Producing type 4 resistant starch using a semi-dry chemical modification process

Abstract

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Description

Producing Type 4 Resistant Starch Using a Semi-Dry Chemical Modification ProcessTECHNICAL FIELDIn one aspect, the invention relates to the production of highly digestion resistant type RS4 starches useful as dietary fiber containing starch from pulse plants more particularly illustrated by the production of type 4 resistant pea starch by cross linking. In another aspect, the invention relates to a semi-dry rather than wet slurry process for the production of RS4 starches from any starch source.BACKGROUNDThe demand for protein alternative derived from non-animal sources such as plantbased protein has generated fast development of new process for extracting proteins from abundant plant crops. One family of crops that is the most abundant source of proteins are pulses, which family includes peans, lentils and beans. Processes for extracting proteins from pulse plants render primarily protein concentrates and isolates along with bulk quantities of crude starch (approximately >60% yield and 60-85% purity) as a by-product. Raw pulse starches mostly contain over 30% amylose and show limited functional properties, such as pasting stability, thermal / shear resistance, acid stability and product shelf life in food applications. In contract, starches from tubers and cereal grains can be easily be obtained at higher purity than pulse starches and have the required functional properties for exploitation in food applications. For this reason, pulse starches have not been widely investigated as a commercially viable alternative starch source for modification for use in food applications. Also, modification of starches from cereal grains, roots and tubers improves starch functionalities in various food applications.One desirable modification in food applications is to reduce the digestibility of starch to lower its caloric value and provide prebiotic benefits to the bacterial biome in the human digestive tract. Starches generally contain three fractions based on digestibility: rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). RS is further classified as RS 1, RS2, RS3, RS4 and RS5 based on the physical and chemical structure and under food regulatory standards is included as part of dietary fiber. RS4 type starch is chemically modified via crosslinking, esterification, transglycosylation, orhydroxypropylation. High levels of RS dietary fiber in food have been considered a powerful benefit to health.Most food starch is isolated and purified from starchy cereal grains, tubers, and roots for example in grain milling operations for processing wheat, rice, sorghum, millet and com or in tuber and root processing of potato and cassava. Pulse starches, on the other hand, are not typically purified and are mostly available as a byproduct of isolating other more valuable components form pulses such as protein and / or vegetable oils. Pulse starch byproducts come in the form of starch concentrates or crude starch in a yield typically greater than about 60% yield of the total starch present and a purity in the range of 60-85%. Native pulse starches contain a wide range of amylose content (20 -70%) and have limited functional properties, such as pasting stability, thermal / shear resistance, acid stability and product shelf life in food applications.Such shortcomings in any starch can be significantly improved by chemical modifications such as phosphorylation through cross-linking, which has widely been used with processing cereal, tuber and root starches and which processes may have the potential to expand the use of pulse starches in for a variety of food and industrial uses. Conventional processes for starch cross-linking use a wet slurry reaction at relatively low solids content and have high usage levels of chemicals resulting in cumbersome and unsustainable operations.Patent US5855946 describes a process of making phosphorylated starch using a wet slurry process (40% solids content) using a mixture of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) in the presence of sodium chloride or sulfate at basic pH and moderate heating. The exact reaction conditions have been published in Cereal Chemistry by Woo K.S. and Seib P.A in 2002.Patent EP1961769 also disclose cross-linking starch in a wet slurry reaction The conditions used were 36-44% solids, 5-16% of STMP or a combination of STMP and STPP (in the range of 5-16% STMP and 0.05-0.16% STPP as a percent of starch weight) with 0.1- 20% sodium sulfate or sodium chloride - again as a percent of starch weight), incubated at 30-50°C for 16-24 h. The pH of slurry was adjusted to 11.5-12 by adding 25% sodium hydroxide. The cross-linked starches had 0.2-0.8% phosphorus and 30-96% total dietary fiber.CN102187996A / WO11111928 A2: discloses a method of preparing a crude crosslinked potato dietary fiber / starch product using a wet slurry of a potato starch by-product at 40-50% solid, 8-12% of mixture of STMP / STPP, 10-12% sulfate incubated at 40-55°C for 1-6 h. The disclosed method of preparation is a conventional slurry