EFFECT OF ROASTING TEMPERATURE ON CORN GRAIN
CHARACTERISTICS 1 , 2 , 3
R. J. Felsman 4, R. W. Harvey, A. C. Linnerud s and F. H. Smith
North Carolina State University 6, Raleigh, 2 7607
SUMMARY
INTRODUCTION
A series of in vitro and in vivo studies were
conducted to evaluate certain grain characteristics of corn roasted at different temperatures.
Density, moisture absorption and dry matter
disappearance (nylon bag) were determined
with samples of raw corn and corn roasted at
five temperatures between 93 and 137 C.
Amino acid concentration and enzymatic glucose release rate were studied with raw corn
and corn roasted at temperatures between 93
and 178 C. Corn roasted at 127 or 137 C had a
greater moisture absorbing capacity, was more
susceptible to enzymatic degradation and resulted in higher dry matter disappearance values
than raw corn or corn roasted at 9 3 , 1 0 4 or 116
C. Corn roasted at 137 C was superior to corn
roasted at 127 C. Density was found to
decrease slowly up to 116 C and then decrease
more rapidly to 127 and 137 C. Lysine concentration was reduced in corn roasted at 137, 148
and 176 C, whereas, arginine levels were reduced only in corn roasted at 176 C.
(Key Words: Roasting, Heat, Ruminant, Grain
Characteristics.)
Various methods of processing grain are
being used by cattle feeders in an attempt to
enhance efficiency of nutrient utilization. Recent!y, interest has developed in dry " c o o k i n g "
or roasting grains with gas or electrically heated
roasters. This process appears to improve the
performance of cattle, is less expensive than
steam flaking and is more suitable for small
feeders.
The influence of various roasting temperatures on the chemical and physical characteristics of corn and feeding value has not been
adequately studied. Perry et al.(1970) and
Burroughs et al. (1970) have reported advantages in both animal gain and feed efficiency
for corn roasted at 149 C. Other roasting
temperatures have not been studies although it
is known that steaming temperatures and pressures are important in improving the feeding
value of steam-flaked grains. High cooking
temperatures have been shown to cause gelatinization of starch and in turn a lowering of
animal performance (Mudd and Perry, 1969).
Experiments reported herein were designed
to evaluate the influence of roasting temperature on nutrient availability, grain characteristics and acceptability to cattle.
1Paper No. 4483 of the Journal Series of the North
Carolina Agricultural Experiment Station, Raleigh.
The use of trade names in this publication does not
imply endorsement by the North Carolina Agricultural
Experiment Station of the products named, nor
criticism of similar ones not mentioned.
2Acknowledgment is given to Miles Labs Inc., The
Marschall Division, Elkhart, Indiana, for supplying the
Diazyme L-100 and to Mix-Mill Inc., Bluffton, Indiana, for supplying the Roast-A-Tron.
a Partial data from a thesis submitted by the Senior
author to the Graduate School, North Carolina State
University, in partial fulfillment of the requirements
for the degree of Doctor of Philosophy.
4Present address: Cooperative Extension Service,
University of Arkansas at Pine Bluff, Post Office Box
82, Pine Bluff, ARK 71601.
s Assistant Professor, Department of Statistics.
6 Department of Animal Science.
7Roast-A-Tron manufactured by Mix-Mill Inc.,
Bluffton, Indiana.
MATERIALS AND METHODS
Samples of corn, yellow, grain, gr 1 U.S. mn
wt 25.5 kg per bushel (4) IRN No. 4-03-004
(corn), roasted at 93, 104, 116, 127 and 137 C
were obtained approximately 45 cm from the
point the corn exited the roaster (a gas operated Roast-A-Tron7). Samples were collected
after the roaster had run at a specific flow rate,
which determined roasting temperature, for 10
to 15 minutes. This was done to allow the
roaster to reach a constant operating temperature. Subsamples were collected in a .95 liter
thermos bottle equipped with a thermometer.
