various -glucans have been extracted from various sources such as fungi , baker 's yeast , barley , oats , and seaweed . the physicochemical properties of -glucans differ depending on characteristics of their primary structure , including linkage type , degree of branching , molecular weight , and conformation ( e.g. , triple helix , single helix , and random coil structures ) [ 1 , 2 ] . -glucans extracted from barley , which mainly contains -(1,3 - 1,4)-d - glucan , have been demonstrated to reduce blood lipid levels , including cholesterol and triglyceride levels [ 35 ] . the mechanisms by which -glucans reduce blood lipid levels have been shown to include prevention of cholesterol reabsorption by adsorption , elimination of bile acid by adsorption , an increase in bile acid synthesis , and suppression of hepatic cholesterol biosynthesis by short - chain fatty acids produced by fermentation with intestinal bacteria [ 68 ] . claims that barley products reduce the danger of coronary heart disease have been endorsed by the food and drug administration of the united states . in addition , -glucans extracted from barley have also been reported to possess various other biologic activities , for example , reducing blood glucose level , enhancing insulin response , protecting against stress ulcers , and restraining allergic reactions . furthermore , -glucans extracted from barley have been used in health products as a diet food , because glucan is a dietary fiber . thus , -glucans extracted from barley have been used extensively as supplements and food additives . whole grain products are recommended for healthy diets , as they are recognized sources of dietary fiber . furthermore , ragaee et al .   demonstrated the antioxidant activity of various cereals such as barley , millet , rye , and sorghum . oxidative stress is considered one of the primary causal factors for aging and various diseases such as arteriosclerosis , cardiovascular disease , cerebral diseases , diabetes , inflammatory diseases , and cancer [ 14 , 15 ] . it is thought that scavenging of reactive oxygen species ( ros ) is important for the prevention of these diseases . if it were to be shown that -glucan , a natural component of grain , exerts antioxidant activity , the utility of -glucan as a polymeric excipient for supplement or food additive would increase further . therefore , the aim of the present study was to examine the antioxidant activity of -glucan to assess potential new health benefits associated with -glucan as a polymeric excipient for supplement and food additive . the effects of the extraction source , extraction method , and molecular size of -glucan on antioxidant activity were also investigated . furthermore , the antioxidant activity of -glucan was compared with that of polymers that are commonly used as food additives . -glucans extracted from barley using different extraction methods and of different molecular sizes , contained more than 70%  -(1,3 - 1,4)-d - glucan ( figure 1(a ) ) , and -glucan isolated from black yeast ( aureobasidium pullulans ) , which contained more than 85%  -(1,3 - 1,6)- d - glucan ( figure 1(b ) ) , were donated by adeka co. ( tokyo , japan ) . -glucan extracted from oats , with an unknown composition , was purchased from megazyme international ireland ltd . gelatin , pectin from apple , pectin from citrus , curdlan , gellan gum , and xanthan gum were purchased from wako pure chemical industrial ltd . concentrations of 0.52.0  w / v% of -glucans or other polymers were prepared by dissolving the molecules in ion - exchanged water . chitosan was dissolved in 0.1  m acetate buffer solution ( ph 4.5 ) , because chitosan did not dissolve in ion - exchanged water . antioxidant activity against hydroxyl radicals in the solution was determined using a radical catch kit ( aloka co. ltd . , the kit measures the amount of hydroxyl radicals generated by the fenton reaction with hydrogen peroxide catalyzed by cobalt using luminol luminescence . briefly , 50  l of cobalt chloride reagent , 50  l of luminal reagent , and 20  l of sample solution were mixed , and , after preincubation at 37c for 5  min , 50  l of hydrogen peroxide reagent was added . the amount of luminescence generated from 80 seconds to 120 seconds after the addition of hydrogen peroxide reagent was detected with a luminescence reader ( accuflex lumi 400 ; alola co. ltd . , was estimated using the following equation : 
 ( 1)radical  scavenge  ( % )  = amount  of  hydroxy  radical  scavengedamount  of  hydroxy  radical  generated100 . as shown in figure 2 , the hydroxyl radical scavenging activity of -glucan differed between different sources of -glucan . in particular , -glucan extracted from barley showed the strongest hydroxyl radical scavenging activity . on the other hand , the hydroxyl radical scavenging activity of -glucans extracted from black yeast or oats was fairly low . furthermore , 0.1  w / v% of -glucan extracted from barley scavenged approximately 60% of the hydroxyl radicals in the system , and the hydroxyl radical scavenging activity of the -glucan increased gradually with an increase in -glucan concentration ( figure 3 ) . -glucans extracted from both barley or oats were found to comprise mainly -(1,3 - 1,4)-d - glucan ( figure 1(a ) ) . on the other hand , -glucan extracted from black yeast comprised mainly -(1,3 - 1,6)-d - glucan ( figure 1(b ) ) . in addition to these differences in linkage type , the properties of -glucans are influenced by the degree of branching , molecular weight , and conformation [ 1 , 2 ] . although the mechanisms by which -glucan scavenges hydroxyl radicals are not yet clarified , the different structures of -glucan , which may be associated with the source and