Low Digestibility Legume Starch

Abstract

The present invention relates to a legume starch characterized in that it has a slowly digestible starch (SDS) content of 30 to 34% by weight and also a very slowly digestible starch (vSDS) content of 34 to 40% by weight.

Description

[Technical field]

[0001] The present invention relates to legume starches, in particular pea starches, having a slowly digestible starch (SDS) content of 30-34% by weight, further characterised by a very slowly digestible starch (vSDS) content of 34-40% by weight (a standard deviation of 2% is allowed for these values ​​to take into account experimental variability).

[0002] The invention also relates to the selection of batches of pea starch having a total content of slowly digestible and very slowly digestible starches of more than 60% by weight and to the use of this controlled content of slowly digestible (SDS) and very slowly digestible (vSDS) starches to ensure a controlled homogeneity of the product. [Background technology]

[0003] From a physiological point of view, in humans or animals, the major portion of carbohydrates ingested in the diet is represented by starch, an energy storage molecule specific to plants and the main component of starchy foods (pasta, flour, potato).

[0004] During digestion, starch molecules are broken down into linear glucan chains, which are then broken down into simple glucose that can be absorbed by the digestive system.

[0005] Starch digestion begins in the oral cavity during chewing by the enzyme salivary amylase.

[0006] This initial breakdown of starch is stopped by the acidity of the stomach but is resumed in the duodenum (the first part of the small intestine) by the action of pancreatic and intestinal amylase.

[0007] The sequential action of all these amylases results in the appearance of a disaccharide known as maltose, which is itself converted into two simple sugars, namely glucose.

[0008] Biochemically synthesized starch, a source of carbohydrate, is one of the most widespread organic substances in the plant kingdom, where starch constitutes the nutritional reserve of living organisms.

[0009] It therefore occurs naturally in the storage organs and tissues of higher plants, in particular in cereal grains (wheat, maize, etc.), legume grains (peas, beans, etc.), potato or cassava tubers, roots, bulbs, stems, and fruits.

[0010] Starch is a mixture of two homopolymers, amylose and amylopectin, which are composed of D-glucose units linked together via α-(1-4) and α-(1-6) bonds, which are the source of branching in the molecular structure.

[0011] These two homopolymers differ with respect to their degree of branching and their degree of polymerization.

[0012] Amylose is slightly branched with short chain branches and has a molecular weight of 10,000 to 1,000,000 daltons. The molecule is made up of 600 to 1,000 glucose molecules.

[0013] Amylopectin is a branched molecule with long chains branched every 24-30 glucose units via α(1-6) bonds. Its molecular weight is in the range of 1,000,000-100,000,000 daltons and its degree of branching is approximately 5%. The entire chain may contain 10,000-100,000 glucose units.

[0014] The ratio of amylose to amylopectin varies depending on the plant from which the starch is derived.

[0015] Starch is stored in storage organs and tissues in a granular state, ie in the form of semicrystalline granules.

[0016] This semi-crystalline state is essentially due to the amylopectin macromolecule.

[0017] In the native state, starch granules have a degree of crystallinity that is in the range of 15 to 45% by weight, depending substantially on the plant of origin and the method carried out for its extraction.

[0018] Thus, when granular starch is viewed under a microscope under polarized light, a distinctive black cross, known as a "Maltese cross", is visible.

[0019] This phenomenon of positive birefringence is due to the semicrystalline organization of these granules, the average orientation of the polymer chains being radial.

[0020] For a more detailed description of granular starch, reference may be made to chapter II entitled "Structure et morphologie du grain d'amidon" ["Structure and morphology of the starch grain"] by S. Pérez in "Initiation a la chimie et a la physico-chimie macromoleculaires" ["Introduction to macromolecule chemistry and physical chemistry"], first edition, 2000, volume 13, pages 41-86, work of Groupe Français d'Etudes et d'Applications des Polymeres [French Polymer Group].

[0021] Dry starch has a moisture content ranging from 12 to 20% by weight, depending on the plant of origin, which of course depends on the residual moisture of the medium (for aw=1, starch can fix up to 0.5 g of water per gram).

[0022] When a starch suspension is heated with excess water to temperatures above 50° C., the starch granules irreversibly swell, disperse, and then dissolve.

