Effect of xanthan gum on the degradation of cereal β-glucan by ascorbic acid

Oat and barley beta-glucans are polysaccharides known for their beneficial effects on glycemia and cholesterol. These physiological effects seem to be related to increased viscosity in the digestive tract. It has recently been shown that free radicals derived from the reaction of ascorbic acid and oxygen can cause a viscosity loss in beta-glucan due to depolymerization through the Fenton reaction. However, recent studies have reported a synergistic effect between xanthan gum and beta-glucan on viscosity in heat-treated fruit juices. Therefore, the objective of this study was to determine if xanthan gum has a protective effect against OH radical-induced depolymerization of beta-glucan by ascorbic acid. Oat beta-glucan (0.4%) solutions were studied in water at pH 4. Ascorbic acid concentrations and viscosity profiles were measured over a period of 56 days. The addition of ascorbic acid caused a rapid decrease in beta-glucan viscosity. The presence of xanthan gum reduced the viscosity loss (p <= 0.0001) but did not provide complete protection for beta-glucan over time. Therefore, incorporation of beta-glucan in food formulations still presents a challenge in ensuring its physical and nutritional stability in the final product. The use of OH radical scavengers such as sugars and antioxidant compounds could be used in addition to xanthan gum to obtain improved protection. (C) 2010 Elsevier Ltd. All rights reserved.