After a 5-min equilibration period, the temperature was read to determine the roasting tern476
JOURNAL OF ANIMAL SCIENCE, Vol. 42, No. 2, 1976
TEMPERATURE FOR ROASTING CORN
perature of the corn. Additional samples were
roasted at temperatures between 137 and 178
C, although the practical limits for continuous
operation of the roaster was 137 C. In all
studies, a raw corn sample was included to serve
as a control. The dry matter of the raw, 93,
104, 116, 127 and 137 C corn samples after
roasting was 89.1, 90.8, 91.4, 92.2, 94.6 and
94.2%, respectively.
Density of the roasted corn samples was
determined by overfilling a tared 400 ml
beaker. The beaker was then leveled, re-weighed
and the weight of the corn determined by
difference. Moisture absorption was determined
by adding 100 g samples of the air dry corn to
containers with screen (1 • 1 mm mesh)
bottoms and placing in an agitating water bath
at 37 C. At 1, 2, 4 and 8 hr the cans were
removed, allowed to drain and weighed. The
amount of water absorbed by the corn was then
calculated.
Dry matter digestibility of the various samples was determined using the nylon bag technique described by Van Keuren and Heinemann
(1962). Digestion periods of 8, 12 and 24 hr
were compared on 3 days using duplicate nylon
bags (38 • 48 threads/cm 2) of similar size
(10 • 11 cm). A 5-g oven-dried sample of corn
was used in all the bags. A fistulated steer was
fed a mixture of 50% raw corn and 50% of 137
C roasted corn for a 14-day period prior to and
during the nylon bag study. The steer was also
fed approximately 1.36 kg of long hay daily.
The susceptibility of corn starch to enzymatic degradation was studied using the procedure of Liang e t al. (1970). A 1 g sample of
ground corn was incubated with an amyloglucosidase s and the release of glucose measured
by the method of Nelson (1944).
Amino acid determinations were made on
the fat-free moisture-free samples using a Model
120B Beckman amino acid analyzer. Samples
were prepared according to procedures outlined
in the instruction manual for the instrument,
At the higher roasting temperatures, the
corn was quite brittle and some kernels were
charred. To measure these effects on animal
acceptability, a 10-day preference trial was
initiated using three Hereford steers weighing
approximately 245 kilograms. During a 14-day
preliminary period, the steers were placed in
8Diazyme L-IO0, Miles Labs Inc., Marschall Division, Elkhart, Indiana 46514.
477
individual stalls with free access to water and
were fed a mixture containing equal parts of
raw, 137 and 171 C roasted corn along with a
mineral, protein and vitamin supplement (nine
parts corn to one part supplement). During the
preliminary period and preference study, each
steer was also fed 1.36 kg of hay daily. At
initiation of the preference study, each steer
was allowed free access to each of the corn
samples (raw, 137 and 171 C roast) mixed with
supplement. Each morning the orts were
weighed to determine consumption and fresh
feed was added. The feed containers were
randomly arranged each morning.
All criteria examined were subjected to
statistical analysis according to Steel and Torrie
(1960). Differences between treatment means
for each criterion were tested using Duncan's
New Multiple Range Test (Steel and Torrie,
1960).
RESULTS A N D DISCUSSION
Grain D e n s i t y . Table 1 contains the mean
weight per cubic centimeter of raw corn and
the five roasted corns. A (P<.05) difference in
density was obtained between roasting temperatures. Expansion of the grain, or decrease in
density occurred at a slow rate until a temperature of 116 C was reached. Thereafter, density
was greatly decreased at 127 C and decreased
somewhat more at 137 C. Percentage decrease
in density ranged up to 41.9% for the 137 C
sample. Perry et al. (1970) reported a 13.3%
decrease in density for corn roasted at about
149 C. The difference between the change they
reported and those reported herein may be due
to the technique used to determine roasting
temperatures.
