Esterified dietary fiber products and methods

A dietary fiber material, e.g. corn bran, having improved color stability is provided. The material is esterified prior to bleaching to decrease the color of the material. Typical dietary fiber materials are the fiber materials produced by the milling of plant seeds such as cereal grains and oilseeds. The esterification of the dietary fiber material corn bran prior to bleaching results in a lighter colored dietary fiber product having enhanced acceptance as a dietary fiber supplement in a variety of food products.

FIELD OF THE INVENTION 
In one aspect, this invention relates to a method of improving the utility 
of dietary fiber material and to the product of such a method. In another 
aspect, this invention relates to a method of decreasing the color of 
dietary fiber material and to the product of such a method. 
BACKGROUND OF THE INVENTION 
The use of fiber material as a dietary fiber supplement is well known, e.g. 
Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 7, p. 628, 635 (3d 
ed. 1979). While consumers are familiar with the dark color of high-bran, 
ready-to-eat breakfast cereals, it would be desirable to decrease the 
color of fiber material to allow its inclusion in a variety of foodstuffs 
without adversely affecting the color of the foodstuff. 
Japanese Patent No. 53-109974, (Hyashi) published Sept. 26, 1978, describes 
a method of bleaching wheat bran to be used in a seasoned wheat bran paste 
that is added to Japanese white radish (daikon) in the production of 
pickled Japanese white radish (takuan). Raw wheat bran is subjected to 
oxidative bleaching (e.g. with hydrogen peroxide) followed by reductive 
bleaching (e.g. with sodium hyposulfite). While conventional bleaching 
methods effect a decrease in the color of corn bran, it is desirable to 
further decrease the color of corn bran and thus improve its acceptance as 
a dietary fiber supplement. 
SUMMARY OF THE INVENTION 
This invention relates to a method of improving the utility of dietary 
fiber material comprising reacting dietary fiber material with an 
esterifying agent. This invention also relates to the product of such a 
method. This invention also relates to a method of decreasing the color of 
dietary fiber material comprising reacting dietary fiber material with an 
esterifying agent to form an esterified dietary fiber material and then 
bleaching said esterified dietary fiber material and to a bleached, 
esterified dietary fiber material produced by said method. 
In preferred embodiments, the dietary fiber material corn bran is reacted 
with a lower aliphatic carboxylic acid, acid halide, ester, or anhydride 
and then bleached with one or more bleaching agents, at least one of said 
agents being an oxidative bleach. In particularly preferred embodiments, 
the bleaching is accomplished by first oxidatively bleaching the dietary 
fiber material reaction product and then reductively bleaching the 
oxidatively bleached product. 
It has been found that corn bran that is reacted with an esterifying agent 
prior to bleaching has improved, i.e. decreased, color as compared to 
unreacted or post-reacted corn bran. This improvement is believed to 
result from the improved color stability of minor constituents of the corn 
bran, e.g. lignin and/or other phenolic materials, which results from 
esterification of materials in the corn bran.

DETAILED DESCRIPTION OF THE INVENTION 
The esterified dietary fiber of this invention is prepared from a source of 
dietary fiber. Dietary fiber material, as used herein, means a material 
comprised of dietary fiber derived from a plant source. Such sources 
include vegetable, cereal and fruit sources. Typical sources are the fiber 
materials produced by the milling of plant seeds, e.g. cereal grains such 
as corn, wheat and rice and oilseeds such as soybean, sunflower and 
cottonseeds. 
The preferred dietary fiber is corn bran. Corn bran is obtained from the 
grain by conventional milling techniques. In wet corn milling, which is 
the most common source of corn bran, corn kernels are steeped in dilute 
sulfurous acid to soften the outer layers of the grain. The moist corn 
kernels are then lightly ground in a mill to separate the intact germ from 
the remainder of the kernel. The germ is separated from the resulting 
cracked kernels by flotation of the germ. The resulting cracked kernels 
are powdered in a burr mill and the hulls (i.e. bran) are removed by 
screening the bran from the remaining starch and protein. The bran, which 
contains protein bound in a matrix comprised of hemicelluloses, cellulose 
and other constituents, are commonly used as, or to produce, a corn gluten 
feed. 
As indicated above, the corn bran starting material of this invention is 
typically obtained by powdering shelled and degermed corn (Zea mays) and 
screening the crude bran from the powdered starch and protein. 
