High-power ultrasound pretreatment for efficient extraction of fractions enriched in pectins and antioxidants from discarded carrots (Daucus carota L.)
Introduction
Food wastes constitute a significant problem for economic, environmental and food security reasons. About one-third of all food produced globally for human consumption (approximately 1.3 billion tons per year) is lost or wasted. Moreover, the major contribution to the food waste comes from vegetables (FAO, 2014). Fruit and vegetable wastes are produced in large quantities in markets, and constitute a big problem in municipal landfills (Varzakas et al., 2016).
Carrot (Daucus carota L. var. sativus), an important vegetable of the Umbelliferae family, is cultivated throughout the world. It is usually chopped, and eaten raw, cooked, fried or steamed and cooked in soups, stews, salads, cakes, as well as prepared meals for babies and pets (Dansa et al., 2017). Carrot is extensively consumed and considered one of the healthier vegetables for being a rich source of bioactive compounds, dietary fiber, carotenoids, minerals, and vitamins (Idrovo Encalada et al., 2016). In Argentina, between 200,000 and 240,000 tons of carrot roots are produced annually (Gaviola, 2013). The highest percentage of production is destined to fresh consumption, including ready-to-eat salads prepared in small scale food industries and greengrocers. A small proportion is destined mainly to the dehydration industry. These processes generate significant volumes of residues (Dansa et al., 2017). In total, about 25–35% of carrots are usually discarded after harvesting or industrialization because of irregular sizes and forms, being in part used as animal feed, while still contains useful compounds like antioxidants and pectins (Chantaro et al., 2008). Therefore, the use of discarded carrots can be a good alternative for obtaining antioxidant carrying pectins with useful rheological properties.
Pectins are complex polysaccharides that are found in the middle lamella and cell wall of all higher plants and, hence, they are part of the dietary fiber. The structure of pectin is composed mainly by d-galacturonic acid units (GalA) of the homogalacturonan (HG) chains, partly esterified with methanol, and neutral sugars (NS) such as l-rhamnose, l-arabinose, and d-galactose of the rhamnogalacturonan I (RG-I) core, as well as other 13 different monosaccharides (Hosseini et al., 2016). Pectin composition and structure depends on the origin, developmental stages, and extraction conditions (Petkowicz et al., 2017). They are widely used as a functional ingredient in the food industry as gelling, thickening and stabilizing, and texturizing agent (do Nascimento et al., 2016), as well as in the pharmaceutical industry for their beneficial health properties as soluble dietary fiber, for reducing blood fat, gut processes, and reducing heart disease, among others (Bagherian et al., 2011).
The commercially available pectin is obtained using conventional extraction by means of a mineral acid (hydrochloric, nitric, and sulfuric acid) and it is recovered by precipitation with ethanol (Chan and Choo, 2013). Some innovative pectin extraction techniques such as ultrasound, microwave, and enzymatic extraction, have been developed to improve the yield and the product quality (Marić et al., 2018). Ultrasound-assisted extraction (UAE) uses high-frequency sounds and solvents to enhance the release and diffusion of cell material. The increase of the mass transfer is produced by the acoustic cavitation induced in a liquid medium, which is one of the beneficial effects of this technology (Wang et al., 2015). There are significant advantages of UAE such as the reduced extraction time, low energy consumption, yield increase, and use of lower volumes of solvent when compared to conventional extractive methods (Tao et al., 2014).
By sequential extraction of the polymers from the isolated cell wall material (alcohol insoluble residue), at low temperatures (18-22 °C), it is possible to ascertain the chemical composition and polymer interactions within cell walls (Fry, 1986; Koh and Melton, 2002; Basanta et al., 2013). This sequential scheme begins with isolation for at least 4 h of the loosely (water-soluble) bound pectins, followed by the extraction for 24 h of the CDTA soluble fraction (calcium crosslinked pectins). The third extractive step is performed for 24 h to obtain the 0.1M Na2CO3 soluble fraction, composed by the remaining pectins that are anchored in the cell wall matrix through covalent bonds like diester bridges of ferulate and galacturonate, as reported by Basanta et al. (2013).
The present study proposes HPUS as a pretreatment to facilitate the subsequent extraction of a PEF from misshapen carrots with 0.1M Na2CO3 aqueous solution at room temperature, with the aim of using a sustainable method for the valorization of vegetable residues as food additives or ingredients. As a prelude to PEF-isolation, the effect of HPUS-power intensity and sonication time on water soaked CP used for PEF extraction was investigated. Thus, the releases of reducing carbohydrates, UA, NS, and proteins were determined in the water solvent after performing HPUS treatments at 20 kHz, and either 20% of constant amplitude for 40 min (A-treatment) or 80% of amplitude for 5–20 min (B-E treatments). The best conditions for the PEF extraction were then selected.
