Malaxation has been recognized as one of the most critical points in the mechanical extraction process for virgin olive oil (VOO). It is a low and continuous kneading of olive paste at a carefully monitored temperature. Through this essential technological operation the small droplets of the oil formed during the milling merge into large drops that can be easily separated with a decanter centrifuge. During this technological phase, a complex and necessary bioprocess takes place in order to determine the quality and composition of the final product. The malaxer is a heat exchanger characterized by a low overall heat transfer coefficient because the ratio of surface area to volume is disadvantageous, so it is important to find an innovative technology to improve heat-exchange. As matter of fact, the malaxing step is the only discontinuous phase in a continuous extraction process. In the next future, the essential challenge of VOO industrial plant manufacturing sector is to design and build advanced machines in order to transform the discontinuous malaxing step in a continuous phase and improve the working capacity of the industrial plants. In order to reduce the malaxing time enhancing the quality of the product, two ultrasound-assisted virgin olive oil extraction processes were tested against the traditional method. The sonication treatment was applied on olives submerged in a water bath (before the crushing) and on olive paste (after the crushing). The ultrasound technology provides a reduction of the malaxing duration improving VOO yields and its minor compounds content. Better extractibility and higher minor compounds contents were obtained by sonicating the olives submerged in a water bath than olive paste. After experimental trials the results were employed to suggest innovative scaling up solutions of the process and new applications of ultrasounds in the VOO industry.

Three different flavoring methods of olive oil were tested employing two different herbs, thyme and oregano. The traditional method consist in the infusion of herbs into the oil. A second scarcely diffused method is based on the addition of herbs to the crushed olives before the malaxation step during the extraction process. The third innovative method is the implementation of the ultrasound before the olive paste malaxation. The objective of the study is to verify the effect of the treatments on the quality of the product, assessed by means of the chemical characteristics, the phenol composition and the radical scavenging activity of the resulting oils. The less favorable method was the addition of herbs directly to the oil. A positive effect was achieved by the addition of herbs to the olive paste and other advantages were attained by the employment of ultrasound. These last two methods allow to produce oils "ready to sell", instead the infused oils need to be filtered. Moreover, the flavoring methods applied during the extraction process determine a significant increment of phenolic content and radical scavenging activity of olive oils. The increments were higher when oregano is used instead of thyme. Ultrasound inhibited the olive polyphenoloxidase, the endogenous enzyme responsible for olive oil phenol oxidation. This treatment of olive paste mixed with herbs before malaxation was revealed as the most favorable method due to the best efficiency, reduced time consumption and minor labor, enhancing the product quality of flavored olive oil.

Malaxation is a basic step in the mechanical olive oil extraction process that may affect yield,\ud quality and health properties of virgin olive oil (VOO). The operative conditions of malaxation,\ud such as temperature and time, are fundamental to favour the oil coalescence process and,\ud consequently, the duration of the VOO extraction process. The aim of this study was to improve\ud the extraction process efficiency by using an ultrasound treatment of olive paste before the\ud malaxation step. The ultrasonic treatment was applied to Coratina and Peranzana, which are two\ud of the most popular Southern Italian olive varieties characterized by extremely different\ud technological performance. Different times of ultrasound treatments were tested (0, 2, 4, 6, 8, 10\ud min) and free acidity, peroxide value, K232, K270, sensory analysis, tocopherols, total carotenoids,\ud chlorophyll and total polyphenols were determined. Results showed that the ultrasound treatment\ud caused a quick heating of the olive paste as a function of the ultrasound treatment time. Times of\ud treatment of 8 and 10 min allowed the reduction of the malaxation phase from 60 to about 40 min.\ud The ultrasound technique improved antioxidant content in both VVOs, except for polyphenols\ud that decreased. However, the reduction of polyphenol concentration in Coratina VOO improved\ud its taste by reducing the bitter and pungent notes, which are not always accepted by consumers

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