Effects of damage of Rhyzoperthadominica in different growth stages on starch composition and microstructure of wheat

Abstract: The Rhyzopertha dominica is one of the most important feeding moths in wheat storage, and it also is the most harmful pest for stored grain in the world. In order to investigate the effects of infestation by Rhyzopertha dominica in different growth and development stages on the morphological characteristics and structure of wheat starch, the temperature of (30±1)℃, the humidity of 75%±5% and the insect population density of 1000/100 g were strictly controlled to ensure the completion of one Rhyzopertha dominica growth cycle and to get the different insect states for the infected wheat. Then the crude starch content, damaged starch content and reducing sugar content of wheat, the morphological characteristics and the structure of starch granule, and the particle size and crystallinity of the wheat starch after infestation by Rhyzopertha dominica in different growth and development stages (the egg, larval, pupa and adult stages) were inspected and analyzed in this paper. The results showed that compared with the control wheat sample, the crude starch content of wheat after the infection by Rhyzopertha dominica in different growth and development stages had a decreasing tendency in a fluctuation way, and except in the egg stage when a slight increase occurred, the crude starch content in all other stages was lower than that of the control, while the content of reducing sugar and the content of damaged starch of wheat after the infection by Rhyzopertha dominica were gradually increased, and both of them were higher than that of the control. The change of median diameter was fluctuated and decreased obviously. The content of crude starch was significantly different in the 4 stages after the infestation, the content of reducing sugar was significantly different in the infested egg and adult stages, and the content of damaged starch of wheat after infestation by Rhyzopertha dominica significantly increased from the egg to adult stage from 2.42% to 5.58%. Compared with the original wheat sample, the change of X-RD (X-ray diffraction) curve of wheat starch was not obvious, and the degree of crystallinity of wheat starches fluctuated between 23.09% and 24.28%, which indicated that there was no significant effect of the infection by Rhyzopertha dominica in different growth and development stages on the crystallinity of starch. The scanning electron microscopy of starch showed that with the development of Rhyzopertha dominica from the egg to the adult stage, the surface of the starch granules in the wheat grain after the infection gradually became rough and incomplete, the shape of the starch granule became irregular, and the starch granules with small particle size increased, the damaged starch content increased, and on the surface of starch granules with large particle size appeared larger pits and damage. It is obvious that the damage by Rhizopertha dominica in different growth stages can cause the change of physical and chemical properties of wheat, and therefore it should pay much attention to the influence of larval stages of Rhyzopertha dominica on the quality of wheat during the wheat storage.