Studies On Lipid Metabolism Affected By Rice Proteins

Rice protein is an important plant protein which is of very high nutritional value because of its unique protein compositions. This paper starts with current studies about the separation of rice protein from rice flour. After measuring the compositions of rice protein, a series of animal experiments are also performed to investigate the effect and its regulatory mechanism of rice protein on lipid metabolism.We applied the alkali-solution and aicd-seperation method to extract rice oprotein and get an yield of 83.3%. The results indicate that the protein concentration of rice protein we extracted is 67.98%, and the protein profiles contain the glutelin fractions of 22 kDa,37～39 kDa,57 kDa and the prolamin fractions of 13 kDa,16 kDa. We also find that by this extracting method there are little differences of amino acids between rice protein and rice flour.We applied different organic solvents to extract rice prolamin and compared the results by the analysis of SDS-PAGE and yield. The results indicate that 55% isopropanol is the optimum extractant for rice prolamin. A series of single-factor experiments and an orthogonal test is then performed to define the optimum process conditions, which are proved to be 'extracting twice at 50℃for 8h with the ratio of liquid to material 10:1. This process can get a yield of 7.54mg·g-1. The extracted fraction of rice prolamin constitutes of 13 kDa and 16 kDa fractions by the analysis of SDS-PAGE.The best way to extract rice glutelin from rice flour we find is to dissolve by alkali and precipitate by acid after treatment with PBS to remove unwanted protein fractions. The glutelin extracted constitutes of the fractions of 22 kDa, 37～39 kDa and 57 kDa.7 weeks old Wistar rats are performed intragastric administration with the extracted rice protein or casein. In comparison with the control subjects, the results show that rice protein can apparently decrease the body weight gain(P < 0.05), liver weight(P < 0.05), plasma triglyceride(P < 0.05) and very low density lipoprotein(P < 0.05). It is also indicated that rice protein can lower the level of plasma total cholesterol(P>0.05 ) and low density lipoprotein(P > 0.05), but there are no significant differences. Rice prolamin is also found to have the ability to significantly lower the level of body weight gain(P < 0.05), liver weight(P < 0.05), very low density lipoprotein(P < 0.05), plasma triglyceride(P < 0.05) plasma total cholesterol(P < 0.05), low density lipoprotein(P < 0.05)and very low density lipoprotein(P < 0.05). We also find the glutelin can significantly lower the level of body weight gain(P < 0.05), liver weight(P < 0.05), and very low density lipoprotein(P < 0.05). It can also decrease the level of plasma triglyceride(P > 0.05) plasma total cholesterol(P > 0.05), low density lipoprotein(P > 0.05) without significant differences. The results show that rice protein, rice prolamin and glutelin all have a reducing effect on the plasma lipid concentration. Furthermore, we find that rice prolamin is the most efficient.After the intragastric administration we performed another free-fed animal experiment under a high-cholesterol and a high-fat diet condition to further investigate the effect of rice protein on the lipid metabolism of growing rats. The results show that under the high-cholesterol condition, in comparison with casein, rice protein can significantly decrease the level of plasma total cholesterol(P < 0.05), very low density lipoprotein(P < 0.05), plasma triglyceride(P < 0.05) and low density lipoprotein(P < 0.05). It can also significantly increase the expression level of malate dehydrogenase(P < 0.05), lipoprotein lipase(P < 0.05), and hepaticlipase(P < 0.05) in liver. At the same time, rice protein is found to have increased the concentration of free fatty acids(P < 0.05) in liver. Under the high-fat condition, in comparison with casein, rice protein can significantly decrease the level of very low density lipoprotein(P < 0.05) and low density lipoprotein(P < 0.05). It can also decrease the plasma total cholesterol and plasma triglyceride(P > 0.05) without significant differences. We also find that rice protein significantly increased the expression level of malate dehydrogenase(P < 0.05), lipoprotein lipase(P < 0.05), and hepaticlipase(P < 0.05) in liver. At the same time, rice protein is found to have increased the concentration of free fatty acids(P < 0.05) in liver.