BACKGROUND OF THE INVENTION Field of the Invention

The present invention is generally directed towards starch that has been modi (led with an organic acid anhydride reagent and methods of preparing the same. In certain embodiments, starch produced according to the present invention exhibits good water solubility and emulsifying characteristics when compared with conventional starches. Further, methods of preparing modified starches according to the present invention do not require further treatment with acids, other than the organic acid anhydride reagent, or enzymes to degrade the starch and make it water soluble.

Description of the Prior Art

Native starch is partially crystalline and not soluble in water at room temperature. Also, native starch molecules are hydrophilic and do not possess emulsifying properties. A number of reference!, such <a> U.S. Patent No. 2,661 ,349 and U.S. Patent No. 6,037,466 disclose introducing hydrophobic groups to the starch by reaction with cyclic dicarboxylic acid anhydrides so that the starch can be used as an emulsion stabilizer.

Octenyl succinc acid anhydride (OSA) treated starch, prepared by adding up to 3% OSA, has been approved by the FDA for food use and can be used in food and beverage applications, such as in encapsulation of vitamins and flavors. Starch may also be reacted with greater than 3% OSA for non-food applications, such as in oil- and peti oleum-based cosmetics, or pharmaceutical pastes, alcohol-based Unions, body deodorant sprays, and encapsulation of fragrances, clouds, and oils. Conventionally, OSΛ-modified starch must undergo acid hydrolysis or enzymatic conversion in order to be converted (or degraded) and rendered water soluble at room temperature. Modified starch that undergoes this further processing may contain acid or enzyme residues. SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, there is provided a method of preparing a lipophilic starch. An organic acid anhydride reagent is added to a starch mixture thereby forming a reaction mixture. The pH of the starch mixture is adjusted to between about 7 to about 1 1 cither before or after addition of the organic acid anhydride reagent. The reaction mixture is dried to a moisture content of between about 0 to about 15% by weight. The dried reaction mixture is heated at a temperature of at least about 100 ⁰ C for between about 1 minute to about 6 hours.

In accordance with another embodiment of the present invention, there is provided a water-soluble, lipophilic starch comprising starch that has been modified with an organic acid anhydride reagent. The modified starch contains less than about 0.5% by weight of one or more mineral acids and/or less than about 0.1 % by weight of starch-degrading enzyme residues. The starch also has a solubility in water at 25 ⁰ C of greater than about 90%. hi accordance with another embodiment of the present invention, there is provided a lipophilic starch comprising a starch that has been modified with an organic acid anhydride reagent. The lipophilic starch, when dispeised in glycerol and viewed with a microscope under polarized light, has a granular shape and is birefringent.

In accordance with yet another embodiment of the present invention, emulsion made with the water-soluble, lipophilic staich are provided. In particular embodiments, the emulsion is very stable, there being no observable phase separation even after storage for 24 hours at 45 ^ϋ C.

In accordance with still another embodiment of the present invention, food products made with the starches described herein are provided. The starch employed in the food product may be a water-soluble, lipophilic starch as described herein, or the starch can be a lipophilic starch made in accordance with the methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure Ia is a microscope photograph of a first emulsion sample prepared Irons sample 7-E after heating at 45 ⁰ C for 24 hours;

Fig. Ib is a microscope photograph of a second emulsion sample prepared from sample 7-E after heating at 45 ^U C for 24 hours;

Fig. 2a is a microscope photograph of sample 7-E suspended in glycerol;

Fig. 2b is a microscope photograph of sample 7-E suspended in glycerol taken under polarized light;

Fig. 3a is a microscope photograph of sample 5-B suspended in glycerol;

Fig. 3b is a microscope photograph of sample 5-B suspended in glycerol taken under polarized light; and Fig. 4 is a graph of gel permission chromatography (GPC) results for samples 5-B and a commercial sample.

