Klara Kraljić

Olive leaf extract activity against Candida albicans and C. dubliniensis – the in vitro viability study

Abstract Olive leaf extract is characterized by a high content of polyphenols (oleuropein, hydroxytyrosol and their derivatives), which is associated with its therapeutic properties. The objective of the present research was to evaluate the antifungal activity of olive leaf extract against Candida albicans ATCC 10231 and C. dubliniensis CBS 7987 strains. Minimum inhibitory concentrations (MIC) of the extract were determined by several in vitro assays. The extract showed a concentration depended effect on the viability of C. albicans with MIC value of 46.875 mg mL-1 and C. dubliniensis with MIC value 62.5 mg mL-1. Most sensitive methods for testing the antifungal effect of the extracts were the trypan blue exclusion method and fluorescent dye exclusion method while MIC could not be determined by the method according to the EUCAST recommendation suggesting that herbal preparations contain compounds that may interfere with this susceptibility testing. The fluorescent dye exclusion method was also used for the assessment of morphological changes in the nuclei of treated cells. According to the obtained results, olive leaf extract is less effective against the tested strains than hydroxytyrosol, an olive plant constituent tested in our previous study.

Changes in 4-vinylsyringol and other phenolics during rapeseed oil refining

The aim of the present study was to examine changes in phenolic compounds during refining of rapeseed oil. In crude rapeseed oil, 4-vinylsyringol (canolol) is the dominant phenolic compound, accounting for 85% of total phenolics. Refining decreased the total amount of phenolic compounds by 90%. NMR and MS analyses of edible rapeseed oil phenolic extracts identified 4-vinylsyringol dimer as the dominant phenolic compound. This phenolic compound appears to form through acid-catalyzed dimerization-aromatic substitution of 4-vinylsyringol monomers. Analysis of rapeseed oils from different stages of the refining process suggest that 4-vinylsyringol dimer forms during the neutralization phase, when H3PO4 acts as a catalyst, or during bleaching, when acid-activated bleaching earth acts as the catalyst. Whether 4-vinylsyringol forms during one or the other phase appears to depend on the phospholipid content of the crude oil. These insights may be useful for designing rapeseed oil refining processes that maximize levels of 4-vinylsyringol dimer.

Tocopherols: Chemical Structure, Bioactivity, and Variability in Croatian Virgin Olive Oils

Virgin olive oil (VOO) represents a rich source of natural antioxidants, with tocopherols as the most effective group of lipophilic, phenolic antioxidants. αTocopherol represents more than 95% of the total tocopherols in virgin olive oil, and it possesses the highest biological activity among members of the vitamin E family. Content and composition of the tocopherols of virgin olive oil depend on several agronomic factors, as well as olive processing and oil storage conditions. In this chapter, the tocopherol homologue activity in virgin olive oil and the biological importance are discussed. Research work is reported on the tocopherol content and composition variability in virgin olive oils of the most widespread Croatian cultivar “Oblica” and Italian cultivar “Leccino.” Factors studied such as year, growing area and olive fruit ripening and their influence on the tocopherol content and composition of virgin olive oils are discussed. The effect of filtration of the oil and storage conditions on tocopherols are also examined.