Effect Of Purple Highland Barley Bran On Physicochemical Properities And Starch Digestion In Vitro Of Chinese Steamed Bread

In China,the rising incidence of diabetes is becoming a major public health problem.The development of low glycemic index(GI)food has become one of the feasible strategies to solve this problem.Chinese steamed bread(CSB)are one of the traditional foods in China.However,because of their high GI? they are not conducive to the prevention of diabetes.While,highland barley bran contains a large amount of dietary fiber,polyphenols and anthocyanins,which can inhibit starch digestion.Therefore,the addition of highland barley bran and its functional ingredients in CSB to delay the blood sugar response has a positive significance in preventing chronic diseases,such as diabetes.However,the addition of bran will lead to a decrease in the specific volume,texture,and sensory quality of the CSB.It means that the research and development of the CSB with highland barley bran is still a challenge.What's more,at present,there are insufficient researches on the application of highland barley bran in food at home and abroad,mainly on the extraction of highland barley bran ingredients and functional activity.Today,low-GI foods are getting more and more attention from consumers.The goal of this research is to develop low-GI CSB.First,the physical characteristics and nutritional composition of purple highland barley bran(PHBB)with different particle sizes are analyzed.Pasting properties for the flour after adding PHBB were studied by RVA.And the specific volume,texture,color and sensory qualities of CSB addition with PHBB were also studied.What's more,the in vitro antioxidant model was used to determine the antioxidant activity of the PHBB-CSB.At the same time,the in vitro starch digestion model was used to determine the in vitro starch digestibility and EGI of the CSB addition with PHBB.In order to verify that the effect of PHBB on the in vitro starch digestion of CSB is related to the phenolics it contains,polyphenol-rich purple highland barley bran extract(PHBE)was also added to CSB,and its in vitro starch digestion curve was studied.Finally,in order to investigate the effect of PHBB on starch digestion in vitro,the effect of PHBB and PHBE on the fluorescence quenching of ?-amylase was also studied.The findings are as follows:1.Study on physicochemical properties of purple highland barley bran with gringing treatmentPHBB was broken up into different particle sizes by grinder and its general composition was analyzed.As for the basic components of bran,ash,starch,crude protein,and crude fat increase continuously with the decrease of bran particle size,in contrast,the total dietary fiber amount is significantly reduced(P<0.05).In terms of physical properties,the waterholding capacity and swelling power of bran all significantly decreased with the decrease of the average particle size(P<0.05).As far as phenolics are concerned,the total phenolic content and total anthocyanin content in bran are increasing with the decrease of the average particle size.It is worth mentioning that the use of different extraction solvents will affect the determination of phenolic content.For example,methanol extract has the highest total phenolic content,followed by ethanol extract and water extract.However,the type of extraction solvent had no significant effect on the total anthocyanin content(P<0.05).In consideration of food safety issues,it is recommended to use pure water as the extraction solvent for phenolics in the PHBB.Finally,HPLC analysis showed that chlorogenic acid,pcoumaric acid,catechin,and quercetin were higher in bran phenolic acid.The results show that in addition to the basic nutritional composition,the PHBB also contains a large amount of phenolic acids and anthocyanin,and its phenolic content,basic nutritional composition and physical properties are all affected by particle size.2.Effect of purple highland barley bran on sensory properties of Chinese steamed breadThe addition of PHBB will cause the peak viscosity,valley viscosity,and final viscosity of the flour to decrease in a concentration-dependent manner.However,by reducing the bran particle size moderately,the deterioration of the pasting characteristics of the mixed powder can be weakened.The addition of PHBB can also lead to a decrease in the specific volume,a dense structure,an increase in hardness and chewability,a decrease in elastic cohesiveness,and a rough taste of CSB;especially when the amount is greater than 20%,the overall sensory acceptance of the steamed bread significantly decreases.However,compared with the CSB in the 442 ?m group,the CSB in the 227 ?m group have less quality change and higher acceptance,which is consistent with the results of pasting properties.The addition of bran will also give the CSB a special color,and the higher the amount of addition,the finer the particle size,the darker the color.The results show that,under the condition of high addition,PHBB addition will cause the CSB to reduce the volume,increase the density,increase the hardness and chewability,deepen the color,and reduce consumer acceptance,but the negative effect can be weakened by reducing the particle size.All in all,in CSB,the recommended amount and particle size of PHBB are 20%and 227 ?m.3.Effect of purple highland barley bran on antioxidant activity and starch digestion of Chinese steamed bread in vitroFirst,the addition of PHBB can significantly increase the total phenolic and anthocyanin content of CSB,as well as DPPH and ABTS free radical scavenging activity,reducing potential,and iron ion reducing power.What's more,the total phenolic content was highly related to the antioxidant activity of PHBB-CSB.Secondly,the addition of PHBB can also significantly reduce balanced concentration(C?),expect glycemic index(EGI),rapidly digestible starch(RDS),slow digestible starch(SDS),and improve resistant starch(RS),but the particle size has no significant effect on it.Similar to PHBB-CSB,the addition of PHBE also reduced the in vitro starch hydrolysis rate and delayed the release of glucose of CSB.Finally,after interaction with PHBB-CSB and PHBE,the synchronous fluorescence spectrum shows that the maximum emission peak of ?-amylase redshift occurs,and the peak value decreases,as the concentration increases.All in all,the addition of PHBB could not only provide antioxidant activity but also inhibit starch digestion of CSB in vitro.At the same time,the addition of PHBB-CSB and PHBE can also slow down the release of glucose in starch digestion in vitro and have a hypoglycemic effect,which means that the effect of PHBB in starch digestion of CSB in vitro is related to phenolics in PHBB.More importantly,PHBB-CSB and PHBE inhibit the activity of ?-amylase by reducing the hydrophobicity of the tryptophan residues in ?-amylase,and consequently inhibit the starch hydrolysis.It means that the inhibition of PHBB on ?-amylase is one of the reasons for reducing the starch digestion of CSB,and the inhibition is also related to its phenolics.