process using the byproduct from potato wet process.National Starch Food Innovation 2005. Application For the Approval Of RS4-Fiber Modified Starch (Phosphate Di-Starch Phosphate) From High Amylose Maize Starch discloses a phosphorylated starch (RS4-fiber) made from high amylose maize starch for use as a novel food ingredient in Europe. The phosphorylated starch was produced by a wet slurry reaction with cross-linking agents using either a high amylose maize starch slurry derived from corn wet milling or a re-slurry of the corn starch in water. The produced RS4 fiber contains about 70-80% fiber (resistant starch) by the AO AC 991.43 method.In EP 1 836 903 Al, starch is typically modified in 30-50% starch slurry with 5-16% sodium trimetaphosphate (STMP), 0.05-0.16% sodium tripolyphosphate (STPP), 0.1-20% sodium sulfate at pH 11-12 and 3O-5O°C for 1-3 hours. The chemically modified starch is further treated by heat treatment at moisture of 20-35% based on the weight of dry starch at 90-120°C for 1-4 hours. The resulted modified, heat-moisture treated starch contains at least 70% TDF based on the weight of starch.Lim S. and Seib P. Preparation and Pasting Properties of Wheat and Corn Starch Phosphates. Cereal Chemistry 70(2): 137-144, 1993, discloses a procedure to produce crosslinked wheat and corn starches using a wet slurry under the following conditions : 45% purified starch solids in a slurry with 5% STPP (starch base), 5% sodium sulfite, pH 8-11 at 27°C for 1 h, then drying to 10-15% moisture at 40°C, then heating at 130°C for 2 h.Polnaya F.J. et al. Physical Properties and Digestibility of Resistant Starch From Phosphorylated Sago Starch. Pakistan Journal of Nutrition. 17(4): 199-206, 2018. Discloses essentially the same method as Lim and Seib (1993).Woo K.S. and Seib P.A. Cross-Linked Resistant Starch: Preparation and Properties. Cereal Chemistry. 79(6): 819-825, 2002 discloses wet slurry reaction conditions to cross link starch with STMP / STPP using 29-33% starch solids, 10-19% (starch base) of a 99:1 (w / w) mixture of STMP / STPP, 0-20% (starch base) sodium sulfate or sodium chloride at pH 11- 12.3 and 25-70°C for 0.5-12 h.There is a need in the art to find more economical ways to make resistant starches in general, and in particular, a way to make such resistant starches from underused and under valued starch sources such as pulse starches.BRIEF SUMMARYThe present invention provides a novel processing technology that produces RS4 type of dietary fiber through chemical modification of starch with cross-linking reagents in a semidry state. The invention is exemplified using a crude pea starch containing 60- 80% wt / wt starch obtained as a byproduct of processing pea starch to make protein concentrates, but is applicable to any pulse starch and is also applicable to forming resistant starches from more conventional grain and tuber sources. The invented process is more economical and more sustainable - involving simple mixing with less usage of chemicals, water, and energy and high reaction efficiency compared to conventional wet slurry modification processes. The invention may be called a dry or semi-dry starch processing method that involves a chemical reaction at 60% or higher solids content, addition of up to 10% mixture of cross-linking reagents (STMP / STPP at ratio of 99-100:0-1) at pH 11-12 adjusted with the sodium hydroxide solution, holding at ambient temperature for 4 to 24 hours, and then washing with water to remove excess chemical residues followed by centrifugation / filtration, drying and grinding. The produced novel starch ingredient contains up to 0.6% phosphorus and up to 99 % total dietary fiber on a dry wt / wt basis.In one embodiment, a method of making a digestion resistant starch product comprises contacting a starch source comprised of at least 50% starch with a mixture of sodium tripolyphosphate (STPP) and sodium trimetaphosphate (STMP) at a temperature of at least 20°C and at a pH of 10 to 12.0 for a time sufficient to convert at least 70% of the starch in the starch source to digestion resistant starch wherein during the contacting, the moisture content of the contacted starch is 50% or less on a wt / wt basis.In another embodiment, a digestion resistant pulse starch product comprises 60-85% wt / wt of starch and 5-10% wt / wt protein, wherein at least 50% of the starch is crosslinked starch and the pulse product contains at least 60% dietary fiber on a wt / wt basis. The dietary fiber includes non-starch polysaccharides present in the pulse starch and the crosslinked starch.BRIEF DESCRIPTION OF THE DRAWINGSFigure 1. Is a graph showing the measured total dietary fiber content produced in a modified pea starch product of the present invention by reacting with the crosslinker mixture of STMP / STPPP at different concentrations relative to the weight of starch.Figure 2 is a graph showing the effect of reaction time on the content of total dietary fiber content produced from reacting a crude pea starch product containing 70% wt / wt starch with 6% and 7% of crosslinker mixture of STMP / STPPP relative to the weight starch according to a method of the present invention. .

