Flash thermal conditioning of olive pastes before malaxation: innovation for best quality
The application of this technology, performed by Alfa Laval, produces significant differences in comparison to the crushed pastes. The virgin olive oil flash thermal conditioning featured a higher concentration of volatile compounds
The traditional malaxation process performs paste mixing and thermal conditioning at the same time, but the thermal
transfer efficiency is generally low, and for this reason, the thermal conditioning of olive pastes is relatively long compared to the optimal processing temperature. This aspect influences the activity involved in oil extraction of the endogenous enzymes, such as pectinases, hemicellulases, and cellulases, as well as the polyphenoloxidase (PPO), peroxidase (POD), and LOX that affect the phenolic and volatile composition of VOO.
The fast heating technology applied to the thermal conditioning of the olive pastes before malaxation is a new approach to the oil mechanical extraction process, which can revise the traditional thermal conditioning applied to the olive
pastes during the oil’s mechanical extraction process. The flash heating of paste after crushing can eliminate the malaxation time required for thermal conditioning with significant impact on the plant’s working capacity, oil yield, and VOO quality.
A scientific work lead by Perugia University investigates the effects of flash thermal conditioning (FTC) on the structure modifications of olive pastes and virgin olive oil volatile and phenolic composition.
After the same disc crusher was used for control, the flash thermal conditioning of olive pastes was obtained using an EVO-Line heat
exchanger from Alfa Laval with 2.5 t/h of capacity, which was heated by hot water at 35 and 40 °C to bring the pastes at 25 or 30 °C,
respectively. The paste was heated instantaneously using the EVO-Line at those fixed temperatures.
In both the cultivars studied, the FTC showed a lower phenolic concentration compared to the same oil obtained by the traditional process. The most important modifications, observed in the Gentile cv., were at 30°C, where the sum of the phenolic fractions of the FTC extra virgin decreased of 81.7 mg/kg with respect to the standard one.
The secoiridoids derivatives, which had higher reductions, were 3,4 DHPEA-EDA and 3,4 DHPEA-EA, whereas the lignans did not show any significant variations. However, these losses were reduced, increasing the malaxation time after FTC treatment. In fact, as observed in Peranzana cv., malaxing the FTC pastes at 30 °C for 0, 5, or 10 min resulted in lower phenol content (expressed as sum) in the relative extra virgin, respectively, of 19.4, 15.1, and 8.1% than that of standard ones. Those results can be explained by considering differences in terms of the activation period of depolymerizing enzymes between the FTC and the traditional process.
Compared to the extra virgin with normal malaxation, (E)-2-hexenal increased 32.4%and 12% in the FTC oil head space when the pastes were malaxed, respectively, at 25 and 30 °C. Even the esters showed higher values in FTC than those obtained by the traditional process. In that case, the augmentation for hexylacetatewas of 56.2% and 62.8% malaxing the FTC pastes at 25 and 30 °C, respectively, while for (Z)-3-hexenyl acetate, the increase was of 61.5% (at 25 °C) and of 63.4% (at 30 °C).
The results on FTC oil of the Peranzana cultivar, malaxedat 30 °C at 0 min, showed the same trend observed in Gentile
The FTC treatment to the olive pastes applied on an industrial mill, with the aim of improving its working capacity, allowed a significant increase of the those volatile compounds responsible for the positive olfactory attributes of the
FTC oils compared to those obtained by traditional malaxation. However, it caused a significant reduction in the
percentage of the oil recovered and of the polyphenols’ content as well. These negative findings were strongly reduced applying a further short malaxation period at 30 °C to the FTC pastes.
In conclusion, optimal operative conditions in terms of time and temperature applied during malaxation after the FTC
treatment can be opportunely chosen for improving the relative virgin olive oil quality, according to the characteristics of olives such as the olives’ cultivar, sanitary state, or maturation index or the growing climatic conditions of the drupes.