Wa er Absorption and Solubility and Amylograph Characteri st ics 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 Fo r many years, cereals and cereal products have been gelatinized or cooked on h ea te d r oll s t o p re pa re s pe ci al ty p ro du ct s. Corn and grain sorghum grits or f l ou rs have been the raw materials used most f r eq ue n tl y. Examination of the roll cooking of several other cereal deri vat ives (ie, grits from wheat, barley, rye, and oat s) ha s shown that rheological characteristics d if fe r w he n t he v ar io us products are processed under like condit ions. Comparisonsmade ofwater absorption (WAI) , watersolubil ity(WSI), and Brabender amylograph patterns oftheresultingproductsrevealednotonly Gas- or steam-heated rolls have been used for many y ea rs t o prepare partially or completely gelatinized starches. flours, an d meals (Powell 1967, Whistler 1970). The degree of cooking of the product g e ne r al l y depends on moisture content, p ar ti cl e size, temperature, roll pressure, and duration of heating. By varying the operatingparameters, 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 Brabenderamylograph patterns. We studied the roll cooking of corn and grain sorghum grits (Anderson e t a l 1 96 9a . 1 96 9b , 1 97 0) and include in this work similarstudies on grits prepared from wheat,barley, rye, and oats. MATERIALS AND METHODS Materials B ar le y, r ye, hard wheat, an d oats were o bt ai ned through commercial channels. Grits were prepared from barley, rye, an d wheat by passing each grain several times through an abrasive dehulling machine to remove the bran, aspirating to recover bran, an d then reducingthedehulledgrains on a rollermill to obtain grits that would pass a no. 12 screen. Oats were dehulled in a scourer, aspirated, an d then milled in a coffee mill to make grits that would pass a no. 12 screen. Chemical analyses of these materials, and of corn and grain sorghum are shown in Table I. Equipment and Experimen tal Methods Fo r these tests, the GF pilot-plant gas-fired roll drier having a I Presented at t he A n nu a l M ee ti ng of th e American Associ ation of Cer eal Chemists. October ~ 5 - 2 9 , 1981, Denver . CO. Mention of fir m names or trade products does n o t i m pl y t h at t h ey areendor s ed or r ec om me nd ed by t he U.S . D ep a rt m en t o f A gr ic ul tu re o ve r o t he r f ir ms or similar product s not mentioned. This article is in the pUblic domain and no t copyrightable. It m ay b e f re el y reprinted with customary crediti ng of the source. TheAmerican Association of Cereal Chemists, Inc., 1982. m a ny s im il ar it ie s b et we en t he d if fe re nt c er ea ls b ut a ls o s om e i nt er es ti ng differences. Cooked grits from oats had considerably lower WAI and WSI values than the other grains under s tu dy ; t he W AI p ea ke d a bo ut 100° F (37° C) lower thanthatof g r it s f r om whea t , b a rl e y, r ye , c o r n. and sorghum. Oat products gave amylograph patterns similar to t ho se of corn, sorghum, and wheat, whereas cooked barley grits gave atypical viscosity patterns, with elevated values at all c r it i ca l p oi nt s. 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 at moisture levels of 15 an d 25%. Roll clearance was set cold at 0.00I in. (0.025 mm), and roll speed was 3 rpm. Ana lyt ical Methods Rolled-cooked grit products were evaluated by measuring their water-absorption index (WAI), water-solubilitvindex(WSI), an d Brabender viscosity patterns. . Th e water-absorption index is t he w ei gh t of gel obtained pe r gram of dry sample through a m od if ic at io n of the method described by Kite et al (1957) for measuring swelling power of starch. A 2.5-g sample of ground product « 6 0 mesh) was suspended in3ml of water at 30°C in a 50-ml tared centrifuge tube, stirred intermittently for 30 min, and centrifugedat 3,000X g fo r IO min. The supernatant li qu id was poured carefully into a tared evaporating dish. Th e r em ai n in g gel was w ei gh ed and the WAI calculated from its weight. As an index of water solubility, the a mo un t o f dried solids recovered by evaporating the supernatant from the water absorption test was expressed as percentage of dry solids in the 2. 5- g sample. The amylograph test was done in the standard manner, with 500 g of 9% (db) suspension of thesample « 6 0 mesh), heated from 29 t o 95° C i n 4 4 m in , h el d at 9 5° C f or 16 min. an d thencooledto50°C in 30 min. Chemical analyses of the grains a nd t he ir grit products were conducted according to AACC methods (19 62 ). Moisture was determined in a Brabender moisture tes ter . RESULTS AND DISCUSSION Only two of the operating factors were varied during the experimental work: the moisture content of the grits and the roll surface temperature. Th e other operating conditions, such as roll pressure, duration of heating, an d particle size of the grits, were Vol. 59, No.4, 1982 265
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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
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