[0023] It is these properties in particular that give starch its desired technological properties.

[0024] In a given temperature range, called the "gelatinization range", the starch granules swell very rapidly and lose their semi-crystalline structure (loss of birefringence).

[0025] All starch granules swell to their limit in the temperature range of approximately 5-10° C. A paste is obtained consisting of swollen starch granules that constitute the dispersed phase and molecules (mainly amylose) that thicken the aqueous continuous phase.

[0026] The rheological properties of the paste depend on the relative proportions of these two phases and on the swelling volume of the starch granules. The gelatinization range varies depending on the plant from which the starch is derived.

[0027] Maximum viscosity is achieved when the starch paste contains many highly swollen starch granules. With continued heating, the starch granules burst and the material disperses in the medium, but dissolution only occurs at temperatures above 100°C.

[0028] Amylose-lipid complexes retard swelling because this combination inhibits the interaction of amylose with water molecules, and temperatures above 90°C are required to obtain complete swelling of the starch granules (because amylomaize forms complexes with lipids).

[0029] The disappearance of starch granules and the dissolution of polymers results in a decrease in viscosity.

[0030] Reducing the temperature of the starch paste (by cooling) causes insolubilization and phase separation of the polymers due to the incompatibility between amylose and amylopectin, and subsequently, crystallization of these polymers is observed.

[0031] This phenomenon is known as retrogradation.

[0032] If the paste contains amylose, it is this first molecule that undergoes retrogradation.

[0033] This consists primarily of the formation of double helices and the combination of these double helices into "crystals" (B-form) which result in a three-dimensional network via junction zones.

[0034] This network forms very rapidly, within a few hours, and during its development, the association of double helices through hydrogen bonds displaces the water molecules associated with the helices, leading to significant syneresis.

[0035] The structural complexity of starch and its physical / chemical properties mean that this type of carbohydrate is absorbed and digested in a variety of ways by humans and animals.

[0036] This is why starch can be classified into three categories according to its digestibility: easily digestible, slowly digestible or non-digestible.

[0037] Starch, which is granular / semi-crystalline in nature, can be converted to resistant starch (RDS) when exposed to heat, pressure, and / or moisture during food processing.

[0038] Slowly digestible starch (SDS) still has a crystalline structure and is less accessible to digestive enzymes, so it takes longer to break down by digestive enzymes than RDS.

[0039] Digestion of this SDS fraction leads to a moderate and regular release of glucose into the blood. These are known as low GI starches (standing for "low glycemic index").

[0040] Therefore, foods with high SDS content induce a lower postprandial glycemic and insulin response than foods with only low SDS content.

[0041] Conversely, RDS is a more nutritious carbohydrate because it releases its glucose into the bloodstream much more quickly.

[0042] So-called resistant starch (RS) can be treated as a fiber that is non-digestible by intestinal enzymes (corn bran, oat fiber, gums, etc.).

[0043] It is recognized in the prior art that total starch is the sum of its three components RDS, SDS, and RS.

[0044] Therefore, these different starch fractions are digested at different rates in the human digestive system.

[0045] Therefore, it is recognized that SDS has a slower digestion rate than RDS. RS are the fractions of starch that resist enzymatic digestion in the small intestine. They can be considered dietary fiber because they are fermented in the large intestine.

[0046] Therefore, the SDS and RDS fractions are available sources of glucose.

[0047] SDS occurs naturally in some of the uncooked grains of cereal plants such as wheat, rice, barley, rye, and corn, and legumes such as peas, beans, and lentils.

[0048] The SDS content is primarily affected by starch gelatinization during food processing.

[0049] In fact, exposure to temperature, pressure and moisture during this process causes the conversion of the SDS fraction into RDS, making the starch more accessible to enzymatic digestion.

[0050] This conversion can be minimized by controlling cooking conditions to limit starch gelatinization.

[0051] Therefore, the original SDS content in a food composition or food product will vary depending on how its preparation was carried out.

[0052] For example, some pastas, parboiled rice, polished barley, and some cookies are known food products that contain high amounts of SDS, in contrast to puffed breakfast cereals or breads, which typically contain little to no SDS.

