[13] Formation of nonvolatile compounds by thermal degradation of β-carotene: Protection by antioxidants

Publisher Summary The most thorough structural data concern the behavior of all- trans - β -carotene in extrusion cooking. This chapter describes a systematic study of the degradation products that absorb in the visible region and compares the results to those obtained after prolonged heating. Studies of the behavior of purified all- trans-β- carotene in extrusion cooking have shown that this type of treatment leads to extensive degradation of the molecule. The fraction of residual nonvolatile compounds at extruder output accounts for only 10–20% of the initial pigment content In commercial preparations of β -carotene for industrial use in which the colorant is coated in a matrix, losses are much lower. Several types of chemical reactions are revealed, including multiple isomerizations on certain trans double bonds leading to modifications of the spatial conformation of the molecule and undoubtedly modifying its stability. In addition, oxidations of the β -carotene molecule occur (epoxy formation, hydroxylation, and ketone function). Oxidative rupture progressively shortens the unsaturated chain. The rates of these degradation phenomena can be decreased by the presence of antioxidants, provided the compounds themselves are heat stable.