TABLE 1. EFFECT OF ROASTING
TEMPERATURE ON CORN DENSITY
Roasting
temperature (C)
Densitya
(g/cm3)
Percent decrease
in density
Raw
93
104
116
127
137
.74 +- .01 b
.71 -+.01 c
.70 +-.01 c
.67 -+.01 d
.49 -+.01 e
.43 +-.01 f
...
4.1 _+ .83
5.4 -+ .16
9.9 +. 1.16
33.8 _+1,70
41.9 _+1.17
aEach value represents the mean -+ standard error
of three observations.
b'c'd'e'fMeans within a column with different
superscripts are significantly different (P<.05),
478
FELSMAN
TABLE 2. EFFECT OF ROASTING TEMPERATURE ON MOISTURE ABSORPTION
Roasting
temperature (C)
Raw
93
104
116
127
137
Moisture absorption (g)a
1 hr
2 hr
4 hr
26.8+ 1.9 d
25.4• .6 d
25.8•
d
26.7 • 2.8 d
40.2• .1 c
47.0• .2 b
34.7• 1.0 d
32.8• .1 d
32.0• .2 d
33.1 • 1.7 d
49.9• .2 c
57.0• .1 b
44.0-+
41.0•
39.4•
40.1 •
59.8•
68.5+
8hr
.8 e
.5 de
.6 d
1.5 d
c
.3 b
51.1•
d
49.5•
d
46.5• 3.2 d
50.3 • 1.8 d
71.2• 1.9 c
83.9• .7 b
aEach value represents the mean • standard error of two observations.
bcde
. .
.
' ' ' Means within a column with different superscripts are significantly different (P<.05).
Moisture Absorption. M o i s t u r e a b s o r p t i o n
values at 0, 1, 2, 4 a n d 8 h r are p r e s e n t e d in
t a b l e 2. T h e c a p a c i t y o f t h e grain t o a b s o r b
w a t e r was i n c r e a s e d ( P < . 0 5 ) w h e n r o a s t e d a t
127 C as c o m p a r e d to t h e r a w c o r n o r grain
r o a s t e d a t l o w e r t e m p e r a t u r e s . A t 137 C a
f u r t h e r increase in m o i s t u r e a b s o r p t i o n was
o b s e r v e d over t h e 127 C r o a s t e d grain. R o a s t i n g
at t e m p e r a t u r e s l o w e r t h a n 127 C r e s u l t e d in n o
increase in 2-hr m o i s t u r e a b s o r p t i o n values o v e r
t h e r a w corn. In general, r o a s t i n g at 93, 1 0 4
a n d 116 C t e n d e d t o r e d u c e m o i s t u r e a b s o r p t i o n a t all times.
Dry Matter Disappearance. Values f o r percent ruminal dry matter disappearance of the
various c o r n s a m p l e s a t 8, 12 a n d 24 h r u s i n g
t h e n y l o n bag t e c h n i q u e are p r e s e n t e d in t a b l e
3. Dry m a t t e r d i s a p p e a r a n c e values were similar
for r a w c o r n a n d c o r n r o a s t e d a t 93, 1 0 4 a n d
116 C a f t e r 8 hours. A f t e r 12 a n d 2 4 h r
digestion periods, slight decreases in p e r c e n t
d i s a p p e a r a n c e were o b s e r v e d w i t h c o r n r o a s t e d
at 104 a n d 116 C. C o r n r o a s t e d at 127 C or 137
C was m o r e c o m p l e t e l y digested t h a n r a w c o r n
a f t e r 8 h r a n d this was also t r u e for c o r n
r o a s t e d at 137 C a f t e r 12 or 2 4 hr digestion
periods. Riggs et al. ( 1 9 7 0 ) r e p o r t e d t h a t
digestibility o f all f r a c t i o n s in p o p p e d grain
sorghum except ether extract, fiber and protein
was significantly h i g h e r for cattle f e d t h e dry
h e a t - t r e a t e d grain t h a n for t h o s e fed n o n - h e a t e d
grain. M c L a r e n a n d M a t s u s h i m a ( 1 9 7 1 ) u s i n g
f i s t u l a t e d steers o b s e r v e d t h a t m o r e s t a r c h
e s c a p e d digestion in t h e r u m e n w h e n c o r n was
10% g e l a t i n i z e d as c o m p a r e d t o 45 or 90%
gelatinized; h o w e v e r , s t a r c h w h i c h escaped digestion in t h e t u r e e n was virtually all digested
in t h e small i n t e s t i n e . This m a y a c c o u n t for t h e
l o w e r values o b s e r v e d for t h e 1 0 4 a n d 116 C
r o a s t e d c o r n as less g e l a t i n i z a t i o n w o u l d be
e x p e c t e d at t h e s e t e m p e r a t u r e s t h a n a t t h e
higher ones. W h i t e et al. ( 1 9 7 3 ) r e p o r t e d t h a t
r o a s t i n g c o r n a t 1 4 9 C d e c r e a s e d in vitro dry
m a t t e r d i s a p p e a r a n c e as c o m p a r e d t o raw corn.
