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Water Absorption and Solubility and Amylograph Characteristics
of Roll-Cooked Small Grain Products!
R. A. ANDERSON, Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture,Peoria, IL 61604
ABSTRACT Cereal Chern. 59(4): 265-269
For many years, cereals and cereal products have been gelatinized or
cooked on hea ted rolls to prepare special ty products. Corn and grain
sorghum grits or flours have been the raw materials used most frequently.
Examination of the roll cooking of several other cereal derivatives (ie, gritsfrom wheat, barley, rye, and oats) has shownthat rheological characteristics
d if fe r when the var ious products are processed under like conditions.
Comparisons made ofwaterabsorption (WAI), watersolubility (WSI), and
Brabender amylograph patterns ofthe resultingproducts revealed not only
Gas- or s team-hea ted rolls have been used for many years to
prepare partially or completely gelatinized starches. flours, and
meals (Powell 1967, Whistler 1970). The degree of cooking of the
product generally depends on moisture content , par ticle size,
temperature, roll pressure, and duration of heating. By varying the
operating parameters, cooked products can be made that exhibit a
range of rheological properties. Products may bealtered to provide
materials with different water absorption and solubilities and with
different viscosity properties, as shown by Brabender amylographpatterns. We studied the roll cooking of corn and grain sorghum
grits (Anderson et al 1969a. 1969b, 1970) and include in this work
similar studies on grits prepared from wheat, barley, rye, and oats.
MATERIALS AND METHODS
MaterialsBarley, rye, hard wheat, and oats were obt ai ned through
commercial channels. Grits were prepared from barley, rye, and
wheat by passing each grain several times through an abrasive
dehulling machine to remove the bran, aspirating to recover bran,
and then reducing the dehulled grains on a roller mill to obtain grits
that would pass a no. 12 screen. Oats were dehul led in a scourer ,
aspirated, and then milled in a coffee mill to make grits that would
pass a no. 12 screen. Chemical analyses of these materials, and o f
corn and grain sorghum are shown in Table I.
Equipment and Experimental MethodsFo r these tests, the GF pilot-plant gas-fired roll drier having a
I Presented at the Annual Meeting of the American Association of Cereal Chemists.
October ~ 5 - 2 9 , 1981, Denver. CO.
Mention of firm names or trade products does not imply that they areendorsed or
recommended by the U.S. Department of Agricul ture over other f irms or similar
products not mentioned.
This a rt ic le is i n t he p Ub li c d om ai n an d not copyrightable. It may be freelyreprinted with customary crediting of the source. TheAmerican Association of
Cereal Chemists, Inc., 1982.
many similarit ies between the different cereals but also some interesting
differences. Cooked grits from oats had considerably lower WAI and WSI
values than the other grains under study; the WAI peaked about 100° F
(37° C) lower than that ofgrits from wheat, barley, rye, corn. and sorghum.Oat products gave amylograph patterns similar to those of corn, sorghum,
and wheat, whereas cooked barley grits gave atypical viscosity patterns,
with elevated values at all critical points.
12-in. diameter (General Food Package Equipment Co .. Benton
Harbor, MI) was used. Grits from the various grains were cooked
on the gas-fired' drier at temperatures ranging from 250 to 570 0 F
(121-299°C) and a t moisture levels of 15 and 25%. Roll clearance
was set cold at 0.00I in. (0.025 mm), and roll speed was 3 rpm.
Analytical MethodsRolled-cooked grit products were evaluated by measuring their
water-absorption index (WAI), water-solubilitv index (WSI), andBrabender viscosity patterns. .
The water-absorption index is the weight of gel obtained per
gram of dry sample through a modif icat ion of the method
descr ibed by Kite et al (1957) for measur ing swelling power of
starch. A 2.5-g sample of ground product «60 mesh) was
suspended in 3ml of water at 30°C in a 50-ml tared centrifuge tube,
stirred intermittently for 30 min, and centrifuged at 3,000 Xg for IO
min. The supernatant li qu id was poured careful ly in to a tar ed
evaporating dish. The remaining gel was weighed and the WAI
calculated from its weight.