[0001] Figure 3. Is graph showing a linear relationship between total dietary fiber and amount of phosphorous content present in a modified pea starch of the present invention.DETAILED DESCRIPTIONThe present disclosure provides a novel technology to produce type 4 resistant (RS4) granular starches through chemical modification of pulse starch with cross-linking reagents in a semidry state. As used herein, “semidry state” means a solids content of 50-80% by weight with the remainder being water. The disclosure is illustrated by use of a pea starch product, but is applicable to any starch product derived from a pulse plant, which includes peas, lentils and beans. In addition, the process is applicable for use in making RS4 granular starches from conventionally isolated starch products from grain, tubers and roots. As used herein a “starch product” is a product derived from a plant source that contains at least 50% starch on a dry solids weight / weight basis.The process disclosed herein is economic and more sustainable than making RS4 type starches using a wet slurry process. The present process involves simple mixing of components with less chemical, water, and energy usage and with higher reaction efficiency than conventional processes. Such processes of the present invention are applicable to non- conventional starch sources such as pulse starches. In the exemplary process, a crude pea starch product was used. Such a product was obtained by peas to obtain a whole pea flour and separating a protein enriched fraction from the pea flour to obtain the peas starch product. A similar process could also be used with any pulse fruit where a starch enriched fraction having at least 50% wt. / wt starch is produced as a byproduct of separating proteins or oils from the pulse. Typically, in the case of peas, the pulse starch product that results from such a separationhas a composition of about 60 to 85% weight percent starch, about 4 to 30 weight percent fiber and about 5 to 15 weight percent protein. The fiber content is typically below 25%.The crude pea starch was mixed with cross-linking reagents (0-10% sodium trimetaphosphate (STMP) / sodium tripolyphosphate (STPP) at ratio of 99-100:0- 1 , starch base) in a commercial mixer by spraying a mixture of STMP / STPP and sodium hydroxide solution under onto the crude starch with continuous mixing. The pH of the mixture was adjusted to 11-12 and the moisture content of the resulting mixture was adjusted to 30-40 % by adding 5 - 10 % sodium hydroxide solution. The mixture was continuously mixed at a low speed for up to 24 hours and then thoroughly washed with water, centrifuged and dried to the final moisture below 10%. Total dietary fiber (TDF) content in starch was measured by AOAC 991.43 method (AO AC Official Methods of Analysis Supplment March 1995) and the phosphorous content was measured using ICP spectroscopy.Figure 1 shows the increase of total dietary fiber (TDF) content in a crude pea starch fraction (70% wt / wt starch) obtained by reacting the same with increasing crosslinker concentrations up to 10% (dry starch base) at 30-40% moisture, pH 10.5- 12 for a reaction time of 20 hours at ambient temperature with continuous mixing. The results indicate that at a ratio of STMP / STPP to starch of 6% or greater over 90% of starch had been converted to resistant starch type 4 (RS4) useful as a dietary fiber.Figure 2 shows the effect of reaction time on the content of TDF in crude pea starch with 6% and 7% crosslinker, at a final moisture content of 40% at pH 11-12 for reaction of up to 20 hours at ambient temperature with continuous mixing. The TDF content increased quickly at first 8 hours and then slowed down. The amount of conversion of the starch to total dietary fiber essentially is maximized in 20 h reaction.Phosphorous content in starch is a key indicator indicating the degree of starch crosslinking. As shown in Figure 3, the phosphorous content is lineally correlated to the amount of TDF produced in the modified pea starch.Table 1 compares the TDF content present in a crosslinked crude pea starch prepared according to the foregoing semi-dry process to that prepared in a conventional wet slurry process where the reaction mixture contained the same crude pea starch at 35% solids wt / wt, with 10% sodium sulfate (starch base), pH 11-12, mixing for 3 h at 45°C. The invented process had much higher reaction efficiency as indicated by TDF content compared to the slurry process.Table 1. Comparison of semi-dry process and slurry process of crude pea starch.To demonstrate the semi dry process of producing RS4 by crosslinking with STMP / STPP for use as total dietary fiber according to the present invention works better than the wet slurry processes with same crosslinkers when used conventional starches other than pulse starches, commercially purified wheat, tapioca and pea starches were used instead of a crude pea starch product. The crosslinking of commercial pure wheat, tapioca and pea starches using the invented process was done using 5% crosslinker (% of starch, ) brought to a moisture content of 40% at pH 11-12 with mixing at ambient temperature for 20 hours. Table 2 shows that starch with high TDF content was produced with three starches, indicating the invented semi-dry modification process can be extended to other sources of starches.Table 2. RS4 type starch as dietary fiber in modified pure tapioca and pea starchesThis disclosure has been described with reference to certain exemplary embodiments, compositions and uses thereof. However, it will be recognized by those of ordinary skill in the art that various substitutions, modifications or combinations of any of the exemplary embodiments may be made without departing from the spirit and scope of the disclosure. Thus, the disclosure is not limited by the description of the exemplary embodiments, but rather by the appended claims as originally filed.

