Study On Ultrasound-assisted Nitrogen-protected Extraction Of Rapeseed Meal Polyphenols And The Synergistic Antioxidant Activity Of Polypeptides And Polyphenols

Rapeseed meal is often treated as a waste after rapeseed oil extraction,which contains polyphenols with high biological activities.Therefore the polyphenols of rapeseed meal lack of utilization.In order to exploit and utilize these resources and overcome the problem of reducing polyphenols activities by free radicals produced by traditional ultrasonic extraction,this study used ultrasound-assisted nitrogen-protected extraction?UANPE?to extract polyphenols from rapeseed meal.Firstly,the inhibition effect of nitrogen filling on free radicals induced by ultrasound was studied by iodine release test.Then,the effects of UANPE on the yield,activity and morphology of rapeseed meal polyphenols were studied.The antioxidant synergism of polyphenols and polypeptides was also studied.Based on this,the molecular mechanism of antioxidant activity of rapeseed meal extracts was preliminarily explored.The main conclusions are given as follows:?1?When nitrogen was filled in the process of ultrasound,the iodine production decreased significantly.The reaction of iodine release under nitrogen-protected ultrasound treatment fits to zero-order reaction kinetics equation,and the rate of iodine release fits the formulation ofV?28?f?7?x?8??28?a?10?bx?10?cx²?10?dx³.Electron paramagnetic resonance?EPR?and hydrogen peroxide content measurements also show that nitrogen filling can significantly reduce the amount of free radicals which were produced by ultrasonic treatment.After ultrasound treatment with nitrogen filling,the hydrogen peroxide content in water changes from 4.40 ug/mL to 2.10ug/mL,which shows that nitrogen filling could inhibit the production of free radicals and effectively prevent the chain reaction of free radicals and the loss of polyphenols'activities.?2?The EC₅₀0 values of DPPH free radical scavenging,ABTS free radical scavenging and iron ion reducing of polyphenols extracted by UANPE are 5.51 mg/L,8.31 mg/L and 59.22 mg/L,respectively.These EC₅₀0 values are lower than those extracted by UAE.The semi-inhibitory concentrations of polyphenols extracted by UANPE on inhibiting the growth of Caco-2 and HepG2 cancer cells are 43.76 ug/mL and 47.58 ug/mL,respectively,which are lower than those extracted by UAE.The results show that the antioxidant activity and anti-proliferation activity of polyphenols extracted by UANPE are stronger than those extracted by UAE.All these results indicate that nitrogen protection can effectively reduce the damage of free radicals to RPs which is induced by ultrasound.Atomic force microscopy?AFM?results show that nitrogen protection can reduce the contact area between RPs and free radicals to minimize the oxidation damage of free radicals to RPs.In addition,UANPE is optimized to extract RPs from rapeseed meal,and the optimum parameters are obtained as follows:60%of ethanol concentration,30?of extraction temperature,1:30 of solid-liquid ratio,5 L/min of nitrogen filling rate,20 min of ultrasonic nitrogen filling time,320 W/L of ultrasonic power density.Under these conditions,the yield of RPs is 13.02 mg/g,and the EC₅₀0 of scavenging DPPH free radicals is0.236 mg/g.?3?The antioxidant interaction between RPs and polypeptides is studied.The antioxidant activity of the two substances is determined after mixing.Crude RPs and crude polypeptides show obvious synergistic effect on scavenging DPPH free radicals.Because of the difference of antioxidant mechanism and reaction conditions,the two substances show the antagonistic effect in reducing power determination.After separation and purification of these two compounds,the concentration and purity of crude RPs increases by 38.59%and 50.38%respectively,EC₅₀0 of scavenging DPPH free radicals decreases by 15.42%,and EC₅₀0 of reducing power increases by 34.98%.In scavenging DPPH free radicals assay,the RPs and polypeptides with different molecular weights?<3 kDa,3 kDa⁵ kDa?show synergistic antioxidant effect.All these results indicate that RPs and polypeptides have the synergistic effects on scavenging DPPH free radicals.