The Preparation By Ultrahigh Pressure-enzymolysis, Properties And Application Of Wheat Resistant Starch

Resistant starch(RS) is defined as the sum of starch and products of starch degradation can not be digested in healthy individuals’ small intestine. RS has become a focus of research in recent years due to the excellent food processing properties and unique physiological functions, such as preventing diabetes, weight control, reducing intestinal disorder and the incidence of colorectal cancer, promoting absorption of vitamin and minerals. Resistant starch type Ⅲ(RS3) is the most main and important one. RS3 is safe, reliable, thermostable and has considerable prospects of industrial production and applications. In this study, wheat starch was selected as raw material and RS3 was prepared by the combination of ultrahigh pressure(UHP) and enzymolysis. Then the physicochemical properties of RS3 including water-holding capacity, resistance to hydrolysis, microstructure, viscosity and crystalline structure were determined. Furthermore, RS3 was added to wheat flour and the crisp chips were producted. In order to determine the best formula, RS3’s effects on the quality of crisp chips were studied. The main research contents and results were as follows:1. The conditions of UHP treatment were investigated by single factor and orthogonal experiments. The results showed that the optimum conditions were that the concentration of starch 20%(W/V), ultrahigh pressure 450 MPa, holding time 10 min and treatment temperature 25 ℃. The yield of RS3 was 9.85% under these conditions. The starch concentration and pressure level had remarkable effects on the yield of RS3.2. On the basis of the optimal UHP treatment conditions as described above, the reaction conditions for enzyme were studied by single factor and orthogonal experiments. The results showed that the optimal conditions were as follows: the adding amount of thermostable α-amylase 5 U/g dry starch, enzymolysis time 30 min, enzymolysis temperature 95 ℃. The adding amount of pullulanase 6 U/g dry starch, debranching treatment time 7 h, treatment temperature 55 ℃. The yield of RS3 reaches 15.16% under these conditions.3. The physicochemical properties of RS3 prepared by UHP combined with enzymolysis were studied. The results showed that compared with native wheat starch, the water-holding capacity of RS3 increased. RS3 was highly resistant to digestion by amylase. Observations by polarized light microscopy and scanning electron microscopy indicated that the granule structure was destroyed mostly. The surface of RS3 was awfully rough with obvious folds. Meanwhile, it was clear that RS3 had the crystalline structure with irregular sheet shape. The crystalline structure of RS3 determined by X-ray diffractometry changed from A-type to a mixture of B and V-type. The result of Infrared Spectrum showed there was no generation of new chemical groups during the formation of RS3. The measurements of pasting characteristics by Rapid Visco Analyzer indicated that RS3 did not gelatinize at 95 ℃, and lost pasting properties that wheat starch had.4. RS3 was added to wheat flour and the crisp chips were producted. RS3’s effects on the quality of crisp chips were studied by single factor and orthogonal experiments. The results showed that the best formula were as follows: the adding amount of RS3 20.0%, sugar 4%, salt 2%, Na HCO3 4%. The crisp chips with this formula had uniform colour and luster, pale yellow, and tasted crisp and delicious. At the same time, the RS3 content in crisp chips had small loss after microwave treatment and its retention rate could reach 85%. It showed that RS3 had good processing stability. The application of RS3 in crisp chips had certain practical significance, and the product had better healthy functions.