the present invention provides a high yield method of pre paring soluble dietary fiber with a low viscosity . ( i ) removing starch and protein from corn hulls ; ( ii ) extracting starch - and protein - removed the corn hulls with an alkaline solution , and filtering the alkaline extract through a filter cloth ; ( iii ) treating the filtrate of step ( ii ) with cellulase and cellobiase ; ( iv ) treating the solution reacted with enzyme of step ( iii ) with an adsorbent , and then filtering it through a membrane filter ; and ( v ) purifying the filtrate . as desired , to further improve the transparency and filterability , step ( iii ) further comprises a step of treatment with xylanase . preferably , before the to enzymatic reaction , the alkaline extract is further desalted and decolorized with an ion exchange resin . the corn hulls used in the present invention are commercially available . as long as the corn hulls are commercially available , all corn hulls can be used without considering their quality level . in the present invention , the generally known methods for removing starch and protein can be used . for example , in the enzymatic method , the corn hulls can be treated with a starch degrading enzyme such as amylase and glucoamylase , and protease . treatment with the starch degrading enzyme and the protease can be done simultaneously or sequentially . in the invention , after removal of starch and protein from corn hulls , the resultant can be filtered through a filter cloth , thereby increasing the recovery rate of corn hulls . to extract hemicellulose , which constitutes 70 % or more of corn hulls , the corn hulls are stirred with the addition of an alkaline solution at a high temperature . the alkaline solution can be naoh , or a mixture of naoh and ca ( oh ) 2 . when only the sodium hydroxide is used , a higher yield , a higher content of dietary fiber , and more advantages in the preparation process can be expected compared to using sodium hydroxide and calcium hydroxide together . in considering the efficient extraction of hemicellulose , it is preferable to use sodium hydroxide at a low concentration . the maximal recovery rate of the extract can be reached by filtering the extract with a filter cloth after alkaline extraction . after neutralizing the extract with acid , the resultant solution is simultaneously treated with cellulase and cellobiase , or cellulase , cellobiase and xylanase . the addition of cellulase , cellobiase , and xylanase makes the extract less viscous , more transparent , and more filterable , thereby making the production process more advantageous . in addition , when the alkaline extract is treated by desalting and decolorization with a cation or anion exchange resin before the enzyme treatment , it is possible to reduce the amount of the enzyme which is required in the following step to produce the same quality of soluble dietary fiber . the solution obtained from the enzyme reaction is treated with an adsorbent such as activated carbon , filtered by membrane filtration , treated with an ion exchange resin , concentrated , and dried , to produce the water - soluble dietary fiber . the preparing method of the soluble dietary fiber from corn hulls is more specifically described in the following . corn hulls obtained from corn starch production are dried to about 5 % of water content . the dried corn hulls are mixed with distilled water in the amount of 10 to 20 times , preferably 15 times by weight of the corn hulls , and the ph is adjusted to ph 5 . 8 to 6 . 0 by the addition of a 3 to 5 % naoh standard solution . after the resultant solution is heated by stirring in a water bath so that the temperature of the solution is 90 to 100 ° c ., the solution is stirred for 1 to 5 hours with the addition of alpha - amylase in the amount of 0 . 05 to 5 %, preferably 0 . 1 to 3 % to the dried corn hulls , and then filtered through a filter cloth , and the corn hulls are then sufficiently washed with water . the alpha - amylase , for example termamyl ( novo nordisk ltd . ), is preferably heat - resistant . the filter cloth can be a generally used one that is made from polyester and polyamide with an internal pore size of 36 to 100 , and preferably 44 to 53 micrometers . destarched corn hulls are then suspended in distilled water in the same ratio as above , and the ph of the solution is adjusted to ph 7 . 0 by the addition of a sodium hydroxide solution . after the resultant solution is heated by stirring in a water bath so that the temperature of the solution is 45 to 55 ° c ., it is stirred for 1 to 5 hours with the addition of protease in the amount of 0 . 