Claims

CLAIMSWhat is claimed is:

1. A method of making a digestion resistant starch product comprising, contacting a starch source comprised of at least 50% starch with a mixture of sodium tripolyphosphate (STPP) and sodium trimetaphosphate (STMP) at ratio of 99-100:0- l nd at a temperature of at least 20 °C and at a pH of 10 to 12.0 for a time sufficient to convert at least 70% of the starch in the starch source to digestion resistant starch wherein during the contacting, the moisture content of the contacted starch is 50% or less on a wt / wt basis.

2. The method of claim 1 wherein the moisture content is 45% or less.

3. The method of claim 1 wherein the moisture content is 15%-45%.

4. The method of claim 1 wherein the moisture content is 25%-40%.

5. The method of claim 1 wherein at least 70% of the starch in the starch source is converted to the digestion resistant starch.

6. The method of claim 1 wherein at least 80% of the starch in the starch source is converted to the digestion resistant starch.

7. The method of claim 1 wherein the pH is 10.5 to 12.0.

8. The method of claim 1 wherein the starch source is a pulse starch product.

9. The method of claim 8 wherein the pulse starch product contains 60%-85% wt / wt starch.

10. The method of claim 8 wherein the pulse starch product is a co-product obtained by separating a protein enriched fraction from a pulse flour.

11. A digestion resistant pulse starch product comprising 60-85% wt / wt of starch and 5- 10% wt / wt protein, wherein at least 50% of the starch is crosslinked starch and the pulse product contains at least 60% dietary fiber on a wt / wt basis where the dietaryfiber includes non-starch polysaccharides present in the pulse starch and the crosslinked starch.

12. The composition of claim 11 wherein the non-starch polysaccharides account for 1 fl- 25 % of the dietary fiber.

13. The composition of claim 11 wherein the crosslinked starch accounts for at least 50% of the weight of the dietary fiber.

14. The composition of claim 11 wherein the crosslinked starch accounts for at least 60% of the weight of the dietary fiber.

15. The composition of claim 11 wherein the crosslinked starch accounts for at least 70% of the weight of the dietary fiber.

16. The composition of claim 11 wherein the crosslinked starch accounts for at least 80% of the weight of the dietary fiber.

17. The composition of claim 11 wherein the pulse starch is obtained by milling pulses to obtain a pulse flour and separating a protein enriched fraction from the pulse flour to obtain the pulse starch prior to crosslinking the starch.

18. The composition of claim 11 wherein the crosslinked starch contains is obtained by cross linking starch in the pulse starch product with sodium tripolyphosphate (STPP) and sodium trimetaphosphate (STMP) and the crosslinked starched contains phosphorous.

19. The composition of claim 18 wherein phosphorous content is 0-0.7%20. The method of claim 1, wherein the starch originates from a cereal grain, a root, or a tuber plant.