As an index of water solubility, the amount o f dried solids
r ecovered by evaporating the supernatant from the water
absorption test was expressed as percentage of dry solids in the
2.5-g sample.
The amylograph tes t was done in the standard manner, with 500
g of 9% (db) suspension of the sample «60 mesh), heated from 29
to 95° C in44 min, held at 95° C for 16 min. and thencooled to 50° C
in 30 min.
Chemical analyses of the grains and their grit products were
conducted according to AACC methods (1962). Moisture was
determined in a Brabender moisture tester.
RESULTS AND DISCUSSION
Only two of the operating factors were varied du ring the
experimental work: the moisture content of the gri ts and the roll
surface temperature. The other operating conditions, such as roll
pressure, duration of heating, and particle size of the grits, were
Vol. 59, No.4, 1982 265
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TABLE IChemical Analysis of Whole Grain and Prepared Grits Used in Cooking Experiments
Wheat Barley
Grain Grits Grain Grits
Moisture, % 12.7 12.2 10.9 12.0Nitrogen, % 2.4 2.2 1.5 1.4Crude fat, % 1.4 0.9 1.6 0.9Crude fiber, % l.7 0.8 4.7 0.6Ash, % 1.6 1.1 2.4 1.I
Rye OatsGrain
Corn Sorghum
Grain Grits Grain Grits Grits Grits
11.8 11.9 9.9 10.0 14.0 12.0
1.8 1.5 1.9 2.6 1.3 1.5
1.5 0.6 4.9 6.7 0.5 0.81.8 0.6 10.6 1.2 0.3l.7 1.3 3.1 l.7 0.4 0.3
265'F1129'CI
\ ~ / ? ~ 0 0 ' F I 2 0 4 ' C I
y
/\I \I \
I \I ' -
/ /
_ /
---
200
500
100
500
100
400
'""'".g 30005
;§ 400
'E:::l
j 300
e<Xl 200
560'FI294'CI
_L-----..- - - - - -ot:=:=r=::::::i:=:::::C::L------L_.l.-----l----I.._.l.---lo 10 20 30 40 50 60 70 80 90
Minutes
1---- Heat • I Hold· I Coo l - - - 1
29'C 95'C 95'C 50'C
Fig. 3. Roll cooking of wheatgrits: Effect of temperature on viscosity (25moisture).
265'F1129'CI
\/
/{/ 450'FI232'C)
/___// 550'F1288'CI
YI
~ .~
/ : , . . - - - - - - - - // o ~ s : = S ~ - ~ _ L _ _ _ _ L _ _L__.L_L..__L_.J
o 10 20 30 40 50 60 70 80 90
Minutes
t----Heat .. I Hold .. I Cool- l
29'C 95'C 95'C 50'C
Fig, 2, Roll cooking wheat grits: Effect of temperature on viscosity (15moisture).
600 r-------------------------,
600r - - - - - - - - - - - - - - - - - - - - ,
tvI
III
25% MOisture/ •
o ..... ° :P/-.......;; ......... ~ /-
-.. _ . ; : ~ ..
. -......--- . 15% Moisture
25%0Moisture_ ' __ .
, , " " - 0---0_O, ......._/' _-.0/ 15% Moisture
o /
...............
14
:= 12tr.l
><Q)
-g 10
.:.c:::::s 8ctr.l.