Section snippets
Chemicals
Chemicals were of analytical grade. α-carotene, β-carotene, lutein, α-, β- and γ-tocopherols, retinol, bovine serum albumin, and d-galacturonic acid standards were of Sigma-Aldrich, while the rest of the chemicals were of Merck Química (Argentina). Deionized water (Milli-Q™, USA) was used.
Ultrasonic treatments in CP
Carrots (Daucus carota L. var. Nantes) harvested in Valle de Uco (Mendoza province, Argentina), discarded after harvesting or industrialization because of irregular sizes and forms, were used in the present
HPUS energy and power
Table 1 summarizes the amplitude and treatment times, as well as the energy and power values displayed by the HPUS equipment (20 kHz constant frequency) while performing the assays in open systems constituted by the dispersion of CP in a volume of water contained into a glass beaker of determined dimensions. On the other hand, adiabatic experiments were performed only to calculate the acoustic energy (eq. (1)) and power (eq. (2)) actually provided by the ultrasound equipment through the
Conclusions
Smaller, twisted, and misshapen carrots discarded at harvesting were used to produce a sugar-exhausted blanched freeze-dried powder (CP; water activity = 0.300) enriched in cell wall polymers, whose whole pectin content (UA: 14.0% w/w) was successfully extracted at room temperature in a short period (1 h) by stirring in 0.1M Na2CO3, when CP was HPUS pretreated in water (1 g:40 mL) for 20 min net time (E treatment: power intensity of ≈10 W/cm2). This PEF had low DM and was co-extracted with
Acknowledgements
The authors are grateful to the University of Buenos Aires [UBACyT 2014-2017 20020130100553BA], ANPCyT [PICT 2013-2088; PICT 2015-2109], and INTA [9.2013.5.39-2189398, PNPA 1126044] for their financial support.
References (32)
- et al.
Comparisons between conventional, microwave-and ultrasound-assisted methods for extraction of pectin from grapefruit
Chem. Eng. Process Process Intensif.
(2011) - et al.
Chemical and functional properties of cell wall polymers from two cherry varieties at two developmental stages
Carbohydr. Polym.
(2013) - et al.
Cherry fibers isolated from harvest residues as valuable dietary fiber and functional food ingredients
J. Food Eng.
(2014) - et al.
Effect of extraction conditions on the yield and chemical properties of pectin from cocoa husks
Food Chem.
(2013) - et al.
Production of antioxidant high dietary fiber powder from carrot peels
LWT Food Sci. Techn.
(2008) - et al.
Formation kinetics and rheology of alginate fluid gels produced by in-situ calcium release
Food Hydrocol.
(2014) - et al.
Optimization of microwave assisted extraction of pectin from sour orange peel and its physicochemical properties
Carbohydr. Polym.
(2016) - et al.
Carrot fiber (CF) composite films for antioxidant preservation: particle size effect
Carbohydr. Polym.
(2016) - et al.
Pectin from carrot pomace: optimization of extraction and physicochemical properties
Carbohydr. Polym.
(2017) - et al.
A new anti-adhesion film synthesized from polygalacturonic acid with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide crosslinker
Biomaterials
(2005)
Protein measurement with the Folin phenol reagent
J. Biol. Chem.
Energy changes during use of high-power ultrasound on food grade surfaces
S. Afr. J. Chem. Eng.
An overview of the traditional and innovative approaches for pectin extraction from plant food wastes and by-products: ultrasound-, microwaves-, and enzyme-assisted extraction
Trends Food Sci. Technol.
Sterilization treatments on polysaccharides: effects and side effects on pectin
Food Hydrocol.
Pectins from food waste: extraction, characterization and properties of watermelon rind pectin
Food Hydrocol.
Ultrasound-assisted extraction of phenolics from wine less: modeling, optimization and stability of extract during storage
Ultrason. Sonochem.
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2022, Food HydrocolloidsCitation Excerpt :It should be noted that vegetable by-product fractions showed higher hemicellulose content that those isolated from fruit wastes (Table 2). It has been reported that pectin from vegetables showed a lower degree of esterification than that obtained from fruits (Encalada et al., 2019b). A moderate positive correlation between GalA content and lignin content of original by-products can be explained because pectin may be more easily separated from lignin than other polysaccharides, leading to a higher pectin purity (expressed as GalA content).