Patent Application: US-201013701046-A

Abstract:
an economically feasible process for manufacturing tagatose is provided . the process includes hydrolyzing lactose to galactose and glucose , separating galatose from hydrolysates , and isomerizing galactose to tagatose with metal hydroxide in an aqueous suspension .

Description:
in an embodiment of the present invention , manufacture of tagatose and glucose from lactose comprises a three - step process including the hydrolysis of lactose , the separation of galactose and glucose , as well as the isomerization of galactose . in the hydrolysis step of this process , a particular hydrolysis procedure is established in ensuring to achieve the effectiveness and the general economic feasibility of the hydrolysis . procedure that uses mineral acid as the hydrolytic catalyst according to the invention is a milder chemical hydrolysis for lactose . it is able to split lactose into to galactose and glucose without byproducts because of the complete and nondestructive characters of the hydrolysis . an additional benefit of using acidic hydrolysis is the reaction may be carried out under higher temperature where the solubility of lactose is higher . this means that more concentrated lactose can be applied in the hydrolysis of the invention . this again means a less acid consumption and a short reaction time for hydrolysis . the acid - catalyzed hydrolysis of this invention minimizes hydrolysis costs and maximizes hydrolysis yields per time unit . the mineral acid usable in the present invention is preferable to be one or more selected from the group consisting of carbonic acid , hydrochloric acid , phosphoric acid and sulfuric acid , and more preferably sulfuric acid . the hydrolysis step is preferable to perform with 0 . 2 - 0 . 6 m mineral acid and perform under temperature between 90 - 120 ° c . by following the above procedure , it is assured to obtain a high conversion ( 95 - 100 %) of lactose with a high yield ( 95 - 100 %) of galactose and glucose . with this procedure , hydrolysis of lactose yields an equimolar mixture of the galactose and glucose . the obtained hydrolysate is cooled , neutralized and demineralized according to known techniques in the art . subsequently , the equimolar mixture of the galactose and glucose are separated into the products of galactose and glucose respectively by any known separation technologies in the art preferably with high performance liquid chromatography ( hplc ). in the chromatographic separation step of this invention , a particular elution profile is established in ensuring to prevent the decomposition of galactose and glucose during hplc separation . addition of 10 . 0 % acetonitrile in water instead of water as eluent has significantly reduced the detection of both galactose and glucose as temperature rises when using a ca 2 + - form carbohydrate column ( table 1 ). removal of water from the start solvent gradient from the combination with acetonitrile has significantly reduced the detection of galactose and glucose when using an amino - bonded silica carbohydrate column . the rate of decomposition of galactose and glucose is a result of elevated temperature and pressure . it is surprisingly found that water is the most effective solvent and stabilizer in the chromatographic separation of galactose and glucose under the hplc conditions . following separation , the separated galactose and glucose solution are evaporated and then crystallized or dried into galactose and glucose crystals or powders , respectively . the obtained glucose can be sold or processed further into a salable product such as high fructose corn syrup . developing the value of glucose can help lower overall production costs . in the isomerization step of this process , a particular alkaline isomerization procedure is established in ensuring to reach the effectiveness and the general economic feasibility of the isomerization . galactose in general undergoes both reversible and irreversible reactions in alkaline aqueous solution with metal ions . the reversible reactions mainly include isomerization of galactose into tagatose . the irreversible reactions mainly include non - oxidative alkaline degradation and oxidative alkaline degradation of galactose into dicarbonyl compounds and acidic species . therefore , a complete isomerization of one monosaccharide galactose into another monosaccharide tagatose may be impossible under these conditions . alkaline isomerization and alkaline degradation of galactose are two synchronous processes observed in the alkaline solution with metal ions . the process of alkaline isomerization of galactose is independent from the process of alkaline degradation of galactose . the isomerization of galactose into tagatose is faster than the degradation of galactose into dicarbonyl compounds and acidic species . maximum production of tagatose is nearly completed within the first 0 . 