Kernel Quality Properties And Extrusion Characteristics Of Maize Varieties

Maize plays an important role in agriculture, feed industry and starch processing industry in China. With the changes of diet structure, the development of starch and oil industry, and the exploitation of bio-energy, as the corn crop, maize's industrial status also grow rapidly. Maize breeding selection has gradually transferred from output to the output and quality both to be the same important. Special corn breeding and production have been taken attention. The research on the qualities of maize varieties has become more and more important. For the best use of maize resources, intensive processing and enhancing the comprehensive value, researching on maize qualities and processing characteristics is of great significance.Extrusion, a high processing technology which makes full use of mixing, stirring, staving, heating, cooking, sterilization, extrusion and shape, is widely used in food and feed industry. In order to produce convenient and new leisure foods with high nutritional value, delicious and various flavors, extrusion will be the focus of food industry. Research on the processing characteristics is the basic work for the development of the maize industry. Maize is the main material for the extruding processing. Reports on the processing characteristics of maize have been reported mostly abroad, but there is no specific review in China, particularly in the systematic research of extrusion.The research took maize varieties from the Huanghe, Huaihe and Haihe plain, China's main maize-producing zone, as experiment material; analyzed the quality properties of maize varieties systematically, and studied the relationship among many qualitative properties of the various maize; The extruding equipment was a Brabender Lab-station of DSE-25 Twin-Screw Extruder (Brabender OHG, German) , on which extrusion properties were studied. The research also had established a systematical parameter regression model between the processing parameters and product properties, analyzed the grain's extrusion characteristic, and optimized the processing parameter of maize extrusion.Main results are as following:Under the same ecological condition, different maize variety properties have different. The differences in 100-kernel weight, 100-kernel volume, crude grease content, crude fiber content, grits ratio and the gelatinization properties were significance, but there are no significance differences in crude protein content, ash content, hardness index, milling ratio, pasting temperature. Through the factor analysis, the appraisal factors of maize quality were selected, which were the processing factor, physical factor, nutrition factor, color factor, fiber factor and the hardness factor; and its characteristics information representation was 83.27%.The material moisture content, the feed rate, the screw rate as well as the processing temperature make extremely complex influences to the maize's extrusion properties and system parameters, and their relationships were not the simple linear relations. The processing parameter, the product properties as well as the system parameters were the quadratic model. The material moisture content and the processing temperature influenced the extrusion properties mostly, the feed rate had a less influence, and the screw rate had the least influence on extrusion properties. With the increase of the material moisture content, the product water content, water-absorption index (WAI), bulk density, product hardness and the shearing stress increased; when reducing the material moisture content, water-solubility index (WSI), radial expansion ratio, color difference, torque, pressure difference as well as specific mechanical energy (SME) trend to be higher. By increasing the extrusion processing temperature, WSI and the shearing stress increased, but the product water content, WAI, radial expansion ratio, color difference, hardness, torque, pressure difference and SME had a decreasing tendency. Feed rate had a positive effect on radial expansion ratio, product temperature, torque, pressure and output, but it had a negative effect on bulk density and SME. With the increase of screw rate, SME increased, but WAI, torque and pressure difference reduced.The properties of various maize extrudates were significant different but the system parameters were small under the same extrusion conditions. The sowing time had a remarkable influence on the maize extrusion properties. Comparing with the summer maize varieties, the spring maize varieties had higher radial expansion ratio, higher WAI, higher output, lower WSI and lower SME. The extrusion characteristics of maize varieties were correlated with the physicochemical properties. Extrudes of maize varieties with higher starch content, lower protein content and lipid content had higher radial expansion ratio, lower bulk density, lower hardness, higher torque, higher 5th zone pressure and SME. The lower protein content, higher starch content varieties may produce products which have a great volume expansion index. Pasting-parameters of maize varieties could be used to predict the extruded qualities and system parameters in the procedures of extrusion. Regulating sowing time may improve physical properties, pasting characteristics and extrusion qualities of maize varieties.The special maize had great differences in their quality characteristics. Both Popping maize and common maize had higher hardness, glassiness rate, and were suitable for processing maize grits; High-oil Maize and waxy maize were quite suitable for maize flour. Comparing to the common maize flour, the waxy maize flour had the lower gelatinization temperature, setback and the final viscosity; the gelatinization temperature of Popping maize flour was higher, break-down was lower, the cold paste stability was better; while the peak viscosity of high-oil Maize flour was the lowest, and the cold paste stability was the worst. The differences of the gelatinization characteristics between special maize varieties were influenced by content, composition of starch, and other ingredients. The extrusion characteristics of special maize were different. Extrudates of the high-oil Maize had high bulk density, WAI as well as the color difference. Extrudates of waxy maize had high WSI, hardness, shearing stress, radial expansion ratio, WAI, and the color difference, while the extrusion system parameter (torque, the 4th pressure, the 5th pressure, pressure difference, SME) were smaller. For the extrusion product of Popping maize, radial expansion ratio was large, and the system parameter was high when extruded. Popping maize had a good extrusion characteristic, which was suitable to process an extrusion product; Waxy maize is suitable for the extrusion products with good solubility, while high-oil maize was not suitable for processing extrusion food.