Accordingly, the crude bran particles initially have a mean particle 
diameter in at least one dimension greater than the powdered starch and 
protein from which it is screened. A major portion of the weight of the 
bran will typically have a mean particle diameter in at least one 
dimension greater than about 1mm. The physical and chemical 
characteristics of the crude bran as produced by milling can be further 
modified prior to esterifying, e.g. particle size reduction, moisture 
content reduction, component extraction, etc. In particular, the crude 
corn bran is generally mechanically refined, i.e. reduced in particle 
size, by conventional techniques, examples of which include milling dried, 
crude bran in a classifying pin mill. The crude bran is generally 
mechanically refined sufficient to allow at least 80 percent to pass a No. 
20 mesh screen (850 micrometer openings). Preferred refined bran will pass 
at least 80% through a No. 60 mesh screen (250 micrometer openings), and 
most preferred will pass at least 95% through a No. 100 mesh screen (150 
micrometer openings) and 90% through a No. 200 mesh screen (75 micrometer 
openings). 
The major constituents of dietary fiber materials are cellulose, and other 
polysaccharides (e.g. hemicellulose, pectin, and plant mucilages). The 
fiber materials also contain phenolic compounds such as lignin and/or 
phenolic moieties which are also susceptible to esterification. The 
carboxylate esterifying agents useful in this invention are compounds 
capable of reacting with the constituents of dietary fiber to form 
covalent bonds thereto through hydroxyl groups in the fiber. 
Typical esterifying agents are carboxylic acids, or halides, esters, or 
anhydrides thereof. Particularly preferred esterifying agents are lower 
aliphatic (C.sub.1 -C.sub.4) carboxylic acids, or halides, esters, or 
anhydrides thereof. Examples of suitable esters include the esters of the 
lower alkanols, e.g. methanol and ethanol. Examples of suitable acid 
halides, include the acid chlorides and the acid bromides. Anhydrides and 
halides are especially preferred as esterifing agents because of their 
high reactivity with corn bran under mild reaction conditions which do not 
promote formation of color bodies in the dietary fiber material. Acetic 
anhydride is an especially preferred esterifying agent, not only because 
of its high reactivity under mild conditions, but also because of the ease 
of removing and treating unreacted anhydride and/or by-products (e.g. 
acetic acid and/or an alkali metal acetate). 
The amount of esterifying agent reacted with said dietary fiber material 
can vary broadly, but should be sufficient to significantly decrease, i.e. 
a decrease perceptible to an unaided human observer, the color of the 
fiber upon bleaching as compared with dietary fiber not reacted with an 
esterifying agent before bleaching. Typical levels of acetylation with 
acetic anhydride will range from about 0.1% to about 5% d.s.b. acetyl 
(--C(O)--CH.sub.3) by weight of reacted dietary fiber material. Typical 
means of measuring the percent acetyl of the reacted dietary fiber 
included nuclear magnetic resonance (NMR) integration techniques and ion 
chromatography of saponified, reacted dietary fiber. The percent acetyl of 
typical crude unreacted corn bran is generally very low, e.g. less than 
500 ppm, in comparison to the percent acetyl of acetylated corn bran. 
Thus, it may not be necessary, particularly with at least moderate levels 
of acetylation (e.g. from about 1% to 2%), to measure the percent acetyl 
of the corn bran starting material to establish a baseline or control 
against which the reacted product is measured. 
The dietary fiber material and esterifying agent can be admixed in any 
manner which will allow the material and agent to come into reactive 
association. Typically the fiber material is slurried with a liquid 
compatible with the fiber material and esterifying agent, e.g. water, and 
the esterifying agent is added to the slurry. An alkaline catalyst is 
preferably also present in the slurry. Such slurries typically contain 
less than 20% solids, by weight. However, it is contemplated that other 
techniques, e.g. fluidized bed techniques, will be useful to place the 
fiber material and esterifying agent in reactive association. 
As noted above, the reaction conditions under which the fiber material is 
reacted with an esterifying agent should be mild to avoid formation of 
color bodies during the reaction. Such conditions generally include mildly 
alkaline (e.g. pH of 8-10) slurry reactions conducted below the boiling 
point of the liquid media of the slurry. If the reacted fiber material is 
isolated prior to bleaching, the condiitons under which it is isolated 
should also be mild. 
The esterified dietary fiber material will have utility as a fibrous 
material in a variety of industrial and/or food applications, particularly 
those where the increased color stability of the dietary fiber resulting 
from esterification will be advantageous. A particularly preferred utility 
is in preparing bleached dietary fiber which is subsequently used as a 
dietary fiber supplement. 
