Transfer Of Phospholipids During The Enzyme Assisted Aqueous Extraction Of Peanut Oil And Its Effect On The Oxidative Stability Of Oil

Enzyme assisted aqueous extraction processing?EAEP?is a green method for edible oil extraction,employing pure water as the main extraction medium with the assistance of food-grade enzyme.Oil and protein can be obtained at the same time during EAEP of peanut oil,and the method has advantages of mild reaction condition,high crude oil quality and high resource utilization rate,thus it has gained much interest.With the development of technology and processing equipment,the EAEP of peanut oil has achieved industrialized.The first production line of EAEP of peanut oil was established in Nantong,Jiangsu province,with daily disposal capacity of 50 tons of peanuts.Yet,some theoretical problems in EAEP are worthy of research.Phospholipids are bioactive substances,widely existed in oilseed cells.The effect of phospholipids on the oxidative stability of lipids is still controversial,because phospholipids may be prooxidants or antioxidants in different systems.During traditional oil extraction technologies,most of the phospholipids in oilseeds are trapped in crude oil.However,the processing of enzyme-assisted aqueous extraction technology of edible oil is totally different from that of traditional oil extraction technologies,and the transfer regularity of phospholipids and their effect on the oxidative stability of oil have not been reported in EAEP.In this dissertation,on basis of the establishment of phospholipids determination method,the transfer,transformation,and partition of peanut phospholipids during EAEP were investigated.After that,the effect of phospholipids on the oxidative stability of EAEP peanut oil was discussed.The main research contents and results are as follows:Firstly,a method was established for the determination of phosphatidylcholine?PC?,phosphatidyl ethanolamine?PE?,phosphatidylinositol?PI?and phosphatidic acid?PA?in raw material,intermediate products,and final products during EAEP of peanut oil by direct-injection HPLC-ELSD.A modified Folch method was used to extract the total fat and the crude extract dissolved in the mobile phase was taken directly into HPLC.The HPLC method was performed on a column of L-Si?250 mm×4.6 mm,5?m?by gradient elution using hexane-isopropanol?2:3,v/v?and hexane-isopropanol-0.025 mol/L CH₃COONH₄?3.6:5.4:1,v/v/v?as the mobile phases,detected by evaporative light-scattering detector.The correlation coefficient of standard curve for each phospholipid in linearity range was more than 0.995,as well as the recoveries of the four phospholipids in peanut were 93.59%¹08.57%with the relative standard deviations?RSDs?no more than 10%at three spiked levels.Secondly,the fate of peanut phospholipids was determined by direct-injection HPLC-ELSD method.The results showed that 22.9%of phospholipids were lost during crushing,and water addition raised a 238.6%increase of PA.57.5%of phospholipids suffered degradation after retained at 60°C for 5 h.Only 19.8%of total phospholipids ended up in cream phase,skim phase and solid phase,and 52.5%of them trapped in cream phase.93.5%of residual PI existed in cream phase.The determination of phosphorus content of crude oil was carried out according to the colorimetric molybdenum blue method.The phosphorus content of crude oil demulsified by various treatment differed from 22.16 to 31.61 mg/kg.Thirdly,ESR was employed to evaluate the effect of phospholipids,?-tocopherol,and TBHQ on the oxidative stability of EAEP peanut oil and purified peanut oil.The results indicated that,when the concentration of PC was below 1000 mg/kg,it had no effect on the oxidation of purified peanut oil,yet it could accelerate oxidation after increasing its concentration.PE inhibited the oxidation of purified peanut oil when its concentration was below 250 mg/kg while accelerated oxidation when its concentration was above 2500 mg/kg.When EAEP peanut oil contained 500 mg/kg PC or 250 mg/kg PE,the phospholipids acted as effective antioxidants.?-tocopherol inhibited EAEP peanut oil oxidation at low concentration and was ineffective at high concentration.TBHQ significantly enhanced the oxidative stability of both purified peanut oil and EAEP peanut oil at just 25 mg/kg.Finally,Schaal oven-storage method was applied to estimate the influence of commercial phospholipids on EAEP peanut oil.The results showed that EAEP peanut oils which added respectively 250 mg/kg lecithin,500 mg/kg lecithin,100 mg/kg cephalin or 200 mg/kg cephalin exhibited better oxidative stability than blank oil,for the peroxide value,conjugated diene and triene value and p-anisidine value were lower during the storage at 62°C for 20 d.