3.2.2 Tocopherols
Tocopherols are recognized as the important antioxidants and nutrient due to their biological activities in olive oil. Four tocopherol isomers were quantified and Table 3 presents the result for all the studied samples. As suggested by previous researches, α-tocopherol was the major tocopherol in olive oil. Moreover, γ-tocopherol content was greater than β-tocopherol expect 7-year-old Koroneiki. In accordance with previous studies, tocopherol contents were highly cultivar-dependent (Bruscatto et al., 2017). The contents of α-tocopherol and total tocopherols in Coratina oils were apparently lower than those in Koroneiki oils but the content of γ-tocopherol was higher. Compared with the tocopherols contents in Coratina and Koroneiki produced from origin region, the oils of same cultivar in this study contained fewer contents of tocopherols (Deiana et al., 2019). As reported by Bruscatto et al., the contents of tocopherols in Coratina were evidently higher than those in Koroneiki oils (Bruscatto et al., 2017). In contrast, Koroneiki oils contained higher levels of tocopherols in this study.
From the perspective of tree age, the content of α- and total tocopherols in VOOs from 7-year-old trees were noticeably higher than those in the samples from 2-year-old and 11-year-old trees of both Coratina and Koroneiki. Meanwhile, the samples from 7-year-old trees contained less γ-tocopherol than those in VOOs from 2-year-old and 11-year-old trees of the two varieties. The increase of α- and total tocopherols with tree age for the oils from trees of 2-7 years was in consistent with the investigations performed by Chtourou et al., who reported that higher total tocopherol was found in VOO from old trees than young trees (Chtourou et al., 2017b). However, the decrease of α- and total tocopherols were found in the oils from trees of 7-11 years. This might be related to the state of the trees. Though olive trees can maintain luxuriant for hundreds or even thousands years in Mediterranean region, the natural life span of Chinese olive tree is very short without the professional cultivation and management under the natural conditions (Deng & Yu, 2011). It was much more difficult to maintain the trees in good condition in Xichang, China.