[0053] The SDS content of foods is traditionally determined using an in vitro method developed by HNENGLYST and coworkers (published in the European Journal of Clinical Nutrition, volume 46, pp S33-S50 in 1992).

[0054] In what follows, we refer to this 1992 methodology "according to ENGLYST."

[0055] This method was developed to mimic the enzymatic digestion that occurs in the small intestine.

[0056] A sample of the product or starch is introduced into the tube in the presence of digestive enzymes and the release of glucose is measured during a 120 minute reaction.

[0057] In this method a distinction is made between: - By measuring the RDS fraction, the rapidly releasing glucose (RAG); in this case, the glucose released between 0 and 20 minutes is measured. - By measuring the SDS fraction, the slowly releasing glucose (SAG); in this case, the glucose released between 20 and 120 minutes is measured. - RS fraction, corresponding to the glucose not released after 120 min, calculated according to the ENGLYST method by the following formula: TS - (RDS + SDS), where TS = total starch (considered equal to 100% by weight when the analysis is carried out on the starch itself).

[0058] Carbohydrate-rich foods that contain more than 50% by weight of available carbohydrate derived from starch that is at least 40% by weight SDS are traditionally considered high SDS foods.

[0059] It is therefore recommended to reduce the glycemic index and insulin production compared to foods with low SDS.

[0060] Of all the starches traditionally used in these food applications, legume starches, and more specifically pea starch, are the best candidates.

[0061] Indeed, pea seeds are known for their high starch content (55-70% by weight on a dry weight basis) and low glycemic index (Ratnayake et al., 2002, Pea starch, composition, structure and properties-A review, in Starch / Starke, 54, 217-234). Summary of the Invention [Problem to be solved by the invention]

[0062] Therefore, native pea starch, which generally has an SDS content of 27-38% by weight according to ENGLYST, is of interest for nutritional applications.

[0063] However, the variability between batches of pea starch does not always meet the described needs, which is due to two main criteria: seasonality (the quality of the pea starch produced can vary between seasons) and the different extraction methods used (the effect of the hot water treatment used during the process).

[0064] In order to guarantee the quality of the pea starch batches, the Applicant Company has found that it is possible to obtain this result by identifying and characterizing the specific SDS content and a fraction not previously characterized by the ENGLYST method, the so-called "very slowly digestible starch" or vSDS fraction.

[0065] The present invention therefore relates to a legume starch, in particular a pea starch, further characterized in that it has a slowly digestible starch (SDS) content of 30-34% by weight and a very slowly digestible starch (vSDS) content of 34-40% by weight (taking into account the inter-experimental variability, a standard deviation of 2% is allowed for these values).

[0066] The invention also relates to the selection of batches of pea starch having a combined content of slowly digestible and very slowly digestible starches of more than 64% by weight and to the use of this controlled content of slowly digestible (SDS) and very slowly digestible (vSDS) starches to ensure a controlled homogeneity of the product.

[0067] For the purposes of the present invention, the term "legume" refers to any plant belonging to the family cesalpiniaceae, mimosaceae or papilionaceae sect., in particular any plant belonging to the family Fabaceae sect., for example pea, common bean, broad bean, field bean, lentil, alfalfa, clover or lupin. The article by R. HOOVER et al. entitled "Composition, structure, functionality and chemical modification of legume starches: a review" published in Can. J. Physiol. Pharmacol. 1991, 69 pp. 79-92, describes various legumes in its tables.

[0068] Preferably, the legume is selected from the group comprising pea, common bean, broad bean and field bean.

[0069] Advantageously, it is the pea, the term "pea" being considered herein in its broadest sense and including in particular: - all wild species of "smooth pea", and - all varieties of "round pea" and "wrinkled pea", regardless of the uses normally intended for these varieties (human food, animal feed and / or other uses); The above mutants have been specifically named "mutant r", "mutant rb", "mutant rug3", "mutant rug4", "mutant rug5", and "mutant lam", as described in a paper by CL HEYDLEY et al., entitled "Developing novel pea starches", Proceedings of the Symposium of the Industrial Biochemistry and Biotechnology Group of the Biochemical Society, 1996, pp. 77-87.

[0070] According to another advantageous variant, legumes (for example pea or field bean seeds) are plants which give rise to grains containing at least 25% by weight, preferably at least 40% by weight, of starch (dry / dry).

