High-power ultrasound in olive paste pretreatment. Effect on process yield and virgin olive oil characteristics

The effect of high-power ultrasound on olive paste, on laboratory thermo-mixing operations for virgin olive oil extraction, has been studied. Direct sonication by an ultrasound probe horn (105W cm2 and 24 kHz) and indirect sonication with an ultrasound-cleaning bath (150 W and 25 kHz) were applied and their effects compared with the conventional thermal treatment.
A quick-heating of olive paste, from ambient (12–20 C) to optimal temperature conditions (28–30 C), and an oil extractability
improvement were observed when applying sonication. Better extractability was obtained by direct sonication for high moisture olives(>50%) whereas indirect sonication gave greater extractability for low moisture olive fruits (<50%).
Optimal application of ultrasound was achieved with direct sonication for 4 min at the beginning of paste malaxation and with indirect sonication during the malaxation time.
Effect of high-power ultrasound on oil quality parameters and nutritional and sensory characteristics were studied. Changes in quality parameters (free acidity value, peroxide value, K270 and K232) were not found, however significant effects on the levels of bitterness, polyphenols, tocopherols (vitamin E), chlorophyll and carotenoids were observed. Oils from sonicated pastes showed lower bitterness and higher content of tocopherols, chlorophylls and carotenoids. Related to sensory characteristics, off-flavour volatiles were not detected in oils from sonication treatments. Total peak areas of volatiles and the ratio hexanal/E-2-hexenal, as determined by SPME analysis, were lower than non-sonicated reference oils; sensory evaluation by panel test showed higher intensity of positive attributes and lesser of negative characteristics than those untreated.

Effect of ultrasound treatment on olive oil

When high-power ultrasound is applied to olive pastes,their effect on chemical, nutritional and sensorial characteristics of oil obtained should be considered. In Table 2 the chemical quality parameters of oils are presented, according to UE Regulation, from the different paste treatments. All the oils obtained were classified into ‘extra virgin’ category. For the first harvesting date nonsignificant differences were found between treatments for acidity value, peroxide value and UV absorbance at 270 nm; only values for K232 in IUSO treatment were found significatively different to DUSO and TEST, with values of 1.465 ± 0.064, 1.570 ± 0.057 and 1.590 ± 0.014, respectively. In general, for quality parameters IUSO oils showed the lowest values.
In second harvesting date, IUSO oils showed again the lowest values for all the quality parameters, with significant differences in peroxide value and K232. In general, no oxidation or hydrolysis effects were observed in oils when ultrasounds were applied.
In Table 2, the effect of olive paste treatments on some important nutritional parameters of the olive oil areshown. Significant differences between mean values for TEST and ultrasound treatments were found for both harvesting dates.