| As a big power of cultivating walnut,China is far ahead because of its large leads in production and development around the world.Compared with other plant protein resources,walnut kernel is high in nutritious value and essential amion acid,which has health function in reducing the risk of coronary heart disease.At present,walnut kernel is mainly considered as an important oil resource,because walnut oil is rich in unsaturated fatty acid and can be sold as um-market edible oil.However,walnut residue after removing oil is generally discarded or processed to cheap fertilizer even if it still includes abundant protein.Consequently,the utilization of walnut residue is extremely insufficient.In order to recycle and utilize walnut kernel expeller efficiently for the purpose of turning the waste into treasure,six protein fractions(albumin,globulin,prolamine,glutelin-1,glutelin-2 and total protein)from walnut kernel expeller were fractionated and characterized.Their nutritional value,physicochemical properties,antioxidant activity and ACE inhibition were also investigated.By experiments,the main conclusions were as follow:1.The major components of walnut kernel expeller protein were glutelin-2(50.77±0.31 g/100g),glutelin-1(21.90±0.02 g/100g),globulin(14.89±0.42 g/100g),albumin(6.63±0.11 g/100g),prolamine(5.81±0.05 g/100g)in turn.Thereinto,glutelin-2 were the predomiant fractions.2.Each walnut kernel expeller protein fraction had its own amino acid composition.All of them were rich in glutamine and arginine,but lack of sulfur-containing amino acid.However,they were still conform to the recommended conditions of FAO/WHO.Relatively speaking,the amino acid composition of walnut kernel expeller total protein was more balanced and its nutritional value was superior overall,which was determined by some factors such as amino acid constitution,contents of essential amino acid,existence of limiting amino acids,digestibility in vitro and so on.3.Among all six protein fractions,the solubility of albumin was the greatest.And for surface hydrophobicity,analysis results of albumin,glutelin-2 and prolamine were better than glutelin-1 obviously.What's more,all of walnut kernel expeller protein fractions showed favourable emulsifying,foaming properties and viscosity at low ionic strength.4.Albumin,and prolamine exhibited higher DPPH radical scavenging activity,97.15%and 93.35%respectively at the same concentration,while globulin showed the lowest scavenging activity.For the reducing power to the Fe2+,prolamine and total protein were both apparently higher than that of BHT which was synthetic antioxidants in contrast.With regard to the hydroxyl radical scavenging activity of protein fractions in the same condition,prolamine(111.20%),total protein(52.80%)and globulin(48.80%)had outstanding performances.And all six protein fractions were higher than the superoxide radical scavenging activity of BHT.Moreover,glutelin-1(50.77%)and total protein(53.61%)possess the inhibiting ability to ACE.5.The optimal enzymolysis technology of walnut kernel expeller total protein,which was obtained by means of hydrolysis through endonuclease(alkaline protease)and single factor test with response surface analysis,was as follow:enzymatic temperature 55.74?,pH 8.79,enzyme amount 5852.82 u/g,substrate concentration 4.06%.The degree of hydrolysis could reach to 10.67%ultimately.6.After the purification that was carried out by chromatographic column of Sephdex G-25,the enzymatic hydrolysate of walnut kernel expeller total protein obtained three fractions whose inhibition rates to ACE were 63.72%,75.91%and 71.67%respectively.And the fraction owning best inhibition ability obtained two components after purifying by chromatographic column of Sephdex G-15.Their ACE inhibition were 55.34%and 76.11%successively. |
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