[0071] "Legume starch" is intended to mean any composition extracted by any means from a legume, in particular from the family Fabaceae in the strict sense, the starch content of which, expressed as a percentage by dry weight relative to the dry weight of said composition, is greater than 40%, preferably greater than 50% and even more preferentially greater than 75%.

[0072] Advantageously, this starch content is greater than 90% by weight (dry / dry). In particular, it may be greater than 95% by weight, including greater than 98% by weight.

[0073] By "native" starch is meant starch that has not been subjected to any chemical modification.

[0074] To determine its content of basic SDS fractions, pea starch, whether according to the invention or not, is analyzed according to the in vitro digestion procedure conditions of the method of HN Englyst et al. in "Classification and measurement of nutritionally important starch fractions", Eur. J. Clin. Nutr., 46 (Supp. 2), S33-S50 (1992).

[0075] This method consists of determining the readily digestible starch (RDS), slowly digestible starch (SDS) and non-digestible (resistant) starch fractions (RS) contained in foods.

[0076] These fractions are identified after enzymatic digestion with pancreatin, amyloglucosidase, and invertase.

[0077] The released glucose is measured colorimetrically using the glucose oxidase kit Glucose GOD FS, reference 1 2500 99 10 923, available from the company DiaSys Dispersion France Sarl, according to the protocol of said kit.

[0078] Details of the method carried out to measure digestion according to ENGLYST are as follows. Reagents used: - Sodium acetate anhydrous (reference number: 71184, SIGMA) - Benzoic acid (Reference number: 242381, manufactured by SIGMA) - CaCl2 (Reference number: 1.02378.0500, manufactured by MERCK) - 0.1M Acetic Acid (Reference Number: 33209, SIGMA) - Porcine pancreatin 8x USP (Reference number: P7545, manufactured by SIGMA) - Amyloglucosidase EC3.2.1.3 (SIGMA, activity ≧260U / mL / approximately 300AGU / mL, catalog number A7095) - Invertase EC3.2.1.26 (SIMA, activity ≥ 300 units / mg solid, catalog number I-4504) - Guar (Reference number: G4129, manufactured by SIGMA) - 66% ethanol

[0079] procedure Preparation of saturated benzoic acid solution

[0080] Weigh out 4 g of benzoic acid in 1 L of RO water and mix. This solution can be stored at room temperature for one month.

[0081] Preparation of 1M / L CaCl2 solution

[0082] Weigh out 1.1098 g of CaCl2 into 10 mL of RO water and mix. This solution can be stored at room temperature for one month.

[0083] Preparation of 0.1M pH 5.2 acetate buffer Weigh 8.203 g of anhydrous sodium acetate into 250 mL of saturated benzoic acid solution. - Add 500mL RO water and mix. - Adjust the pH to 5.2 ± 0.5 using 0.1 M acetic acid. - Make up to 1000mL in a volumetric flask with RO water. - Add 4 mL of 1 M CaCl2 solution to 1 L of prepared buffer. - Mix and check the pH. This solution can be stored at 4° C. for one month.

[0084] Preparation of guar gum solutions in acetate buffer -Weigh exactly 750 mg of guar gum into 300 mL of acetate buffer. - Keep under continuous stirring.

[0085] Preparation of samples to be analyzed and enzymes to be used

[0086] Sample preparation -Weigh out exactly 0.8 g of dry starch to be tested. - Add 20 mL of 0.1 M acetate buffer - pH 5.2 + guar gum. - Place the vial in a water bath at 37°C with stirring for 15 minutes. - Take 0.1 mL of the solution obtained at T=0 min and then add 0.9 mL of 66° ethanol (i.e. a 10-fold dilution). At time T=0 min, the amount of glucose (as %) is determined by colorimetry. Blanks and standards (weigh out 0.5 g of anhydrous dextrose) are made under the same conditions as the sample preparation.

[0087] Preparation of enzyme cocktail

[0088] The enzyme cocktail is designed to test 12 samples and should be prepared on the day according to the following protocol.

[0089] Preparation of Porcine Pancreatin 8x USP

[0090] Prepare four solutions of pancreatin to obtain 54 mL of supernatant.