DETAILED DESCRIPTION OF THE PREFERRED EiMBODIMENT

The present invention provides a method for introducing a hydrophobic group onto starch molecules, degrading the starch, and making the starch water soluble. The starch to be modified according to the present invention may be native, converted, or derivatized. Exemplary starches include those derived from corn, potato, wheat, rice, tapioca, sago, sorghum, waxy maize, waxy wheat, waxy potato, or high amylose corn.

In certain embodiments, the process begins by preparing a starch mixture that has a neutral io basic pH. In one embodiment., ihe starch mixture may be in the form of a starch slurry prepared by mixing the staich with watci, an alcohol, oi utliei υiganic solvent, such at> toluene. In one particular embodiment, the slurry is prepared with water and/or alcohol, wherein the alcohol is selected from the group consisting of ^* methanol eihanol isopropyl alcohol, and niixuues thcreol. The pH υi the imxtiuu υi siuiiy is adjusted lυ between about 7 to about 1 1 by the addition of a base. In certain embodiments, the base is selected from the group consisting of meial and non-metal hydroxides, oxides, carbonates, and mixtures thereof In further embodiments, the base is selected from the group consisting of sodium hydroxide, ammonium hydroxide, ammonium carbonate, ammonium bicarbonate, and mixtures thereof. In still other embodiments, the pll of the mixture or slurry is adjusted to between about 8 to about 1 1 , or even to between about 8.5 to about 1 0.

Next, the starch mixture is processed to obtain a starch cake. In certain embodiments, this processing step involves removing liquid from the slurry, such as by filtration. To the starch cake, an organic acid anhydride reagent is added thereby forming a reaction mixture. In certain embodiments, the organic acid anhydride reagent has the general formula O

C

/ \

O R- -R'

\ /

O

wherein R is a dimethylene or trimethylene group and R ¹ is a linear, branched or cyclic alkyl, alkenyi. aralkyl or aralkenyl group having 2 to 20 carbon atoms. In further embodiments, the organic acid anhydride reagent is octenyl succininc acid anhydride (OSA). The organic acid anhydride reagent is generally added to the cake ai a level of between about 0.5% to about 100% by weight, based upon the dry weight of the starch. In still other embodiments, the organic acid anhydride reagent is generally added to the case at a level of between about 1 % to about 25% by weight, or even between about 2% to about 9% by weight, based upon the dry weight of the starch. The organic acid anhydride may be added to or mixed with the starch cake by any means known to those of skill in the art, such as, for example, by spraying.

In another embodiment according to the present invention, a starch slurry is prepared and the ui gαnit acid anhydride reagent is added to the slurry and mixed. Mixing of the organic acid anhydride reagent and starch slurry may be accomplished by any number of means known in the art. The pli of the starch slurry may be adjusted to the desired level eilher be lore or a Her addition of the organic acid anhydride reagent. In one particular embodiment, the OS-modified starch slurry is filtered to obtain a starch cake. Tn yet another embodiment, the OS-modified starch is recovered by spray drying. After permitting the reaction between the starch and oiganic acid anhydride reagent to proceed for a predetermined period of time, the reaction mixture is dried to a moisture content of between about 0 to about 15% by weight. In other embodiments, the reaction mixture is dried to a moisture content of between about 0% to about 10%, or even between about 0% to about 6% by weight. In certain embodiments, the drying step comprises heating the reaction mixture to a temperature of less than about Ϊ4O°C. or between about 25°C to about 90 ⁰ C, or between about 30 ⁰ C to about 60 ⁰ C.

Once the desired moisture content is reached, the dried reaction mixture is heated at a lemperature of at least about 100 ⁰ C, or between about 100 ⁰ C to about 200 ⁰ C, or between about 140 ⁰ C to about 18O ⁰ C. This heating step may be carried out for between about 1 minute to about 6 hours, or between about 30 minutes to about 4 hours, or between about 1 to 3 hours. Both the drying and heating steps may be carried out with any suitable apparatus known to those of skill in the art, including forced air ovens, dextrinizers, and fluidized bed dryers.

