Use of Nam Dokmai ripe mango peel waste as a potential source of pectin, and its pharmaceutical applications

Abstract

This study aimed to utilize ripe mango (Mangifera indica cv. Nam Dokmai) peel by-product as a source of a low methoxy! pectin produced by de-esterification for pharmaceutical applications. In this study, pectin from mango peel (MPP) was extracted by microwave-assisted extraction and analyzed its physicochemical properties in comparison with commercial low methoxyl pectin (LMP) possessing 29% degree of esterification (DE). The results revealed that MPP contained 75% galacturonic acid (GalA). Its DE determined by titration and 'H NMR was 79% which classified the MPP as a high methoxyl pectin (HMP). In FTIR spectra, the carboxymethyl ester (1732 cm-1) and free carboxylic peaks (1637 and 1404 cm-1) were observed in both LMP and MPP. Furthermore, specific different bands did not appear in comparison between LMP and MPP. Both LMP and MPP exhibited same pattern of TGA curves displaying 3 regions. Water sorption kinetics showed that LMP possessed higher adsorption capacity than MPP. The Guggenheim-Anderson-de Boer (GAB) model showed that the LMP exhibited higher water sorption than MPP did because of the higher number of carboxylic groups. De-esterification experiment was designed by central composite design to plot surface response curve. Optimal condition to obtain 29% DE was 3.05 mL of 1 N NaOH at 25'C. The prepared de-esterified pectin (DP) from MPP was classified as LMP (29.40 % DE) with 69 % GalA. The prepared de-esterified pectin (DP) was compared to commercial LMP with 29 % of degree of esterification (DE). FTIR spectra of DP was similar LMP and MPP. Moreover, the spectra indicated that pectin backbone was not changed by de-esterification process. The carboxymethyl ester (1740 cm-1) and free carboxylic (1600 and 1420 cm-1) peaks ere also observed in DP, LMP and MPP. Interestingly, LMP and DP films exhibited insignificant difference (p > 0.05) in puncture strength (13.72 ± 1.85 and 11.13 t 0.64 N/mm2 for LMP and DP films, respectively), percent elongation (2.75 ± 0.29 and 2.52 ± 0.44 % for LMP and DP films, respectively) and Young's modulus (67.69 ± 3.35 and 61.79 ± 4.45 N/mmP for LMP and DP films, respectively). De-esterified pectin containing clindamycin HCI (DPC) and low methoxyl pectin containing clindamycin HC1 (LMPC) films demonstrated 93.47 ± 4.71 and 98.79 ± 2.69 % of drug loading content, respectively. Mechanical properties of LMPC and DPC films were improved perhaps by their crystal structures and a plasticizing effect of clindamycin HC1 loaded into the films. DPC film exhibited similar drug release profile as compared with LMPC film. In antibacterial test, LMPC film showed 41.11 ± 0.33 and 76.30 ± 0.98 mm of growth inhibition zones against S. aureus and C. acnes, respectively. Whereas DPC film showed 40.78 ± 0.37 and 74.04 ± 1.12 mm of the growth inhibition zones against S. aureus and C. acnes, respectively. Antibacterial activity of the LMPC film, the DPC film and clindamycin commercial product was not significantly different (p > 0.05). The results of this study suggest that mango peel pectin can be de-esterified and utilized as an LMP and the de-esterified pectin has the potential for use as a film forming agent, similar to LMP. In addition, the remarkable use of de-esterified mango peel pectin to prepare films, as shown by our study, holds a great promise as an alternative material for an anti-bacterial product.