Real-Scale Integral Valorization of Waste Orange Peel via Hydrodynamic Cavitation

Abstract

Waste orange peel represents a heavy burden for the orange juice industry, estimated in several million tons per year worldwide; nevertheless, this by-product is endowed with valuable bioactive compounds, such as pectin, polyphenols and terpenes. The potential value of the waste orange peel has stimulated the search for extraction processes, alternative or complementary to landfilling or to the integral energy conversion. This study introduces controlled hydrodynamic cavitation processes, as a new route to the integral valorization of this by-product, based on simple equipment, speed, effectiveness and efficiency, scalability, and compliance with green extraction principles. Waste orange peel, in batches of several kg, was processed in more than 100 L of water, absent any other raw materials, in a device comprising a Venturi-shaped cavitation reactor. The extractions of pectin, endowed with a very low degree of esterification, polyphenols (flavanones and hydroxycinnamic acid derivatives), and terpenes (mainly d-limonene) were effective and fast (high yield, few min of process time), as well as the biomethane generation potential of the process residues was effectively exploited. The achieved results proved the viability of the proposed route to the integral valorization of waste orange peel, though wide margins exist for further improvements.

Exceptional Antioxidant, Non-Cytotoxic Activity of Integral Lemon Pectin from Hydrodynamic Cavitation

“…These results open the route to the development of a number of new, integral pectin-based nutraceutical formulations based on the simple, low cost, scalable and efficient hydrodynamic cavitation extraction process applied to waste lemon peel suspended in water, while meeting all the principles of natural product green extraction [8,9].…”

“…The main structural difference with the extraction process applied to waste orange peel is that now the HCassisted extraction was carried out in a sealed reactor in order to minimize the loss of the lemon peel's volatile components. This was one of the recommendations arisen from the previous study describing the waste orange peel treatment [9]. In detail, 34 kg of fresh waste lemon peel obtained from organically grown Siracusa lemons (Citrus limon, cultivar 'femminello') by an in-line extractor at a juice factory kindly donated by a company (Campisi Citrus, Siracusa, Italy) were first grinded in ice with an electric blender and then added along with 120 L of tap water to the HC device.…”

“…Amid them, perhaps the most promising method from the industrial viewpoint is the extraction based on controlled hydrodynamic cavitation (HC) [8]. Originally demonstrated in the citrus fruit field with waste orange peel on semi-industrial scale (42 kg of raw material in 142 L water) [9], the process quickly affords extraction and separation of water soluble and insoluble bioproducts with practically no degradation neither of pectin nor of the valued phytochemicals contained in the orange peel.…”

“…The HC extraction device, including a closed hydraulic loop (total volume capacity around 230 L), a centrifugal pump (Lowara, Vicenza, Italy, ESHE 50-160/ 75) with 7.5 kW nominal mechanical power and rotation speed of 2900 rpm, and a Venturi-shaped HC reactor, has been described in detail elsewhere [9]. The main structural difference with the extraction process applied to waste orange peel is that now the HCassisted extraction was carried out in a sealed reactor in order to minimize the loss of the lemon peel's volatile components.…”

“…The HC-based citrus peel extraction is actually so effective [9], that virtually all water-soluble compounds are brought in solution. Furthermore, explaining the exquisite smell of the integral lemon pectin obtained we know from the waste orange peel experiment carried out under similar HC extraction conditions, that the citrus essential oil contained in the peel is emulsified in a ultrastable nanoemulsion dispersed in the aqueous phase [9]. Accordingly, we call Integro-Pectin (In-Pec) the integral pectin samples thereby obtained.…”