Ci>
C;;6
:
4
8
e:t:s:>< 6)
'"Cc::
c::.S: 4-ec
'"ce:t:.... 2)
-"s:0
400 DF(204 DC)
TemperatureFig. 1. Roll cooking of wheat grits: Effect of temperature and moisture on
water-absorption index (WAI) and water-solubility index (WSI).
constant throughout the study.In Figs. 1-3, results are given for the roll processing of wheat
grits. Peak WAI appears to be about 6, occurring at 25% moistureand 400°F (204°C); this peak was not reached with the 15%
moisture sample. The WAI of the 15% sample leveled off at thehigher temperatures because starch degradation was occurring,evidenced by toasting and by the viscosity patterns (Figs. 2 and 3).The WSI decreased slightly as temperature was increased at both
moisture levels to 400-425°F (204-218°C), then rose rather
rapidly. Characteristic viscosity patterns were obtained, with initialpaste viscosity (29°C) increasingwith an increase in temperature ofroll cooking, and the final cooked paste viscosity (50°C)
decreasing. Degradation occurred in both the 15 and 25% moistures'amples that were roll cooked at 550° F (288° C), as evidenced by
lower peak and final cooked paste viscosities. At maximum WAI,peak viscosity was 280 Brabender units (BU) at 15% moisture and450°F (232° C) and 480 BU at 25% moisture and 400° F (204° C).Figures 4-6 show the results obtained from the roll cooking of
barley grits. As shown in Fig. 4, the WAI follows a typical curveboth moisture levels. In the 25% moisture sample, the maximu
WAI of 8 is reached at about 425° F (218°C), after whichdecreases. At 15% moisture, WAI never reaches the maximumpeaking at about 7 at 460° F (238°C) and then falling off. The W
remains level at 5until about 425°F (218°C) and then progressiveincreases, with the 25% moisture sample increasing at a slightgreater rate.
Figure 5showsviscositycurves for barleygrits processed at 15moisture at three different temperatures. The initial paste viscosi
(29°C) increases as temperature of roll cooking increases; this alsoccurs with the 25% moisture samples (Fig. 6). Viscosity peaks
maximum WAI occurred at 460°F (238°C) for 15% moistusample and at 410° F (2100 C) for the 25% moisture sample. Theviscosity peaks are the highest we have seen for any of the grainstudied, varying from about 1,500 BU for the 15% moisture sampat 460°F (238°C) to 1,800 BU for the 25% moisture sample410°F (210°C). Final cooked paste viscosities (50°C) decreasecharacteristically as the roll cooking temperatures were increase
266 CEREAL CHEMISTRY
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41 O'FI21 O'CI
\ //
\ // 550'FI2SS'CI.... . / ../
' - -.../, ../
.../ ........_---------__ -_ - --
O l . .- - . . .L - - - - - - - I - - - - . . . .L - - - - - - I
6
o 25% Moisture
, ~ " " " ' ' ' ' ' ' ' ' ' - ' ' 0 ..0/ ...........
/ 0 ~ /
4 / /o
fill
2-- - - '
6L--...L------l.----...L------.-4
8
300
1200
XQJ
"1:lc:
2000 r - - - - - - - - - - - - - - - - - - -
lS00
14 , . - - - - - - - - - - - - - ~
1500
10
J ~ ~ 1 5 % Moisture V80__~ ~ ~ . '
2= .... - = - ~ " 025% Moisture
oL----I_--l._-L_-L_..l-_.L-_L----l_--L_....Jo 10 20 30 40 50 60 70 80 90
Minutes
f - - - - - Heat • 1 Hold • 1 Coo l - - - J
29'C 95'C 95'C 50'C
Fig. 6. Roll cooking barley grits: Effect of temperature on viscosity (25%
moisture).
12 0
- II:l
3: /10
QJ /1:l
-= /G
8:E 25% Moisture/:::s 0C 7CI:l
,1fiJ •Q; 6 15% MOistureca ~ - ~ ~ ~ ~ - - - ~ . - -:
4
8 25% Moisture _0= .....
« / . " , . . . s .; 0
6 / '0QJ
0 / ~ 1:l
-=c:Q
4:Es'"..0
«2
Q;cas
0
As with wheat, some starch degradation occurred with samples thatwere roll cooked at 550° F (288° C), as shown by lower peak and
final cooked paste viscosity for both tempering treatments.
