| Cottonseed meal, contain abundant cottonseed protein, is an important proteinresources to be developed in urgent need in China. The key problem is the existence ofpoisonous free gossypol in cottonseed, leading to low utilization of cottonseed meal.Previous studies have mostly focused on application of cottonseed meal in feed afterdegossypoled, preparation of edible cottonseed protein isolated, however, is seldomresearched. Using degossypoled cottonseed meal as material, this paper mainly studythe extraction and preparation of raffinose and cottonseed protein from cottonseed meal.In addition, functional properties of cottonseed protein isolated is also explored forfurther utilization of cottonseed meal.Initially, degossypoled process in liquid-liquid phase was conducted to obtaincottonseed meal with0.016%content of free gossypol after treated, less than0.045%required by Food and Drug administration of America, which pave the way to preparingedible isolated cottonseed protein as follows.Then, raffinose with6.52%content was extracted from cottonseed meal using acidsolution. The influence of single factor on the leaching rate of raffinose was analyzed,based on which, the order of factors that affect the leaching rate of raffinose wasidentified by orthogonal experiment: ratio of meal to liquid> temperature> time> pH.At the same time,91.5%leaching rate of raffinose was achieved under optimal processconditions: ratio of meal to liquid was1:10, temperature was65℃, time was90min, pHwas2.0.Later, membrane separation technology was used to purify and concentrate theraffinose leaching solution. Comparing the purification process of microfiltrationmembrane A and microfiltration membrane B as well as the concentration process ofnanofiltration membrane DK and nanofiltration membrane DL, microfiltrationmembrane A was selected to purify raffinose leaching, the raffinose transmittance was97.8%and the retention rate of impurities was34.8%. Nanofiltration membrane DL wasselected to concentrate the raffinose leaching, the retention rate of raffinose was99.7%,and the purity of raffinose was98.2%after be dried.After that, cottonseed protein isolated was prepared by alkaline extraction and acidprecipitation. Single factor experiments demonstrated the order of factor that affect theextraction rate of cottonseed protein: pH> temperature> time> ratio of meal to liquid.Meanwhile, optimal conditions were determined by response surface methodology: pHwas11.6, temperature was60℃, time was2.0h, ratio of meal and liquid was1:15. Inthis condition, the extraction rate of cottonseed protein was80.37%and the purity ofcottonseed protein was90.63%, the content of free gossypol in cottonseed protein was0.015%. The isoelectric point of the cottonseed protein was measured to be pH=4.6. andthe remaining cottonseed protein in residue was hydrolyzed by alcalase. Under optimalconditions(pH was9.5, the amount of enzyme was240U/g, temperature was60℃, time was3.0h), the enzymatic extraction rate of protein was9.5%. The cottonseed protein inacid extraction solution and enzymatic solution were mixed, the total extraction rate ofcottonseed protein was17.7%and the purity of cottonseed protein was62.14%.Finally, physicochemical and functional properties of cottonseed protein isolatedwere researched. The results showed that, amino acids in cottonseed protein isolatedwere in full range and reasonable form. Except for methionine, the content of otheressential amino acids were above the standard which FAO/WHO recommended. Thedenaturalization temperature of the cottonseed protein isolated which extracted fromcottonseed meal was68.35℃, hydrophobicity was256.7, water absorption ability was3.87g/g, and oil absorption ability was2.02g/g. The solubility, foaming ability andemulsifying activity were easily influenced by pH. Deviating more from the isoelectricpoint, better performance can be obtained. In other words, the performance was theworst when at the isoelectric point of the cottonseed protein. |
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