orange juice was stored for up to 4 weeks at 4 and 20 degrees C or was heated at 70 and 100 degrees C and, then, both limonoids were quantitatively determined by means of high performance liquid chromatography-mass spectrometry/mass spectrometry (multiple reaction monitoring). The data obtained showed first evidence for the use of the C-17-epilimonin/limonin ratio as a suitable marker for the analytical determination of the thermal input applied during processing orange juice products.