Underestimated sources of flavonoids, limonoids and dietary fibre: Availability in lemon's by-products
Introduction
Citrus industry generates a considerable amount of by-products (or waste) with high amounts of valuable bioactive components. In fact, the annual Citrus world production is over 100 million metric tonnes, and lemon is one of the main Citrus crops, with a world annual production of over 6.0 million tonnes (United States Department of Agriculture – Foreign Agricultural Service, 2014). The Italian annual production of Citrus fruits is about 37 thousand tonnes. Lemon fruits constitute a considerable amount (about 5 thousand tonnes a year) of the Italian market (ISTAT, 2013) and more than 30% of the total production is industrially processed. Essential oil and juice are the main products obtained, and the amount of by-products generated from the industrial processes is consistent. The by-products obtained from lemon transformation are represented by peels, pulps, seeds and waste water. These are known to be rich in bioactive molecules (Atrooz, 2009, Bocco et al, 1998, Barreca et al, 2011, Yang et al, 2011), such as flavonoids, limonoids, phenolic acids, coumarins, furocoumarins, polymethoxyflavones, and carotenoids. Citrus peel and pulp also represent an important source of dietary fibre since they provide a well balanced amount of water soluble fraction (Gorinstein et al, 2001, Griguelmo-Miguel, Martin-Belloso, 1999, Prosky et al, 1992). Recently Chinapongtitiwat, Jongaroontaprangsee, Chewchan, and Devahastin (2013) reported the amount of soluble dietary fibre (SDF) determined in different Citrus ranging between 34.2% and 46.6% of the total dietary fibre amount (TDF). These ratios are ideal, considering that the optimal intake of SDF should be above 30% of the TDF. All these compounds can be recovered from the wastes and recycled for different uses, thus reducing the costs of waste disposal as well as the amount of total waste.
Recent literature data report on the utilization of different food industry by-products, such as proteolytic enzymes recovery from sardine by-products (Castro-Cesena, Del Pilar Sanchez-Saavedra, & Marquez-Rocha, 2012); natural dyes for textile dyeing from olive mill wastewater (Meksi, Haddar, Hammami, & Mhenni, 2012), functional proteins from canned and fresh tuna by-products (Sanmartin et al., 2012), adsorbent for removal of Pb(II) and Ni(II) from water from pigeon peas hulls waste (Ramana, Reddy, Yu, & Seshaiah, 2012), herpes Simplex virus inhibitors from apple pomace (Alvarez et al., 2012), phenolics compounds recovery from tomato leaves (Taveira et al., 2012), tomato waste (Cetkovic et al., 2012) and from olive oil by-products (Herrero et al., 2011); flavonoids (Sommella et al, 2014, Yang et al, 2011) and dietary fibre (Marin et al, 2007, Tanaka et al, 2012) recovered from Citrus-processing by-products.
Numerous articles are found in the literature reporting on the distribution of flavonoids, limonoids, phenolic acids, coumarins, furocoumarins, polymethoxyflavones, and carotenoids, in Citrus fruits. These are mainly analyzed by HPLC, as demonstrated by many different publications dealing with the determination of flavonoids (Chinapongtitiwat et al, 2013, Dugo et al, 2005, Gattuso et al, 2007, Russo et al, 2011), carotenoids (Agocs et al, 2007, Bonaccorsi et al, 2003, Giuffrida et al, 2006, Rouseff et al, 1996), coumarins and furocoumarins (Bonaccorsi et al, 1999, Dugo et al, 2009, Russo et al, 2012), and limonoids (Chinapongtitiwat et al, 2013, Manners, 2007).
The antioxidant activity of these bioactive molecules is well assessed (Atrooz, 2009, Bocco et al, 1998, Chen et al, 2010, Cook, Samman, 1996, Manners, 2007, Patil et al, 2009, Pernice et al, 2009). Carotenoids and flavonoids have been implicated in the protection against cancer, prevention of serious human health disorders such as heart and cardiovascular diseases, macular degeneration, cataracts, osteoporosis, hypertension and hyperlipidaemia (Gattuso et al, 2007, Rao, Rao, 2007, Srinivasan, Pani, 2013). Coumarins have also been demonstrated to exert many pharmacological and toxicological activities (Kleiner et al, 2008, Middleton et al, 2000, Murray et al, 1982, Row et al, 2006), possessing antibacterial (Kayser & Kolodziej, 1999), antiplatelet aggregation, anti-HIV (Wu et al., 2001) and intestinal anti-inflammatory (Luchini et al., 2008) properties. Moreover, flavanones and flavons exhibit beneficial effects on capillary fragility, anti-inflammatory, antimicrobial and antiviral activities, and possess the capability to inhibit human platelet aggregation, antiallergenic, and antiulcer properties and hypocholesterolaemic effects (Borrelli, Izzo, 2000, Di Donna et al, 2014, Middleton, Kandaswami, 1992, Tijburg et al, 1997, Wightman, 2004).
Dietary fibre has been proven to exert different beneficial effects, and its intake has beneficial effects on risk factors for developing chronic diseases. In fact, dietary reference intakes (DRI, 2002/2005) recommend consumption of 25 g of fibre for adult women and 38 g for adult men, based on epidemiologic studies showing protection against cardiovascular disease (Fernandez-Lopez et al, 2004, Guillon, Champ, 2000, Harris, Ferguson, 1999, Lipkin et al, 1999). Moreover, in addition to its nutritional role, dietary fibre is also desirable for its functional and technological properties (Marin et al., 2007).
This study, which is a part of a more extended project aimed to endorse the use of the waste produced by Italian agro-food industries, is focused on the evaluation of different lemon-processing by-products as potential sources of bioactive molecules and dietary fibre. The samples (juice, waste water, peels, pulps and seeds) provided by the local Citrus industries were thus analyzed by RP-HPLC/PDA/MS.
Section snippets
Materials and samples
This research was carried out on a 48°Brix concentrated lemon juice and on the by-products resulting from the entire industrial process, namely waste water, peels, pulp and seeds. The whole samples were collected at local Citrus plants located in Barcellona Pozzo di Gotto (Messina, Italy). For the determination of polyphenols the samples of waste water and of concentrated lemon juice were analyzed without any pre-treatment, while all the other samples were subjected to solvent extraction before
Results and discussion
The identification and quantification of polyphenols, oxygen heterocyclic compounds and carotenoids in various lemon-processing by-products was attained by means of RP-HPLC in combination with UV and MS detectors. When possible, the identification of compounds was confirmed by comparison with standard materials.
The validation process showed a good linearity for all methods used to determine the different chemical classes studied in this work, as shown in Table 1 relative to LOD and LOQ. In
Acknowledgements
The Project was funded by the “Italian Ministry for the University and Research (MIUR)” within the National Operative Project “Hi-Life Health Products from the industry of foods”. Project ID: PON01_01499.
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