| Starch granules differing in size differs in the proportions of amylose and amylopectin and characteristics of these molecules, and in the non-starch components in starch granules such as lipids and proteins. These components and size distribution of starch granules will affect starch chemical properties, such as granule swelling, gelatinization properties, pasting/rheological behaviors. Based on differences in characteristics and properties, the proportion of different classes of starch granules in wheat flour has an effect on the quality of traditional wheat-based products. Flour from wheat cultivar Yangmai158 was use to elucidate the differences in physico-chemical properties of different classes of starch granules, and the different classes of starch granules affect pasting properties of wheat starch in this study. The main results were as follows.1 Optimization of isolated and purified of wheat starch Isolation and purification of wheat starch were affected by many factors. With the diminution of centrifugation time, the maximum particle diameter of wheat starch decreased. Ethanol can be used to extract the remanent prolamin in suspension. The optimum isolated and purified condition was as follows:centrifuged time 12 min, ethanol solvent. During the isolation of A and B type of wheat starch, the response surface method was used with the difference between the maximum particle diameter of B-type starch and the minimum particle diameter of A-type starch (BMax-AMin) as the response value. Rregression analysis of the experimental data by Design expert 7.0 indicated that the optimum sedimentation in a water column and elutriation separated A-and B-type starch granule condition was as follows:sedimentation temperature 21.3℃, sedimentation time 0.96 h, volumes 12.84 ml, sedimentation 9 times. The optimum microsieving temperature was 0℃.2 Physico-chemical properties of A-and B-type starch granules in wheat Starch granule image of scanning electron microscopy (SEM) showed that there was obvious difference in size between A-type and B-type starch granules, A-type granules are larger in size, lenticular in shape, and B-type starch granules, which are smaller in size, more spherical in shape. The A-type and B-type starch granules were completely isolated, since the starch granule type was unique in each group of starch. The parcel size of A-type starch granule was 4.45-44.46μm and contained 1.23×1010 granules per gram starch, while of B-granule was 0.47-11.16μm and 13.79×1010, respectively. By number, B-type granules comprise up to the most of granules within the wheat endosperm. The A-type granule fractions exclusively exhibited higher Amylose content than the respective B-type granule fractions. Compared with the A-type granules, B-type granules had higher pasting temperature, less viscosities of peak, trough, breakdown, final and setback. When the fraction of B-type granules(by weight) increased, the viscosities of peak, trough, breakdown, final and setback of reconstituted starch decreased, but the pasting temperature increased. B-type granules contributed greatly to the pasting properties of the reconstituted starches, when the fraction of B-type granules was less than 30%. Effects of starch granule size distribution on pasting property of reconstituted starch decreased when the fraction of B-type granules higher than 30%.3 Physico-chemical properties of different classes of starch granules in wheat Starch granule image of scanning electron microscopy (SEM) showed that the microsieving could separate the G1, G2, G3, G4 and G5. there were 14.74,6.65,1.61,0.94 and 0.36×1010 granules per gram starch, respectively, in G1, G2, G3, G4 and G5. Amylose content in G1, G2, G3, G4 and G5 was 20.38,24.01,27.16,28.39 and 27.67%, respectively. Compared with the other type granules, G1 had higher pasting temperature, less viscosities of peak, trough, breakdown, final and setback. It was found amylase content had high correlation with viscosities of peak (r=0.946, P<0.05), trough(r=0.913, P<0.05), breakdown (r=0.954, P<0.05), fmal(r=0.904, P<0.05) and setback (r=0.938, P< 0.05), but negatively correlation with swelling power(r=-0.964, P<0.01). The number of granules per gram starch was negatively correlated with amylase content (r=-0.969, P< 0.01) and viscosities of peak (r=-0.973, P<0.01), trough(r=-0.965, P<0.01), breakdown (r=-0.895, P< 0.05), fmal(r=-0.949, P< 0.05) and setback (r=-0.947, P< 0.05). G1 and G2 were correlation with pasting temperature, G3 and G5 were correlation with final viscosities, G4 was correlation with peak viscosities. In conclusion, the different classes of starch granules have differences in amylose conten t and the number of granules per gram starch. And these difference affect granule swelling and pasting properties. The different classes of starch granules affect pasting properties of wheat starch, but also the quality of wheat starch. |
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