Effects Of Milling Methods On Properties Of Tartary Buckwheat Flour

Tartary buckwheat(Fagopyrum tataricum),as a unique food medicine dual-use cereal crop,contains rich nutrients,including starch,protein,dietary fiber,and polyphenolic compounds.It has been well known by human in the world because of the low glycemic index and the healthy benefit of keeping the stable of blood sugar.However,milling is the basic work in food processing industry,and it is also one of the vital processing.So studies on processing are of great practical significance.Several types of grinders,including ultrafine milling,steel milling,stone milling and wet milling were used to prepare tartary buckwheat flour in the current study.The flour prepared by different grinders was investigated in terms of its nutritional quality,content and antioxidant property of polyphenols,processing characteristics and in-vitro starch digestibility.Results of this study will provide a theoretical basis for the processing of tartary buckwheat.The main results of this study were as follows:(1)Different milling methods have a significant effect on nutrition compounds of tartary buckwheat flour.Flour milled by stone milling and ultrafine milling exhibited the largest crude protein,crude fat,crude fiber and trace elements content,followed by steel milling flour and wet milling flour.And compared with stone milling flour,the content of crude protein,crude fat and crude fiber of wet milling flour decreased by 42.52% ? 47.05% ? 52.38%,respectively.However,flour milled by steel milling may have longer shelf life as lower moisture content,12.04%,which will conducive to the flour storage.(2)Ultrafine tartary buckwheat flour and stone tartary buckwheat flour contained remarkably higher total phenolic content and antioxidant activity than that milled by steel milling and wet milling.The level of total phenolic and total flavonoids content in tartary buckwheat flour varied from(448.70±3.58)to(722.66±8.10)mg gallic acid eq./100 g DW and(611.34±6.34)to(1682.23±7.73)mg rutin eq./100 g DW,respectively.With regard to the results by HPLC analysis,9 polyphenol compounds(protocatechuic acid,p-hydroxybenzoic acid,vanillic acid,epicatechin,p-coumaric acid,ferulic acid,rutin,quercetin,and ellagic acid)were identified and revealed that rutin and quercetin were the dominant phenolic compounds in flour milled by dry milling and wet milling.The content of rutin and quercetin ranged from(403.51±2.52)to(895.94±5.20)mg/100 g DW in flour milled by dry milling and(553.67±2.32)mg/100 g DW in flour milled by wet milling,respectively.Moreover antioxidant capacities of different flour were decreased in the following order: ultrafine tartary buckwheat flour > stone tartary buckwheat flour > wet tartary buckwheat flour > steel tartary buckwheat flour,which positively correlated with total phenolic and total flavonoids content.(3)Milling methods have a significant effect on the processing characteristics of tartary buckwheat flour.Ultrafine milling has a strategic role in reducing the average particle size(D[4,3]=32.09 um)and increasing bright color(L=88.92)and peak viscosity(7 589 cp).In addition,tartary buckwheat flour made by stone milling has higher solubility and thermal stability.While wet milling fraction with the lowest damaged starch content(4.25%)also has the best freeze-thaw stability and the lowest set back,which makes it easy to processe gelled food.And in the processing of frozen food,wet milling flour can be preferentially considered.(4)According to the result of in vitro starch digestibility,tartary buckwheat flour milled by stone had the lowest starch hydrolysis rate and rapid digest starch content,which was14.94%and significantly lower than the other three samples(P<0.05).Conversely,tartary buckwheat flour milled by ultrafine milling with 31.25% rapid digest starch exhibited the highest starch hydrolysis rate in the whole process,which was double than that of stone tartary buckwheat flour.So stone milling method is a healthy way to prepare low glycemic index food.