05 to 5 %, preferably 0 . 2 to 2 %, filtered through the filter cloth , and washed by the same method as above , to obtain starch - and protein - removed corn hulls . the proteases include fungi enzymes such as flavourzyme derived from asperfillus oryzae , alkalase derived from bacillus licheniformis , and the like . when filtration is performed with the filter cloth , the recovery rate of corn hulls is higher than with centrifugation , which is shown in example 1 . the hemicellulose is extracted from the starch - and protein - removed corn hulls with an alkaline solution . the corn hulls filtered can be used directly , or after being dried to some extent . the resultant corn hulls can be mixed with a sodium hydroxide solution at a low concentration of 0 . 1 to 3 %, preferably 0 . 5 to 0 . 7 % in the amount of 15 to 25 times , preferably 20 to 25 times by weight of the corn hulls . then the hemicellulose is extracted by heating the mixture in a water bath , and stirring at 70 to 90 ° c . for 1 to 5 hours . the resultant is then cooled to room temperature , and filtered by vacuum filtration with a filter cloth to is produce the extract . the same type of filter cloth as used in the first step can be used . as shown in example 3 , when filtering with a filter cloth , the recovery rate and transparency of the alkaline extract increases , thereby improving the filterability and final yield in the following process , compared to centrifugation . after preparing the alkaline extract , the solution can be directly treated with enzymes such as cellulose , cellobiase , and xylanase , etc . however , before the enzyme treatment , the alkaline extract can be further desalted and decolorized with an ion exchange resin . this case has advantages in that a smaller amount of enzymes is required in the enzyme reaction , and it results in a higher yield than with direct enzyme treatment without desalting and decolorization . the ion exchange resin which is generally used for preparation of starch sweetner can be used in the desalting and decolorizing step . as examples , a strongly acidic cation exchange resin or a weakly basic anion exchange resin can be used . the ion exchange resins can be added in the amount of 1 to 10 times , and preferably 4 times the volume of the dried corn hulls . for example , a cation exchange resin including the strongly acidic styrene resin sk1b can be used , and the anion exchange resin s that can be used include a strongly basic cl - type and a weakly basic oh - type styrene resin . the ph of the alkaline extract , or the desalted and decolorized alkaline extract , is adjusted to ph 4 . 0 to 5 . 5 , preferably 4 . 7 to 5 . 0 , which is optimum for enzymes . then the temperature of the resultant solution is adjusted to an appropriate temperature for the active enzymes by heating it in a water bath , and it is treated with cellulase and cellobiase while stirring . preferably , xylanase may be used for treatment together with the cellulase and cellobiase , thereby obtaining an enzyme hydrolysate with an improved filterability , low viscosity , and high transparency . in regard to the preferred dosage content of the enzymes , when the alkaline extract is directly treated with enzymes , the dosage of cellulase and cellobiase are the same , at 0 . 1 to 5 %, preferably 0 . 1 to 3 %, respectively . when the amount of the enzymes is lower , it is difficult to perform the following processes , such as the filtering step . when the amount of the enzymes is higher , the reaction time is reduced , but the production costs increase . when the alkaline extract is treated with enzymes after a desalting and decolorizing step , 10 to 90 parts by weight of cellobiase to 100 parts by weight of cellulase can produce a final product with a quality level equivalent to that of an enzyme reaction on an alkaline extract lacking the desalting and decolorizing step . the content of cellulase can be 0 . 1 to 5 wt % to weight of lo dried corn hulls . the cellobiase can be used in the amount of 0 . 1 to 5 wt %, preferably 0 . 1 to 3 wt %, to weight of the dried corn hulls . the enzyme reaction mixture is treated with an adsorbent , and then filtered . the adsorbents include activated carbon , an adsorbing resin such as polystyrene , and the like . to obtain a transparent extract , the filtration process can be performed with a membrane filter with a pore size of 0 . 