Non-starch Constituents Influence The In Vitro Digestibility Of Naked Oat (Avena Nuda L.) Starch

Naked oat?Avena nuda L.?is a traditional miscellaneous cereal in China and is one of the world's most popular cereals with the highest nutritional value.Compared with other starchy foods,naked oat is not easy to digest and the postprandial blood glucose value is medium.It is a healthy food suitable for diabetes.In the present study,the effects of non-starch nutritional components including proteins,lipids and?-glucan in naked oat flour on the in vitro digestibility and physicochemical properties of starch were investigated.The bioactive compounds in naked oat were extracted and their composition was analyzed by HPLC-MS.The inhibitory effect and the type of inhibition of?-amylase and?-glucosidase by the free and bound extracts were studied.And the effect of ethanol extracts from naked oat powder on the digestibility and sensory quality of starch were compared.The main conclusions are as follows:?i?The digestibility of cereals was rice>corn>millet>buckwheat>naked oat.Among them,naked oat has the lowest estimated glycemic index?e GI?of 67.61.The final enzyme hydrolysis rate and e GI of starch in naked oat flour increased after the removal of non-starch constituents,with a decreasing order of naked oat starch?NOS?>de-?-glucan flour?D?-NOF?>de-proteins flour?DP-NOF?>de-lipids flour?DG-NOF?>naked oat flour?NOF?.The content of rapidly digested starch?RDS?increased,and the content of resistant starch?RS?decreased in NOF after removing the non-starch nutritional components.Overall,?-glucan has the highest effect on starch digestibility in naked oat flour,followed by lipids and proteins.?ii?Scanning electron microscopy?SEM?results showed that most of the NOS particles were irregular polyhedron,elliptical.The particle size was in the range of 3.3?15.9?m.The surface of naked oat starch particles were covered by lipids and proteins,so that the starch particles cannot be completely exposed.The solubility and swelling power of naked oat flour without non-starch nutritional components increased,indicating that the presence of these components hindered the entry of water and enzymes into the starch granules.?iii?The crystalline structure of NOF was A-type,whereas the treatment of removing protein or?-glucan made NOF appear V-type crystal structure.The relative crystallinity decreased after removing non-starch nutritional components and showed a negative correlation?r=-0.995?with e GI.The removal of non-starch nutritional components resulted in an increase of starch short-range molecular order,which was significantly correlated with e GI?r=0.908?.The T_o,T_pand T_cof DP-NOF,DG-NOF and NOF were reduced to a certain extent,while the related values of D?-NOF increased.The enthalpy??H?of DP-NOF and NOS increased,while the?H of DG-NOF and D?-NOF decreased.?iv?The content of total phenol,total flavonoid,and total saponin was 0.36,1.53 and 1.28 mg/g DW in NOF,respectively.HPLC-MS analysis showed that the free components mainly included 17compounds such as ergosterol-7,3'-dimethyl ether,4-coumarylcholine,hesperetin-7-O-neohesperidoside,ginsenoside Re and scoparone,and 9 substances were mainly detected in the bound components including ferulic acid,4-coumarylcholine,and trans-4-coumaric acid.The extract of free and bound components of NOF showed a dose-dependent inhibitory effect on?-amylase and?-glucosidase.The IC₅₀of the free components to?-amylase and?-glucosidase were 0.09 and 0.57 mg/m L,respectively,while the IC₅₀of the binding component were 1.33 and 0.15 mg/m L,respectively.The type of inhibition of?-amylase by extracts of free and bound components of NOF was reversible anti-competitive inhibition,and the type of inhibition of?-glucosidase was reversible linear mixed inhibition.The monomer substance ginsenoside Re has poor inhibitory effects on?-amylase and?-glucosidase.Soyasaponin Ba has a poor inhibitory effect on?-amylase,but it has a better inhibitory effect on?-glucosidase(IC₅₀=0.34 mg/m L),and the inhibition type was reversible non-competitive.?v?After adding the extract into potato starch,corn starch,pea starch,and naked oat starch,the enzymatic hydrolysis curves of the four starch-extract complexes all decreased slightly.The RDS content of the complexes decreased,and the SDS and RS content increased.The brightness value?L?and hue angle?H?of the four complexes decreased,the red-green value?a?,yellow-blue value?b?and saturation value?C?increased.The color difference values??E?were all greater than 6.The color of the complexes has changed to some extent,and the taste was slightly astringent,but showed little effect on the overall sensory characteristics of starch.