L’extraction des glycosides

L’extraction des glycosides

Epidemiological studies have suggested the beneficial effects of citrus fruits (rich in flavanones) against many degenerative diseases like cardiovascular diseases and some cancers (Benavente-Garcia, Castillo, Marin, Ortuno, & Rio, 1997; Tripoli, Guardia, Giammanco, Majo, & Giammanco, 2007). These positive influences on human health has significantly increased the citrus consumption in the last few years and it is continuously increasing with an estimated world production of citrus fruits up to 72 million tons in the session 2007-08, among which the major commercially important orange fruits accounts for about 45 million tons (USDA, 2008). The domestic and industrial use of these large quantities of citrus fruits, especially for the production of juice, results in the accumulation of high amounts of by- products such as peel, seed, cell and membrane residues which account for about half of the fruit weight. These by-products can be used for the production of molasses, pectins, essential oils, limonene and cattle feed (Bocco, Cuvelier, Richard, & Berset, 1998; Jeong et al., 2004; Li, Smith, & Hossain, 2006). In addition, citrus by-products are a good source of phenolic compounds, especially the characteristic flavanone glycosides which mainly include naringin, hesperidin, narirutin, and neohesperidin. Currently, their extraction from citrus peels has attracted considerable scientific interest to use them as natural antioxidants mainly in foods to prevent the rancidity and oxidation of lipids (Anagnostopoulou, Kefalas, Papageorgiou, Assimopoulou, & Boskou, 2006; Peschel et al., 2006; Zia-ur-Rehman, 2006). Indeed, in recent years, a lot of research has focused on plants and their by-products to extract natural and low-cost antioxidants that can replace synthetic additives such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), which might be liver-damaging, carcinogenic (Ak & Gülçin, 2008) and more generally toxic (Moure et al., 2001).

Up to now, several conventional extraction techniques have been reported for the extraction of phenols from citrus peels like solvent extraction (Anagnostopoulou, Kefalas, Papageorgiou, Assimopoulou, & Boskou, 2006; Jeong et al., 2004; Li, Smith, & Hossain, 2006a; Manthey & Grohmanu, 1996; Xu, Ye, Chen, & Liu, 2007; Zia-ur-Rehman, 2006), hot water extraction (Xu et al., 2008), alkaline extraction (Bocco, Cuvelier, Richard, & Berset, 1998; Curto, Tripodo, Leuzzi, Giuffrè, & Vaccarino, 1992), resin-based extraction (Calvarano, Postorino, Gionfriddo, Calvarano, & Bovalo, 1996; Kim, Kim, Lee, & Kim, 2007), enzyme-assisted extraction (Li, Smith, & Hossain, 2006b), electron beam- and γ- irradiation-based extractions (Kim, Lee, Lee, Nam, & Lee, 2008; Oufedjikh, Mahrouz, Amiot, & Lacroix, 2000) and supercritical fluid extraction (Giannuzzo, Boggetti, Nazareno, & Mishima, 2003). These conventional or more innovative extraction techniques may either cause the degradation of the targeted compounds due to high temperature and long extraction times as in solvent extractions, or pose some health-related risks due to the unawareness of safety criteria during irradiation. Furthermore, enzyme-assisted extraction is limited due to problems of enzyme denaturation. With the development of the “Green Chemistry” concept during the last few years, environment-friendly techniques are becoming more and more attractive. The extraction of bioactive compounds under ultrasound irradiation (20-100 kHz) is one of the upcoming extraction techniques that can offer high reproducibility in shorter times, simplified manipulation, reduced solvent consumption and temperature and lower energy input (Chemat, Tomao, & Virot, 2008).

During sonication, the cavitation process causes the swelling of cells or the breakdown of cell walls, which allow high diffusion rates across the cell wall in the first case or a simple washing-out of the cell contents in the second (Vinatoru, 2001). Besides the solvent, temperature and pressure, better recoveries of cell contents can be obtained by optimizing ultrasound application factors including frequency, sonication power and time, as well as ultrasonic wave distribution (Wang & Weller, 2006). Optimization of ultrasound-assisted extraction (UAE) has been described recently to extract hesperidin from Penggan (Citrus reticulata) peel (Ma et al., 2008a), phenolic acids and flavanone glycosides from Satsuma Mandarin (Citrus unshiu Marc) peel (Ma et al., 2008b; Ma, Chen, Liu, & Ye, 2009) and total phenolic contents from Penggan peel (Ma, Chen, Liu, & Ye, 2008c) (see table 1). In these works, methanol came up as a suitable extraction solvent to reach good yields of the above- mentioned phenolic compounds. However, environmentally benign and non-toxic food grade organic solvents like ethanol, n-butanol and isopropanol are recommended by the US Food and Drug Administration for extraction purposes (Bartnick, Mohler, & Houlihan, 2006). A literature search did not yield any reference about earlier reports on the UAE of phenolic compounds from orange peels by using food grade solvents. The objective of this work is to outline the potentiality of UAE in the fast preparation of extracts rich in polyphenols (especially flavanone glycosides) from orange peels in good yields. Several parameters that could potentially affect the extraction efficiency were evaluated and optimized using a statistical experimental design approach. Finally, the optimized UAE The solvents used were of analytical grade and supplied by VWR International (Darmstadt, Germany). Flavanone glycosides (naringin, hesperidin) were purchased from Extrasynthese (Genay, France), caffeic acid from Sigma-Aldrich (Steinhaus, Germany), and trolox from Acros Organics (Slangerup, Denmark). DPPH (2,2-diphenyl-1-picrylhydrazyl), AAPH (2,2′-azobis (2-methyl)propionamidine dihydrochloride) and fluoresceine were obtained from Alfa Aesar (Karlsruhe, Germany), Sigma-Aldrich (Steinhaus, Germany) and Acros Organics (Morris Plains, USA), respectively.

 

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