5 micrometer or less , and preferably 0 . 45 to 0 . 2 micrometer or less . the final purification of the extract can be performed by desalting and decolorizing with an ion exchange resin which is generally used in the preparation process of dietary fiber . for example , the ion exchange resins include a strongly acidic cation exchange resin , a weakly basic anion exchange resin , and a mixed ion exchange resin . the mixed resin can be a mixture of an activated strongly acidic cation exchange resin and a strongly basic anion exchange resin , in the volume ratio of 1 : 2 . for example , the cation exchange resins include a strongly acidic styrene resin sk1b , and the anion exchange resins include a strongly basic cl - type styrene resin and a weakly basic oh - type styrene resin . the finally purified enzyme hydrolysate is concentrated to a 10 % solution under vacuum , and is then freeze - dried or spray - dried to produce powder . the employment of the third step in the preparation process for the dietary fiber can omit the purification process with the cation exchange resin or to anion exchange resin , resulting in simplifying the preparation process . the following examples are intended only to illustrate the invention and are not intended to limit the scope of the invention as defined by the claims . dried corn hulls ( 2 . 8 % of water content ) were added to distilled water in the amount of 15 times by weight of the dried corn hulls , and the ph was adjusted to 5 . 8 with 1n naoh while mixing with a mechanical stirrer . the mixture was heated in a 95 ° c . water bath , reacted for 2 hours with the addition of heat - resistant alpha - amylase ( novo nordisk ltd ., termamyl 120 ls , denmark ) in the amount of 2 . 0 % to the dried corn hulls , filtered by a polyester filter cloth ( samsung canvas , 55 - 5528 , korea ), and washed with distilled water . the destarched corn hulls were added to distilled water in the amount of 15 times by weight of the dried corn hulls , and the ph was adjusted to 7 . 0 with 1n naoh while mixing with a mechanical stirrer . the mixture was reacted with the addition of protease ( novo nordisk ltd ., flavourzyme , denmark ) in the amount of 2 . 0 % to the dried corn hulls for 2 hours in a 50 ° c . water bath , filtered by a polyester filter cloth ( samsung canvas , 55 - 5528 , korea ), and washed with distilled water . the resultant was dried in an oven at 50 ° c ., to produce starch - and protein - removed corn hulls . the yield of corn hulls is shown in table 1 . the same method as in example 1 was used , except that instead of flavourzyme , alkalase ( novo nordisk ltd ., alkalase , denmark ) in the amount of 2 . 0 % to the dried corn hulls was reacted for 2 h ours in a 55 ° c . water bath , to produce starch - and protein - removed corn hulls . the yield of corn hulls is shown in table 1 . the same method as in example 1 was used , except that after the treatment of alpha - amylase and protease , the resultant solution was centrifuged at 3 , 000 rpm instead of filtering with the filter cloth , to produce starch - and protein - removed corn hulls . the yield of corn hulls is shown in table 1 . 37 g of starch - and protein - remvoed corn hulls prepared according to example 1 were mixed with 1 l of a 0 . 5 % naoh solution , and stirred in an 80 ° c . water bath for 3 hours , and filtered through a filter cloth to produce a primary alkaline extract . the yield and transparency as measured with a spectrophotometer are shown in table 2 the corn hulls obtained in comparative example 1 were treated with an alkaline solution as in example 3 , and then they were centrifuged instead of filtered , to produce an alkaline extract . the yield and transparency as measured with a spectrophotometer are shown in table 2 . the results show that the yield and transparency with vacuum filtration are higher than with the centrifugation method . the ph of 1 . 2 l of the primary extract obtained in example 3 ( 27 . 7 g of solid content ) was adjusted to ph 4 . 8 by the addition of 10 % hcl , and cellulase ( novo nordisk ltd , celluclast , denmark ) and cellobiase ( novo nordisk ltd ., to novozyme 188 , denmark ) were added in the amount of 3 % by weight of the dried corn hulls in a 50 ° c . water bath . then , the viscosity , filterability , and transparency of the resultant solution were measured , and the results are shown in table 3 . to compare the results , the above process was repeated , except that only 3 . 