Process Improvement On Aqueous Enzymatic Extraction Of Peony Seed Oil And Investigation On Protein Properties

Peony seeds contains 29%?34%oil,in which has high level of linolenic acid,tocopherol and polyphenols;protein content is 18%?22%,which is a kind of plant protein with the abundant of amino acids composition.Enzyme assisted aqueous extraction process(EAEP)can obtain peony seed oil and proteins simultaneously.It also has the advantages including mild reaction conditions,excellent oil quality,and high utilization rate of by-products.However,the process has the drawbacks of complicated steps,low oil yield and high cost of enzyme.In order to simplify the process and reduce the cost based on the preliminary research in the laboratory.The acid soaking plus roasting pretreatment were adopted to extraction of peony seed oil process in this study.The objectives were to investigate the effect of the pretreatment on extraction of peony seed oil,quality of the oil,and the peony seed protein properties.The main content and results of the research included:Firstly,peony seeds were pretreatment by acid soaking plus roasting,and soaking plus roasting.The effect of pretreatments on yields of oil and oil quality were studied.Acid soaking plus roasting improved oil yields.The results of confocal laser scanning microscope(CLSM)showed that the effect of acid soaking plus roasting pretreatment destroyed the cell structure.Based on the pretreatment,the optimal extraction conditions were obtained as follows:peony seeds were soaked in 0.15 mol/L citric acid solution for 6 h and dried at 100?.Solid-liquid ratio 1:5,the 0.50%(w/w)pectinase enzymolysis for 1 h,50?,pH 4.5,alkaline extraction at pH 9,50? for 1 h and residue was further extracted by aqueous phase at pH 9,50? for 1 h.Under the above conditions,total oil yield reached 90.81%.Therefore,compared with the ethanol-assisted aqueous enzymatic extraction process,acid soaking plus roasting pretreatment was simpler and more effective,the consumption of pectinase reduced by 22.60%,and water consumption reduced by 28.60%.Meanwhile,acid soaking plus roasting pretreatment could not significantly affect the fatty acid content and composition.The quality of oil was in line with the standard peony seed oil.Secondly,the effect of acid soaking plus roasting pretreatment on the properties of peony seed protein were investigated.Acid soaking plus roasting pretreatment caused denaturation of peony seed protein.It showed that the protein structure was partially unfolded,then surface hydrophobicity of peony seed protein increased.From SDS-PAGE,the pretreatment caused the dissociation of large molecular weight subunits into small subunits.In addition,the denaturation temperature of peony seed protein decreased from 106.20? to 103.10?,and denaturation enthalpy decreased from 7.38 J/g to 2.02 J/g.The change of peony seed protein structure further affected functional properties.Solubility decreased from 85.06%to 69.17%at pH 7.0.The emulsify ability reduced to 78.75 m2/g,while the emulsify stability improved.Acid soaking plus roasting pretreatment improved fat holding capacity,which increased to 6.53 g/g.In terms of foam properties,foam ability and foam stability were improved.Moreover,the effect of acid soaking plus roasting pretreatment on emulsifying properties of peony seed protein was investigated.The results showed the pretreatment caused denaturation of peony seed protein,and solubility reduced by 15.89%,which affected emulsifying ability of peony seed protein.At 5 mg/mL of protein concentration,the d43 and flocculation index of the peony seed protein emulsion obtained by pretreatment were larger than that of the untreated.As the concentration increased to 30 mg/mL,the d43 and flocculation index gradually decreased,which effectively inhibited the floating in emulsion.According to LCSM,low protein concentration cannot encapsulate the oil droplets,causing the droplets to flocculate;high protein concentration can well wrap oil,which indicated that high concentration can reduce adverse effect of acid soaking plus roasting on emulsifying ability of peony seed protein.Finally,peony seed proteins treated by different pretreatment were added to sausage.The results showed that protein treated with acid soaking plus roasting can improve the cooking loss rate(8.57%)of sausage significantly.And the protein also improved hardness,elasticity,chewiness of sausage.During storage,the hardness and elasticity were better maintained.The total phenol content in the peony seed protein obtained by the pretreatment was 3.11 mg/g,which greatly improved the oxidation stability of sausage during storage.