Abstract
The effect of partial acid hydrolysis on the physical and chemical properties of galactomannan, arabinoxylan, and xyloglucan was investigated. Polysaccharides were treated at 50 °C with hydrochloric acid for 3–48 h. Portions of isopropanol (i-PrOH) were added sequentially to the hydrolyzates, resulting in fractions that were collected by centrifugation. As expected, a significant reduction of weight-average molecular weight (Mw) was observed with increasing hydrolysis time. Fractional precipitation was successfully applied to collect at least one polymer fraction with dispersity (Đ) close to one for each polysaccharide. The monosaccharide composition analysis showed that the partial hydrolysis usually lowered the relative amount of side chains, with the exception of galactomannan, where the composition remained largely unaffected. Estimation of the polymer conformation in solution, through evaluation of the Mark-Houwink parameter coefficient (α), confirmed that acid hydrolysis influenced the polysaccharides’ conformation. It was demonstrated that acid treatment in dilute solution followed by fractional isopropanol precipitation is a method, extendible to a variety of polysaccharides, to obtain materials of decreased molecular weight and low dispersity with slightly altered overall composition and conformation.
Highlights
Many water-soluble polysaccharide applications are based on their physicochemical behavior in aqueous solutions
Comparing the two galactomannans after 3 and 24 h of hydrolysis, we found that the quantity of isopropanol necessary to start the precipitation was higher for GM38 (16 and 19% after 3 and 24 h hydrolysis, respectively) than for GM21 (14 and 15% after 3 and 24 h hydrolysis, respectively)
Based on the experimental results, we can conclude that the combination of acid treatment of dietary fibers and consecutive precipitation with isopropanol produces a collection of water-soluble polysaccharide fractions with a wide range of lower molecular weight (Mw) and Ð, leading to products with functional diversity
Summary
Many water-soluble polysaccharide applications are based on their physicochemical behavior in aqueous solutions. Intrinsic viscosity is strongly correlated to the molecular weight (Mw ), and the polymer conformation is affected by many parameters such as the Mw , dispersity of the sample, its degree of branching, and its connectivity in the backbone [1,2,3]. Since the solubility of a polysaccharide decreases with the increase of its molecular weight, lower Mw polysaccharides are often chosen, especially considering their applications in the food industry as functional foods. A characterization of these polymers in terms of size, dispersity, chemical composition, and conformation is essential to find a correlation between their properties and their potential industrial implementation. A study carried out by Mikkonen and colleagues [6]
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