Effects Of Pre-roasting On The Release Behavior And Quality Of Peanut Oil During The Enzymatic Aqueous Extraction Process

The enzymatic aqueous extraction technology can obtain peanut oil and proteins simultaneously,with the advantages including mild reaction conditions,environment-friendly and etc.However,there are still problems to this technique,for instance emulsification and low flavor intensity of the produced peanut oil.Due to insufficient research of the emulsification phenomenon during enzymolysis,current demulsification techniques have the drawbacks of high investment and long process time;in addition,although a few studies have been performed on improvement of flavor intensity of the extracted peanut oil by pre-roasting peanuts,they mainly focus on optimization of the pre-roasting conditions and the employed approach has the drawbacks of low efficiency and poor quality products.Based on this,infrared-radiation,oven and microwave pre-roasting were adopted to pre-roast peanuts in this study.The objectives were to investigate the effects of pre-roasting on release behavior and quality properties of the peanut oil produced during enzymatic aqueous extraction process;to further study the emulsification behavior of peanut oil as well as the stabilization mechanism of these emulsions;therefore,to provide the theoretical basis and data supporting for the optimization of the enzymatic aqueous extraction process of peanut oil.The main content and results of the research included:Peanuts were moderately pre-roasted by infrared radiation,oven and microwave respectively,and then the pre-roasting effects on yields and quality properties of the peanut oil produced during enzymatic aqueous extraction process were evaluated.The results showed that during the enzymatic aqueous extraction process,the free oil yield of peanuts pre-roasted by infrared-radiation was significantly higher than that of other peanut samples,and it was 83.51 ± 1.30%.Besides,peanut oil extracted from the infrared-radiation pre-roasted peanuts had the highest amount of tocopherol and polyphenol content,which were 478.09 mg/kg and 5.39 mg/kg respectively;the oxidative induction duration of this oil was 11.73 ± 0.14 h,which indicated the best oxidation stability.Therefore,it can be seen that the infrared-radiation technique which was of high efficiency and low damage property could be applied to peanuts during the enzymatic aqueous extraction process to increase the extraction efficiency and quality properties of the peanut oil.The microscopy was adopted to observe the changes in the microstructure of the differently roasted peanuts cotyledon and changes in the cotyledon morphology during the enzymatic extraction process;the structural and functional properties of proteins extracted from these peanuts were also evaluated,consequently,pre-roasting effects on the release behavior of peanut oil during the extraction process was investigated with the free oil yield as a reference.The results indicated that infrared-radiation pre-roasting was able to destroy the membrane of the oil bodies and consequently the oil appeared as coalesced status;besides,microwave pre-roasting also apparently disrupted the cell wall of the cotyledon cells,while the completely collapsed cell structure was observed in the oven pre-roasted samples.In addition,pre-roasting could significantly increase the solubility,the emulsifying ability and the emulsion stability of the peanut proteins,with the microwave pre-roasting has the most significant effects,which increased by 18.57%,24.66% and 455.97% respectively compared with the control.In this study,the higher difference between the total oil yield and the free oil yield,the more serious emulsification occurred.The disruptions in the microstructure of the peanut cotyledon were able to accelerate the release of oil,meanwhile,the effects of pre-roasting on the release behavior of peanut oil during the enzymatic aqueous extraction process were probably conducted by changing the functional properties of the peanut proteins.The free oil yield of the microwave roasted peanuts during the extraction process was the lowest,and this was probably related to the significantly increased emulsifying ability of peanut proteins in the microwave roasted peanuts.The oil yields,the degree of hydrolysis of proteins,the composition of the emulsions and the molecular weight distribution of the interface proteins under various extraction durations were investigated,and therefore,the emulsification behavior of peanut oil and the stabilization mechanism of these emulsions were further studied.The results indicated that during the enzymatic aqueous extraction process,peanut oil was mainly released by Alcalase 2.4L from the aqueous phase through hydrolyzing the proteins,for instance oleosins,and the effective enzymatic extraction duration was 60 min;enzymes also hydrolyzed the interface proteins,which thus changed the composition and structure of the emulsions,while there was no influence on the free oil yields was produced.With the proceeding of the enzymolysis,the major composition of emulsifiers in the emulsions changed.Within the first 60 min of the hydrolysis,proteins were the major emulsifiers.When continuing the extraction to 120 min,the interface proteins were hydrolyzed or displaced by small molecular weight proteins(polypeptides),as a result,phospholipids and cell debris substituted the proteins to be the major emulsifiers in the emulsions to stabilize the emulsions.