0 % by weight of the cellulase was used . in addition , the ph of the same primary extract as above was adjusted to ph 4 . 8 by the addition of 10 % hcl , and cellulase ( novo nordisk ltd , celluclast , denmark ), cellobiase ( novo nordisk ltd ., novozyme 188 , denmark ), and xylanase ( biocatalyst co ., depot 333p , uk ) in the amount of 3 % by weight of the dried corn hulls were added simultaneously to the extract , reacted in a 60 ° c . water bath for 3 hours . then , the viscosity , the filterability , and the transparency of the resultant solution were measured , and the results are shown in table 3 . 2 . 5 g of activated carbon ( norit co ., kb - b , holland ) were added to an enzyme hydrolysate of three enzymes , it was heated to 95 ° c . for 30 seconds , and cooled to room temperature . the resultant was primarily filtered into filter paper ( advantec co ., toyo 5a , japan ), and then secondly into filter paper ( whatman international ltd ., gf / b , uk ) in a glass filter under vacuum . then , the resultant was filtered through a membrane with a pore size of 0 . 45 micrometers ( gelman co ., metricel , usa ) and a membrane with a pore size of 0 . 2 micrometers ( gelman co ., super - 200 , usa ). the obtained filtrate was treated with a strongly acidic cation exchange resin ( samyang co ., sk - 1b , korea ), a weakly basic and strongly basic anion exchange resin ( samyang co ., wa 30 ; pa 408 , korea ), and a resin mixture ( strongly acidic cation exchange resin and strongly basic anion exchange resin in the ratio of 1 : 2 ) at each step , it was stirred in a 40 ° c . water bath for 1 . 5 hours , filtered , and desalted and decolorized . finally , the resultant was concentrated with a vacuum evaporator ( eyela , ne - 1v , japan ), so that the concentration of the soluble dietary fiber was measured to be 10 % ( w / w ). the final yield of soluble dietary fiber to raw corn hulls was 23 . 1 %. as a result of measurement of the fiber with a prosky - aoac method , the content of soluble dietary fiber was 91 . 9 %, and the results of typical analysis are shown in table 4 . to perform the desalting and decolorizing process , the ph of 1 . 2 l of primary extract obtained in example 3 ( 27 . 7 g of solid content ) was adjusted to ph 6 . 0 by adding 10 % hcl , and 200 ml of the strongly acidic cation exchange resin ( samyang co ., sk - 1b , korea ) and the weakly basic anion exchange resin ( samyang co ., wa 30 , korea ) were added sequentially , it was stirred in a 40 ° c . water bath for 1 . 5 hours , and then filtered . the ph of the resultant solution was adjusted to ph 4 . 8 , cellulase ( novo nordisk ltd , celluclast , denmark ) and cellobiase ( novo nordisk ltd ., novozyme 188 , denmark ) were added in the amount of 2 % and 0 . 4 % by weight of the dried corn hulls respectively , and it was reacted for 3 hours in a 50 ° c . water bath . then , the viscosity , the filterability , and the transparency of the resultant solution were measured , and the results are shown in table 5 . to compare the results , the above process was repeated , except that only 2 . 0 % of the cellulase was used . in addition , the ph of the same primary extract as above was adjusted to ph 6 . 0 , and then it was desalted and decolorized according to the method as mentioned above . then , the ph of the resultant solution was adjusted to 4 . 8 , cellulase ( novo nordisk ltd , celluclast , denmark ), cellobiase ( novo nordisk ltd ., novozyme 188 , denmark ), and xylanase ( biocatalyst co ., depol 333p , uk ) were added simultaneously in the amount of 2 . 0 %, 0 . 4 %, and 2 . 0 % by weight of the dried corn hulls respectively , and it was reacted in a 55 ° c . water bath for 3 hours . then , the viscosity , the filterability , and the transparency of the resultant solution were measured , and the results are shown in table 5 . 2 . 5 g of the activated carbon ( norit co ., kb - b , holland ) were added to an hydrolysate of three enzymes , it was heated to 95 ° c . for 30 seconds , and cooled to room temperature . the resultant was primarily filtered into filter paper ( advantec co ., toyo 5a , japan ), and then secondly into filter paper ( whatman international ltd ., gf / b , uk ) in a glass filter under vacuum . then , the resultant was filtered into a membrane with a pore size of 0 . 45 micrometers ( gelman co ., metricel , usa ) and a membrane with a pore size of 0 . 