Studies on polysaccharides from leaf skin of Aloe barbadensis Miller: Part II. Structural characteristics and molecular properties of two lower molecular weight fractions

Abstract

Aloe barbadensis Miller (Aloe vera) has long been used in food, cosmetic and pharmaceutical industries. The solid wastes such as the spikes and the outer green skins are usually separated from the inner gel and discarded during the process of Aloe vera leaves. Three kinds of polysaccharides (designated as ASP-4N, ASP-6N and ASP-8N) were successfully purified from the leaf skin of Aloe vera in our previous work. The present study aimed to analyze the structural and molecular features of ASP-6N and ASP-8N using methylation and GC-MS, NMR, high performance size-exclusion chromatography coupled with multi-angle laser light scattering (HPSEC-MALLS) and scanning electron microscopy (SEM) techniques. Results showed that ASP-6N and ASP-8N were β-(1→4)-glucomannans with acetyl groups, which may attach to O-2, O-3 or O-6 of mannopyranosyl residues in the backbone as mono-, di-, or tri-acetylated forms. HPSEC-MALLS analysis indicated that the polysaccharide fractions from Aloe leaf skin adopted various conformations in the aqueous solution depending on their molecular mass. The polysaccharides had fibrous, ribbon-like and spherical morphology by SEM observation.