Study On Mechanism Of Aqueous Enzymatic Extraction Of Peanut Protein And Oil Body

Peanut is an important oil crop in China.It is very important to study and develop peanut protein and oil in depth and systematically,so as to improve the value of peanut products and ensure the national safety of oilseeds.In China,aqueous enzymatic extraction of peanut protein and oil has been one of the hot research in the area of oil processing.This technology provides the products with high nutritional value and the attributes of safe,friendly environments.However this extraction method also has disadvantages,including the hydrolyzed form of proteins recovered,and a large quantity of emulsion causing difficulty of protein and oil separation.In this study,based on the sufficient research of peanut microcosmic structure,a new approach for extraction and separation of peanut protein and oil has been developed.The main idea proposed was to extract the peanut protein and oil body with the original state simultaneously through enzymolysis of peanut cell wall.This method can not only recover peanut protein and oil effectively but also provide the products with higher values and the unhydrolyzed form of proteins.The different factors affecting the extraction efficiency of peanut protein and oil body,including the effect of peanut cell microstructure,the composition of peanut,change of particle size,and different enzymatic conditions of viscozymel were researched in this study.Meanwhile,the physical and chemical properties of peanut protein and oil body extracted by viscozymel was also analyzed.The mechanism of extraction of peanut protein and oil body was further explored through cell wall degradation with viscozymel.Firstly,the effect of microstructure and composition of peanut on the extraction of peanut protein and oil body was studied.It showed that the protein content was positively correlated with the size of protein body and protein quantity,at the same time the fat content was positively correlated with the number of oil bodies but no correlation with the size of oil body.The correlation between the compositions of peanuts including protein,fat,moisture,ash,crude fiber and saturated fatty acid（C16:0,C18:0,C20:0,C22:0,C24:0）,O/L value,the amino acid content of the membrane proteins and the extraction rate of protein and oil body was studied.In terms of the extraction rate of peanut protein,the influencing factors by descending orders were showed as the following:the amino acid content of membrane proteins,O/L value,ash and protein content.With regard to the yield of oil body,the descending order of influencing factors was found as the following:saturated fatty acid（C16:0,C18:0,C20:0,C22:0,C24:0）content,O/L value,fat content,the amino acid of the membrane proteins,crude fiber content.Secondly,the effects of the change of particle size of the powders on the extraction rate of peanut protein and the yield of oil body were also studied in this research.It showed that common dried milling（the high speed universal crusher）is beneficial to the extraction of peanut protein and oil body comparing with the methods of frozen-dried milling added by liquid nitrogen and also the electric grinding.When peanut was pulverized by high speed universal crusher,the yield of oil body reached 40%with D90 77.7-80.9μm or the volume average particle size 31.8-39.0μm;and the protein extraction rate reached 81.6%when D90was 58.3-80.9μm or the volume average particle size was 20.1-39.0μm.Thirdly,the effects of enzyme types and enzymatic conditions on the extraction rate of peanut protein and the yield of oil body were studied.The results showed that the viscozymel could effectively reduce the content of cellulose,hemicellulose,and pectin in the peanut cell wall comparing with that degraded by cellulase,hemicellulase,and pectinase.Consequently a higher oil body yield was obtained.Based on this,the conditions for the extraction of peanut protein and oil body with viscozymel were optimized.The extraction rate of peanut protein and the yield of oil body were 78.60%and 48.44%respectively under the conditions of temperature 52.0℃,solid-liquid ratio 1:4,enzyme concentration 1.35%,and the time 90 minutes for enzymatic reaction.Fourthly,the physicochemical properties of peanut protein and oil body recovered with viscozymel were further studied.The results demonstrated that the extracted peanut protein powder had the similar solubility and foaming property to that of the self-made low-temperature skimmed peanut protein powder.In addition,the emulsifying activity,stability and the foaming stability of the peanut protein extracted with viscozymel were better than that obtained with the latter method.The extracted peanut oil body was stable（zeta>20 m V）at the conditions of far from isoelectric point（p H 4.8）,low salt concentration（Na Cl<10 mmo L/L）and constant temperature（35-55℃）,and there was no obvious aggregation and creaming phenomenon.The results of mass spectrometry of peanut membrane protein showed that the subunits of the proteins were 46.869 k D,44.419 k D,42.326 k D,34.112 k D,33.584 k D,25.483 k D,25.483 k D,13.413 k D,18.808 k D,15.864k D.Finally,followed by the analysis of the changes of the composition and infrared spectra of peanut cell wall under different univariate conditions via viscozymel reactions,it was found that peanut protein extraction rate and oil body yield closely related with the degradation of cell wall components through enzymolysis during the extraction process.Moreover,The degradation degree of CDTA soluble pectin and cellulose had a great effect on the extraction rate of peanut protein and the yield of oil body.Viscozymel hydrolysis achieved the effective degradation of the cell wall structure of peanut through acting on the C–O,C–C stretching,CH₂symmetric bending in the cellulose;C–O,C-C stretching in the pectin;O–C–O asymmetric stretching in the hemicellulose.