2 micrometers ( gelman co ., super - 200 , usa ). the obtained filtrate was added to 200 ml of a resin mixture of a strongly acidic cation exchange resin ( samyang co ., sk - 1b , korea ) and a weakly basic anion exchange resin ( samyang co ., wa 30 ; pa 408 , korea ) in the volume ratio of 1 : 2 , and stirred in a 40 ° c . water bath for 1 . 5 hours to complete the final purification process . finally , the resultant solution was concentrated with a vacuum evaporator ( eyela , ne - 1v , japan ), so that the concentration of the soluble dietary fiber was measured be to 10 % ( w / w ). the final yield of soluble dietary fiber to raw corn hulls was 24 . 5 %. as a result of measurement of the fiber with a prosky - aoac method , the content of soluble dietary fiber was 92 . 1 %, and the results of typical analysis are shown in table 6 . this example was produced according to the same method of example 4 , except that xylanase derived from aspergillus niger ( novo nordisk ltd ., shearzyme 500 l , denmark ) was used instead of xylanse . the final yield of dietary fiber to raw corn hulls was 20 . 4 %, and the content of dietary fiber was 90 . 7 %. 200 g of corn hulls ( 5 . 7 % of water content ) were mixed with distilled water so that the final concentration was 8 %, 1n naoh solution was added while mixing with an a mechanical stirrer , to a ph of 5 . 8 . the mixture was heated in a 95 ° c . water bath , reacted with the addition of the heat - resistant alpha - amylase of example 1 in the amount of 1 . 0 % ( v / w ) to the dried corn hulls , for 2 hours , and filtered with a filter cloth . the destarched corn hulls were added to 3 . 0 l of distilled water , and the ph was adjusted to 7 . 0 with 1n naoh solution . the mixture was reacted with protease ( novo nordisk ltd ., flavourzyme , denmark ) in the amount of 1 . 0 ( w / w ) % to the dried corn hulls for 3 hours in a 50 ° c . water bath , filtered with a filter cloth , and dried in an oven at 50 ° c ., to produce starch - and protein - removed corn hulls . the yield of corn hulls was 74 . 0 %. to perform alkaline extraction , the starch - and protein - removed corn hulls were mixed with 3 l of a 0 . 5 % naoh solution , and stirred in a 40 ° c . water bath for 24 hours and filtered through a filter cloth to produce a primary alkaline extract . the ph of the primary extract was adjusted to ph 4 . 8 by addition of 10 % of hcl , and cellulase ( novo nordisk ltd , celluclast , denmark ) and cellobiase ( novo nordisk ltd ., novozyme 188 , denmark ) in the amount of 1 . 0 % by weight of the dried corn hulls were respectively added , and reacted in a 50 ° c . water bath for 5 hours . after the reaction , 10 % ( w / w ) of the activated carbon ( norit co ., kb - b , holland ) to corn hulls was added to the hydrolysate of three enzymes , it was heated to 95 ° c . for 30 seconds , and cooled to room temperature . the resultant was finally filtered with a membrane with a pore size of 0 . 45 micrometers ( gelman co ., metricel , usa ). as in the method of example 3 , the desalting and decolorizing steps were performed with three steps of ion exchange resin treatment . the resultant solution was concentrated so that the final concentration was 10 % ( w / w ), and then the final yield of soluble dietary fiber to the raw dried corn hulls was calculated . as a result , the yield was 21 . 5 %, and the content of the fiber was 86 . 4 %. according to the method of example 1 , 300 g of corn hulls were added to distilled water in the amount of 15 times by weight of the corn hulls , and then starch and protein were removed with enzyme sequentially . the yield of starch - and protein - removed corn hulls was 68 . 6 %. alkaline extraction was performed on the corn hulls with 5 l of 0 . 5 % naoh , and then the resultant solution was divided into two groups . 5 % of cellulase and 5 % ( v / w ) of cellobiase to the dried corn hulls were added to one group , and reacted at 50 ° c . for 5 hours . 5 % ( v / w ) of cellulase , 5 % ( v / w ) of cellobiase , and 5 % ( v / w ) of xylanase to the dried corn hulls were added simultaneously to the other group and reacted at 60 ° c . for 5 hours . the two groups were treated according to the purification process as above . then , the concentrations of dietary fiber solution were adjusted to 5 % ( w / w ) at room temperature , and the viscosities were measured . as a result , with the treatment of cellulase and cellobiase , the viscosity was 10 . 0 cps . with the treatment of cellulase , cellobiase , and xylanase , the viscosity was 9 . 0 cps . for reference , arabic gum ( msc co ., no . 10308 , korea ), which is usually used as an emulsion stabilizer for food , had a viscosity of 6 . 