In certain embodiments according to the present invention, the starch modified with the organic acid anhydride reagent docs not undergo a subsequent acid hydrolysis step. Thus, the need to hydroly/e the modified starch with a mineral acid such as HCl or H ₂ SO ₄ is eliminated. Likewise, the present invention eliminates the need for enzymatic conversion of the modified starch, such as with α-amylasc or any enzyme within the amylase family, in order to degrade the starch. Therefore, it is an advantage of certain embodiments of the present invention that the starch produced contains essentially no residues of such mineral acids or enzymes.

The modified starch prepared in accordance with the present invention mav be water insoluble, partially watei soluble, oi completely watet soluble Water solubility υflhe modified starch is measured by a refractometer. A 10% solids dispersion is prepared, ccntrifugcd. and the supernatant is analyzed by the refractυmeter. In certain embodiments, the modified starch has a solubility in water at 25 ⁰ C of greater than about 90%, or greater than about 95%, or even greater than about 98%.

As noted above, it is possible to piepaie muuifieu btaicli acuυiding to the present invention wherein the starch is degraded, so as to improve the water solubility thereof, without the addition of mineral acids or starch-degrading enzymes (e.g . amylase en/ymes). Therefore, in certain embodiments, the modified starch will have a water solubility as described herein and contain less than about 0.5%, or less than about 0.1 %, or even less than 0.01% by weight of mineral acid. Additionally or alternatively, the water soluble modified starch will contain less than about 0.1% by weight, or even less than 0.01% by weight of starch-degrading enzyme residues. As used herein, the term "'"starch-degrading enzyme residues" can refer to the en/ymes themselves or to denatured forms of the en/ymes. In alternate embodiments, the water-soluble, modified starches are substantially free of mineral acid and/or starch-degrading enzyme residues.

In other embodiments according to the present invention, a lipophilic starch comprising a starch that has been modified with an organic acid anhydride reagent may be prepared, which, when suspended in glycerol and viewed with a microscope under polarized light, has a granular shape and is birefringent. Also, the water-soluble, lipophilic starches described above may also possess these characteristics.

The starches described above and those starches made in accordance with the methods described herein, particularly those starches that are water soluble, can be used in the formation of emulsions. The emulsions produced with the modi fled starch exhibit excellent stability with no observable phase separation even upon storage of the emulsion at 45 ⁰ C for 24 hours.

Exemplar}' emulsions include those comprising essential oils, such as orange oil. 1 he emulsions may be prepared in any manner known in the art.

The starches described above and those starches made in accordance with the methods described herein can also be used in various food products. Also, the modified starches used in food products need not necessarily exhibit a high level of w ^r atcr solubility, so long as the lipophilic starch is made by a method according to the present invention.

EXAMPLES The following examples set forth the effects of pi I, temperature, and exposure times on degree of substitution, reaction efficiency, and solubility of the modified starch. It is to be understood, however, that these examples arc provided by way of illustration and nothing the: ein should be taken as a limitation upon the overall scope of the invention. Materials and Methods

Octcnyl succinic acid anhydride ("OSA ^" ) w,as obtained from Gulf Bay port Chemicals L. P. (Pasadena, ^' IX). Waxy maize starch (Λmoica IT) was provided by National Starch and Chemical (Bridgewater. NJ). All other chemicals used in the following examples were analytical grade Titration Method 1

In the following examples, degree of substitution (''D. S. ^" ') was measured by titration. For the insoluble modi lied starches reacted with 3% OSA, 5.00 g dry weight of the starch was suspended in 20.0 inL of 0.100 M HCl, and stirred for 30 minuies. The suspension was filtered through a piece of No.2 filter paper (Whatman Internal Ltd.). and the residue was washed with water until no Cl ^" could be detected by 0.1 M AgNO ₃ solution. The starch was then re-suspended in 300 rnL water and heated in a boiling water bath for 20 minutes. After cooling down, the starch solution was iitraied with 0. J 00 IVl NaOH solution, using phenolphthalein as an indicator.