5 hour , whereas degradation of galactose reaches the high value in the second hour of the reaction , respectively ( see table 2 ). the initial galactose concentration was 18 % by weight in deionized water . the concentration of calcium hydroxide as alkaline reagent was 8 % by weight in deionized water . the rate of alkaline isomerization of galactose is dependent on the rate of alkaline degradation of galactose . it is surprisingly found that galactose undergoes the isomerization while essentially avoiding degradation in alkaline aqueous suspension with metal ions . the equilibrium between the substrate of galactose and the products of tagatose and degradated products are altered toward tagatose while the reaction is performed in the alkaline suspension . as a result , the yield of tagatose formed in the isomerization becomes the highest via prevention of the concurrent degradation in alkaline suspension of galactose . the isomerization step c ) is preferable to be carried out by reaction of an aqueous suspension of galactose with sodium afuminate and metal hydroxide or the mixture thereof . the metal hydroxide preferably is one or more selected from the group consisting of aluminum hydroxide , barium hydroxide , calcium hydroxide , magnesium hydroxide , and strontium hydroxide , more preferably calcium hydroxide . the isomerization step is preferably performed with a molar ratio for metal hydroxide : galactose of 0 . 5 : 1 - 2 : 1 . the isomerization step is preferably performed at 0 - 30 ° c . the isomerization of galactose is preferable to be carried out by adding an aqueous slurry of metal hydroxide into a suspension of galactose . the term “ slurry of metal hydroxide ” in the present application refers to an aqueous suspension that contains metal hydroxide more than that could be dissolved in the water under stirring . the slurry of metal hydroxide in the present application may be prepared by any technology known in the art , such as by adding metal hydroxide into water under stirring . the slurry of metal hydroxide is preferably to be a slurry of calcium hydroxide in water . the term “ suspension of galactose ” in the present application refers to a solution that contains galactose more than that could be dissolved in the solvent . the excessive galactose contained in the solvent stays as insoluble solutes homogenously distributed throughout the liquid under stirring . the suspension of galactose in the present application preferably has a galactose content of more than 30 % by weight in water , more preferably 50 - 70 % by weight . the solubility of galactose varies depending on the adopted reacting conditions such as temperature and pressure etc ., and thus the amount of galactose added in the suspension of galactose may also vary accordingly . the suspension of galactose in the present application may be prepared according to any known technology in the art , for example by mixing the galactose with water under stirring . the overall production costs is further lowered by preventing the alkaline degradation of galactose . the following is a description of the preferred embodiment of the isomerization step of this process which comprises preparing an aqueous suspension of galactose with a galactose content of more than 50 % and less than 70 % by weight , said suspension is maintained at a temperature of 0 - 30 ° c ., and preferably 5 - 15 ° c . ; preparing an aqueous slurry of ca ( oh ) 2 ( preferably & gt ; 24 % by weight ) by adding ca ( oh ) 2 to water or by adding calcium oxide ( cao ) ( preferably & gt ; 18 % by weight ) to water , said slurry is maintained at a temperature of 0 - 30 ° c ., and preferably 5 - 15 ° c . ; introducing the ca ( oh ) 2 slurry into the suspension of galactose under stirring for 2 hours while maintaining this temperature ; stopping the reaction by neutralizing the reaction mixture with most common mineral acids such as hydrochloric acid , phosphoric acid , sulfuric acid and preferably carbonic acid that frees the tagatose from intermediate calcium hydroxide - tagatose complex and forms a poorly soluble calcium salt ; removing the salts by a combination of filtration and ion exchange ; and recovering the pure tagatose by concentrating the solution and thus crystallizing the obtained product . in the neutralization step , the temperature is preferably to be kept within 0 - 20 ° c . as long as the ph value is still relatively alkaline . once the ph approaches neutral , the cooling and the introduction of mineral acid are discontinued . the process of the invention is distinguished particularly by its extraordinary economy . it can be performed without expensive apparatus . due to its economy , it is particularly well suited for the production of tagatose and glucose on a large commercial scale , and in this it is very much superior to the manufacturing processes known hitherto . the economical production and highest yield of tagatose and glucose obtained in this invention are unprecedented . the following example illustrates the present invention , which shall not be considered as limitation to the present invention . lactose ( purity ≧ 99 %) was produced from whey by ultrafiltration followed by crystallization . 10 l 36 % lactose in 0 . 4 m sulfuric acid ( wlv ) was carried out with stirring at 100 ° c . the progress of the hydrolysis was monitored by hplc each 0 . 5 hour , as described below . after 2 hours lactose was completely hydrolyzed into its subunits galactose and glucose . the hydrolyzate was found to contain 1764 g galactose , and 1728 g glucose based on 3600 g lactose added , showing a 99 % conversion of lactose , and a yield of 49 % galactose and a yield of 48 % glucose . an aliquots of the reaction mixture was withdrawn from the reactor and diluted ten - fold with deionized water . the reaction mixture was neutralized and filtered through 0 . 2 μm filter . the detection was done by waters hplc using a bio - rad aminex hpx - 87 c column ( ca 2 + form ) and a water 2414 differential refractometer . the eluent was deionized water with 0 . 005 % calcium acetate ( w / v ). the column temperature was 85 ° c . and the flow rate was 0 . 