The esterified dietary fiber can be bleached, typically by otherwise 
conventional bleaching techniques, to decrease the color thereof. Both 
oxidative bleaching techniques and reductive bleaching techniques are 
useful and, indeed, the preferred bleaching technique is a serial 
combination of the two techniques with the oxidative bleaching 
accomplished first, followed by reductive bleaching. Examples of 
conventional oxidative bleaching agents are peroxides (e.g. alkali metal 
or hydrogen), chlorites, peracids and ozone. Examples of conventional 
reductive bleaching agents are bisulfites. dithionites and borohydrides. 
Preferred bleaching techniques include oxidative bleaching with peracetic 
acid or hydrogen peroxide at a pH between about 5 and about 10, followed 
by reductive bleaching with dithionite. 
Following bleaching, the bleached dietary fiber material is isolated from 
the bleaching medium by any convenient means, e.g. filtration, 
centrifugation, etc. The isolated fiber can be washed, e.g. with an 
alcohol, to further decrease the color thereof, but such washing is not 
critical to the invention in its broadest scope. The isolated fiber 
material is preferably dried, preferably under mild conditions, e.g. at 
less than 80.degree. C., to form a free-flowing particulate. 
The bleached dietary fiber material produced by the practice of this 
invention will have improved organoleptic properties thus improving its 
utility as a dietary fiber supplement. The supplement can be incorporated 
in a variety of foodstuffs which conventionally have, or are susceptible 
to incorporation of, a fibrous component. Typical examples of such 
foodstuffs include baked goods wherein the supplement is added to the 
dough before baking, e.g. bread (loaves, rolls, buns, and the like), 
crackers, cookies and biscuits. 
The following examples illustrate the invention and are not intended to 
limit the scope thereof. All parts, percentages, and ratios are by weight 
unless noted otherwise. 
EXAMPLE 1 
Pre-acetylation and Peracetic Acid Oxidation 
To a 2 liter round bottom flask was added 200 g. or corn bran (having a 
particle size such that at least 95% passed a No. 100 mesh (150 micrometer 
openings) screen and at least 90% passed a No. 200 mesh (75 micrometer 
openings) screen, available as Staley.sup.R Refined Corn Bran SRCB-Ultra 
from A. E. Staley Mfg. Co., Decatur, IL, hereinafter referred to as 
"ultrafine corn bran") and 800 g. water. The pH was adjusted to 10.0 by 
dropwise addition of 5% sodium hydroxide at room temperature. Acetic 
anhydride (14.2g) was added from a dropping funnel over a 23 minute 
period. The pH was maintained at 9-9.5 by simultaneous addition of 5% 
sodium hydroxide. After addition of acetic anhydride was complete, the 
mixture was allowed to stir at room temperature for 15 minutes. The pH was 
then adjusted to 7.0 with dilute hydrochloric acid, while increasing the 
temperature to 60.degree. C. in a water bath. To the mixture was added 
6.86 g. of a 35% solution of peracetic acid. After 2 hours, 0.53 g. of 15% 
sodium bisulfite solution was added followed by 2.0 g. of sodium 
dithionite. The mixture was stirred at 60.degree. C. for 15 minutes. Then 
filtered and washed with water. The color of the dried product was 
measured using a Gardner color instrument. (Model XL-10, Gardner 
Laboratories, Inc., Bethesda, MD). The Gardner color numbers reported 
below are percent reflectance of wavelengths corresponding to G, A, and B 
which in turn correspond to the X, Y, and Z values of the 1931 Commission 
Internationale de l'Eclairage (CIE) as follows: G=(Y), A=1.277(X)-0.213(Z) 
and B=0.847(Z). In practice, the higher the G, A, and B numbers, the 
lighter the color of the product. A product having a B value lower than 
the G and A values indicates a yellow color. 
The Gardner color of the product of Example 1: G-79.5, A-83.1, B-60.7. 
The color the dry corn bran starting material: G-67.7, A-72.0, B-50.3. 
EXAMPLE 2 
Pre-acetylation and Peracetic Acid Oxidation 
The procedure of Example 1 was repeated except that the amount of acetic 
anhydride was reduced to 9.5 g. Gardner Color: G-79.0, A-82.7, B-60.1. 
COMATIVE EXAMPLE A 
Non-acetylation and Peracetic Acid Oxidation 
The procedure of Example 1 was repeated except that the acetylation step 
was omitted. Gardner Color: G-76.8, A-81.l, B-56.3 
EXAMPLE 3 
Pre-acetylation and Peracetic Acid Oxidation w/Alcohol Wash 
The procedure of Example 1 was repeated except the wet filter cake was 
placed in a flask with 3A ethanol and stirred at 60.degree. C. for 1 hour, 
filtered and washed with 3A ethanol. Gardner Color: G-83.8, A-86.5, B-69.1 
COMATIVE EXAMPLE B 
Non-acetylation and Peracetic Acid Oxidation w/Alcohol Wash 
The procedure of Example 3 was repeated except the acetylation step was 
omitted. Gardner Color: G-80.6, A-83.8, B-63.5. 