The control used is described in each example. The % bound octcnyl succinate (OS), D. S., and reaction efficiency ("R. E.") were calculated using the following equations: % OS = (V ₁ - V ₂ ) x 0.1 x 21 W

where % OS is the percentage weight of OS in OS modified starch, V ₁ is the titration volume of NaOH (mL) for OS starch, V ₂ is the titration volume of NaOH (ml) for control, and W is the dry weight (g) of the OS starch.

D.S. - 162 x % OS

210 - 209 x % OS

R-K. = %OS of OS starch X 100%

%OSA added to the starch Titration Method 2

The bound OS content for modified starches reacted with greater than 3% OSA, partially and completely soluble OS starches was determined, by first suspending 5.0Og dry weight of the starch in 20.0 mL of methanol and filtered. The cake was re-suspended in a 20 mL mixture of

0.100 M HCl and methanol (1 :9, w/w) and stirred for 30 minutes. The starch was filtered and washed with a 4OmL mixture υf water and nioihdnol (1 .9, Ww), and then dispersed in 300 mL water. For the completely soluble samples, the solutions were titrated by 0.100 M NaOH directly. Tor partially soluble starches, the suspensions were cooked in a boiling water bath for

20 minutes and the solutions were titrated after cooling down. Phenolphthalein was used as an indicator. The D. S., %OS and R. R. were calculated by the same equations above in method 1.

Solubility of OS starch

A potable refractometer was used to check the solubility of the OS starch. Λ ] 0% solids suspension was prepared, centrifuged, and the supernatant was analyzed by the refractometer.

EXAMPLE 1

In this example, NaOH was used to adjust the initial pi I of the starch slurry and the resulting effects on the degree of substitution ("D.S. ^" ') and reaction efficiency ('"R. E.'") of the starch were measured.

Waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation. The pH of the starch slurry was adjusted to 7.5 and 9.5 with 3% (w/w) NaOH. The suspension was filtered and the starch cake was mixed with 3% OSA (based on the dry weight of starch) using a mixer (Model K45SSWH, KitchenAid, St. Joseph, MI) at 2nd speed for 15 minutes. The mixture was dried in a forced-air oven at 35°C overnight until the moisture content was below 12%. The starch mixture was spread over an oven pan (38cm x26 cm) and heated at 16O ⁰ C for 1 hour, 2 hours, or 4 hours. Native waxy maize starch was used as a control. Degree of substitution and reaction efficiency were measured by titration method 1 . pH after treatment w as measured by suspending a portion of the treated starch in water (10% solids by weight).

As shown in Table 1, D. S. and R.E. were greater at a the higher pH and longer heat treatment times.

Table 1 : Sample adjusted to pH /.5 and 9.5 by NaUH and heat treated at 16O ⁰ C

EXAMP] ,F 2

In this example, Na ₁ CO, was used to adjust the initial pH of the starch slurr) and the resulting effects on Degree of Substitution ("D.S. ^" '), reaction efficiency ('"R.E."), and starch solubility were measured.

Waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation. A weighed amount OfNa ₂ CO ₃ was added to the starch slurry, lhe experiments were earned out as described in Example 1 , except that sample 2-A was heated at 160 ⁰ C for 4 hours, then was reheated at 190 ⁰ C for 2 hours. In contrast, sample 2-B was heated at 190 ⁰ C for 2 hours. D.S. and R.E. of the samples heat treated at 190 ⁰ C were calculated using titration method 2. D.S. and R.E of other samples were determined by titration method 1 .

As shown in Table 2, the more basic Na ₇ CO ,-trcatcd starch slurries generally produced higher D.S. and R.E. values. The highest D.S. was achieved at pH 10.3. In addition, solubility of the starch was found to be higher when the starch slurry combined with Na ₂ CO ₃ was exposed to higher temperatures, such as in Samples 2-A and 2-B.