Results of the processing of rye grits are given in Figs. 7-9. TheWAI and WSI obtained from these studies gave patterns similar to
those obtained from wheat grits, except at a slightly higher level(Fig. 7). Peak WAI was about 7and, as with wheat, a similar dip in
WSI appeared. Charact eris tic viscosity pa tte rn s again were
obtained from the products of roll-cooked rye grits. Peak
viscosities at maximum WAI were higher than wheat bu t lowerthan barley. These peaks occurred at 450 BU for the 15%,450°F
(232° C) sample and at 990 BU for the 25%,405° F (207° C)sample.
Starch degradation occurs at 550°F (288° C) in both samples.The WAI for cooked oats does not follow the usual pattern
observed with the other cereals tested (Fig. 10). Maximum WAI isabout 4, occurring at 375 0 F (191 °C) for the 15% moisture sample
an d at 325°F (163°C) for the 25% moisture sample. In the other
400 0F(204°C)
Temperature
Fig. 4. Roll cooking of barley grits: Effectof temperature and moisture onwater-absorption index (WAI) and water-solubility index (WAI).
lS00 r - - - - - - - - - - - - - - - - - - - - ~
o"====:::::r:::_..l.----l_--L_...L-_L---l._-L--.Jo 10 20 30 40 50 60 70 SO 90
Minutes
f - - - - - Heat .. I Hold • I Cool---J
29'C 95'C 95'C 50'C
Fig. 5. Roll cooking barley grits: Effect of temperature on viscosity (15%
moisture).
1200
900
'2=>
600
Id5
300
450'FI232'CI
250'FI121'CI
/ ------- .../s'50'FI28S'CI
..-...._-----_ ... .."""",.- ...
o! = ; : r , ; ; ; ; ; ; ; ; ; ; ~ = _ . . L _ _ _ l _ _ _ _ L - - - . J _ . . L _ - L ~o 10 20 30 40 50 60 70 SO 90
Minutes
I Heat • 1 Hold • I Cool- - -J
29'C 95'C 95'C 50'C
Fig. 8. Roll cooking of rye grits: Effect of temperature on viscosity (15%
moisture).
Temperature
Fig. 7. Roll cooking of rye grits: Effect of temperature an d moisture on
water-absorption index (WAI) and water-solubility index (WSI).265'F1129'CI
300
600
1500
, 1200
:5
1900
ti;
Vol. 59, No.4, 1982 267
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90
555'FI290'CI
80000000
1500
1200
:3 900
-g
= 600cD
I
300
10 ,----------------------,
when compared to the other cereals. After a slight increase, peakin
at abou t 300° F (149°C ), the WSI decreased to a minimum
400-425°F (204-218° C) and then rose sharply as temperatur
were increased. Figure 11 shows viscosi ty curves for oa t gri
processed at 15% moisture and at four different temperature
Initial paste viscosity (29° C) was the same for samples cooked
25% moistur e (Fig. 12). In both moisture series, peak viscosi
occurred in samples cooked at 265° F (129° C). With the exceptio
of the 25% moisture sample cooked at 320° F (160° C), final cooke
paste viscosi ty (50° C) decreased as temperature increased in
manner similar to that observed with viscosity patterns of the oth
cereals roll cooked under like conditions.