COMATIVE EXAMPLE C 
Post-acetylation and Peracetic Acid Oxidation 
To a 2 liter round bottom flask was added 200g ultrafine corn bran and 800g 
water. The flask was placed in a water bath set at 60.degree. C. After 
temperature equilibration, 6.86g of a 35% solution of peracetic acid was 
added and mixed for 3 hours. After adding 0.40g of a 15% sodium bisulfite 
solution, the flask was purged with nitrogen and 2.0g of sodium dithionite 
was added. After 15 min, the pH was adjusted to 10.0 by addition of 5% 
sodium hydroxide solution. The pH was maintained at 9.5 to 10.0 while 
adding 14.2g of acetic anhydride, dropwise. After completing addition the 
mixture was stirred for 15 min. The pH was adjusted to 4.5 with dilute 
hydrochloric acid, filtered and washed within water. After air drying the 
Gardner color was measured. Gardner Color: G-66.9, A-71.9, B-41.9 
COMATIVE EXAMPLE D 
Non-acetylation w/Acetic Acid and Peracetic Acid Oxidation 
To a 2 liter round bottom flask was added 200g of ultrafine corn bran and 
800g water and 16.7g of glacial acetic acid. The pH was adjusted to 5.0 
with 5% sodium hydroxide. The flask was placed in a 60.degree. C. water 
bath and 6.86g of a 35% solution of peracetic acid was added. The mixture 
was stirred for 2 hours and then 0.8g of a 15% solution of sodium 
bisulfite was added. The flask was purged with nitrogen and 2.0g of sodium 
dithionite was added. After 30 minutes the mixture was filtered, washed 
with water and air dried. Gardner Color: G-77.7, A-81.6, B-58.9 
COMATIVE EXAMPLE E 
Pre-propoxylation and Peracetic Acid Oxidation 
To a 2 liter round bottom flask was added 200g ultrafine corn bran and 800g 
water. The pH was adjusted to 10.0 by addition of 5% sodium hydroxide 
solution. After addition of 15.8g of propylene oxide, the flask was 
stoppered and stirred for 3 hours at room temperature. The flask was 
placed in a water bath at 60.degree. C. and the pH adjusted to 7.0 with 
dilute hydrochloric acid. After temperature equilibration, 6.86g of a 35% 
solution of peracetic acid was added and allowed to stir for 11/2 hours. 
After addition of 2.0g of a 15% solution of sodium bisulfite, 2.0g of 
sodium dithionite was added and allowed to stir at 60.degree. C. for 15 
minutes. The mixture was filtered, washed and air dried. Gardner Color: 
G-75.7, A-79.9, B-54.7 
COMATIVE EXAMPLE E 
Non-acetylation and Hydrogen Peroxide Oxidation 
To a 2 liter flask was added 200g ultrafine corn bran and 800g of 0.1M 
solution of sodium bicarbonate and sodium hydroxide having a pH of 10.0. 
The flask was placed in a water bath at 60.degree. C. The pH was adjusted 
to 9.0 with 2.5N sodium hydroxide. 17.4g of 30% hydrogen peroxide was 
added. The mixture was stirred and maintained at pH 8.5-9.0 for 90 min. 
The pH was then adjusted to 6.0 using 85% phosphoric acid. 8.0g of 15% 
sodium bisulfite solution was added to destroy excess hydrogen peroxide. 
The flask was purged with nitrogen and 3.3g of sodium dithionite was 
added. After 30 minutes the pH was adjusted to 4.5 with 85% phosphoric 
acid. The mixture was filtered, washed with water and air dried. Gardner 
Color: G-81.0, A-84,8, B-58.5. 
COMATIVE EXAMPLE G 
Non-acetylation and Hydrogen Peroxide Oxidation w/Alcohol Wash 
The procedure of Comparative Example F was followed except that after 
filtration, the west cake was reslurried in 3A alcohol. The slurry was 
stirred at 60.degree. C. for 1 hour, filtered and washed with 3A alcohol. 
Product was air dried. Gardner Color: G-82.9, A-86.0, B-64.4. 
EXAMPLE 4 
Pre-acetylation and Hydrogen Peroxide Oxidation 
w/Alcohol Wash 
To a 2 liter round bottom flask was added 200g ultrafine corn bran and 800g 
water. The pH was adjusted to 9.0 with 5% sodium hydroxide solution. The 
pH was maintained at 8.5-9.0 within 5% sodium hydroxide while adding 14.2g 
of acetic anhydride dropwise. After addition was complete the mixture was 
stirred for 20 minutes at pH 8.5-9.0. The pH was then adjusted to 6.5 with 
85% phosphoric acid and the flask was placed in a water bath at 60.degree. 