Table 2: Samples adjusted to different pll values by Na ₂ CO ₃ and heat treated at 16O ⁰ C

EXAMPLE 3

In this example. NIl ₁ IlCO ₃ was used to adjust the initial pH and the resulting effects on Degree of Substitution ("D.S.' ^" ), reaction efficiency ("R.E. ^" '), and starch solubility were measured.

Waxy maize starch (100 g) was suspended in distilled water (150 rnL) with agitation. A weighed amount of NH ₁₁ HCO ₃ was added to the suspension. The experiment was carried out as described in Example 1 . Sample 3-A was heated at 160 ⁰ C for 4 hours was reheated at 190 ⁰ C for 2 hours. D. S. and R.H. were measured by titration method 2.

As shown in Table 3, the use OfNII ₄ HCO ₃ was effective in achieving relatively high D. S. and R.E. values especially when the starch was heated for longer periods of time and/or at higher temperatures. In addition, it was shown that use OfNH ₄ HCO ₃ in conjunction with a higher heat treatment temperature (19O ⁰ C) greatly increased the solubility of the sample.

Table 3: Samples adjusted to pll 8.57 by NII ₄ IICO ₃ , and heat treated at 160 ⁰ C

EXAMPLES 4-6 In these examples the weight OfNII ₄ IiCO ₃ added to ihe sxaich slurry was \aried and ihe effects on degree of substitution ("D. S."), reaction efficiency (''11.E. ^" ), and starch solubility were measured.

Waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation. The pH of the starch slurry was adjusted to between 8.0 - 8.8 by the addition of varying amounts Of NII ₁ IICO ₃ . T he experiments were carried out as described in Example 1 ; however, the heating temperature was adjusted to 170 ⁰ C, 18(TC, or 190"C, and heating time was adjusted to Vτ hour, 1 hour, 2 hours, or 4 hours. A starch sample without adding OSA was prepared as a control. D. S. and R.L. were measured by titration method 2.

As shown in Fables 4-6, increased amounts OfNH ₄ HCO. and longer exposure to higher temperatures led to an increase in D. S., R.E., and solubility of the starch. Table 4: Samples adjusted to pi I 8.0 by NH ₄ HCO ₃ (0.27% by starch dry weight) and heat treated at different temperatures.

Table 5: Samples adjusted to pH 8.5 by NII ₄ IICO ₃ (3.85% by starch diy weight) arid heat treated at different temperatures.

Tablc 6: Samples adjusted to pH 8.75 by NH ₄ HCO, (6.29% by starch dry weight) and heal treated at different temperatures.

FXAMPLF 7

In this example, the viscosities exhibited by different starch samples from hxamples 4, 5, and 6 were measured.

Viscosity of the starch sample ¹⁵ was determined by a Brookfield viscometer (RVDVIl 4 Pro, Brookfield Engineering Laboratories, Inc., Middlcboro, MA) with a CS4-18 spindle and a SC4-13 RPY chamber at 25 ⁰ C. Starch solutions of 30% and 50% solids of lab made starches and a commercial starch were prepared and added to the chamber. The commercial starch is a converted (degraded), OSA-modifϊcd starch obtained from National Starch LLC, Bridgewater, NJ. The spindle speed (RPM) was selected. The reading of shear stress (SS). shear rate (SR), viscosity (cP) and % (torque) are shown in Table 7.

Viscosity oi a starch solution reflects the molecular weight ol a starch sample. Compared with a commercial sample, the lab made starch sample showed higher viscosity indicating that the molecular size of the lab made sample was higher than that of the commercial sample.

Table 7: Viscosity of OS starch and a commercial starch solution

EXAMPLE 8

Tn this example, the effect of grinding the starch prior to heat treatment on solubility was measured.

Waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation. The pll of the starch slurry was adjusted to 8.45 by different weights OfNIl ₄ IICO ₃ (Table 8). The experiment was carried out as in Example 1. However, the heating temperature was adjusted to 170 ⁰ C or 180 ⁰ C. and heating time was 2 hours. For sample 7-D. the OSA-modified starch was sieved by a 200-mesh sifter after heating. For sample 7-E, the starch mixture before heating was ground by an analytical mill (A-IO, Tekmar) and sieved through a 200-mesh sifter. The starch was thinly spread over an oven pan (38cm *26 cm) and heated at 18O ⁰ C for 2 hours. A starch sample without adding OSA was prepared as a control. D. S. and R.E. were measured by titration method 2.

Solubility of the OS starch dispersed in an aqueous medium (10%, w/w) was analy/ed by a potable rcfractomcicr before ccntrifugation (''SBC") The starch solution was ccntrifυgcd at 3500 rpm for 5 minutes and the supernatant was analyzed by the rciractometcr as well ("SAC").

As shown in Tabic 8, grinding of the starch prior to heat treatment appeared to have a slight positive effect on the solubility of the starch product when compared to samples that had not undergone grinding.

Table 8: Samples adjusted to pH 8.45 by NH ₄ HCO ₃ (6.29% by starch dry weight) and heat treated at different temperatures.

* Cake moisture: 50.20%

EXAMPLE 9 This Example describes an embodiment of the present application directed to a non-food application using a 5% OSA treatment.

Waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation.

The pll of the starch slurry was adjusted to 8.30 with 3.02 g NH ₄ HCO ₃ . The suspension was filtered and the starch cake was mixed with 5% OSA (based on the weight of starch) by a mixer (Model K45SSWH, KitchenAid, St. Joseph, MI) at 2 ^nd speed for 15 minutes. The mixture was dried in an air oven at 35 ⁰ C overnight until the moisture content was below 12%. The mixture was then spread over an oven pan (38cm ^χ 26 cm) and heated at 180 ⁰ C for 2 hours. Afterwards, the starch mixture was ground by an analytical mill (A-I O, Tekmar) and sieved through a 200- mcsh sifter. Λ starch sample without adding OSA was prepared as a control. D. S. and R.E. were measured by titration method 2.

The bound OS content was 4.77%. The D.S. and R.E. of the OS starch were 0.0386 and 93.43%, respectively. Solubility of the OS starch was analyzed by a potable refractometer. The starch solution ( 10%, w/w) vvas ccntrifugcd at 3500 rpm for 5 minutes. The solubility of the material was found to be 86%

EXAMPLE 10

In this example, wheat starch (100 g) was suspended in distilled water (150 mL) with agitation. The pi I of the starch slurry was adjusted to 8.45 by adding 3.02 g NH ₁ I ICO _v flic experiment was carried out as described in Example 9 except that 3% OSA was added, fhc bound OS content was 2.59%. The D.S. of the OS starch was 0.0205, and the R.E. was 94.33%.

The solubility of the OS starch was 75%.

EXAMPLE 11

In this example an emulsion of sample 7-E was prepared. OS starch (8.0g, dry basis) was mixed with sodium benzoatc (0.1 g), citric acid (0.2g) and water (50.40 mL) in a Waring blender

(Model 31BL92, Dynamics Corporation of America). The mixture was blended at low speed

(powerstat at 25-30) for 2 minutes. Orange oil (8g) was slowly added to the mixture over 30 seconds and the mixture was blended for an additional 30 seconds. The jar was then covered and blendcd at a high speed (powcrstat at 100) for 2 minutes. The emulsion solution was permitted to rest in the blender for 30 minutes and transferred to a tall glass jar (10 oz.). The jar was capped and heated at 45 ⁰ C in an air oven for 24 hours. The emulsion was very stable after heating at 45 ⁰ C for 24 hours. Microscope photographs of the emulsion were taken and are shown in Figs. Ia and Ib and depict a small oil droplet size.

