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5) Servili M., Taticchi A., Esposto S., Urbani S., Selvaggini R., Montedoro GF. (2008) Monitoringof the oxygen concentration during malaxation: application of head-space sensors to improvevirgin olive oil quality. VI International Symposium on Olive Growing. 9-13 September2008, Evora, Portugal.Sensory and healthy properties of Virgin Olive Oil (VOO) are highly related to its volatile and phenolic composition.The occurrence of these substances in the oil depends from various endogenous oxidoreductase activitiesof olive fruit that are activated during processing, such as poliphenoloxidase (PPO) and peroxidase (POD, whichpromote hydrophylic phenols oxidation during malaxation, and lipoxigenase (LPO) that catalyzes the genesis ofC5 and C6 saturated and unsaturated aldehydes, alcohols, and esters responsible for the desirable sensory notesof VOO. The malaxation process parameters, in terms of temperature, length and oxygen concentration, affectthe all the mentioned enzymatic activity determining strong modifications in the VOO quality. The technologicalapproach to the control of the enzymatic activities has been attempted through the optimization of the malaxationtemperature and the time of exposure of olive pastes to the air contact and recently the CO 2 emission from malaxedpastes has been described. The oxygen control in the pastes during malaxation, may be an new technologicalparameter to regulate the enzymatic activities that affect phenolic and volatile composition of VOO. In thiswork the monitoring of CO 2 and O 2 concentration during olive paste malaxation in industrial scale was carriedout in different malaxer head space O 2 compositions.Results show that the O 2 concentration in the malaxer head space did not affect the CO 2 production duringprocessing while strong modifications were observed for the phenolic composition of olive pastes and VOOs.The aroma production during malaxation, on the contrary, seem to be hardly affected by the O 2 concentration inthe malaxer head space.SISTAL - SOCIETA’ ITALIANA DI SCIENZE E TECNOLOGIE ALIMENTARIDipartimento di Scienze e Tecnologie Agroalimentari, Università degli Studi della TusciaVia San Camillo de Lellis, 01100 ViterboTel.: 0761- 35 74 94/7 , Fax: 0761- 35 74 98, e-mail: mmoresi@unitus.it365