[0091] To do this: -Weigh out 2.5 g of Porcine Pancreatin 8X USP. - Add 20mL RO water and mix for 10 minutes. - Centrifuge the solution at 1500G for 10 minutes. - Collect 13.5 mL of supernatant.

[0092] Preparation of amyloglucosidase - Dilute 3.7 mL of amyloglucosidase EC3.2.1.3 solution with 4.3 mL of RO water and mix for 10 minutes. - Take 6 mL of this new solution and add to 54 mL of pancreatic supernatant and mix.

[0093] Preparation of invertase Weigh out 50 mg of invertase EC 3.2.1.26. Add 6 mL of RO water and mix for 10 minutes. Take 4 mL of this new solution and add to the 54 mL of pancreatin supernatant and mix.

[0094] Digestion Protocol - Add 5 mL of enzyme cocktail to the sample preparation. - Incubate for 120 minutes at 37°C in a constant temperature bath with agitation. - 0.1 mL of the solution obtained at T=20 min and T=120 min is taken and then 0.9 mL of 66° ethanol is added (i.e. a dilution factor of 10). - Mix the sample and centrifuge at 1500G for 3 minutes. At times T=20 min and T=120 min, the amount of glucose (as %) is determined by colorimetry.

[0095] Determination of free glucose (fg) and total glucose (tg) levels

[0096] Free glucose (FG) levels correspond to measurements taken at time 0 min.

[0097] Total glucose (TG) levels are measured as follows. - Take 0.25 mL of the solution obtained at T=120 min in an "Eppendorf" type tube. Add 0.25 mL of 4N hydrochloric acid and mix. - Place the tube in a 100°C water bath in dry mode for 45 minutes and allow to cool to room temperature. - Neutralize the hydrolyzed solution with 0.25 mL of 4N sodium hydroxide. -Add 0.25mL RO water and mix. - Dilute 10 times with RO water (0.1 mL in 0.9 mL), i.e. a final dilution of 40 times.

[0098] Identification of RDS, SDS and RS

[0099] Determine the glucose released at the following times: - T=0 min (initial glucose content) - T=20 min (glucose content released after 20 min) - T = 120 min (glucose content released after 120 min).

[0100] According to the ENGLYST method:

[0101]

number

[0102] Identification of the RDS, SDS, and RS fractions is performed as follows: - RDS=(G20-FG)×0.9 - SDS=(G120-G20)×0.9 - RS=TS-(RDS+SDS) (in the formula, TS=(TG-FG)×0.9)

[0103] According to this method, native pea starch typically has an RDS content of 13-16% by weight, an SDS content of 27-38% by weight, and an RS content of 45-56% by weight, these values ​​being expressed with a standard deviation of 2% to take into account experimental variability.

[0104] The Applicant recommends first selecting pea starch batches with an SDS content of 30-34% by weight which are more likely to meet the required digestibility criteria, and then identifying the very slowly digestible starch (vSDS) content.

[0105] After much lengthy investigation, the Applicant Company has found that, in contrast to what was established by ENGLYST, the so-called digestion resistant (RS) fraction is digested unless the reaction kinetics are stopped at 120 min.

[0106] To the best of the applicant's knowledge, only CHUNG et al. in Carbohydrates Polymer, vol 75, pp 436-447, in 2009, proposed to classify pea starch based on hydrolysis conditions slightly different from those in ENGLYST, i.e., the SDS fraction digested in 20-180 min.

[0107] This modification results in an increased content of "slowly digestible" starch, calculated on the basis of an SDS fraction that no longer corresponds to the formula reported by Englyst, which limits the reaction kinetics to 120 min.

[0108] The Applicant Company extended the ENGLYST digestion kinetics up to 500 minutes and observed that digestion of legume starch, particularly pea starch, continued beyond the 120 minute time point, reaching a plateau of maximum digestibility at 420 minutes.

[0109] The Applicant therefore decided to take advantage of this new, even more slowly digestible starch to define a "very slowly digestible" or vSDS ingredient according to the present invention.

[0110] Moreover, and this is one of the key points for extending the ENGLYST test as generally accepted in the prior art, this vSDS percentage corresponds to the digestion of a subfraction of the RS content of legume starches, particularly pea starches, as originally defined by ENGLYST from 120 min onwards, while the RDS and SDS contents remain unchanged.

