Abstract:

Objective: The aim of this paper is to study the effect of heat treatment on phenolic content and antioxidant activity of Camellia oleifera seeds. Method: C. oleifera seeds were heated by hot air, infrared radiation and microwave radiation. After the heating treatment, the changes of polyphenol content and antioxidant activity in C. oleifera seed oil and the cake were analyzed. Result: The results showed that the changes of polyphenols and antioxidant activity in pressed oil of camellia seeds heated by three methods were similar. The total phenol content in oil changed little after heating at low temperature (90 and 120℃ in hot air and infrared, 245 W, 420 W and 560 W microwave). After heating at high temperature (150 C in hot air and 700 W microwave), the polyphenol content and antioxidant ability of camellia seed oil increased obviously. At the end of heating, the content of polyphenols reached 26.84, 94.34 and 84.51 μg·g^-1, respectively, which was 2.8, 12.4 and 11.0 times higher than the unheated control, and the antioxidant activity (%, ABTS^·+) reached 48.91%, 96.29% and 97.01% respectively, which was 6.11, 13.0 and 13.1 times higher than control. The variation of polyphenols in pressed cake C. oleifera seeds is similar to that in camellia oil. Total phenol content and antioxidant activity did not change much after low temperature heating, while it increased after high temperature heating for a period of time. At the end of heating, total phenol content increased by 14.4%, 42.5% and 34.45%, respectively, and the antioxidant activity (%, ABTS^·+) increased by 27.9%, 46.2% and 32.1%, respectively. The change of antioxidant activity of polyphenols in the cake was different after infrared heating at different temperatures, but the change trend was similar to that of polyphenols content. The increase of polyphenol content in the cake after heating may be due to the hydrolysis of cell wall, the increase of phenolic dissolution, or the release of bound phenols. The increase of the antioxidant activity (%, ABTS^·+) may also include the contribution of other polar antioxidants (methanol/water extraction) such as Maillard reaction products induced by heating. The specific reason remains to be further studied. Conclusion: High temperature heating of Camellia oleifera seeds can improve the polyphenol content and antioxidant activity of C oleifera seed oil and the cake. The thermal efficiency of the three heating processes is microwave > infrared > hot air. In production practice, short-term high temperature heating of infrared can be used to increase the phenol content of camellia oil. The results of this study provide a theoretical basis for exploring the mechanism of physicochemical changes of C. oleifera seeds during processing, and a technical support for the processing technology of C. oleifera seed oil.

Key words: oil-tea Camellia seed oil, oil-tea camellia cake, heat, polyphenolics, antioxidant activity