3.6 Assessment of antioxidant activity of purified γ-tocopherol compared with α- and δ-tocopherol by Rancimat
The higher induction period (IP) value indicates the better oxidation stability of oil and the stronger antioxidant activity of the corresponding antioxidant.
The effects of α-, γ- and δ-tocopherol at 0, 50, 150, 250, 500 and 1000 mg/kg on the IP of lard at 120 °C were showed in Table 4. Results showed that the IP values of lard with γ-T at all concentrations (0-1000 mg/kg) were significantly prolonged at 120 °C compared with the control lard without γ-T (p<0.05), and the IP values of lard gradually increased with the concentrations of γ-T increased from 50 mg/kg to 150, 250, 500, and 1000 mg/kg (p<0.05). The effect of α- and δ-tocopherol on IP value of lard was similar to that of γ-tocopherol. However, at the same addition, the IP value of lard with γ-tocopherol was higher than that of the lard with δ-tocopherol, and the IP value of lard with α-tocopherol was lowest. This indicated that the antioxidant activity of γ-T was strongest, followed by δ-T and α-T in lard.
Additionally, the antioxidant activities of α-, γ- and δ-tocopherol were compared with that of the synthetic antioxidant BHT using Rancimat at 120 °C (Table 4). Results showed that the IP values of lard with α-, γ- and δ-tocopherol of 200 mg/kg were (4.59±0.04), (8.02±0.08) and (6.48±0.11) h, respectively. This indicated that the antioxidant activity of γ-T was strongest among these three tocopherol monomers. The IP value of lard with 200 mg/kg BHT was (4.27±0.16) h, which was significantly shorter than that of γ-tocopherol at the same addition (p<0.05). Even more, The IP value (4.52±0.07) h of lard with 50 mg/kg γ-tocopherol was higher than that of lard with 200 mg/kg BHT (p<0.05). This indicated that the antioxidant capacity of γ-tocopherol at 50 mg/kg in lard was stronger than that of BHT at the maximum residue limit (200 mg/kg). Therefore, γ-tocopherol was a good choice to replace BHT in terms of human health and antioxidant capacity.