The study examined the effects of olive oil storage on the content of biophenols, alkyl esters and sensory characteristics of fresh and one and two years of stored olive oils. Monitoring of the biophenolic composition of fresh oil revealed that some secoiridoid compounds are more abundant in certain varieties, in particular DMO-AgL-dA, DML-Agl-dA, L-Agl-dA in the cv. ‘Istrska belica’, DMO-AgL-dA in the cv. 'Leccino' and DMO-Agl-dA and O-Agl-A in the cv. 'Maurino '.The statistical test showed that differences in the content of total biophenols and the content of oleuropine and ligstroside derivatives between cv. ‘Istrska belica’ and other varieties were statistically significant (ztotal = -5.049, ptotal <0.005; zsec = -4.063, psc <0.005). The values differred according to the variety and the crop year. With the Wilcoxon-Mann-Whitney statistical test, the differences between the degree of bitterness and pungency in olive oils in the ‘Istrska belica’ variety were statistically significant (zbitterness = -3,111, pbitterness = 0,002, zpungency = -3,688, p <0.005). 168 samples of oils were analyzed, and the results confirmed the correlation between the content of fatty acid alkyl esters and the detected sensory defects. With the statistical test Spearman rank corr., we have shown that correlations are weak, but statistically significant for the sensory descriptor of heated and alkyl esters of fatty acids (rs = 0.3906) and for the sensory descriptions of the rancidity and alkyl esters of fatty acids (rs = 0.2995). In the second series of studies the influence of filtration on the quality and stability of olive oil was studied. The stability of olive oil depends primarily on the content of antioxidants (biophenols and tocopherols) and fatty acid composition, while sensory score is very important for monitoring the quality. From the results of the monitoring of the fatty acid composition and the content of tocopherols and biophenols, only the difference between cultivars is evident, there are no noticeable differences between unfiltered and filtered oils, as well as between fresh and 6 months old oils stored at room temperature. Significant differences were found in the sensory scores and in the levels of tyrosol and hydroxythyrosol, both were higher in unfiltered oils. In the third series of studies we carried out the first irrigation experiment for olives to study the drought stress in the cv. ‘Istrska belica’. In addition to the dynamics of water consumption, the crop quantity (kg/ha), the content of oil in the olive drupes (wt. %) and the fatty acid composition, the content and composition of biophenols in oil samples were determined.
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