Comparisons of WAI values of grits from different graincooked at 25% moisture overa range of temperatures are given
Fig. 13. Data fo r corn and sorghumare from Andersonet al (1969
1969b). Characteristic WAI curves were obtained from all th
g rains ex cept oa ts, with WAI peaking for all but oats
temperatures from 400°F (204° C) to 450°F (232°C). The curve fo
oats showed very little change over the complete range
temperatures used. The peculiar behavior of oa t grits perhaps ca
be attributed to the considerably greater amount of oil and crud
f iber present in oats. Although not shown, the water solubility
cooked grits from the different grains was similar, ie, with little
no change in WSI until about 400°F (204° C), then increasingas th
temperature of cooking was increased. Wheat and rye showed th
highest WSI, which was attained at 550°F (288°C). A small peak
about 300°F (149° C) on the WSI curve for oat grits was not note
on the others, bu t the remainder of the curve followed thcharacteristics of the other grains. However, the value at 550°
(288° C) was somewhat less than those from the other grains und
study.
Table II gives comparative amylographdata for selected sampl
of roll-cooked grits from the different grains studied. Except fo
corn. all samples were cooked at 25% moisture content and
approximately 400° F (204° C). The corn sample was cooked
50
Minutes
f - - - - - Heat • I Hold • I Cool-j
29cC 95'C 95'C 50'C
Fig. 12. Roll cooking of oat grits: Effect of temperature on viscosity (25
moisture).
260'FI127CCI
550'FI2BB'C!
/ '
/ , - -405 cFI207'CI
- - - - ~ . . ; " " "
/' ./ \
/ \/ / \
_/--
4
300
900
t 600
cD
10 r----------------. . . ,
2 ' - - - - L . . - - - - . . L - - - - - . . . 1 . - - - - - - - - '
cereals, maximum WAI generally occurred from 410° F (210°C) to
450° F (232° C), and WAI was 6 or higher. For the cooked oats,
WAI increased at high cooking temperatures after showinga slight
decrease. This phenomenon did not occur with WAI of o ther
cereals, in which WAI declined after reaching maximum. Oat grits
cooked at 500° F or higher (260° C) started browningand exhibited
other appearance characteristics similar to those noted with the
other cereals cooked at temperatures exceeding 500° F (260° C).
Water-solubility index curves indicate rather atypical patterns
21. . . . - - . . . J . - - -_--- I . . . . ! - -- j
« 8s:x
'"c-= 6c::
.
.. Q
o'".Q«
1200 , - - - - - - - - - - - - - - - - - - - - - - ,
400 DF
(204DC)
Temperature
Fig. 10. Roll cooking of oat grits: Effect of temperat.ure and moisture onwater-absorption index (W AI) and water-solubility index (WSI).
o ~ ~ ~ ~ : : . = . : : : : : : r : : . : : : = . : i = - - - L - - - - l . _ . . L - - L ~o 10 20 30 40 50 60 70 BO 90
Minutes
f---- Heat • 1 Hold -I Cool-j
29'C 95'S 95'C 50'C
Fig. 9. Roll cooking of rye grits: Effect of temperature on viscosity (25%
moisture).
Rye
8arley - - - : : / . Corn
\ /,-' 7 ...... /", ' " -- "-/'" ,,---""""""'=.---,
....'" ,At::-:::.\------- ............."" -/--- ......:--., ..
/' /" : / '" Grain Sorghum Wheat - - - - - - ~ _Co1 ~ ~ ~ ~ Oats
;;: 4 ./~ ~ - - - - - - - / -------~ - - - - - - - - - - - - - - -
1200
900
'" ,
::>
m 600""m"";:"" 300
o~ ~ ! ! ! ' ! ! ! ! ! ! ! ! ! ! ! ! ! ! E : = : ; ; = = = = : : = . : : : : r . : ~ _ . . . . L - - - . Jo 10 20 30 40 50 60 70 80 90
Minutes
f---- Heat .. I Hold • I Cool-j
29'C 95'C 95'C 50'C
Fig. 11. Roll cooking of oat grits: Effect of temperature on viscosity (15%
moisture).
300'F 400'F1149'CI i204'CI
Fig. 13. Roll cooking studies: Water-absorptiondifferent grains roll cooked at 25% moisture.
