Effects of pre-processing low temperature conditioning of olives on volatile organic compound (VOC) profiles of fruit paste and oil

Temperature is a key regulator in respect to the quality of the produced oil. Three different conditioning temperatures utilizing washing water were applied on olives (cv. Leccino) harvested in correspondence of two different ripening stages, semi-ripe (Jaén index 2.69) and ripe (3.82). Mesocarp temperatures of fruit before crushing were 10, 15 and 19°C. The produced paste and oil were analyzed in terms of VOC profiling by SMPE-GC-MS. Multivariate analysis (Partial Least Squares regression, PLS), showed that lowering the temperature before crushing had a profound effect on the olive paste in respect to the VOCs abundance and resulted in modification of VOC profiles in both semi-ripe and ripe olive samples. PLS analysis showed a clear separation of the paste samples depending on the pre-processing temperature conditioning. Lower temperature samples grouped mainly with C6 compounds namely hexanal, 2-hexenal, and 3-hexen-1-ol, known to be associated with green/bitter sensory perceptions. Samples processed at a temperature of 19°C grouped in opposite PLS quadrants and were in general associated with compounds (mainly C6 and C5 alcohols) recognized to give sweet/fruity perceptions (1-hexanol, 2-hexen-1-ol (Z), 2-penten-1-ol (E) and (Z)), and also other compounds associated with off-flavours (1-penten-3-ol, 1-penten-3-one, acetic acid). Lowering temperature of olives before crushing appears to be effective for improving the aroma quality of olive paste and the resulting olive oil with higher levels of aldehydes and a reduction of defect-related VOCs.