Preparation of β-cyclodextrin/polysaccharide foams using saponin

Abstract

Cyclodextrins, cyclic oligosaccharides with a hydrophobic cavity that form inclusion complexes with nonpolar molecules, can be used to functionalize other polysaccharides. Xanthan gum, locust bean gum or chitosan can be crosslinked using citric acid in the presence of β-cyclodextrin to produce insoluble matrices. In this work, polymeric foams based on those polysaccharides and saponin have been prepared using a green synthesis method to increase the porosity of the matrices. The saponin of soapbark (Quillaja saponaria) has been used to obtain foams using different procedures. The influence of the synthesis path on the porosity of the materials and their corresponding sorption capacities in the aqueous phase were evaluated.

Keywords: chitosan; cyclodextrin polymers; green synthesis; locust bean gum; saponin; sorption; xanthan gum.

Figure 1

Quillaja saponin foamability (left) and foam stability over time for the β-cyclodextrin/polysaccharide (CS: chitosan, LBG: locust bean gum) mixtures (right).

Figure 2

SEM images of crushed β-c-LBG as a function of the synthesis pathways (see below, Experimental section). Part “45Pow” of Figure 2 was reprinted from [39], Carbohydrate Polymers, vol. 288, by M. Petitjean; N. Lamberto; A. Zornoza; J. R. Isasi, “Green synthesis and chemometric characterization of hydrophobic xanthan matrices: Interactions with phenolic compounds“, article no. 119387, Copyright 2022 The Authors, with permission from Elsevier. Published by Elsevier Ltd, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, https://creativecommons.org/licenses/by-nc-nd/4.0/. This content is not subject to CC BY 4.0.

Figure 3

SEM of β-c_sp after crosslinking with or without washing the sample.

Figure 4

β-c_sp (left) and c-CS_sp (right) matrices unwashed showing the “foam-like” morphologies.

Figure 5

Values (in mg/g) of equivalent ‘free β-cyclodextrin’ in the polysaccharide (PS) matrices, as a function of the synthesis path (top), and comparisons between the liquid and foam saponin matrices with (bottom left) or without cyclodextrin (bottom right).

Figure 6

1-Naphthol isotherms of crosslinked β-cyclodextrin/polysaccharides (blue curves for chitosan, red for locust bean gum, green for xanthan gum) with saponin (yellow curves correspond to cyclodextrin matrices, without polysaccharide).

Figure 7

Sorption of phenols (V, vanillin; Ph, phenol; m-c, m-cresol; 4eP, 4-ethylphenol; Eu, eugenol) in β-cyclodextrin/polysaccharides (xanthan, XG; chitosan, CS; and locust bean gum, LBG) with saponin (sp) produced by different pathways (liquid and foam).

Figure 8

Six synthesis routes (*lyophilized matrices) used to prepare samples β-c-XG_sp; β-c-LBG_sp; β-c-CS_sp using β-cyclodextrin (β), citric acid (c), xanthan gum (XG), locust bean gum (LBG) and chitosan (CS) with saponin (sp) in different physical forms (see also Table 1).