3.4 Hierarchical cluster analysis
HCA is an unsupervised classification method, which finishes
classification by grouping samples of similar properties. In the present
study, two variables were involved into the HCA analysis. One group
included major fatty acids with more than 0.5% level together with all
minor components; the other one was consist of the structure of phenolic
compounds. The dendrograms constructed by standardized data are
presented in Fig.4.
As can be seen in Fig.4 (a), Coratina and Koroneiki oils were completely
divided into two categories. In addition, the oils from 2-year-old and
11-year-old trees were separated from the oils from 7-year-old trees for
both Coratina and Koroneiki. The result demonstrated that the chemical
compositions of olive oil were highly cultivar-dependent while tree age
had a certain influence on the characteristics of the same varieties. As
shown in Fig.4 (b), the oils from 2-year-old Coratina and Koroneiki
trees were classified as a group. The structure of phenolic compounds in
oil from 7-year-old Koroneiki trees was similar with that from
11-year-old Koroneiki trees. When the 5 distance threshold was chosen,
7-year-old Coratina oil was grouped in the same cluster with 7-year-old
and 11-year-old Koroneiki oils. 11-year-old Coratina oil was divided
into this cluster at 7 distance threshold. The results implied that both
cultivar and tree age have apparent effects the structure of phenolic
compounds.