Virk and Sogi (2004) extracted pectins from apple peel using HCl and citric acid and also observed that citric acid was more effective than HCl in terms of yield. As showed in Table 5, CA-HYP fraction presented low moisture content (2.7 g/100 g) with high carbohydrate content (64.0 g/100 g CA-HYP), followed by proteins and phenolics (13.8 and 9.4 g/100 g, respectively). Monosaccharide composition showed that CA-HYP contains mainly uronic acid (65.1 g/100 g fraction). Rhamnose and galactose were found in higher proportions than the other monosaccharides. Similar monosaccharide composition was found for pectins from sugar beet pulp (Morris & Ralet, 2011), Améliorée mango peels ( Koubala et al.,
2008), okra ( Sengkhamparn, Verhoef, Schols, Sajjanantakul, & Voragen, 2009) and optimized cacao pod www.selleckchem.com/products/apo866-fk866.html husks pectin obtained with nitric acid ( Vriesmann, Teófilo, et al., 2011). The proportion of GalA Ivacaftor units methyl-esterified at C-6 in relation to the total GalA units defines the degree of methyl-esterification (DE), which classifies pectins as high-methoxyl
(HM pectins, DE > 50%) and low-methoxyl (LM pectins, DE < 50%). Degree of acetylation (DA) is the proportion of acetyl groups in relation to the total GalA units of the pectin. Both the DE and DA have a significant impact on pectin functional properties, influencing solubilization and gelation properties (Rolin, 1993). In contrast to native pectins (very often HM with low acetyl content) (Voragen Thymidylate synthase et al., 1995), CA-HYP contained low-methoxyl pectins with high acetyl content (DE: 40.3%; DA: 15.9%; Table 5). LM pectins highly acetylated were also obtained from sugar beet pulp (Yapo, Robert, Etienne, Wathelet, & Paquot, 2007) and okra (Sengkhamparn et al., 2009). 13C NMR spectroscopy of CA-HYP (Fig. 3) allowed the investigation of its chemical
structure. Signals of esterified and un-esterified units of α-d-GalA from homogalacturonans were identified at δ 100.0 and 99.3, respectively, with their respective C-6 signals at δ 170.6 and 173.5, from methyl ester carbonyl carbons and carboxyl carbons, respectively. Signals of methyl carbons of esterified carbonyls in GalA units appeared at δ 52.8, whereas those of acetyl groups appeared at δ 20.4. Rhamnogalacturonans were also identified in CA-HYP. Characteristic signals of C-1 and CH3-6 signals from Rha units appeared at δ 98.5 and 16.6, respectively. The anomeric region also showed signals at δ 103.3 and 102.4 from β-1,4-d-Gal units (substituted or not at O-6, respectively). In the aromatic carbons region, signals at δ 115.1, 116.2, 144.0 and 154.8 were identified, suggesting the presence of phenolic compounds. All assignments were based on literature values ( Vriesmann, Amboni, et al., 2011; Vriesmann, Teófilo, et al., 2011; Westereng, Michaelsen, Samuelsen, & Knutsen, 2008).