Enzymatic Extraction Of Millet Bran Protein And Study On Its Properties

Millet is an important kind of food crops and a good type of cereals in our country. It is short in growth cycle, wide in adaptation environment and rich in nutrients. Millet bran is the by-product in processing of millet and used as feed or discarded in the past. However, studies have shown that millet bran contains a lot of nutrients including protein, fat and vitamins and is becoming more and more attractive. Millet bran is huge in yield, low in price and high in protein content, so it can become an excellent source of natural protein. There are a variety of grain protein extraction methods including chemical methods as Ultrasonic wave and physical methods as acid-base extraction. Enzymatic extraction is a safe and effective extraction method. Enzymatic extraction is simple in operation, mild in reaction, little in environmental impact, easy in post-processing and is a better method to maintain the natural characteristics of protein. It has a good application prospect in actual production.Shanxi millet bran was studied as raw material and the properties of millet bran protein were explored in this research. The influence of a variety of physical and chemical conditions to the functional properties of millet bran protein was also studied. Response surface experiments and orthogonal experiments were used to optimize the enzymatic extraction process of millet bran protein. This research provided a theoretical basis for the practical application in future. The findings were as follows:1. The main components content of millet bran was determined and the protein content was13.53%. Globulin, albumin, gluten and gliadin were extracted as four kinds of millet bran main protein and the content of gluten was highest. The four kinds of protein were considered to contain all17amino acids which could be detected by amino acid analyzer. The content of Glu was highest in Globulin, gluten, gliadin and the content of Leu was highest in albumin. The molecular weight of the four kinds of protein was determined in the way of SDS-PAGE. The molecular mass of globulin subunits were mainly distributed in120,85,50,23kD, gluten subunits were mainly distributed in24kD and albumin subunits were mainly distributed in85,25,17kD.2. Pectinase was screened as the enzyme used to extract millet bran protein. Factors as hydrolysis temperature, hydrolysis time, pH, account of enzyme and solid to liquid ratio which could affect the extraction rate of millet bran protein were studied. Fractional factorial experiments and response surface experiments were used to optimize the condition of protein extraction. Fractional factorial experiments showed that the hydrolysis time and solid to liquid ratio had a significant effect. Steepest ascent experiment was used to approach the maximum response region. Central composite experiments were used to study the main factors which could affect of the extraction rate of millet bran protein and establish regression equation between influencing factors and response value. The optimum extraction conditions were as followed:temperature20℃(room temperature), hydrolysis time3.93h, pH4.7, amount of enzyme1000U, solid to liquid ratio1:77. In the optimum conditions, the theoretical extraction rate of millet bran protein was32.83%and the actual results verified the predicted value.3. The millet bran residue was used to extract gliadin in the ways of ethanol extraction and acetone precipitation. The extraction conditions of gliadin were optimized in orthogonal test L9(34) which had four factors and three levels. The high and low levels of ethanol concentration, extraction temperature, extraction time and solid-liquid ratio were determined in single factor experiments. Orthogonal experiments showed that the optimum extraction conditions were ethanol concentration80%, extraction temperature40℃, extraction time40min, solid-liquid ratio1:12. In the optimum conditions, the highest extraction rate was28.43%. Above all, the total extraction rate of millet bran protein was60.57%.4. Factors as pH, temperature, NaCl concentration which could affect the functional properties of millet bran protein were studied. The isoelectric point of millet bran protein was pH3.5. The water-absorbent of protein was lowest around the isoelectric point and highest when the temperature was50℃, NaCl concentration was0.6mol/L. The oil-absorbent of protein was reduced with increasing temperature and weakest when it was heated in40℃for40min. The solubility of protein was weakest around the isoelectric point, significantly increased with increasing pH, increased and then decreased with increasing NaCl concentration. The highest value of solubility was detected when the NaCl concentration was0.4mol/L.5. The foaming property of millet bran protein decreased after increasing with raising pH and temperature, it reached the maximum in pH7.0,50℃. The impact of these two factors on the foaming stability was little. The stability slightly decreased with increasing pH and decreased after increasing with raising temperature. The highest point of foaming stability was at70℃. The emulsification property and emulsion stability of millet bran protein increased with raising protein concentration and reached the maximum when the protein concentration was1.5%. The emulsification property increased significantly in alkaline environment and the maximum value of emulsion stability was at pH7.0. The emulsification property decreased after increasing with raising NaCl concentration. The emulsion stability increased slowly when the NaCl concentration was between0.1-0.4mol/L and significantly reduced when the concentration was higher than0.4mol/L.