STABILITY OF β‐CAROTENE IN THERMAL OILS

The isomerization and decay of β‐carotene in thermal oils were monitored using high‐performance liquid chromatography and UV–vis spectroscopy (UV). For the first time, the effects of temperature, dissolved oxygen, oil type and antioxidants on the stability of β‐carotene were systematically investigated by first‐order kinetics. Isomerization of all‐trans‐ to cis‐isomer was a dominating reaction in the initial period (about 3 h for 140–180C). Lower temperature and oil with more unsaturated fatty acids gave positive effects on the β‐carotene stability, whereas the dissolved oxygen slowed the decay rate at several conditions (150–180C of soybean oil, 140–180C of peanut oil and 140–150C of ODO). The antioxidants significantly protected β‐carotene only when the temperature was lower than 150C, and they almost did not affect the β‐carotene stability when the dissolved oxygen was removed. PRACTICAL APPLICATIONS As thermal treatment of β‐carotene in oils become popular during food processing, and the stability of β‐carotene is most related to its potential health benefits and nutritive value, the study on isomerization and decay kinetics of β‐carotene in thermal oils is particularly important. We found that when β‐carotene in oil was heated at 140–180C, isomerization was a dominating reaction in the initial period (about 2–4 h). The following decay of β‐carotene of most conditions followed first‐order kinetics. When β‐carotene was dissolved in thermal oils, low temperature and oil with more unsaturated fatty acids gave positive effects on the β‐carotene stability. Moreover, β‐carotene always became more sensitive to temperature when dissolved oxygen is removed and antioxidants are added. Those positive impacts were effective only below 150C.