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.