[0111] Thus, in contrast to what is known in the prior art, and in particular by CHUNG et al. mentioned above, the present invention does not involve modifying the operating conditions of the ENGLYST test to artificially increase the SDS level, but rather adopts operating conditions which make it possible to identify the actual glucose releasing capacity of the legume starch considered, and in particular of the pea starch, by extending the ENGLYST digestion to its end point, defined here by the plateau reached at time 420 min.

[0112] The invention therefore further relates to a method for determining the vSDS fraction content of a legume starch, this determination being carried out by measuring the glucose release by extending the ENGLYST digestion up to its end point, defined by the plateau reached at time 420 min. Finally, the invention further relates to the use of the measurement of the very slowly digestible starch content of a legume starch for obtaining a starch according to the invention.

[0113] By measuring glucose release at time 420 minutes, a new formula can be developed that allows: 1) Correction of the RS fraction values ​​(in this case referred to as "corrected RS") based on the observation that maximum digestibility is reached at a plateau after 420 min of digestion. The corrected RS (non-digestible fraction after 420 min) is then estimated to be equal to 100-(T420 x 0.9). The correction factor of 0.9 is required for the calculation of the fraction according to the ENGLSYT method. 2) Estimation of vSDS content by simple calculation: vSDS=100-(RDS+SDS+corrected RS)

[0114] The invention will be better understood by reading the following examples, which are intended as illustrations and which merely refer to certain particular embodiments and certain advantageous properties according to the invention, and are non-limiting. [Brief description of the drawings]

[0115] [Figure 1]FIG. 1 shows the kinetics according to ENGLYST up to 120 min.

[0116] [Diagram 2] FIG. 2 repeats the data from FIG. 1 and extends the kinetics to 420 min. EXAMPLES

[0117] Example 1: A batch of native pea starch manufactured by the Applicant Company under the trade name N735 (designated batch WS88V) was analysed according to ENGLYST (1992) up to a reaction time of 120 minutes and then up to a reaction time of 420 minutes.

[0118] Table 1 below shows the RDS, SDS and RS contents in weight percent as calculated by the conventional ENGLYST method.

[0119] [Table 1]

[0120] By extending the digestion kinetics to 420 min and measuring the glucose released after 420 min, the corrected RS and vSDS contents in weight percentages reported in Table 2 below were calculated.

[0121] [Table 2]

[0122] Example 2: Extensive characterization and selection of the digestive profiles of different pea starch batches

[0123] Extensive digestion kinetics have been carried out on a further 14 batches of native pea starch extracted by the Applicant Company to determine not only batch-to-batch variability in digestibility but also to define the batch most suitable for the intended use. Table 3 below shows the contents in weight percent of RDS, SDS, RS and vSDS.

[0124] [Table 3]

[0125] Thus, if we define our pea starches by an SDS content of 30-34% by weight and a vSDS content of 34-40% by weight (standard deviation 2%), it follows that we have to exclude batches WX24V (SDS too low) and W9167 (SDS content within acceptable limits but vSDS content too low). This selection method ensures that only pea starch batches with controlled homogeneity and a combined content of slowly and very slowly digestible starches above 64% by weight are obtained.

Claims

1. A legume starch which is pea starch, comprising: having a slowly digestible starch (SDS) content of 30-34% by weight and also a very slowly digestible starch (vSDS) content of 34-40% by weight; The very slowly digestible starch is characterized as being a starch in which ENGLYST digestion reaches a plateau of maximum digestibility at 420 minutes.

2. 2. Starch according to claim 1, characterized in that it has a combined content of slowly digestible and very slowly digestible starches of more than 64% by weight.

3. 1. A method for determining the vSDS content of legume starch, said content being determined by measuring glucose release by extending ENGLYST digestion to its end point, defined by a plateau reached at time 420 minutes; The legume starch is pea starch; The method of claim 1, wherein the vSDS is a starch in which ENGLYST digestion reaches a plateau of maximum digestibility at 420 minutes.

4. Use of the method according to claim 3, which determines the content of very slowly digestible starch in the legume starch, to obtain the starch described in any one of claims 1 to 2.

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