Study On Preparation,Properties And Application Of Debranched Acetylated Rice Starch

Rice starch,as a kind of natural renewable resources,has been widely used in many areas owing to its tiny particles,fine texture,unique physical and chemical properties.The functional characteristics of rice starch were apparently improved or increased by the chemical,physical or biological modification so that the rice starch was capable of being widely applied.The debranched acetylated rice starch was prepared by using rice starch as a raw material,first debranching by pullulanase,and then acetylating by acetic anhydride.The debranching degree of debranched rice starch was determined by DNS method,and the substitution degree of debranched acetylated rice starch was determined by the acid-base titration method.The effect of factors such as the amount of pullulanase,debranching time,debranching temperature and pH on the debranching degree of debranched rice starch,and the influence of the reaction time,reaction temperature,pH and the amount of acetic anhydride on the substitution degree of debranched acetylated rice starch were investigated,respectively.On the basis of single factor experiment,the reaction conditions for preparing debranched rice starch and debranched acetylated rice starch were optimized with the response surface methodology.The effects of debranching and acetylation on the blue value,freeze-thaw stability,swelling power,acid resistance,alkali resistance of rice starch were also investigated.The structure,thermal property and particle morphology of the debranched rice starch and debranched acetylated rice starch were compared and analyzed by the infrared spectrometer,differential scanning calorimeter,thermogravimetric analyzer,X-ray diffraction,polarizing microscope and scanning electron microscope.The optimal technological conditions for preparing the debranched rice starch were:amount of pullulanase 60 U/g,debranching time 2 h,debranching temperature 55 ? and pH 4.5,respectively.The optimal technological conditions for preparing the debranched acetylated rice starch were:reaction time 2 h,reaction temperature 40 ?,pH 8.5 and the amount of acetic anhydride 8%,respectively.After rice starch was modified by the debranching and acetylation,its acid resistance,alkali resistance,the surface number of hydroxyl groups and blue value increased,but its swelling capability decreased.After rice starch was modified by the pullulanase,the retrogradation increased,but the freeze-thaw stability was decreased.After rice starch being acetylated,its retrogradation decreased,but the freeze-thaw stability was increased.The onset decomposition temperature,end decomposition temperature and rate of mass loss of debranched rice starch and debranched acetylated rice starch were less than those of rice starch.It suggested that the debranching and acetylation increased thermal stability of the rice starch.The crystal structure of rice starch particles belonged to the A-type.After debranching,the crystal structure of debranched rice starch and debranched acetylated rice starch granules belonged to a B-type.The polarization crosses existed on the rice starch particles.After rice starch was branched,however,the polarization crosses completely disappeared on debranched rice starch granules,and its particle shape and size were also obviously changed.The absorption peak of debranched acetylated rice starch at the wave number 1729 cm-1 attributed to the characteristic peak of the carbonyl groups.It proved that the carbonyl groups were successfully introduced into the molecules of debranched acetylated rice starch owing to the acetylation.After rice starch was modified by the debranching and acetylation,the tensile strength and elongation at break of its film were increased.