6 ml per minute . the hplc system was calibrated before use with a mixed standard sugars at a known concentration . comparable analyses were performed in the ligand - exchange mode on a ca 2 + - form aminex hpx - 87c column using a waters hplc system with a waters 2414 differential refractometer . the column temperature was 65 ° c ., 75 ° c . and 85 ° c ., and the eluent was water and 10 % acetonitrile in water ( v / v ), respectively . the flow rate was 0 . 6 ml per min . all analytical samples were diluted with deionized water and filtered through a 0 . 2 μm filter prior to hplc - analysis . the results revealed a drop in the detection of both galactose and glucose as column temperature was elevated but no similar effect was detected on tagatose when using 10 % acetonitrile in water as eluent . the column temperature effect was found to be more pronounced for galactose ( 34 % reduction ) than for glucose ( 13 % reduction ). the systematic decrease of both galactose and glucose was not observed when using water as eluent . calcium hydroxide slurry ( 37 % by weight , 5m ) was prepared by carefully mixing calcium oxide ( cao , called lime or quicklime ) with deionized water and cooled to about 5 to 15 ° c . galactose solution ( 18 % by weight , 1m ) was prepared by dissolving galactose in deionized water and cooled to about 5 to 15 ° c . at that temperature , 1 l of the calcium hydroxide slurry were gradually added into the 5 l of galactose solution under stirring and cooling , the temperature not being allowed to rise above 20 ° c . the progress of the reaction was monitored by hplc analysis each 0 . 5 hour , as described in example 1 . this resulted in the formation of a mass which gradually became jelly - like , becoming increasingly viscous upon one hour of standing in the cold state . after approximately 2 hours , galactose conversion reached greater than 95 % and the reaction was terminated by slowly adding carbonic acid until the ph was below 7 . as the gel dissolved , tagatose released and calcium carbonate precipitated in the reaction mixture . the calcium carbonate solids were separated from the reaction mixture by filter press . the analysis of the solution showed that 900 g of galactose had been consumed and 486 g of tagatose had been produced with a conversion of 100 % and a yield of 54 . 8 %. the filtrate containing tagatose was deionized through ion - exchange resins according to known procedures . the collected deionized filtrate was concentrated via evaporation to form a thick syrup . tagatose was crystallized from the syrup by addition of ethanol and cooling in a freezer . tagatose crystals were refined with 95 % ethanol to obtain a composition of 99 . 1 % tagatose and 0 . 9 % unknown . calcium hydroxide slurry ( 49 % by weight , 6 . 67m ) was prepared by carefully mixing calcium oxide with deionized water and cooled to about 5 to 15 ° c . galactose suspension ( 55 % by weight , 3 . 08m ) was prepared by mixing galactose in deionized water and cooled to about 5 to 15 ° c . at that temperature , 2 . 2 l of the calcium hydroxide slurry were gradually added to the 5 l of galactose suspension under strong agitation and good cooling , the temperature was not allowed to rise above 20 ° c . the progress of the reaction was monitored by hplc analysis each 0 . 5 hour , as described in example 1 . this resulted in the formation of a mass which gradually became jelly - like , becoming increasingly viscous upon one hour of standing in cold state . after approximately 2 hours , galactose conversion reached greater than 95 % and the reaction was terminated by slowly adding carbonic acid until the ph was below 7 . in this process , the precipitate dissolved to release tagatose and calcium carbonate precipitated . the calcium carbonate solids were separated from the reaction mixture by filter press . the analysis of the solution showed that 2772 g of galactose had been consumed and 2550 g of tagatose had been produced with a conversion of 100 % and a yield of 92 %. the calcium hydroxide slurry converted 554 g / l galactose to 510 g / l tagatose within 2 hours , the tagatose productivity with alkaline isomerization in suspension was 255 g / l · h . the identity of the tagatose manufactured according to the present invention was achieved via reference standard sugars by a waters hplc system together with a waters 2414 differential refractometer on a ca 2 + - form aminex hpx - 87c column ( bio - rad ) using the conditions described in the method of assay . sugars used as reference standards were lactose , glucose , galactose and tagatose and were of the best commercial grade from sigma . hplc elution profiles of a reference standard mixture containing lactose , glucose , galactose and tagatose and of three representative batches of tagatose products are shown in fig2 . the retention time for the chromatogram of the tagatose product corresponds to that for tagatose in the chromatogram of reference standard mixture . results of hplc data confirming the identity of the tagatose manufactured according to the present invention are identical to the commercial tagatose in the reference standard mixture . although the invention has been described with preferred embodiments , it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art . such variations and modifications are to be considered within the purview and the scope of the claims appended hereto . 1 . prenosil j e ., stuker e ., and bourne j r . 1987 . formation of oligosaccharides during enzymatic lactose : part i : state of art . biotechnol bioeng . 30 : 1019 - 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