The Study On The Preparation Of Defatted Flaxseed Peptides And Its Antioxidant Activity

After solvent extraction or mechanical compression of the oil,the residue is called?defatted flaxseed?,in which the protein content is32-49%.It is commonly used as animal feed protein but has no added value.In this thesis,two methods of were used to extract flaxseed protein from defatted flaxseed meal:ultrasonic cleaning and ultrasonic cavitation.Defatted flaxseed protein was hydrolyzed to obtain biologically active peptides,followed by vitro antioxidant activity evaluation.The results are as follows:Firstly,defatted flaxseed protein was extracted by ultrasonic cleaning and ultrasonic cavitation.The protein extraction rate of ultrasonic cavitation was 82.6%in 30min,while the protein extraction rate of ultrasonic cleaning is 52.0%in 30min.Secondly,defatted flaxseed protein was preheated and then hydrolyzed by Alcalase with different hydrolysis conditions.The hydrolyzing rate at 60?pH=9.0 was easy to control.Different sizes polypeptide chains were obtained at this condition for further antioxidant activity evaluation.Finally,the antioxidant activity of defatted flaxseed peptides were determined by DPPH assay,the ferric reducing antioxidant powder?FRAP?and the ABTS bleaching assay.The results shows that hydrolysis duration of flaxseed protein had no significant effect on DPPH free radical inhibition rate of defatted flaxseed peptides.The scavenging activity of DPPH free radicals of un-hydrolyzed defatted flaxseed protein was the lowest:EC₅₀?half maximal effective concentration?:1918.7?g/?L.After3h hydrolyzation,the scavenging activity was increased and the EC₅₀dropped to 1387.6?g/?L.The DPPH free radicals inhibition rate of ascorbic acid was much higher than defatted flaxseed peptides:EC₅₀:26.4?g/?L.After hydrolyzed for 3h,its FRAP capacity and its ABTS radical scavenging capacity was about twice that of crude protein,which was equivalent to 4160?M ferric sulphate?FRAP method?or 234?M Trolox?ABTS method?.The results showed that the smaller the molecular weight of the protein and its hydrolyzate?peptides?,the stronger the antioxidant activities of FRAP and ABTS assay is:71.88?g/?L of un-hydrolyzed protein,equivalent to 1956?M ferrous sulfate?FRAP method?or 101?M Trolox?ABTS method?.Using Alcalase can effectively control the hydrolysis rate and obtain peptides with different hydrolysis degree,which have antioxidant activities.