Analytical evaluation of virgin olive oil of first and second extraction

Virgin olive oils from percolation (first extraction) have been compared wi th the corresponding oils from centrifugation (second extraction). The form er were characterized by (i) higher contents of total phenols, o-diphenols, hydroxytyrosol, tyrosol-aglycons, tocopherols, trans-2-hexenal, total vola tiles, and waxes; (ii) higher values of resistance to autoxidation and of t urbidity; (iii) higher sensory scores; (iv) higher ratios of campesterol/st igmasterol, traits-2-hexenal/hexanal, and trans-2-hexenal/total volatiles; (v) lower contents of chlorophylls, pheophytins, sterols, and aliphatic and triterpene alcohols; (vi) lower alcoholic index and color indices; (vii) s imilar values of acidity, peroxide index, and UV (ultraviolet) spectrophoto metric indices; (viii) similar percentages of saturated and unsaturated fat ty acids, triglycerides, and diglycerides; and (ix) similar values of glyce ridic indices. Stigmastadienes, trans-oleic, trans-linoleic, and trans-lino lenic acid isomers were not detected in the two genuine oil kinds. Hence, t he qualitative level of the first extraction oil was superior to the second extraction one.