| Arachin and conarachin are the major fractions of peanut protein, which accounted for about80%of total protein content. At present, there is no industrial separation method of protein fractions. And thefunctional properties of the protein components feature restrict their application in the food. In this way,the application channel of peanut protein can be widened. Our research employed cryoprecipitation toseparate arachin and conarachin based on the cryoprecipitation property of arachin. Transglutaminase(TG) was employed to crosslink the protein fractions, modify their gel properties and the application ofmodified samples in sausage was achieved. Moreover, the physicochemical and structuralcharacteristics of peanut protein fractions were analyzed and compared before andafter TG modification and the modification mechanism of peanut protein components was revealed. Theresults were listed below.According to the characteristics of peanut protein components under different temperature,preparation technology was studied for its industrialization. To take the extraction ratio of arachin as anindex, a technology for extracting arachin and conarachin was studied by using cryoprecipitation. Onthe basis twice extraction, the extraction conditions were optimized by orthogonal experimental. Theoptimum extraction conditions were as follows: the rate of solution to solid5:10(w/v), pH value7.1,buffer concentration0.4mol/L, cryo-time4h. Under these conditions, the arachin extraction rate was53.60%. After the extraction of arachin, the supernatant was conarachin. The purity of arachin andconarachin was76.40%and64.10%respectively prepared by vacuum drying,74.30%and62.73%prepared by spray drying. Different type of drying exerted significant effect on the purity of peanutproteins (P＜0.05).TG enzyme was employed to crosslink peanut protein fractions and the modification process isoptimized, with gel hardness as indicator. The optimum modification conditions of arachin were asfollows: TG amount12U/g, pH value10.0, treatment time1.5h, temperature40°C. The gel strength ofmodified arachin was195.91g under the condition. Similarly, the optimum modification of conarachinconditions were as follows: TG amount15U/g, pH value7.0, treatment time2.8h, temperature40°C.The gel strength of modified arachin was100.67g under the condition. The water binding capability(WBC) and fat binding capability (FBC) of arachin were2.43g/g and2.80g/g, respectively, and theWBC and FBC of conarachin were3.26g/g and2.20g/g, respectively, which was significant (P<0.05).Through the textural analysis of emulsion fat, the usage of modified arachin/conarachin in sausage wasworkable.Physicochemical and structural properties of protein fractions were analyzed and compared beforeand after TG modification and the modification mechanism of peanut protein components was revealed.The results of SDS-PAGE showed that conarachin was more effectively crosslinked by TG than arachinwith respect to intra and intermolecular interactions. Moreover the acidic subunits (40.5、37.5、35.5kDa)was more effectively crosslinked by TG basic subunits (23.5kDa). The solubility of arachin-rich fraction is reduced by66.13%by TG-catalyzed crosslinking while the solubility of conarachin-richfraction decreased only by36.91%after TG treatment. Size exclusion chromatograph (SEC) profiles ofcross-linked arachin/conarachin have suggested that the protein crosslinked and produced highmolecular weight aggregates after TG treated. The analysis of DSC thermograms has showed that thedenaturation temperature of conarachin increased by10°C, but that of arachin is not obvious. Thecontent of free amino groups of arachin and conarachin significantly decreased after TG crosslinked(P<0.05), with decreasing degree22.5%for arachin and25.5%for conarachin. The SH content ofprotein fractions decreased gradually with the increasing of TG addition and time extension. The surfacehydrophobicity of peanut protein fractions was significantly decreased with reduction by74.6%forarachin and57.0%for conarachin.Samples of the modified protein components were applied to meat sausage, the application insausage was achieved and the addition amounts of modified fractions were confirmed. Incorporationof modified arachin and conarachin in the sausage formulation had no effect on production rate due tovacuum packing (P>0.05), maintaining99%. With the increasing addition of modifiedarachin/conarachin, the water loss rate (reduction by7.19%for arachin sausage and22.49%forconarachin sausage) and L value (lightness) of sausage reduced gradually and the difference wassignificant (P<0.05). But the a value (redness) and b value (yellowness) increased significantly (P<0.05).Compared with the control, the change of arachin colour was26.19%, and that of conarachin was53.57%. Under the condition of different addition (3%,5%,10%,15%) of peanut fractions, the gelhardness of sausage made by modified arachin/conarachin was above2000g, which indicated themodified arachin/conarachin could be applied in the sausage. The springiness decreased gradually as theincreasing of TG-treated protein fractions. There was no significant difference (P>0.05) in cohesivenessbetween control and TG-treated protein sausage samples. Chewiness values of the sausages withmodified arachin were greater than that with treated conarachin. |
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