Abstract: Response surface methodology was employed to optimize the process parameters for enzyme-assisted alkaline extraction of soluble dietary fiber (SDF) from defatted coconut flour. A quadratic polynomial model was built and validated. The yield of SDF was investigated with respect to four variables, enzyme concentration, enzymatic hydrolysis time, alkali concentration and alkaline hydrolysis time. The optimized conditions were as follows: enzyme concentration (α-amylase + glucoamylase, 1:1) 0.5%, enzymatic hydrolysis time 50 min, NaOH concentration 5%, and alkaline hydrolysis time 40 min. Under these conditions, the yield of SDF was 11.78%, and the water-holding capacity, swelling-capacity and oil-holding capacity of the SDF obtained were 3.8 g/g, 3.1 mL/g and 5.2 g/g, respectively. Infrared spectral analysis indicated that there were a large number of hydrogen bonds in the associated state in the SDF. HPLC results indicated that the SDF was composed of 9 monosaccharides, with mannose, galactose, galactosamine and gum sugar being predominant (537.21, 39.48, 40.38 and 15.83 mg/L, respectively).

Key words: defatted coconut flour, soluble dietary fiber, response surface methodology, monosaccharide composition