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 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, without any other raw materials, in a device comprising a Venturi-shaped cavitation reactor. The extractions of pectin (with a remarkably low degree of esterification), polyphenols (flavanones and hydroxycinnamic acid derivatives), and terpenes (mainly d-limonene) were effective and efficient (high yields within a few min of process time). The biomethane generation potential of the process residues was determined. 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.

Towards a new treatment against polymicrobial infections: high antibacterial activity of lemon IntegroPectin againstPseudomonas aeruginosaandEscherichia coli

“…The lemon peel was derived by an in-line extractor at a lemon juice factory and directly processed on semi-industrial scale (34 kg of waste lemon peel of organically grown Siracusa lemons in 120 L tap water) using the same cavitation conditions lately developed to process waste orange peel. [12] Easily dissolved in water, the resulting yellow pectin flakes obtained after freeze drying have a pleasant lemon smell and are completely devoid of cytotoxic activity against human pulmonary cells up to high concentration (1 mg/mL). [13] Furthermore, lemon IntPec has an extremely high content of polyphenols adsorbed at its surface: 0.88 mg GAE/g (in terms of gallic acid equivalents, or GAE, per dry gram of pectin) versus 8.3×10 -3 mg GAE/g for the lemon peel of the cultivar with the highest biophenol concentration.…”

“…[22] However, scholars in Taiwan in 2014 reported lack of any antibacterial activity of citrus pectin against P. aeruginosa. [23] We make the hypothesis that the antibacterial action of lemon IntegroPectin is due to a synergistic combination of i) the pectic polymer, ii) the lemon oil adsorbed at its surface (the citrus essential oil is present in the form of a highly stable nanoemulsion in the aqueous phase after the hydrocavitation process), [12] and iii) the lemon flavonoids highly concentrated (with respect to the citrus peel) at the surface of lyophilized IntPec. [13] Likewise to other citrus oils, lemon oil is particularly active against Gram-positive bacteria, even though selected Gramnegative bacteria such as E. coli and Campylobacter jejuni are inhibited by lemon oil due to the presence of oxygenated monoterpenes exhibiting much stronger antimicrobial activity than hydrocarbon monoterpenes present in the essential oil.…”

Superior Antibacterial Activity of Integral Lemon Pectin From Hydrodynamic Cavitation

“…[15] Pectin showed the highest antibacterial activity at pH 6 with minimum inhibitory concentration (MIC) values ranging from 0.39 mg mL À 1 to 3.125 mg mL À 1 . [11] We have lately reported the discovery of IntegroPectin, namely citrus pectin isolated from orange [16] or lemon [17] peel via controlled hydrodynamic cavitation carried out on waste orange peel or waste lemon peel in water only.…”

“…[17] We now report that lemon IntegroPectin shows also significant antimicrobial activity against S. aureus, considerably higher than commercial citrus pectin obtained via hydrolysis with mineral acids of dried lemon peel, followed by prolonged 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 separation and purification of the inevitably degraded pectic polymer. [18] The antimicrobial activities of lemon IntegroPectin obtained using the same process described in previous studies [17,16] and commercial citrus pectin (galacturonic acid � 74.0 %, dried basis) purchased from Sigma-Aldrich (Merck Life Science, Milan, Italy) were tested against Staphylococcus aureus ATCC 25923 strain.…”

“…We ascribe the aforementioned difference between Integro-Pectin and commercial citrus pectin to the combined antibacterial action of lemon oil (present in IntegroPectin in the form of a highly stable nanoemulsion in the aqueous phase after the hydrocavitation process), [16] and of the water-soluble lemon flavonoids found in abundant amount at the surface of lyophilized IntegroPectin where they are responsible also for the powerful antioxidant activity of lemon IntegroPectin. [17] Lemon oil is known to exert antibacterial activity against food-borne bacteria, though being the least effective in reducing S. aureus strain when compared to mandarine (the best), grapefruit and orange oil.…”