Effect Of High Pressure And Heat Treatment On The Formation Of Sweet Potato Resistant Starch

With sweet potato starch as raw material, the effects of physical modification of ultra high pressure treatment and heat treatment on structure, physicochemical properties and in vitro digestibility of sweet potato resistant starch were investigated. The scanning electron microscope(SEM), X-ray diffraction(XRD), fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC) and rapid visco analyzer(RVA) were used to determine the changes of the structural, thermal and pasting properties of sweet potato starch, and the swelling power, solubility and in vitro digestibility were also tested to evaluate its physicochemical properties. The results showed that:(1) For the RGR cycle treatment at 75℃, the intensity of crystal absorption peak and heat absorption peak of sweet potato starch weaken, while its gelatinization enthalpy decreased, gelatinization temperature increased, and gelatinization temperature range got smaller. After RGR cycle treatments at 95 and 121℃, the X-ray diffraction patterns of sweet potato starches conversed from A-type to B-type, of which the fully gelatinization made the heat absorption peak disappear completely. In addition, the RGR cycle treatments resulted in the decrease of starch viscosity characteristic value, the weakening of retrogradation trend, and the increase of the slowly digestible starch(SDS) content. The SDS of sweet potato starch for one RGR cycle treatment(RGR-1) at 121 °C was highest, which was 29.25%.(2) The starch granule morphology was damaged, presenting irregular lumps after RGR treatments. The X-ray diffraction patterns of sweet potato starches changed significantly, conversing from A-type to B-type. As the increasing of the concentration and treated times, the swelling power and solubility of sweet potato starch decreased. The slowly digestible starch(SDS) and resistant starch(RS) content of sweet potato starches treated by RGR-1 at a concentration of 10% were highest, which were 29.83% and 39.82%, respectively.(3) The crystallinity of sweet potato starches was increased at low pressure level. With the increase of pressure, the X-ray diffraction patterns conversed from A-type to weaker B-type after 600 MPa HHPR treatment. Var ious viscosity characteristic value and retrogradation trend were significantly reduced(P<0.05), and the stability of paste was improved. Different with heat treated samples, ultra high pressure destroyed the hydrogen bonding, the enzyme resistance was wakened, and the digestive properties ware also improved. RS content was less than different temperature heat treated and RGR treated samples, handle up to 26.13% by 600 MPa HHPR-3 treatment.(4) The FT-IR result show that, ultra high pressure combined with heat treatment was contributed to the damage degree of particles, and the impact on the crystalline structure is greater than a single ultra high pressure and heat treatment. The conversion of crystallization type can be observed after 400 MPa,70℃ treatment. Because of the collaborative modification, gelatinization temperature was increased, and the heat absorption peak shift was obviously changed. At this time, the glass transition phase process of sweet potato starches was accelerated. With different pressure combined with heat treatment, RDS and SDS content in sweet potato starches were increased, while the RS content declined. Moreover, the digestion rate of collaborative modification was faster than HHPR treated samples, and the resistance was weakened. The sum of the RDS and SDS content of the samples treated by 600 MPa,60℃ can reach to 85.8%.