Malaxation is one of the most determining process steps for the final quality of virgin olive oil (VOO). It is also the only discontinuous operation in industrial plants working with two or three phases decanters, often requiring long kneading times to maximize process efficiency, which can negatively affect the VOO quality. In order to overcome these drawbacks and fulfill market and consumer exigencies, VOO research and industry have worked towards the development of innovative and sustainable plant engineering solutions. High power ultrasound (HPU) has well proven its potential as a fast, quality-improving and cost-effective technology in the food industry, but it was not until recently that application on the VOO sector was considered. The aim of this study is to further explore the potential ultrasoundassisted extraction (UAE) as a suitable process alternative, shedding light in the technology’s impact on process parameters, such as extraction time and yield, and basic, nutritional and sensorial VOO quality, in relation with olive maturation stage and cultivar. This work represents the first effort to implement ultrasound (US) technology in VOO production at a semi-industrial scale, with an ultrasonic device especially designed for the purpose. Moreover, an innovative approach of US application, performed after the malaxation step, was studied. Mono-varietal virgin olive oils were produced from two cultivars typical of the Calabria region, Carolea and Ottobratica, from the present crop year, at two different ripening stages (end of October and beginning of November), in a low-scale mill plant, with a working capacity of 150 kg/h. Experimental trials were carried out by processing 50 kg batches of olives, performing a 30 min malaxation step, in the control samples and a 15 min malaxation of plus sonication, for a total time of 15 min, in treated samples. HPU application was carried out by sonication of olive pastes after the malaxation step, in a stateof- the-art ultrasonic reactor, integrated in the low-scale plant between the malaxer and the two-phase decanter centrifuge. The reactor’s characteristics were the following: ultrasonic frequency of 25 kHz; specific ultrasonic power of 520 W/L. The process flow rate was 0.056 L/s and the residence time inside the reactor was 34.2 s. Eight VOO samples were obtained and tested in control-treated pairs. Basic quality parameters free acidity, peroxide value, specific extinction coefficients K232 and K270 and sensory analysis were assessed. Moreover, yield efficiency, fatty acid composition, total tocopherol, phenol and volatile content, as well as phenolic and volatile profile, were determined. In the experimental conditions tested, US treatment did not affect VOO quality parameters, which were within the legal limits for virgin edible oils. US treated oils showed greater concentrations of PUFA and a higher content in minor compounds, apart from tocopherols, which slightly decreased. Consistent and significative increases of total phenolic content, namely lignans and sericoridoids, and C6 (aldehydes and alcohols) and C5 (penten dimers) volatile compounds, were verified as a result of US treatment. Oils from sonicated pastes showed improved sensorial quality, with an intensity increase of fruity, bitter and pungent notes. From an engineering standpoint, UAE improved mass and heat transfer efficiency, giving better oil extractability and yields while significantly reducing malaxation time (by half), without compromising VOO quality. The results obtained from experimental trials were employed to suggest an upscaling solution of the UAE process, complemented by a cost-volume-profit financial projection. Industrial UAE showed to be viable from the financial perspective, reducing olive milling associated cost by 3% per unit (0.75 L) and overall VOO cost by 0.14 € per unit. The results of this study represent a step forward in achieving process continuity and may constitute a stepping-stone for UAE widespread industrial implementation in the VOO sector. US implementation in VOO production would thus represent a minor and strategic investment, with a net advantage in operation cost, production efficiency, product quality and process sustainability.
| Date of Award | 26 Oct 2015 |
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| Original language | English |
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| Awarding Institution | - Universidade Católica Portuguesa
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| Supervisor | Alessandra Bendini (Supervisor), Ana Maria Gomes (Co-Supervisor) & Enrico Valli (Co-Supervisor) |
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