500'F(260'CI
index of grits from
268 CEREAL CHEMISTRY
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TABLE II
Amylograph Data for Roll-Cooked and Uncooked Cereal-Derived Grits
Viscosity'Final Cooked Paste
Sample ViscosityIdentification at 29°C at 95°C Peak at 95° C for 16 min (50°C)
BarlevC o ~ k e d b 605 1.200 1,820 470 850Uncooked 10 I.l40 1,140 580 1.240
Rye
Cooked" 330 575 1,100 450 780Uncooked 20 200 230 210 540
Wheat
Cookedb 60 420 480 240 505
Uncooked 0 180 180 180 390Oats
Cookedb
30 420 450 360 960Uncooked 20 380 405 280 850
Corn'
Cooked" 320 260 490 210 450Uncooked 30 280 280 330 730
Sorghum'
Cooked' 170 240 330 240 330Uncooked 20 300 300 280 700
'I n Brabender units.
bCooked at ~ 4 0 0 ° F (204°C) at 25% moisture.
,Anderson et al (1969a, 1969b).
dCooked at ~ 4 6 5 ° F (240° C) at 20% moisture.
465°F (240° C) at 20% moisture. Amylograph data for uncooked
grits from the grains are also included. The viscosity data followedthe amylograph patterns expected from both the cooked and
uncooked grits, Viscosity developed slowly as the temperature of
the material was being increased to the point of gelatinization, at
which viscosity peaked, of ten dramatically. It decreased when
material was stirred at 95° C for 16 min, and once again increased
during the cooling cycle to the final cooked paste viscosityat 50°C.
Uncooked wheat , oats, rye. corn, and sorghum gri ts had similar
amylograph pat terns, with some minor variations. Uncookedbarleygrits, on the other hand. gave unusually high values for both
peak and final cooked paste viscosity. Viscosity values that werehigher than usual also were obtained from the cooked barley grits.
Cooked rye grits gave a some\vhat higher viscosity pattern than didthe wheat. oats, corn, or grain sorghum.
These studies show that a b road range of products possessing
dif ferent vi scos ity character is ti cs can be made by roll cookingcereal grits under different conditions of temperature and moisture.
Furthermore, the various cereal grains, either cooked or uncooked,
can exhibit viscous properties that differ from one another.
LITERATURE CITED
AMERICAN ASSOC IATION OF CEREAL CHEMISTS. 1962.
Approved Methods of the AACC. Methods 08-01, 30-20, 32-15, and
46-10, approved April 1961. The Association, St. Paul. MN.
ANDERSON. R. A., CONWAY, H. F., PFEIFER, V. F., and GRIFFIN,
E. L., Jr. 1969a. Gelat in izat ion of corn gri ts by rol l and extrusion
cooking. Cereal Sci. Today 14:4-12.
ANDERSON, R. A.. CONWAY. H. F. , PFEIFER, V. F., and GRIFFIN,
E. L., Jr . 1969b. Roll and extrusion cooking of grain sorghum grits.
Cereal Sci. Today 14:372-375.
ANDERSON, R. A .• CONWAY. H. F., and PEPLINSKI. A. J. 1970.Gelatinization of corn gri ts by roll cooking , ext rusion cooking and
steaming. Staerke 22: 130-135.
KITE, F. E., SCHOCH. T. J.. and LEACH. H. W. 1957. Granule swelling
and paste viscosity of thick-boiling starches. Bakers Dig. 31(4):42-44.
POWELL, E. L. 1967. Production and use of pregelatinized starch. Page
523 in: Starch: Chemistry and Technology. Vol. II. R. L. Whistler and
E. F. Paschall, eds. Academic Press, New York.
WHISTLER, R. L. 1970. Industrial uses of corn starches. Page 171 in:
Corn: Culture, Processing, Products. G. E. Inglett, ed. Avi Publishing
Co., Westport, CT.
[Received October 19, 1981. Accepted January 25, 1982J
Vol. 59. No.4. 1982 269