extraction method of obtaining -glucan , may influence antioxidant activity . first , the barley was crushed and then extracted under neutral , acidic ( 50  mm citrate buffer aqueous solution ( ph 4.0 ) ) , or alkaline ( 50  mm carbonate buffer aqueous solution ( ph 9.0 ) ) conditions with warm water at 50c . after solid - liquid separation , the liquid phase was condensed . the hydroxyl radical scavenging activity of -glucan extracted from barley using the different extraction methods is shown in figure 4 . the hydroxyl radical scavenging activity of -glucans extracted under an acid condition or an alkali condition was slightly higher compared with that when -glucans were extracted under a neutral condition with warm water . the -glucans extracted from barley used in this study comprised more than 70%  -(1,3 - 1,4)-d - glucan , but also contained other components ( i.e. , proteins , lipids , saccharides , and dietary fiber ) . the hydroxyl radical scavenging activity of almost pure -(1,3 - 1,4)-d - glucan , which was obtained by repeated recrystallization of -glucan extracted under neutral conditions with warm water ( 50c ) , was 43  1% . although the possibility that other components contributed to the radical scavenging activity of -glucan can not be completely ruled out , this finding shows that the greater part of the hydroxyl radical scavenging activity was caused by -(1,3 - 1,4)-d - glucan . however , -glucan extract is generally used without further refinement for supplements or food additives . these findings demonstrate that -glucans extracted using a variety of extraction methods , from acidic to alkaline conditions , have high radical scavenging activity . the molecular weight of -glucan extracted from barley with warm water is 40,000100,000  da ; the oligomer prepared from the macromolecule -glucan by enzymatic degradation with lichenase has a molecular weight of approximately 2,000  da ( as described by the manufacturer ( adeka co. , tokyo , japan ) ) . as shown in figure 5 , the hydroxyl radical scavenging activity of -glucan was reduced with a decrease in molecular size . however , antioxidant activity was reduced only by about half , even when molecular weight was reduced by about 1/201/50 . this finding indicates that -glucan exerts hydroxyl radical scavenging activity across a wide range of molecular sizes . the hydroxyl radical scavenging activity of various polymers was determined and compared with that of -glucan . in this experiment , the hydroxyl radical scavenging activity of 1% xanthan gum could not be determined due to its high viscosity ; therefore , 0.5% was used . as shown in figure 6 , pectin from apple or citrus , chitosan , and xanthan gum showed hydroxyl radical scavenging activity . however , the hydroxyl radical scavenging activity of each of these polymers , which are used as food additives , was inferior to that of -glucan extracted from barley . the polymers pullulan , dextrin , and curdlan , which are copolymers of glucose , were also assessed . pullulan is a linear -1,4  :  1,6-d - glucan consisting predominantly of repeating maltotrioses ( consisting of 3 d - glucose molecules linked with -1,4 glycosidic bonds ) linked by -1,6-glucosidic bonds . dextrin is also a -1,4-d - glucan or -1,6-d - glucan , whereas curdlan is a linear -1,3-d - glucan consisting of -(1,3)-linked d - glucose residue . hydroxyl radical scavenging activity was not observed for curdlan , though curdlan is a -glucan ; further , no antioxidative activity was observed for pullulan or dextrin . this finding indicates that the hydroxyl radical scavenging activity of -glucan is affected by the primary structure of the molecule , including linkage type , degree of branching , molecular weight , and conformation . hydroxyl radicals have the strongest reactivity and oxidation power among ros . the ability to scavenge ros is a precious property for the prevention of various diseases and aging . in this study , it was shown that -glucan extracted from barley exerts significant antioxidant activity , in addition to the various biologic activities previously described . the amount of antioxidant activity of -glucan was influenced by the different physiologic properties ( e.g. , structure and molecular size ) of -glucan , which varied depending on the source and extraction method used . furthermore , the hydroxyl scavenging activity of -glucan was significantly higher than that of various polymers that are used as food additives . these results indicate that -glucan has promise as a polymeric excipient for supplement and food additive with antioxidant and other benefits , which may contribute to enhancing health and beauty .
-glucans extracted from barley , which mainly contains -(1,3 - 1,4)-d - glucan , are used extensively as supplements and food additives due to their wide biologic activities , including a reduction in blood lipid level . in this study , 
 the antioxidant activity of -glucan was examined to assess potential new benefits associated with -glucan , because oxidative stress is considered one of the primary causal factors for various diseases and aging . 
 -glucan extracted from barley was found to possess significant antioxidant activity . 
 the amount of antioxidant activity was influenced by different physiologic properties ( e.g. , structure and molecular size ) of -glucan , which varied depending on the source and extraction method used . 
 the antioxidant activity of -glucan was significantly higher than that of various polymers that are used as food additives . 
 these results indicate that -glucan has promise as a polymeric excipient for supplement and food additive with antioxidant and other benefits , which may contribute to enhancing health and beauty .