Properties and chemical compositions of monovarietal virgin olive oil at different ripening stages: A study on olive cultivation in Northwest China

The olive management in China is rarely reported. This study evaluates the influence of drupes ripening on virgin olive oil (VOO) quality of four main varieties (Olea europaea L., cultivars Ezhi-8, Koroneiki, Leccion, and Frontoio) cultivated in Northwest China. Quality indices, fatty acid profiles, polyphenols, terpenic acids, tocopherols, and squalene contents are tested at four ripening stages from September to November. The contents of linolenic acid, saturated fatty acids, triterpenic acids, and squalene in all VOO samples decreased during ripening; in contrast, the oleic acid, linoleic acid, nervonic acid (first reported in VOOs), cinnamic acid, p-coumaric acid, apigenin, and naringenin (contents) increased. The dynamics of the major phenolic compounds, such as hydroxytyrosol, tyrosol, and secoiridoids, were cultivar-dependent. The two-way ANOVA and Fisher's LSD test showed that oil compositions varied depending on the ripeness stage and cultivar. Moreover, this latter had more influence than harvest dates on the VOO features. Besides, by applying the orthogonal partial least squares discriminant analysis, several key metabolites (C18:1, oleanolic acid, maslinic acid, oleacein, oleocanthal, and alpha-tocopherol) differentiate the four cultivars. In contrast, squalene, oleanolic acid, maslinic acid, oleocanthal, luteolin, and alpha-tocopherol could effectively differentiate the four harvesting dates.