EXAMPLE 12

In this example, Samples 7-E and 5-B (both heat treated for 4 hours) were suspended in glycerol and viewed with a microscope under normal and polarized light. Figures 2a and 2b depict Sample 7-E under normal and polarized light, respectively. Figures 3a and 3b depict Sample 5-B under normal and polarized light, respectively. Figures 2b and 3b show that starch granules of both samples had maltese crosses and were bircfringcnt when viewed under polarized light. The results suggest that certain molecular order of starch granules remained after OSA modification.

EXAMPLE 13

In this example, Sample 5-B (heat treated for 1 hour, 2 hours, and 4 hours) and a commercial sample (same as used in Example 7 above) were analyzed by gel permission chromatography (GPC). The starch (0.1% by weight) was uihpeiScd in DMSO and heated in a boiling water bath for 1 hour. Then the solution was analyzed by the GPC. lhe results arc shown in Fig. 4. The lab made OS samples exhibited larger molecular weights than the commercial sample.

EXAMPLE 14 In this example, waxy maize starch (100 g) was suspended in distilled water (150 mL) with agitation. The pli of the starch slurry was adjusted to 8.46 by the addition of 3.02 g NH ₄ HCO ₃ . The suspension was filtered and the starch cake was mixed with 50% OSA (by the weight of starch). The mixture was dried in an air oven at 35 ⁰ C overnight until the moisture content was below 12%. The starch mixture was heated in the air-forced oven at 130 ⁰ C for 1 h and then 105 ⁰ C for 6 h. After the product was cooled to 25°C, a sample (5 g) was washed twice with methanol (50 ml). The D. S. of the methanol-washed product was then measured by titration method 1 and the value was determined to be 0.0138. EXAMPLR 15

In this example, an OS starch was prepared and the D. S. measured by an NMR method described as follows. The starch sample (0.1 g) was dissolved in 0.5 mL of D ₂ O and freeze-dried. The D ₂ O-exchanged starch (0.07 g) was dissolved in D ₉ O (0.60 mL) for NMR analysis. ¹ H NMR 1 D spectra were recorded on a 400 MH/ Varian NMR spectrometer at 25 ⁰ C. fhe NMR spectrometer was equipped with a 5 -mm diameter, triple-resonance, inverse

-detection, pulse-field-gradient probe operating at 399.74 MIIz. The ¹ II spectra were collected in 64 individual scans with a sweep width of 16 ppm and a delay time of 1 s. Sodium

3-(trimethylsilyl) - propionate-2,2,3,3-d ₄ (TSF) was used as a reference (0 ppm). Chemical shifts are reported in parts per million (ppm). DS was calculated from the NMR spectra by using the following equation: -5

¹ S 39 ' -ϊ-5 12 ' M 96 * ^~ '4 61 ^ M D I

where I ₀₉₄ is the integrals of methyl protons. I ₅ , ₉ , 1 _{5 12} , 1 _{4 96} , 1 _{4 6} , and I _{4 51} are the integrals of the anomeric proton.

Waxy maize starch ( 100 g) was suspended in distilled water (1 50 mL) with agitation. The pi I of the starch slurry was adjusted to 8.45 by 3.02 g NfI ₄ HCO ₃ . The suspension was filtered and the starch cake was mixed with 3% OSΛ (by the weight of starch) by a mixer (Model K45SSWII, KitehenΛid. St. Joseph, MI) at 2nd speed for 15min. 1 he mixture was dried in an air oven at 35°C overnight until the moisture content was below ] 2%. 1 lie starch mixture (31.12 g) was mixed with sodium aluminum phosphate (SΛP) (3.09 g). The pH of the starch sample was 4. ^Q 0 with SAJP, The starch was heated in the air-forced oven at 180 ⁰ C for 2 h. After the product was cooled to room temperature, a sample (0.15g) was extracted by methanol (2 ml), and the extraction was repeated. The sample (0.07g) was dissolved in D ₂ O (0.6 mL) and the D. S. of the product was measured by the NMR method to be 0.01989.