| Peanut protein is an excellent plant protein with high nutritional values. The protein content of the peanut cake is high, but it has not been fully utilized and was wasted extremely. In this paper, preparation of peanut protein isolate was researched from peanut cake through a traditional method of alkali extraction and precipitation. The components of PPI and its subunits, nutritional and functional properties were comprehensively studied. In addition, the edible films of peanut protein isolate were prepared and applied to tomatoes fresh-keeping successfully. The results aimed to provide reference and new approaches to making good use of peanut protein isolate.The main research results were as follows:The extraction technique of peanut protein isolate was optimized via response surface methodology. The results showed that the optimum extraction conditions were as follows:liquid-solid ratio 9:1, pH 9.0, extraction temperature 62℃, extraction time 60 min, under such conditions, the extraction rate of peanut protein isolate was up to 90.92%, the purity of it can reach 91.34%, which was consistent with the predicted value.There were 17 major subunits in the peanut protein isolate with Mr 13.7,14.3,16.8, 20.6,24.3,25.3,31.1,35.0,38.1,46.7,48.6,52.8,76.2,82.6,93.4,109.9,134.8 kDa. After the purification by ammonium sulfate and gel filtration of Sephacryl S-200 HR, Native-PAGE and SDS-PAGE showed that PPI had 3 major components, they were arachin, conarachin and 2S protein respectively. Amino acid analysis indicated that amino acid contents of PPI were fully above the recommended intake for people by FAO/WHO.The functional properties of peanut protein isolate were studied. The water holding capacity and oil binding capacity of PPI were both highest at protein concentration about 4% or the temperature 40℃. The solubility of it was highest at the temperature 70℃, when pH<4.0 or>7.0, the PPI solubility reached above 90%. Both emulsion capacity values and emulsion stability values of PPI were about 50% at protein concentration 0.4%, ionic concentration 0.6% or pH<4.0 or>7.0. Foaming ability and foaming stability were lower relatively.The gelatin of PPI was formed with excellent properties at the lowest protein concentration 16%, the denaturation temperature of it was 70℃. The rheology properties and texture profile properties were shown that the gelatin of PPI was formed easier at pH 3.0 than pH 7.0; the salty ions decreased the capability of PPI to form the gelation. Compared with Na+, Ca2+ was advantageous to form the strong gelatin in the protein.The properties of the edible peanut protein isolate films were studied, the effects of different additives on the films were significantly. The properties of peanut protein isolate films added 0.4% dodecanoic acid were mostly improved, especially on water vapor permeability properties(4.90 g/h·m2); the second was the film added 1% starch and the third was the film added 0.2% glucose. The results of tomatoes fresh-keeping with film coat showed that the coated film could restrain the loss of water, hardness reduction and prolong the shelf-life of the tomatoes effectively. |
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