Analytical evaluation of virgin olive oil of first and second extraction.

Virgin olive oils from percolation (first extraction) have been compared with the corresponding oils from centrifugation (second extraction). The former were characterized by (i) higher contents of total phenols, o-diphenols, hydroxytyrosol, tyrosol-aglycons, tocopherols, trans-2-hexenal, total volatiles, and waxes; (ii) higher values of resistance to autoxidation and of turbidity; (iii) higher sensory scores; (iv) higher ratios of campesterol/stigmasterol, trans-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) similar values of acidity, peroxide index, and UV (ultraviolet) spectrophotometric indices; (viii) similar percentages of saturated and unsaturated fatty acids, triglycerides, and diglycerides; and (ix) similar values of glyceridic indices. Stigmastadienes, trans-oleic, trans-linoleic, and trans-linolenic acid isomers were not detected in the two genuine oil kinds. Hence, the qualitative level of the first extraction oil was superior to the second extraction one.