A method to process microalgae biomass and produce high-value chemicals from microalgae biomass is disclosed. The method uses the same biomass cells to extract more than one component such as are lipids, water-soluble chemicals, carotenoids, polysaccharides and algae meal. The method is a sequence of physical and chemical treatments. Water soluble polysaccharides produced by the method exhibit properties of low viscosity at low shear thinning. A method for extracting dietary fiber from microalgal biomass is disclosed. Compositions of water-soluble polysaccharides that are fermented slowly by colon microbiota with less gas production than commercial dietary fiber FOS are disclosed. The present inventions described herein provide a method of improving colon health by increasing butyrate during a microalgal dietary fiber fermenting process by colonic microbiota.