Process for preparing starchy products

Abstract: The invention relates to a starch composition containing a relatively high proportion of so-called "resistant starch" structures. The compositions of the invention are obtrained by debranching an aqueous slurry of a gelatinized starch and retrograding the resulting product.

Description: The present invention relates to a starch composition containing a relatively high proportion of so-called "resistant starch" structures. It has been known for many years that starches, which commonly consist of varying proportions of amylose and amylopectin, may be subjected to an enzymatic treatment which reduces the content of the highly branched amylopectin and increases the content of short-chain amylose structures (see, for example, US patent 3,729,380). It is also known that the products of such enzymatic treatment are more prone to retrogradation than normal starches and produce in this manner compositions containing increased amounts of resistant starch structures. Resistant starch (RS) is resistant to attack by alpha-amylase and may be used therefore as a low calorie bulking component in food compositions so contributing to the dietary fibre content of such compositions. The treatment of the starch with the debranching enzyme takes place in an aqueous slurry which, for handling reasons, cannot be too concentrated. It would clearly be attractive therefore to be able to use a starchy composition at a higher concentration of the starch material treated. WO-A-90/15147 discloses a process for making a product containing RS which comprises mixing starch having an amylose content greater than 50%, preferably greater than 70%, and water, heating the mixture above 100°C, cooling the heated mixture to form a retrograded starch gel, comminuting the gel and treating it with an amylolytic enzyme and concentrating the resistant starch in the product by removing digested starch fractions. EP-A-564893 and US-A-5,281,276 describe and claim a process for the production of a RS product containing at least about 15% RS in which an aqueous slurry of starch containing at least 40% amylose is gelatinised and debranched by treatment with a debranching enzyme which hydrolyses 1,6-glucosidic bonds in the starch molecules, the debranched product subsequently being retrograded to produce RS. The optimum starch concentration in the aqueous slurry is said to be about 15% and the Examples of EP-A-564 893 illustrate the process by using starch slurries containing 14% to 17% starch respectively. The starch starting material contains at least 40% amylose and for a corn (maize) starch containing 25% amylose it is shown that no RS is formed in the process. As the percentage of amylose in the starch starting material increases above 40% so does the RS in the product of the process until a starch containing 100% amylose is shown to produce a product containing 50.3% RS. We have now found a method of producing a starch composition containing a relatively large amount of RS structures from a starting material which contains less than 40% amylose and which can be debranched in slurries containing more than 15% solids. Accordingly, the invention is a process for the production of a product containing RS structures in which an aqueous slurry of a gelatinised starch is debranched by a debranching enzyme and the resulting product retrograded and which is characterised in that the aqueous slurry contains at least 20% by weight solids and is a slurry of a maltodextrin derived from a root or tuber starch containing less than 40% amylose and in that the product comprises at least 25% by weight RS. The product of the process comprises at least about 25% by weight RS, preferably 30% by weight or more RS, particularly over 50% by weight RS. The maltodextrin used in the present invention is obtained by hydrolysis, either acid or enzyme catalysed, of a root or tuber starch. Preferably the maltodextrin is a potato starch maltodextrin which suitably has a DE (dextrose equivalent) of 1 to 19, preferably 2 to 10 and more preferably 2 to 5. Such potato starch maltodextrins are produced from potato starch containing about 25% amylose. Other root or tuber starch maltodextrins which may be used in the process include tapioca maltodextrins. The aqueous slurry of the maltodextrins used in the process according to the invention contains at least 20% by weight solids but may be more concentrated and may contain 30% by weight or more solids. The debranching enzymes which may be used in the process are those known for this purpose i.e., pullulanases and isoamylases or mixtures thereof. Depending upon the nature of the specific enzyme chosen, the debranching may be carried out at a temperature in the range of 25°C to 70°C, preferably 50°C to 60°C, and at a pH in the range of 3 to 7.5, preferably in the range 5 to 6. The treatment generally lasts up to 24 hours and at its conclusion the enzyme is deactivated by lowering the pH to 3 or less and/or by increasing the temperature to above that tolerated by the enzyme in question. On completion of the enzymatic treatment the retrogradation of the amylose structures is effected by allowing the aqueous reaction product to stand, suitably at a temperature in the range of 0 to 30°C and for a period of up to three days, more preferably for a period of 1 to 36 hours. Following the completion of the retrogradation the composition is dried, e.g., by spray drying, to give a powdered product containing up to 60% by weight RS particularly 25 to 55% by weight RS which is suitable for use as a component of various food compositions. The invention will now be further described by reference to the following Examples in which the determinations of RS were made by the following method. A 5% by weight suspension in water of the retrograded starch product is thoroughly homogenised in an acetate buffer solution. The acetate buffer is made by dissolving 8.2 g anhydrous sodium acetate in 250 ml of a saturated aqueous solution of benzoic acid, adding 4 ml of 1M calcium chloride and making up 800 ml with distilled water before adjusting the pH to 5.2 with acetic acid and finally making up to 1000 ml with distilled water. 25 ml of the suspension are incubated with 1 ml pancreatic solution for 24 hours at 37°C in a shaking water bath. The incubation suspension is next stirred into 119 ml of 95% alcohol, filtered and the filtration residue dried and its starch content determined according to the relationship: R S = starch content of the residue (on a dry basis) x 100 starch content of the suspension before incubation (on a dry basis) The pancreatic solution is made by stirring 2 g pancreatin with 12 ml distilled water for 10 minutes, centrifuging and using the supernatant liquid as the pancreatic solution. Example 1 25 kg potato starch maltodextrin with a dextrose equivalent of about 3 was dissolved in water to give a concentration of 25% by weight. The suspension was heated to 50°C and the pH adjusted to 5.0. After adding 25 ml isoamylase (product EN102 of Hayashibara Biochemical Laboratories Inc), the reaction was allowed to proceed for 20 hours after which time the temperature was increased to 80°C and the pH reduced to 3.0 for 1 hour in order to deactivate the enzyme. The average Mol. wt. after debranching was 13680 as determined by gel permeation chromatography (GPC). The amount of oligomers with a degree of polymerisation (DP) ≤ 10 was 22%. After readjustment of the pH to 5.0 the suspension was cooled to 4°C and held at this temperature for 24 hours. The weak gel that formed was easily destroyed by stirring and the suspension finally brought to 15% by weight by dilution with water and spray dried. This product contained 28.9% RS compared with the maltodextrin before debranching which formed only 7.3% RS under comparable retrogradation conditions. Example 2 This example demonstrates the influence of the retrogradation conditions on the formation of resistant starch. The debranched maltodextrin used was essentially the same as that described in Example 1. For 24 hours retrogradation the following conditions were compared: concentration 10%, 30% by weight temperature 4°C; 25°C The following amounts of RS (% by weight) were detected: 10% 30% 4°C 31.8 28.5 25°C 27.2 26.4 This Example shows that retrogradation at 25°C gives only a slightly lower figure for resistant starch compared with retrogradation at 4°C. The lower concentration of debranched starch (10% by weight) in the slurry leads to the formation of a slightly increased amount of resistant starch compared with the slurry containing 30% by weight debranched starch. Examples 3 to 5 In Examples 3 to 5 the process used was the same as that described in Example 1 replacing the potato starch maltodextrin by other starting materials within the scope of the present invention. These starting materials and the experimental results obtained are given in the following table. R.S. % Example Starting Material M.wt(Mw) before debranching M.wt(Mw)after debranching Oligomers DP≤ 10 before debranching after debranching 3 Acid thinned potato starch 52,180 9340 4.5 % 20.0 51.8 4 Potato starch pyrodextrin 106,500 11,530 5.8 % 4.9 28.0 5 Tapioca starch maltodextrin (DE approx 2) 129,600 19,770 13 % 2.4 25.6 Example 6 A regular corn starch maltodextrin with a dextrose equivalent of 3 was treated in the same way as that described for potato maltodextrin in Example 1. After debranching the product had an average Mol. Wt. of 14390 as determined by the GPC and contained 20% oligosaccharides with DP≤10. The product was retrograded at respectively 4°C and 25°C for 24 hours. The following amounts of resistant starch were determined: 4°C = 10.0% 25°C = 8.3% This example shows that a debranched corn maltodextrin forms much less RS than a debranched potato maltodextrin under the same conditions of treatment. Because the amylose contents of corn starch and potato starch differ only marginally the amylose content cannot be the reason for the large difference in resistant starch. It seems probable therefore that debranching of the partially hydrolysed potato amylopectin liberates more linear fragments which are capable of being retrograded to resistant structures. Example 7 A waxy maize starch maltodextrin with a DE of about 4 was treated by the process described in Example 1. The debranched product was found to have a Mw of 12010 but after holding at 4°C for 24 hours the amount of resistant starch (RS) which was formed amounted to only 0.3%.

