| Cottonseed is richest in China. The by-product of cottonseed after oil extraction, cottonseed meal, had high protein content and cheap price. It was a kind of important protein resources for exploitation and utilization. Due to the limitation of gossypol toxicity, studies mainly focused on detoxification to feed animals. Preparation and properties of protein was seldom researched at present. Using pre-pressed cottonseed meal as material, this article systematically studied cottonseed protein production, including protein concentrate production and the extraction of isolated protein, and the functional properties, in order to provide an alternative effective approach for deep utilization of cottonseed meal.Firstly, cottonseed meal was hydrolyzed with Viscozyme L and glucoamylase, and then immersioned by alcohol to preparate protein concentration. The result illustrated that, glucoamylase 1600 U/g, ViscozymeL 0.60 fbg/g, solvent/solid ratio 10, 50℃to hydrolyzed 140 min, then 70% ethanol concentration, solvent/solid ratio 7, 60℃dipped 2 times, every time 45 min. The protein content of cottonseed protein concentrate was 64.39%.Secondly, cottonseed protein isolate (CPI) was extracted by alkaline extraction and acid precipitation. According to the single factor and response surface methodology, the optimum conditions were determined: pH11, temperature 60℃, solvent/solid ratio 16.5, reaction time 105 min. The protein extraction rate was 67.27%, the purity was 86.16% and the yield was 56.02%. Then, the remaining dregs were further hydrolyzed by Alcalase. The ratio of extraction was 24.42%. The total extraction ratio was improved to 91.69% by two steps extraction.Thirdly, physicochemical and functional properties of protein extracted from the high and low temperature pretreatment cottonseed meal were researched. Result indicated that, amino acid composition of CPI was completed and the content was rich. Besides Lys, the content of the other amino acids was fully above the recommended intake for children from 2 to 5 years old by FAO/WHO. Through protein classification, we conclude that main protein of high-temperature pretreatment meal wad globulin and gluten, and low-temperature pretreatment meal was globulin and albumin. The denaturalization temperatures of protein from high and low temperature pretreatment meal were 87.27℃, 92.73℃respectively. Carbonyl content and hydrophobicity of high temperature pretreatment peotein increased. SDS-PAGE analysis showed the protein was mainly composed of eight bands with molecular weights: 59.7 kDa, 53.6kDa。Functional characteristics of CPI were inferior to SPI. The environmental factors, such as pH, salt concentration, temperature etc. could affect functional properties. With appropriate increasing of salt concentration and temperature, functional characteristics were improved. Effect of salt concentration on protein from low-temperature treatment meal was especially significant. Compared with two proteins,we could conclude that when cottonseed oil was extracted and processed, protein denaturalization resulted in declined extraction ratio, nutritional value and functional properties. It illustrated the process of oil extraction was important to the later treatment of cottonseed meal.Finally, cottonseed protein was enzymatic modified using Trypsin. With the increase of hydrolysis, solubility increased. The solubility of DH3.47 was 88.10% and DH11.34 was 92.40% at pH7, increased by 67.70% than before. Emulsifying activity was best at DH6.37, which was 130.44 m~2/g, improved by 87.30%. The higher hydrolysis degree could result in improvement of foaming ability, at DH11.35 which was 170%, increased by 120%. Therefore appropriate enzyme hydrolysis could improve functional properties of cottonseed protein obviously.
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