Preparation And Properties Of Slowly Digestible Starches

Slowly digestible starches were defined as starches which were digested completely in small intestine of human, between 20 to 120 minutes, but the speed was slow. At present people prepared SDS mainly by enzyme, physical and chemical methods. This paper used waxy corn starch as material systemly studied to prepare SDS by debranching enzyme and recrystallization, octenyl succinic anhydride modifying, and hydrothermal treatment, then researched properties and mechanism of SDS.Firstly, SDS was prepared by Pullulanase debranching then recrystaled. The effects of amount of Pullulanase, debranched time and recrystallization time on SDS content were studied. When concentration of Pullulanase was 20ASPU/g, debranched time was 6 hour and storaged 3 days at 4℃, content of SDS was 21.26%. The properties of SDS were determined by Scanning Electron Microscopy (SEM), x-ray dirffaction and Differential Scanning Calorimeter (DSC). Results showed that starch granule appearance changed remarkly and structure disappeared. Compared with native starch, crystal form of starch changed from A to B type, besides, DSC determination showed that To,Tp,Tc all increased,△H decreased remarkly, and these change had good relation with SDS content.Secondly, SDS was prepared by octenyl succinic anhydride modifying. Researches showed that introduced big chemical group in favour of SDS formation by hindering enzymolysis, in addition, SDS content increased and digestibility reduced constantly as the degree of substitution improved. Compared with native starch, these modified starches had low pasting temperature, high peak viscosity, solubility and degree of swelling improved a lot. Besides, thermal parameters such as To,Tp,Tc and△H all reduced. Esterified starches still maintained A type crystal structure.Thirdly, SDS was prepared by two kinds of hydrothermal treatment such as Annealing and Heat-Moisture Treatment (HMT). The effects of temperature, moisture and time on SDS content by annealing were investigated, and concluded that SDS content reach up to 8.35% when moisture was 60%, temperature 55℃and action time was 36 hours. Annealing changed starches'properties obviously, improved SDS content and reduced digestibility because of long time hydrothermal treatment. As far as HMT was concerned, the effect of treatment temperature, moisture and time on SDS content were also studied, when moisture was 35%, temperature 120℃and treated time was 10 hours, SDS got 9.25% maximum, reduce digestibility remarkly by generating SDS and Resistant Starches. Compared with native starch, HMT made swelling power, viscosity reduce, pasting temperature, To,Tp and Tc increase, but didn't change crystal structure.In conclution, by studying these three kinds of preparing methods on SDS content and starch digestibility. Considered that method of enzyme-debranching and recrystallization could achieve a good deal of SDS, which was very potential for SDS preparation.