Claims: A process for the production of a product containing resistant starch (RS) structures by debranching an aqueous slurry of a gelatinised starch by means of a debranching enzyme and retrograding the resulting product, characterised in that the aqueous slurry comprises at least 20% by weight solids and is a slurry of a maltodextrin derived from a root or tuber starch containing less than 40% amylose and in that the product comprises at least 25% by weight RS. A process according to claim 1, characterised in that the product of the process comprises at least 30% by weight RS. A process according to claim 1, characterised in that the maltodextrin is a potato starch maltodextrin. A process according to any one of claims 1 to 3, characterised in that the maltodextrin has a dextrose equivalent (DE) of from 2 to 10. A process according to claim 4, wherein the maltodextrin has a DE of from 2 to 5. A process according to any one of the preceding claims characterised in that the aqueous slurry comprises 30% by weight or more solids. A process according to any one of the preceding claims characterised in that the debranching enzyme is a pullulanase or isoamylase or mixtures thereof, the debranching process is carried out at a temperature in the range of 25°C to 75°C and at a pH in the range 3 to 7.5. A process according to any one of the preceding claims characterised in that the retrogradation is carried out by allowing the aqueous, debranched starch product to stand, preferably at a temperature in the range of 0 to 30°C and for a time period in the range of 1 to 36 hours. A process according to any one of the preceding claims characterised in that the product after retrogradation is spray dried to give a powdered product containing from 25 to 60% by weight RS. A process according to claim 9, wherein the product after retrogradation is spray dried to give a powdered product containing from 25 to 55% by weight RS.

Inventors: ANGER HORST, KETTLITZ BERND, MOORTHAMER EDWIN, STOOF GISELA, ANGER, HORST, KETTLITZ, BERND, MOORTHAMER, EDWIN, STOOF, GISELA
Applicants: CERESTAR HOLDING BV
Application year: 1995
Main classification: C12P19
IPC codes: A23L1, C08B30, C12P19