C. 17.0g of 30% hydrogen peroxide solution was added and the pH was 
maintained at 6.5 by addition of 2.5N sodium hydroxide as needed. After 90 
minutes 30g of a 15% solution of sodium bisulfite was added. The flask was 
purged with nitrogen and 3.3g of sodium dithionite was added. After 20 
minutes the pH was adjusted to 4.5 with phosphoric acid. The mixture was 
filtered and washed with water. The wet cake was reslurried in 3A alcohol 
and stirred at room temperature for 1 hour. The product was filtered and 
air dried. Gardner color: G-86.5, A-89.0, B-67.7. 
The results of Examples 1-3 and A-E are summarized in Table 1 below. The 
results of Examples 4, F, and G summarized in Table 2 below. 
TABLE 1 
______________________________________ 
Color of Peracetic Acid Oxidation Products 
Alcohol 
Gardner Color 
Example Acetylation 
Wash G A B 
______________________________________ 
Control None 67.7 72.0 50.3 
1 Pre- 79.5 83.1 60.7 
2 Pre- 79.0 82.7 60.1 
A Non- 76.8 81.1 56.3 
3 Pre- X 83.8 86.5 69.1 
B Non- X 80.6 83.8 63.5 
C Post- 66.9 71.9 41.4 
D Non- 77.7 81.6 58.9 
E Non-* 75.7 79.9 54.7 
______________________________________ 
*Pre-propoxylated 
The results shown in Table 1 indicate that none of the acetylation 
alternatives, including pre-propoxylation are as effective as 
pre-acetylation. Indeed, the post-acetylated material(Example C) had more 
color than the non-acetylated control(Example A). 
TABLE 2 
______________________________________ 
Color of Hydrogen Peroxide Oxidation Products 
Alcohol 
Gardner Color 
Example Acetylation 
Wash G A B 
______________________________________ 
F Non 81.0 84.8 58.5 
G Non X 82.9 86.0 64.4 
4 Pre X 86.5 89.0 67.7 
______________________________________ 
The results shown in Table 2 indicate that substitution of hydrogen 
peroxide for peracetic acid yields similar results. 
EXAMPLE 5 
The following example illustrates a post-bleaching oxidation of residual 
sulfites to decrease the level of residual sulfites and thereby improve 
the bran's utility as a dietary supplement and a method useful for 
determining the level of acetylation of the corn bran. 
In a 10 gallon tank reactor 5.5 kg of ultrafine corn bran was added to 23.5 
kg of water. The pH was adjusted to 9.0 with a 5% solution of sodium 
hydroxide. Acetic anhydride (390.5g) was added over a 35 minute period. 
The pH was maintained at 8.5 - 9.0 by simultaneous addition of a 5% 
solution of sodium hydroxide. The mixture was stirred at room temperature 
for 10 minutes for addition of acetic anhydride was complete. The pH was 
adjusted to 5.0 with 85% phosphoric acid and the mixture was heated to 
50.degree. C. A 35% peracetic acid solution was added and allowed to stir 
for five hours. Excess peracetic acid was destroyed by addition of 34g of 
a 15% aqueous solution of sodium bisulfite. The reactor was purged with 
nitrogen and heated to 60.degree. C. Sodium dithionite (55.0g) was added 
and allowed to stir for 30 minutes. The mixture was then cooled to room 
temperature and purged with air for 21/2 hours to oxidize excess sodium 
dithionite. Sulfite byproducts were oxidized to sulfate by addition of 72g 
of 30% aqueous hydrogen peroxide. The slurry was filtered and washed with 
water. The wet filter cake was reslurried in sufficient 3A alcohol to 
produce a 75% alcohol, 25% water solvent mixture accounting for water in 
the filter cake. The slurry was stirred for 30 minutes at room temperature 
and filtered. The product was air dried at room temperature. 
Gardner color: G81.9 A-85.5 B-63.7 
The bleached bran was analyzed for acetate by saponification with 0.33N 
sodium hydroxide at 50.degree. C. for 6 hours. The filtrate was analyzed 
for acetate ion by HPLC using a Biorad HPX87H ion exclusion column. The 
mobile phase was 1mM octanesulfonic acid at a flow rate of 0.5ml/min. Ions 
were detected by a conductivity detector. The bleached bran was found to 
contain 1.2% acetate. Unbleached bran contained 371ppm (0.037%) acetate.