Optimization on the Process of Chemical Modification of Apple Dietary Fiber through Orthogonal Regression Design.Technology of modification of apple dietary fiber by acid,alkali process was optimized with orthogonal regression design.The orthogonal models were established to express the relationship between temperature(X1),pH(X2),time(X3) as shown in the acid and alkali process equations:y^=-5.907+0.174X1-0.377X2+0.946,y^=3.698-0.113X1+2.816X2-1.093X3.According to these models the best condition for acid method was 96℃,3h,in pH3.7,while the alkali method was at 63℃,0.4h at pH11.6.The highest yield of SDF by acid,alkali process was 12.2% and 28.8%,respectively.Experiment results were similar with theoretical prediction of 11.8% and 28.1%.The factor order on SDF yield by acid,alkali process was temperature>time>pH,pH> time>temperature respectively.Under the modified acid,alkali process,the average water holding capacity increased 363.1%,236.4% and expansibility of SDF increased 48.2% and 52.8% compared with previous method.