Molecular weight of guar gum affects short-chain fatty acid profile in vitro

Dietary fibre intake prevents chronic diseases and maintains health. Usual dietary fibre intake is about half that found to protect against cardiovascular disease and body weight gain so strategies to increase fibre content of foods are needed. Barriers to higher fibre consumption include low intakes of whole grains, vegetables, fruits and legumes and the difficulty formulating processed foods with higher fibre content. Viscous fibres such as guar gum are difficult to incorporate into processed foods and drinks unless they are hydrolysed. The low viscosity of partially hydrolysed guar gum (PHGG) makes it easy to use in beverages and food systems, but questions remain about its physiological effectiveness. To determine whether molecular weight of guar gum affects fermentation, we measured the fermentation of four molecular weight guar gums by in vitro batch fermentation with human faecal inoculum. Samples were removed at 0, 4, 8, 12, and 24 hours and total short chain fatty acids (SCFA), acetate, propionate, and butyrate were measured by gas chromatography. Molar ratios of acetate were slightly, proportionally related to molecular weight, while molar ratios of propionate were slightly, inversely related to molecular weight. Molar ratios of butyrate were not related to molecular weight. These results show that molecular weight of PHGG affects short chain fatty acid production. Thus, modified guar gums, made less viscous to add to processed foods and drinks, have different fermentation patterns than native guar gum. Viscosity of fibres must be considered when predicting physiological effectiveness of fibre.