Oat Protein Isolate:Extraction, Protein Subunits And Functional Properties

Oat is a special crop in Shanxi Province. Oat protein is of higher quality among the plant proteins. In this work, a range of physicochemical tests were applied to oat protein isolated by two methods from a new oat cultivar named JinYan14. To optimize the extraction process of oat protein, alkali-extraction and acid-precipitation method and enzymatic method were carried out respectively. Then SDS-PAGE was used to analyze the protein subunits. The functional properties of oat protein including solubility, water-holding capacity, oil-holding capacity, foaming properties, emulsifying properties, viscosity and gel characteristics at different pH, temperature and ionic intensity were analyzed.Results:The optimum process conditions of alkali-extraction and acid-precipitation method were as follows:pH10.11, liquid-to-solid ratio15.96:1, temperature50.87℃and digestion time93.56min. Under these conditions, the yield of oat protein could amount to64.23%, with purity of86.4%, and the isoelectric point (pI) of oat protein was4.2with the isolation rate of94.65%. In the process of enzymatic method, the proteases were sifted first among alkaline protease, neutral protease and acidic protease, and alkaline protease was selected with the highest yield. The optimum process conditions with alkaline protease were as follows:enzyme dosage (E/S)100.36U/g, enzymolysis pH10.5, liquid-to-solid ratio18:1, enzymolysis temperature53.49℃and enzymolysis time60min. Under these conditions, the yield of oat protein could amount to84.09%, with purity of89.16%, which is higher than that of alkali-extraction and acid-precipitation method. The pI of oat protein was4.4, with the isolation rate of93.33%.SDS-PAGE analysis suggested that the quantity and content of protein subunits were different according to their extracting methods, but they had something in common. The bands of oat protein ranged from14.0to65.2ku, and most of them concentrated on38.1-40.0ku and20.8～20.9ku. Besides, compared with alkaline method, enzymatic method had several bands deletion:58.6ku、53.0ku、42.5ku、29.3ku、28.0ku、25.7ku. And the content of macromolecular subunits of EOPI decreased, while that of micromolecule subunits increased.The functional properties of oat protein isolated by the two methods were quite different under the same experimental conditions. The functional properties of oat protein isolate extracted by alkali-extraction and acid-precipitation method (AOPI) including water-holding capacity, oil-holding capacity, foaming capacity, foaming stability, emulsifying stability and gel characteristics (springiness, cohesiveness, chewiness, adhesiveness) were better than that of enzymatic method (EOPI).But solubility, emulsifying capacity, viscosity and other gel characteristics (fracture, hardness) were worse than that of EOPI.Moreover, pH, temperature and ionic intensity had significant effects on the functional properties of oat protein.(1) Influence of pH on the functional properties of oat protein:The nitrogen solubility index (NSI), foaming properties, emulsifying capacity and viscosity reached the minimum at pI, while emulsifying stability was the maximum. When pH was far away from pI, NSI, foaming properties, emulsifying capacity and viscosity gradually increased, but emulsifying stability decreased.(2) Influence of temperature and ionic intensity on the functional properties of oat protein:NSI, foaming stability, foaming capacity, emulsifying capacity and viscosity increased with the increasing of temperature and ionic intensity at first and then followed by a decrease.(3) Oat protein could form protein gel under the conditions of pH7.5～8.0, temperature95～100℃.