Extraction, Modification And Processing Properties Of Rice Bran Protein By Ultrasound-Reductant

Rice bran is the main by-products produced during the rice processing. It was called providential nutrient source. The production of rice is huge in china. Currently, nutrition and function of rice bran have been applied with low added value, due to most of rice bran mainly used for animal feed. Rice bran protein is one, of the main nutritions in rice bran. It has been recognized by food scientists and consumers, because of its high biological potency, reasonable amino acid composition, high digestibility and hypoallergenic. However, due to low protein extraction and low solubility, which limit its application in rencent years. Therefore, the paper is aim to estabfish a highly green and efficient extraction technology for rice bran protein using ultrasound-reductant-assisted method; The optimal conditions of improving rice bran protein solubility was determined by different modification method, and to investigat modification emechanism from protein function and structure relationship. A theoretical basis was provided for the applycation of rice bran protein, and to expand the applications of rice bran proteins on various types of food. The main results are as follows.(1) Optimization of ultrasound-reductant-assisted extraction of rice bran protein: A combinatorial method of ultrasound-reductant was applied for rice bran protein extraction from defatted rice bran. The protein extracting ratio was used as the index to confirm the optimal condition for rice protein extraction by the response surface analysis method. To estabfish the optimum extraction conditions using regression model of four factors under the weak alkali(pH=8)and low temperature (45℃)solution condition:reductant L-cysteine concentration 0.07%, redictopn time 1.5 h, ultrasonic power 280 w, ultrasonic time 8 min. Under the optimum condition, the yield and purity of rice bran protein were 46.59% and 82% respectively. The present bran protein yield was16.62%,9.35% and 7.4%, higher than that from extraction without ultrasonic-reductant, extraction with ultrasonic wave only and extraction with reductant only respectively.(2) Optimization of the modification on rice bran protein solubility:The effect on rice bran protein solubility treated by five reductants (sodium sulfite, DTT, Vc, sodium erythorbate, L-cysteine) was compared. The results showed that sodium sulfite, L-cysteine treatment could promote the solubility of rice bran protein with significant differences (p<0.05), increasing of 3.0% and 4.8%. L-cysteine treatment showed the best on promoting the solubility of rice bran protein. Meanwhile, Vc, sodium erythorbate and DTT treatment could reduce the solubility of rice bran protein. The effect on rice bran protein solubility treated by six methods(microfluidization, microfluidization-L-cysteine, microfluidization-citric acid, ultrasound-L-cysteine, ultrasound-L-citric acid, ultrasound) was compared. The results showed that microfluidization, microfluidization-L-cysteine, ultrasound-L-cysteine, ultrasound treatment could promote the solubility of rice bran protein with significant differences (p<0.05). The combinatorial method of ultrasound-L-cysteine treatment was the most effective method, which was respectively 10.57%,8.21% and 2.51% higher than those of microfluidization, microfluidization-L-cysteine, ultrasound method; Microfluidization-citric acid and ultrasound-L-citric acid treatment decrease the solubility of rice bran protein, which was respectively 22.31% and 20.96% lower than control. The solubility was used as the index to confirm the optimal condition by the response surface analysis method. To estabfish the optimum modification conditions under the neutral (pH=7) and low temperature (45 ℃):reductant L-cysteine concentration 0.2%, ultrasonic power 320 w, ultrasonic time 10 min, rice bran protein concentration 1%. Under the optimum condition, the solubility of rice bran protein were 63.57%. The solubility of protein were increasing of 24%, compared with its control.(3) Effect of different modification methods on function of rice bran protein: The functional properties including solubility, water absorption, oil absorption, foaming and foaming stability properties and the-SH content, protein and emulsion size of rice bran proteins which were prepared by four methods(microfluidization, ultrasound, microfluidization-L-cysteine, ultrasound-L-cysteine) was compared. The results showed that the solubility, oil absorption, foaming and foaming stability and the-SH content were higher than its control. The functional properties of rice bran proteins which were prepared by ultrasound-L-cysteine treatment were best in all, and its solubility was respectively increasing of 3.5%,7.8%,5.8%, compared with ultrasound, microfluidization, microfluidization-L-cysteine. The protein prepared by four methods (microfluidization, microfluidization-L-cysteine, ultrasound, ultrasound-L-cysteine) size were respectively 114μm,162.3μm, 163.6μm and 166.2μm and emulsion size were respectively 28.6μm,30.6μm,31.6μm and 35.1 μm smaller than its control.(4) Effect of different modification methods on the secondary structure of rice bran protein:The FT-IR and CD spectrum was used to indicate the secondary structure of rice bran protein. The FT-IR result showed that:the secondary structure of rice bran protein mainly was a-helix. After treatment, the a-helix decreased, β-sheet increased. The CD spectrum result showed that:P-sheet increased after treatment, same with the FT-IR result. The results showed that pH and heat could change the secondary structure of rice bran protein with significant differences. From pH2 to pH7, a-helix increased and P-turns and random coil decreased; From pH7 to pH10, a-helix decreased and β-sheet increased, β-turns and random coil had no change. Under pH2, a-helix decreased and β-sheet increased after heating. Under pH7, a-helix decreased and random coil increased after heating. Under pH10, β-sheet decreased and β-turns and random coil increased.