Abstract: In order to prepare the high-quality dietary fiber,ultra high pressure (UHP) processing was used to study the effects on dietary fiber from Malus asiatica Nakai residue.These parameters such as ratio of solid to liquid,pressure and processing time were optimized by response surface methodology.The physical and chemical properties such as the water holding capacity(WHC),oil holding capacity(OHC),swelling capacity(SC) and functional properties of the dietary fiber processed by UHP were analyzed.And the microstructure and functional groups were characterized by scanning electron microscopy(SEM) and infrared spectra.The results showed that the optimum preparation conditions were as follows:pressure was 300 MPa,processing time was 15 min and ratio of solid to liquid reached 1∶19.30(g/mL).Under the optimum processing conditions,the SDF content,WHC,OHC,SC,cation exchanging capacity,cholesterol adsorption amount and glucose adsorption capacity of the dietary fiber processed by UHP were 21.71%,7.81 g/g,8.03 g/g,7.20 mL/g,0.78 mmol/g,14.31 mg/g and 8.20 mg/g,respectively,compared with untreated samples,it had a significant improvement(P<0.05).Meanwhile,the dietary fiber from M. asiatica residue processed by UHP was observed with SEM and showed that the microstructure was irregular shape,loose and porous surface with lattice-like and flake-like structure.The infrared spectra analysis showed that the characteristic absorption peaks of cellulose,hemicelluloses and lignin were found in the dietary fiber processed by UHP.

Key words: Malus asiatica Nakai residue, dietary fiber, ultra high pressure (UHP), response surface methodology optimization, microstructural characteristics