Preparation, Structure And Characteristics Of Slowly Digestible Starch From Waxy Wheat Starch

Slowly digestible starch (SDS), as a novel functional food and ingredient, could be digested slowly in the gastrointestinal tract, and plays an important role in maintaining the stability of postprandial blood glucose and prevention of diabetes and obesity. So SDS is becoming a hot topic in the fields of food science and modern nutrition. In this study, waxy wheat starch was isolated from waxy wheat by the alkali treatment. Three different physical methods including repeated-retrogradation treatment, temperature-cycled-intermittent retrogradation treatment, and ultra-high pressure-retrogradation treatment were used to prepare SDS from waxy wheat starch, and their structural characteristics and formation mechanism were investigated.Firstly, repeated-retrogradation treatment was used to prepare SDS from waxy wheat starch, and the effects of slurry concentration, gelatinization temperature, retrogradation time interval, and the times of retrogradation on the formation of SDS were investigated. Under the conditions of slurry concentration of 50%(w/v), gelatinization temperature of 110 ℃, retrogradation time interval of 48 h, and dual-retrogradation (DR) treatment, the content of SDS reached up to 44.41%. Compared with native waxy wheat starch, X-ray diffraction patterns of the treated samples were altered from A-type to B-type, and the relative crystallinity of those decreased to different extents; the thermodynamics parameters decreased dramatically; scanning electron micrographs revealed that the starch granuals were destroyed and the surfaces of those exhibited a net-like structure with numerous cavities to different degrees.Secondly, temperature-cycled-intermittent retrogradation treatment was used to prepare SDS from waxy wheat starch, and the effects of slurry concentration, gelatinization temperature, temperature-cycled condition, temperature-cycled retrogradation time interval, and individual retrogradation time on the formation of SDS were investigated. Under the conditions of slurry concentration of 50%(w/v), gelatinization temperature of 110 ℃, temperature-cycled condition of 4/25 ℃, temperature-cycled retrogradation time interval of 36 h, and individual retrogradation time of 3 d, the content of SDS reached up to 42.24%. Compared with the native starch sample, X-ray diffraction patterns of the treated samples were altered from A-type to B-type, the relative crystallinity of those decreased, and the value of △H decreased, but the pasting temperature and peak viscosity increased. Meanwhile, the effects of temperature-cycled-intermittent retrogradation, temperature-cycled-continuous retrogradation, isothermal-intermittent retrogradation, and isothermal-continuous retrogradation treatments on in vitro digestibility and structural characteristics of starch samples were investigated.Thirdly, ultra-high pressure-retrogradation treatment was used to prepare SDS from waxy wheat starch, and the effects of slurry concentration, treatment time, ultra-high pressure, retrogradation time on the formation of SDS were investigated. Under the conditions of slurry concentration of 10%(w/v), treatment time of 30 min, ultra-high pressure of 600 MPa, and retrogradation at 4 ℃ for 4 d, the content of SDS reached up to 31.12%. X-ray diffraction patterns of treated starch samples varied differently across the pressure intensity. With the increase in the pressure intensity the relative crystallinity of treated samples decreased, the pasting temperature changed, the peak viscosity decreased, and the destruction degrees of treated starch samples increased,In conclusion, the investigation on the effects of the above three different physical treatments on the content of SDS and the characteristics showed that temperature-cycled-intermittent retrogradation treatment was the best one among these three methods to prepare high quality SDS from waxy wheat starch, and was also potential for SDS preparation.