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Abstract
We prepared humo-pectic hydrogels through ionotropic gelation by crosslinking natural pectins of different degree of methyl-esterification with either humic substances (HS) extracted from cow manure compost or humic-like substances (HULIS) from depolymerized lignocellulose biorefinery waste. The hydrogels were characterized by solid-state 13C-NMR spectroscopy, scanning electron microscopy, spectroscopic magnetic resonance imaging and rheological analyses. Their ability to work as controlled release systems was tested by following the release kinetics of a previously incorporated model phenolic compound, like phloroglucinol. Our results indicated that the release properties of hydrogels were influenced by the molecular composition of HS and HULIS and by the different degrees of methyl-esterification of pectins. The hydrogel made by the high methoxyl pectin and HS showed the fastest rate of phloroglucinol release, and this was attributed not only to its morphological structure and crosslinking density but also to the least formation of ionic interactions between phloroglucinol and the polysaccharidic chains. Our study suggests that the efficiency of novel humo-pectic hydrogels as sustainable carriers of agroproducts to crops is related to a careful choice of the characteristics of their components.
Highlights
In recent years, natural polymers have attracted increasing attention due to their natural abundance and widespread applications as biomaterials
We prepared humo-pectic hydrogels by crosslinking, in the presence of calcium ions, pectins of different degrees of methyl-esterification with either humic substances (HS) extracted from cow manure compost or humic-like substances (HULIS)
Our results showed that hydrogels composed by pectins only and those obtained by combining pectins and HULIS had a greater capacity to control the release of a model compound than hydrogels prepared by blending pectins and HS
Summary
Natural polymers have attracted increasing attention due to their natural abundance and widespread applications as biomaterials. Pectins are biodegradable and biocompatible polymers located in the primary cell wall and middle lamella of many plants [1]. They are widely used in the pharmaceutical and food industries for a large number of applications, such as gelling agents, thickeners, stabilizers and emulsifiers [2,3], as well as carriers for nasal, ocular, and oral drug delivery [4,5,6,7] and wound healing [8]. HGA is the major component of pectic polysaccharides and consists in linear polymers, mainly composed of α-(1→4)-DMolecules 2020, 25, 2936; doi:10.3390/molecules25122936 www.mdpi.com/journal/molecules
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