| Currently,the use of sorghum is mainly focused on starch bioconversion,but there were very few studies on sorghum protein.In this paper,sorghum protein was extracted by two methods including alkaline process and extrusion-amylase synergistic method,and then the ACE inhibitory peptides were prepared by enzymatic hydrolysis with protease to enhance the utilization efficiency of sorghum protein.The study provides a theoretical basis for the high-value processing and utilization of sorghum protein.The main experimental results were as follows:The crude protein content(Dry base)of sorghum flour used in this experiment was 10.17%.The effects of NaOH concentration,solid-liquid ratio,extraction temperature and time on the extraction yield of sorghum protein were studied.The orthogonal experiment optimization conditions were as follows:NaOH concentration 0.15%,solid-liquid ratio 1:14,temperature 40 ?,reaction time 1.5 h,and the extraction yield of protein was 21.57%under these parameters.Finally,the purity of protein was 85.47%,and the digestibility in vitro was about 74.32%.It was shown from analysis of the amino acid composition of the protein(SP1)that sorghum is rich in aromatic amino acids,hydrophobic amino acids,branched chain amino acids,thus sorghum alkali soluble protein was ideal protein material to prepare ACE inhibitory peptides.Trypsin?papain?protamex?alcalase and flavourzyme were applied to hydrolyze the sorghum,and the alcalase was choosen to be the best one for the enzymatic hydrolysis through the comparison of hydrolysis degree and ACE inhibition rate.The effects of substrate concentration,enzyme concentration,pH,temperature and reaction time on the ACE inhibition rate of the hydrolyzate were investigated by single factor test.On this basis,taking ACE inhibitory rate as response value,Box-Behnken design and response surface methodology(RSM)were used to optimize the enzymolysis conditions.The results showed that the optimum conditions were as follows:amount of enzyme was 2360U/g,pH 7.95,enzymatic temperature at 55.5 ?for 1.68h,and the inhibitory rate of ACE was 75.98%.Sorghum flour was pretreated by extrusion under different temperature and material moisture content.Then add high temperature alpha amylase to extract protein after extrusion.With moisture content and extrusion temperature increased,the extraction yield and purity first increased and then decreased.The in-vitro digestibility of sorghum protein is also affected by extrusion conditions,which increased with increasing moisture content and extrusion temperature.ACE inhibitory peptides were prepared from sorghum protein.The inhibition rate and degree of hydrolysis increased with the increase of moisture content,extrusion temperature and amylase content.The optimum extraction conditions were obtained by orthogonal test as follows:amylase content of 2U/g,moisture content of 19%and extrusion temperature of 165?.The purity of sorghum protein was 79.23%,and the extraction rate was 83.2%.It was shown from analysis of the amino acid composition of the protein(SP2)that the sorghum protein was also rich in aromatic amino acids,hydrophobic amino acids,branched chain amino acids.The ACE inhibitory peptides(ACEIP1 and ACEIP2)were prepared by hydrolysis of two kinds of sorghum protein(SP1 and SP2).The half inhibitory concentration IC50 and stability of hydrolysates were compared.The results showed that IC50 value of ACEIP1 and ACEIP2 were 2.05mg/ml and 1.96mg/ml,respectively.Stability tests showed that both ACEIP1 and ACEIP2 has goodresistance toacid,alkaline,intestinal enzymes digestionandthermal stability.Considering the efficiency of protein extraction method and the feasibility of production,ACEIP2 was purified by gel filtration chromatography Sephadex G-25.The two ACE inhibitory activity components la(IC50=1.084mg/ml)and Ib(0.244mg/ml)were isolated.The results showed that small molecular weight polypeptide components have high ACE inhibitory activity. |
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