Patent Abstract:
a method for preparing a purple sweet potato concentrate that is free from starch , rich in anthocyanins , phenolic compounds , minerals , and soluble dietary fiber with low viscosity , attractive color , and with natural sweetness is presented . the method first prepares and liquefies the purple sweet potatoes and fixes the colorization by adjusting the ph value . next , amylase and an enzyme complex of hemicellulase , pectinase , cellulase , glucoamylase and protease are added in sequence under conditions effective to produce the juice with the above mentioned properties . the juice is then centrifuged and membrane - filtered to produce a purified purple sweet potato juice which is vacuum - concentrated to yield a purple sweet potato concentrate . purple sweet potato powder can be obtained by vacuum drying the sediment and concentrate mixture .

Detailed Description:
reference will now be made in detail to some embodiments of the invention , examples of which are illustrated in the accompanying drawings . although the present invention has been described in connection with certain specific embodiments for instructional purposes , the present invention is not limited thereto . accordingly , various modifications , adaptations , and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims . fig1 is a detailed description of a manufacturing process of purple sweet potato juice and dried powder by using an enzyme complex of amylase , hemicellulase , pectinase , cellulase , glucoamylase , and protease according to the present invention . the process is partitioned into five phases , namely , preprocessing , liquefying , enzyme treatment , filtration and harvesting as depicted in fig1 . during the preprocessing phase at block 101 , raw fresh potatoes or dried purple sweet potatoes are sterilized . the sterilized purple sweet potatoes then are liquefied at liquefying phases at block 102 . at block 103 , enzyme treatment on liquefied psp produces psp suspension which goes through the separation and filtration phase at block 104 to produce purified psp juice . in harvesting phase at block 105 , purified psp juice is concentrated to produce psp concentrates for packaging , and at block 106 , psp dried powder is collected and packaged . the details of each phase are illustrated in the following figures . fig2 shows the details of the preprocessing phase . fresh purple sweet potato is soaked and washed with water at step 201 . the process can also accommodate dried purple sweet potatoes . in such case , the dried purple sweet potatoes will be soaked , washed and macerated with filtered water at step 202 . in either case , the cleaned and macerated purple sweet potatoes will be sterilized by steaming at 80 ° c . to 125 ° c . for 20 to 80 minutes at step 203 . the steaming also serves as a process to de - activate the enzymes in the potatoes . at the end of the preprocessing process , a batch of sterilized purple sweet potatoes is obtained and is ready to be liquefied in liquefying treatment phase at step 204 which is described in fig3 . fig3 illustrates the liquefying process . the batch of sterilized purple sweet potatoes is then ground and blended to obtain a consistent puree at step 301 . step 302 involves color fixation by adjusting the ph to 2 . 5 - 5 . 5 by using citric acid . color fixed psp puree is then liquefied at step 303 by adding treated water . for fresh raw purple sweet potato , treated water of 0 . 5 to 3 times its weight is added . for dried purple sweet potatoes , it is necessary to add 2 to 8 times its weight of treated water . the liquefied purple sweet potatoes are ready for the enzyme treatment phase at step 304 which is described in fig4 . fig4 depicts the enzyme treatment process . the liquefied purple sweet potato is warmed up to 90 ° c . to 110 ° c . for 1 to 6 minutes at step 401 . after the liquefied psp cools down , its ph is adjusted to 4 . 0 to 7 . 0 by using citric acid before adding 5 to 15 skbu / g amylase solution to the slurry at step 402 . the temperature is maintained at 40 ° c . to 65 ° c . for 1 to 3 hours . amylase is an enzyme that catalyzes the breakdown of starch into maltodextrins and glucoamylase converts maltodextrins to maltose and glucose . at step 403 , ph value of cooled down liquefied psp is adjusted between 3 . 0 to 5 . 0 , and then 5 to 36 u / g of an enzyme complex ( hemicellulase 0 to 15 %, pectinase 0 to 20 %, cellulase 0 to 15 %, glucoamylase 35 % to 95 %, and protease 0 to 15 %) is added to the liquefied psp while maintaining the temperature between 40 . degree . c . to 70 . degree . c . for 1 to 5 hours . hemicellulase breaks cross - linking polymeric hemicellulose so the cell wall becomes more susceptible to other enzymatic defragmentation . pectinase breaks down pectin , a polysaccharide substrate that is found in the cell walls of the purple sweet potatoes converting it to glucose . pectinase also attacks dissolved pectin . consequently , its viscosity is reduced because of the degradation of soluble high molecular weight materials in the juice . rupture of cell wall membranes is a major key to increase the juice yield . it should be noted that pectin is not the only ingredient of cell wall . cellulase is used here to attack the cellulose content of the cell wall , which helps improve further the yield of the juice by breaking open the cells to release more active pigments contain in cell vacuoles . glucoamylase breaks the bonds near the ends of large carbohydrates such as the remaining starches , releasing maltose and free glucose . finally , protease hydrolyses proteins in the slurry to amino acids that further lowers the viscosity of the juice . the combined enzymatic treatment converts the slurry mixture to a lower viscosity purple sweet potato juice by removing the starch and pectins for a better yield of the juice . at step 404 , the psp suspension is then heated to 80 . degree . c . to 90 . degree . c . for 1 minute to 10 minutes for enzyme deactivation . the resulting purple