Structure-activity Relationship And Directed Hydrolyzing Of Lotus Seed Protein For The Protein Polypeptide

Lotus seed is a seed from the edible and medicinal lotus plant (Nelumbo nucifera Gaerten). The lotus seed is the best from Hunan province. It is reported that lotus seed with rich in protein is a quality protein resource. It shows the well balanced amino acid composition compared with the FAO/WHO pattern. The utilization of the lotus seed in the world lags behind, implying that more basic researches are needed before large-scale application. Therefore, it is very important to process the proteins and protein polypeptide with high value from lotus seeds.The protein powder treated by the process of salt extraction, acid precipitation and then spraying drying meet the enterprise standard in American. The powder has 18 different amino acids, which the content of essential amino acids is up to the FAO/WHO standard 36.0%. On the basis of the estimation of the nutritive value of lotus seed proteins, the protein powder is possesses high nutritive quality, and the process of spraying drying can keep the protein physicochemical and nutritive properties, and natural quality.Fourier transform infrared spectroscopy (FTIR) was used to investigate changes in secondary structures of the four protein fractions. The results showed that there were similar secondary structures between albumin and globulin. The contents of ordered structure fractions in the albumin and globulin extracted throught 0.1 mol/L NaCl solution were up to 55%, respectively. At the same time, those of the prolamin extrated by alcohol and glutelin by NaOH solution were only about 40%, respectively. The stabilities and structural ordering characters of albumin and globulin were higher than those of the prolamin and glutelin.The pretreated powder could be at the hydrolysis best using papain, when the seed protein suspension was pretreated by microwave with 800 W for 120 s. Response Surface Methodology (RSM) experimental design was carried out in which the effects of the four factors such as protein concentration, pH, reaction temperature and enzyme amount on degrees of hydrolysis in the reaction by papain hydrolysis were studied. The optimal conditions were 55.28℃, pH 5.6,16.48 g/L protein concentration and enzymatic concentration 0.49 g/L, when the degree of hydrolysis 34.90%. The degree of hydrolysis using the protein pretreated by microwave as the reaction substrate was higher than that pretreated by heat, which was raised by 7.47% compared to that pretreated by heat.The bioreaction mechanism and kinetic behavior of protein hydrolysis using papain inculding the process of single substrate, substrate inhibition and diffusion were investigated in order to establish a reaction-diffusion model. The kinetic parameters were obtained from the model. At the initial protein concentration from 4.68 to 13.63 g·L-1, the enzymetic reaction tallied the reaction-diffusion model with no-inhibition of substrate. When the initial protein concentration were from 13.63 to 27.26 g·L-1, the reaction was consistent with the reaction-diffusion model with substrate inhibition. The theoretical values agreed basically with the experimental values, and the relative error was 3.24%(less than 5%).