7 cps . after the starch and protein were removed from the corn hulls according to the method of example 1 , the resultant was divided into two groups . one group was treated with 0 . 5 % of an alkaline mixture which included naoh and ca ( oh ) 2 in the same ratio in the amount of 20 times by weight of corn hulls . the other group was treated with 0 . 5 % of a naoh solution in the same amount , and reacted at 80 ° c . for 3 hours . as disclosed in example 4 , the resultant solutions were treated with the three kinds of enzymes in the amount of 3 % respectively , reacted , purified , and the yield was calculated . as a result , in the case of treatment with naoh and ca ( oh ) 2 , the yield was 15 . 1 %, and the content of dietary fiber was 72 . 7 %. in the case of treatment with naoh , the yield was 20 . 1 %, and the content of dietary fiber was 84 . 3 %. after the starch and protein were removed from the corn hulls according to the method of example 1 , the resultant was divided into three groups . the groups were treated with a 0 . 1 %, 0 . 5 %, and 1 . 0 % naoh solution in the amount of 20 times by weight of corn hulls , respectively . as disclosed in example 4 , the resultant solutions were treated with the three kinds of enzymes in the amount of 3 % respectively , reacted , purified , and the yield was calculated . as a result , when treating with 0 . 1 %, 0 . 5 %, and 1 . 0 % naoh , the yields were 3 . 3 %, 30 . 0 %, and 33 . 4 %, respectively . however , the treatment with 1 . 0 % naoh caused the formation of salt in a relatively large amount during neutralizing process , resulting in a high load during the purification process . after the starch and protein were removed from the corn hulls according to the method of example 1 , the resultant was divided into three groups . the groups were treated with a 0 . 5 % naoh solution in the amount of 20 times by weight of corn hulls for 1 , 3 , and 10 hours , respectively . as disclosed in example 4 , the resultant solutions were treated with the three kinds of enzymes in the amount of 3 % respectively , reacted , purified , and the yield was calculated . as a result , when treatment time was 1 , 3 , and 10 hours , the yields were 24 . 9 %, 27 . 9 %, and 26 . 7 %, respectively . after the starch and protein were removed from the corn hulls according to the method of example 1 , the resultant was divided into three groups . the groups were treated with a 0 . 5 % naoh solution in the amount of 20 times by weight of corn hulls for 3 hours at 40 , 60 , and 80 ° c ., respectively . as disclosed in example 4 , the resultant solutions were treated with the three kinds of enzymes in the amount of 3 % respectively , reacted , purified , and the yield was calculated . as a result , when treatment temperature was 40 , 60 , and 80 ° c ., the yields were 8 . 5 %, 15 . 4 %, and 21 . 7 %, respectively . lecithin powder ( central soya co ., centrolex d , usa ), arabic gum ( msc co ., 10308 , korea ), and two kinds of dietary fiber extracted from corn hulls at 2 % ( w / w ) respectively were added to a mixture of soy bean oil and distilled water , emulsified with a homogenizer at 20 , 000 rpm for 5 minutes , and the viscosity of the emulsion was measured . as a result , the viscosity was 23 cps for lecithin powder , 35 cps for arabic gum , 55 cps for dietary fiber obtained by treating with cellulase and cellobiase , and 50 cps for dietary fiber obtained by treating with cellulase , cellobiase , and xylanse . in addition , the state of emulsion in a 100 ml mass cylinder was investigated . as a result , all the samples showed good emulsion stability . after 10 days , a lower aqueous layer separation occurred for all the samples . after 30 days , a lower aqueous layer completely separated from the upper oil layer for the sample including lecithin , but the emulsion of the samples including arabic gum and dietary fiber extracted from corn hulls kept comparatively stable .
the present invention relates to a high yield process for producing soluble dietary fiber from corn hull . more specifically , the present invention comprises removing starch and protein with enzymes from corn hull which is by - product of wet - milling process for production of corn starch , extracting the resultant with alkaline solution to form a alkaline extract , treating the alkaline extract with enzymes , and drying the enzyme - treated solution , to produce dietary fiber with low viscosity and containing hemicellulose as a major component at high yield .