sweet potato suspension is ready to be separated at step 405 which is further described in fig5 . fig5 describes the separation and purification processes . the psp cloudy suspension obtained from the enzyme treatment phase is press - filtered or centrifuged to separate the supernatant from the sediment at step 501 . the sediment will be harvested to produce tried psp powder at step 504 . the supernatant is further purified by membrane filtration at step 502 . the liquid thus obtained has a brix value of 6 ° to 12 °. after nano - filtration and / or reverse osmosis at step 503 , a purified purple sweet potato juice is obtained , which is now ready for harvesting at step 504 . fig6 shows the harvesting process . the purified purple sweet potato juice is subject to a controlled temperature vacuum concentration process at 25 ° c . to 85 ° c ., at step 601 and a final purple sweet potato concentrate with brix 55 ° is obtained . the purple sweet potato concentrate has more than 0 . 5 % anthocyanins ( w / w ) and 1 to 2 % phenolic compounds ( w / w ) and ready to be packaged at step 603 . also , the sediment can be combined with concentrated juice to be vacuum concentrated and dried to yield the purple sweet potato powder at step 602 for packaging at step 603 . the following examples are provided to illustrate embodiments of the present invention but are by no means intended to limit its scope . one example of producing psp juice and powers using the process in the present invention is described . 18 kg raw fresh purple sweet potatoes are soaked , washed and sterilized and at the same time de - activating the existing enzymes . then they are ground and blended while its color is fixed by adjusting its ph value to 5 . 5 . next , 45 kg water is added and the puree is liquefied . the liquid purple sweet potato juice is then warmed up to 90 . degree . c . to 110 . degree . c . for 6 minutes . adjust its ph value to 5 . 5 , add 10 skbu / g of amylase solution , and maintain the temperature at 50 . degree . c . to 55 . degree . c . let the solution rest for 2 hours . then adjust the ph value to 4 . 0 to 4 . 5 and then add 26 u / g the enzyme complex of hemicellulase , pectinase , cellulase , glugoamylase , and protease . maintain the temperature between 45 . degree . c . to 60 . degree . c . let it rest for 3 hours . the solution is then filtered by pressure filtration and centrifugation to remove the residues . the solution is further filtered with a microporous membrane with inlet pressure of 0 . 15 to 0 . 25 mpa , resulting a brix . sup .° 10 solution . then the solution is pushed through a nano filtration system and a vacuum low - temperature scraper film evaporator to obtain a brix . sup .° 60 purple sweet potato extract that contains 0 . 52 % of anthocyanin and 1 . 2 % of phenolic compounds . a purified purple sweet potato powder can be obtained from centrifuged sediment and filtered residues and dried in vacuum . another example of producing psp juice and powers using the process in the present invention is described . 15 kg raw fresh purple sweet potatoes are soaked , washed and sterilized and at the same time de - activating the existing enzymes . then they are ground and blended while its color is fixed by adjusting its ph value to 5 . 0 . next , 40 kg water is added and the puree is liquefied . the liquid purple sweet potato juice is then warmed up to 90 ° c . to 110 ° c . for 5 minutes . adjust its ph value to 5 . 0 , add 10 skbu / g of amylase solution , and maintain the temperature at 60 ° c . to 65 ° c . let the solution rest for 2 . 5 hours . then adjust the ph value to 4 . 0 to 4 . 5 and then add 22 u / g the enzyme complex of hemicellulase , pectinase , cellulose , glugoamylase , and protease . maintain the temperature between 55 ° c .- 65 ° c . let it stand for 2 . 5 hours . the solution is then filtered by pressure filtration and centrifugation to remove the residues . the solution is further filtered with a microporous membrane with inlet pressure of 0 . 15 to 0 . 25 mpa , resulting in a brix ° 8 solution . then the solution is pushed through a nano filtration system and a vacuum low - temperature scraper film evaporator to obtain a brix ° 56 purple sweet potato extract that contains 0 . 5 % of anthocyanin and 1 % of phenolic compounds . a purple sweet potato powder can be obtained from centrifuged sediment and filtered residue and dried in vacuum . one more example of producing psp juice and powers using the process in the present invention is described . 15 kg dried purple sweet potatoes are soaked , washed and sterilized and at the same time de - activating the existing enzymes . then they are ground and blended while its color is fixed by adjusting its ph value to 5 . 0 . next , 65 kg water is added and the puree is liquefied . the liquid purple sweet potato juice is then warmed up to 90 . degree . c . to 110 . degree . c . for 5 minutes . adjust its ph value to 5 . 0 , add 8 skbu / g of amylase solution , and maintain the temperature at 60 . degree . c . to 65 . degree . c . let the solution rest for 3 hours . then adjust the ph value to 4 . 0 to 4 . 5 and then add 33 u / g the enzyme complex of hemicellulase , pectinase , cellulase , glugoamylase , and protease maintain the temperature between 60 . degree . c . to 65 . degree . c . let it rest for 4 . 5 hours . the solution is then filtered by pressure filtration and centrifugation to remove the residues . the solution is further filtered with a microporous membrane with inlet pressure of 0 . 15 to 0 . 25 mpa , resulting a brix . sup .° 8 solution . then the solution is pushed through a nano filtration system , reverse osmosis system and a vacuum low - temperature scraper film evaporator to obtain a brix . sup .° 55 purple sweet potato extract that contains 0 . 46 % of anthocyanin and 0 . 8 % of phenolic compounds . a purified purple sweet potato powder can be obtained from centrifuged sediment and filtered residue and dried in vacuum . 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