Study On The Phenolic Acids And Their ?-glucosidase Inhibitory Activity In Coix Lachryma-jobi L.Bran-hull

Coix lachryma-jobi L.,belonging to the Poaceae family,is abundantly produced in China.Coix bran-hull(CBH),as a by-product of coix seed during processing,is of a huge yeild.Currently,there is no effective way to take advantage of the CBH,just as feed for livestock,which not only reduced the utilization rate of coix,but also cause economic loss of the company.Herein,CBH's chemical components was studied,and the optimized pNPG method was used to assay ?-glucosidase inhibitory activities,which may provide theoretical basis and scientific guidance for the development of hypoglycemic functional products from coix bran-hull,as well as effective utilization of the resource.The bran and hull were the coat and husk of coix seed respectively,which were generally produced in the form of mixture.In order to distinguish the difference between them,HPLC and GC-MS were used to investigate the chemical composition.The results showed that there was no significant difference between bran and hull,and both contained fatty acids as the main components.Following,the comparative analysis of chemical constituents and ?-glucosidase inhibitory activities between petroleum ether phase(PE)and ethyl acetate phase(EA)of CBH extract were studied.And the results showed that the chemical constituents of PE and EA were quite different,with the PE was rich in fatty acids.The ?-glucosidase inhibitory activity of PE and EA at 1.5 mg/mL were 76.3�0.41%and 44.9 �0.19%,respectively.In order to understand the components with ?-glucosidase inhibitory activity in CBH,the chemical constituents of EA were separated with silica gel column,Sephadex LH-20 gel column and ODS column.And then 15 compounds were isolated and identified:caffic acid methyl ester(1),allantoin(2),p-coumaric acid(3),p-coumaric acid methyl ester(4),p-hydroxybenzoic acid(5),methyl(E)-3-(4-hydroxy-3-methoxyphenyl)acrylate(6),2-hydroxyethyl(E)-3-(4-hydroxyphenyl)acrylate(7),(E)-3-(4-methoxyphenyl)acrylic acid(8),3-hydroxy-4-methoxybenzoic acid(9),9-octadecenoic acid(10),2,3-dihydroxy-1-(4'-hydroxy-3'-methoxyphenyl)propan-1-one(11),2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone(12),1,3,5-trimethoxybenzene(13),2-(2-hydroxyethyl)-3-methylfumaric acid(14),and methyl(3-hydroxy-2-oxo-2,3-dihydroindol-3-yl)-acetate(15),in which compounds 2,7,11,14,and 15 were isolated from coix for the first time.The optimized pNPG method was used to test the ?-glucosidase inhibitory activity of compounds,which revealed that compounds 1(IC50=87.5�3.27?M),4(IC50=30.2�0.69?M),7(IC20=9.4�0.47,?M,and 10(IC50=6.0 �0.11 ?M)displayed stronger inhibitory effect than the positive control acarbose(IC50=668.1�0.97?M).The results of enzyme kinetics showed that the inhibition type of compounds 1,4,and 7 to a-glucosidase was non-competitive,while 10 was a mixed inhibitor of ?-glucosidase.Molecular docking of compound 7 with ?-glucosidase was also carried out,and the result showed the non-competitive inhibition of compound 7 to?-glucosidase.As the major chemical constituents of CBH,the total phenolic acids were extracted,and the standard curves of isolated phenolic acid was defined.It showed that when theconcentration ranged from 0.1 to 1.0 mg/mL,all the standard curves had a good linear relationship(r2>0.996).The percentage composition determination indicated that compounds 3,4,and 5 were the main phenolic acid compounds in the bran-hull.Moreover,the ?-glucosidase inhibition rate of total phenolic acid was up to 87.5%when the concentration was 1.0 mg/mL,which provide material basis for coix bran-hull developed into hypoglycemic functional products.