Effect of extraction system, stage of ripeness, and kneading temperature on the sterol composition of virgin olive oils

Abstract

Abstract Comparative extraction trials were carried out among a classical pressing, a dual‐, and a three‐phase centrifugation system using olive crops of Koroneiki variety. Two different kneading temperatures, 30 and 45°C, were tested at three stages of ripeness for two consecutive years of harvest, 1995–1996 and 1996–1997. Composition of the sterol fraction was determined in the resulting olive oil samples ( n =72). Stigmasterol was found to be affected by the extraction system; it was obtained in the highest amount in the pressing system. The ratio campesterol/stigmasterol was significantly higher in oils extracted by dual‐ and three‐phase centrifugation. Sterols were significantly affected by the ripening stage of the fruit. During December, the ratio campesterol/stigmasterol reached the maximal and β‐sitosterol the minimal values; this appears to be the optimal period for harvesting the olives. Comparison of the different kneading temperatures showed that at 30°C, Δ 5 ‐avenasterol and campesterol/stigmasterol ratio reached higher values than at 45°C.