Studies On Processing Quality Of Waxy Corn Flour And Different Milling Method

Waxy corn has the important food application value. This study was focused on the processing quality of waxy corn flour in order to provide theory foundation for processing, which has great significance for advancing the traditional and new food developing, providing appraisal means on waxy corn breeding and promoting waxy corn deep processing. Seven different varieties of waxy corn grain and three milling methods as dry milling, wet milling and extrusion milling was used, while glutinous rice flour and waxy corn starch was adopted to compare with it. This report also discussed the influence of different milling methods of waxy corn flour on processing quality. The main results were as follows:1. There was less difference of the starch content among different varieties of waxy corn, whose main difference lied in protein content and fat content, the variation coefficient were 8.74% and 16.84% respectively. The different milling method had great influence on the damaged starch. The extrusion milling damaged the starch granule easily, so the flour has more damaged starch content. It had great difference in damaged starch content and protein content among waxy corn flour, waxy corn starch and glutinous rice flour.2. The flour from different varieties of waxy corn had the great variation degree in Breakdown, Peak, Trough and Final viscosity with variation coefficient of 48.14%, 30.01%, 30.03% and 25.72% respectively. The variation coefficient of Setback was 13.36%, while the Peak Time and Peak Temperature had the least among the pasting parameters. The correlation coefficient of waxy corn flour between Peak and Trough, Final viscosity and Setback, Trough and Setback, Trough and Final Viscosity, Final Viscosity and Setback both exceed 0.938, which were significant at 0.01level. Waxy corn flour had stronger Peak, Trough, Breakdown, Final Viscosity and Setback compared with waxy corn starch and glutinous rice flour. Waxy corn flour had great expansibility and showed strong combining capability with water during pasting.3. Waxy corn flour had stronger soluble rate, expansibility and combing ability with water than waxy corn starch and glutinous rice flour. Waxy corn flour showed great transparency and stability. It was less digestible than glutinous rice flour. Waxy corn flour had better freeze-thaw and less gelation characteristics than glutinous rice flour.4. Waxy corn flour was pseudoplastic fluid and showed shear thinning flow as waxy corn starch and glutinous rice flour in rheological properties. Its rheological model behaved in accordance with the power lawτ=k·γm. Different varieties of waxy corn had the same basic rheological model. The glutinous constant k had the great variation coefficient of 55.05%, while the fluid character index m had less variation coefficient of 3.92%. Factors showed great influence on rheological properties of waxy corn flour. The higher the temperature was, the lower the shear stress and apparent viscosity was. Waxy corn flour had the greatly concentration effect at 6%, when the concentration was lower than 6%, the glutinous constant k rose with concentration rising, while the concentration was higher than 6%, the glutinous constant k dropped with concentration rising. For pH value, waxy corn flour showed trough value when pH value was 5, once the pH value exceeded 5, the shear stress and apparent viscosity rose with pH value rising. Medium such as sugar, citric acid and salt can remarkable reduce the shear stress and apparent viscosity. Waxy corn flour had good anti-shear stability and commonly thixotropy.5. The pasting parameters of wet milling method remarkably exceeded dry milling method and extrusion milling method. The wet milling method showed excellent forming paste ability, the best expansibility and fairly good transparency, the best freeze-thaw ability, gelation characteristics, the strongest anti-retrogradation ability among the three milling methods. The flour paste from wet milling method had the best shear stress and apparent viscosity and exhibited excellent sticky character compared with others method under the same temperature and shear rate. The extrusion milling method had not obvious pasting procedure. The fluid character index of flour paste from extrusion milling method was near 1, which showed Newtonian Fluid character. The extrusion milling method had the best soluble rate and the worst paste transparency, less water retaining capability, greatest acidolysis rate and the lowest enzymolysis rate. The dry milling method had good anti-retrogradation ability, water retaining capability and paste stability. Altogether the dry milling method had medial properties among the three milling methods.