Impact of high-pressure carbon dioxide combined with thermal treatment on degradation of red beet (Beta vulgaris L.) pigments

A combined high-pressure carbon dioxide (HP-CO2) and thermal degradation reaction of betanin and isobetanin in aqueous solution was investigated and can be described by a first-order decay. At 45 degrees C, the degradation rate constant (k) for each pigment component significantly increased (the half-life (t(1/2)) decreased, p < 0.05) with elevated pressure. Furthermore, HP-CO2 treatment led to lower k values (higher t(1/2) values) than thermal treatment. However, k and t(1/2) values approached those of thermal treatment when the pressure was > 30 MPa combined with temperatures exceeding 55 OC. Moreover, betanin was more stable than isobetanin under HP-CO2. E-a values ranged from 94.01 kJ/mol for betanin and 97.16 kJ/mol for isobetanin at atmospheric pressure to 170.83 and 142.69 kJ/mol at 50 MPa, respectively. A higher pressure and temperature as well as longer exposure time resulted in higher values of L*, b*, C*, and ho. HP-CO2 induced more degradation products from betanin and isobetanin than thermal treatment with an identical temperature and exposure time.