Effects of 3 Processing Methods on the Physicochemical Properties, Structural Characteristics, and in Vitro Hypoglycemic Activity of Insoluble Dietary Fiber from Mulberry Leaves

In this study, mulberry leaves insoluble dietary fiber (MIDF) was prepared by enzymatic method, acid alkali method and enzymatic complex acid alkali method with the residues of water extracted mulberry leaves from 'Morus alba L. cv. Longsang 1' in Heilongjiang Province as raw material. The effects of different preparation methods on the physicochemical properties, structure characteristics and hypoglycemic activity in vitro of MIDF were investigated. The results showed that the changes of MIDF physicochemical, structure properties and hypoglycemic activity were related to the extraction method. Compared with mulberry leaves water extract residue (RMIDF), all the three preparation methods significantly reduced crude protein and starch content, as well as particle size. Conversely, these methods enhanced oil holding capacity, viscosity and α-amylase inhibition ability (P<0.05). The surface structure of the sample treated by acid alkali method (CMIDF) was more loose and had the highest viscosity. The MIDF prepared by enzymatic method (EMIDF) showed the highest cellulose content of 49.78%±0.93%. The method also had the maximum water holding capacity (4.83±0.04 g/g), water swelling capacity (2.70±0.24 mL/g) and oil holding capacity (3.26±0.21 g/g). The MIDF prepared by enzyme complex acid alkali method (ECMIDF) exhibited the highest hemicellulose content (36.11%±0.31%) and the smallest particle size. Furthermore, this method displayed the greatest specific surface area, as well as superior in vitro hypoglycemic activity, with glucose adsorption and α-amylase inhibitory capacities 2.44 and 1.85 times higher than those of RMIDF, respectively. Comprehensive analysis showed that the specific surface area of MIDF was larger by acid alkali method, and the physicochemical properties of MIDF could be improved by enzymatic method. The structural modification and increased viscosity resulting from the two methods combined of ECMIDF contribute to enhancing its hypoglycemic activity.