Process for the fractionation of cereal brans
A process for the fractionation of valuable fractions from cereal brans (e.g. wheat, barley and oat brans, and rice polish) is described. In particular, this invention describes a two step process, in which the said bran is first subjected to a combination of enzymatic treatment and wet milling, followed by sequential centrifugation and ultrafiltration, which aims at physically separating the main bran factions, i.e. insoluble phase (pericarp and aleurone layer), germ-rich fraction, residual endosperm fraction and soluble sugars. A second step consists of fractionating cereal brans substantially free of soluble compounds, hence insoluble phase from the above-mentioned first step, by enzymatic treatment with xylanases and/or beta-glucanase and wet milling, followed by sequential centrifugation and ultrafiltration, which aims at physically separating the main fractions, i.e. insoluble phase (remaining cell wall components), protein-rich fraction, soluble hemicellulose and oligosaccharide, and therefore maximizes the extraction rate of valuable cell wall components and aleurone cells from previously cleaned bran.
1. A process for the wet fractionation of cereal bran obtained after a primary milling of one or more of the cereals of the group comprising wheat, barley, oat, rye and triticale resulting in the substantial removal of the endosperm, into protein, sugar and insoluble fractions, a process wherein bran substantially devoid of the endosperm is subjected to a first enzymatic treatment, utilizing a combination of enzymes of the group containing starch-hydrolysing enzymes, and aqueous wet milling, followed by a separating step whereby resultant aqueous slurry/suspension is separated into an insoluble fibrous fraction and a soluble fraction, whereby said soluble fraction is further separated by centrifugal forces into a germ-rich fraction and an endosperm- and sugar-rich fraction, said endosperm- and sugar-rich fraction is further separated into proteins and sugars and;
said insoluble fibrous fraction containing a cleaned bran consisting of both insoluble pericap and aleurone fractions, is further subjected to a hydrolyzation by a second enzymatic treatment utilizing a combination of one or a mixture of enzymes of the group non-starch polysaceharidases, and aqueous wet-milling, and a subsequent step whereby the resultant hydrolysate is separated into an insoluble phase and a soluble phase.
2. A process according to claim 1 , wherein the first enzymatic treatment is accomplished using a starch degrading enzyme of the groups amylases and amyloglucosidases.
3. A process according to claim 1 , wherein the second enzymatic treatment is carried out using at least one non-starch degrading polysaccharidase in the form of cellulases, hemicellulases mainly xylanases, beta-glucanases, and pectinases, and/or phytases.
4. A process according to claim 1 , wherein the insoluble phase obtained from the hydrolysate and containing primarily insoluble fibers, of the group comprising cellulose, lignin, less accessible hemicellulose, residual aleurone cells and cell wall bound proteins is spray dried, and;
the soluble phase obtained from the hydrolysate containing soluble hemicellulose, oligosaccharides, sugars and proteins, and said soluble phase is further separated into a heavy phase containing mainly aleurone cell protein and a light phase containing hemicellulose in the form of soluble hemicellulose and oligosaccharides, and;
said light phase is further separated by size exclusion technique into soluble hemicellulose (medium molecular size fraction) and oligosaccharides mixed with sugars (small molecular size fraction).
5. A process according to claim 1 , wherein cleaned bran is cereal bran substantially free of both in water or less polar solvents soluble compounds, derived from wheat, barley, oat, rye or triticale.
6. A process according to claim 1 , wherein the combination of intermittent wet milling with enzymatic treatment is arranged to increase the rate of enzymatic hydrolysis of the substrate thereby improving the overall hydrolysis performance and the subsequent separation of the various fractions by density/solubility and molecular size.
7. A process according to claim 3 , wherein the second enzymatic treatment is accomplished using xylanases with high beta 1-4-xylanase (pentosanase) and/or beta-glucanase activity.
8. A process according to claim 1 , wherein the first enzymatic treatment is carried out for less than 3 hours at a pH of 4 to 7.5, at a temperature from 50 to 90° C., and at an enzymatic activity of at least 1 IU/g of substrate.
9. A process according to claim 1 , wherein the second enzymatic treatment is carried out for less than 3 hours at a pH of 4 to 7, at a temperature from 35 to 80° C., and at an enzymatic activity of at least 1 IU/g of substrate.
10. A process according to claim 8 , wherein the first enzymatic treatment is carried out for less than 3 hours at a pH of 4.5 to 7 and at a temperature from 50 to 75° C., at an enzymatic activity of at least 200 to 1500 IU/g of substrate.
11. A process according to claim 9 , wherein the first enzymatic treatment is carried out for less than 3 hours at a pH of 4.5 to 5.5 and at a temperature from 40 to 50° C., at an enzymatic activity of at least 200 to 1500 IU/g of substrate.
12. A process according to claim 1 , wherein the first enzymatic treatment and aqueous wet milling is followed by an enzyme inactivation by wet heat treatment.
13. A process according to claim 1 , wherein the second enzymatic treatment and aqueous wet milling is followed by an enzyme inactivation by wet heat treatment.