Enzymatic Preparation And Application Of Chinese Chestnut Slowly Digestible Starch

In order to expend the processing and utilization of Chinese chestnut, the starch was debranched with Pullulanase followed by heating and cooling to form products with high slowly digestible starch (SDS) content, which can improve the nutritional value of Chinese chestnut starch. This study mainly focused on optimizing the enzymatic preparation of Chinese chestnut SDS, then the digestibility, structure, physicochemical properties of starch were investigated. Based on above results, the modified starch was added in cookies to improve its slow digestibility.Based on the Englyst in vitro test for measuring SDS content in starch, the Box-Behnken response surface method were carried to optimize the SDS preparation after single factor experiment. The results indicated that the optimum preparation conditions were obtained as follows:the starch suspensions concentration 8%, the enzyme addition amount 8.90 PUN/g starch, hydrolysis time 6.3 h and cooling at 4 ℃ for 52.2 h. Under the optimum conditions, the content of SDS was 41.91%, which was close to the predicted value of 42.31%. Compared with the content of SDS in native chestnut starch and cooked chestnut starch, it increased 5.43 times and 1.25 times, respectively. The enzyme hydrolysis kinetics showed that in 20～120 min the hydrolysis rate of modified chestnut starch increased by 40% which can prove its slow digestibility.Observed by scanning electron microscope (SEM), native chestnut starch had smooth granule surface without sharp edges, cracks and concave, while the modified chestnut starch granules became bigger, and its surface has needle aperture. The features with stronger steric hindrance and narrow channel provide a-amylase an opportunity to hydrolysis slowly from starch granule inside to outside. The X-ray diffraction (XRD) analysis showed that the crystallization type of modified starch has changed from Cb type to V type with only a little C type characteristic. More crystal nucleus formed but the crystal is not perfect, so, it’s helpful to hydrolysis slowly.Modified starch properties including thermal properties, gel structure, swelling, absorbent and freeze-thaw stability were analyzed by differential scanning calorimetry (DSC), texture profile analysis (TPA) and other test technology. Results show that the modified chestnut starch gelatinization temperature was increased, the swelling and freeze-thaw stability not as good as native starch, the starch gel’s hardness, chewiness, cohesiveness, adhesiveness were decreased while gumminess was increased, The different properties showed that enzymatic modification has change the molecular structure, ratio of straight/branched chain and aggregation state of chestnut starch.According to the characteristics of modified Chinese chestnut starch, the different proportions of chestnut SDS were added in cookies, with non-SDS-added cookie as a control. It could be concluded that adding 25% chestnut SDS in wheat flour could improve the slow digestibility of cookies, which also had good sensory quality and structure characteristics. As a result, modified chestnut starch can be used to manufacture SDS cookies.