A l t h o u g h t h e r o a s t i n g t e m p e r a t u r e ( 1 4 9 C)
r e p o r t e d b y t h e s e w o r k e r s is h i g h e r t h a n t h a t
used in this s t u d y , t h e dry m a t t e r values (92.6)
of t h e r o a s t e d c o r n used in t h e w o r k of White
TABLE 3. EFFECT OF ROASTING TEMPERATURE ON PERCENT
RUMINAL DRY MATTER DISAPPEARANCE
Percent disappearance a
Roasting
temperature (C)
8 hr
12 hr
Raw
13.4 • 1.5 c
13.5 • 1.4 c
13.1 -+ 1.5 c
13.3 • 1.1 c
18.8•
b
21.0 • 1.6 b
23.8 •
22.1 •
19.4 •
20.8 •
25.1•
28.4 •
93
104
116
127
137
24 hr
2.0 cd
1.8 cd
2.0 d
2.3 cd
.8 bc
1.6 b
aEach value represents the mean • standard error of six observations.
b'c'd'eMeans within a column with different superscripts are significantly different (P<.05).
40.3
38.2
36.0
35.4
43.3
46.0
-+ 1.7 cd
• 1.9 de
• 3.0 de
• 2.1 e
•
bc
• 2.4 b
TEMPERATURE FOR ROASTING CORN
et al. (1973) indicates that differences in the
method of measuring roasting temperatures
may account for part of this discrepancy. Also,
electric heat was used in the study of White et
al. (1973) as opposed to gas in this study and
this may be a factor.
llinman and Johnson (1974) reported that
micronized sorghum had a significantly greater
dry matter loss than dry rolled sorghum after a
12-hr in vitro digestion and that increasing
degree of micronizing tended to increase the
12-hr digestion. They also reported that 24-hr
in vitro digestion for the dry rolled sorghum
was lower than for the micronized sorghum but
the difference was significant only for the high
degree of micronizing.
McNeil et al. (1971) reported that total
digestion of starch was higher in steers fed
steam-flaked and reconstituted sorghum, apparently the result of increased ruminal starch
digestion. These workers further stated that
heat alone did not appear to be the major
factor due to the differences in ruminal digestion of carbohydrates observed with the steamflaked and micronized grain. McNeill et al.
(1975) reported that the effect of method of
processing upon solubility of the protein matrix
encapsuling starch granules in the endosperm of
sorghum seems to be the major factor affecting
efficiency of utilization. The differences in
density, moisture ~bsorption and dry matter
disappearance observed with corn roasted at
116 and 127 C would suggest that major
changes occur in the starch granules of corn
within this range of temperature.
E n z y m a t i c Glucose Release. Mean glucose
TABLE 4. EFFECT OF ROASTING
TEMPERATURE ON GLUCOSE RELEASE
Glucose r e l e a s e a
(mg/g dry matter)
Roasting
temperatu re (C)
1 hr
5 hr
Raw
93
104
116
127
137
33.8 • 6.2 d
30.0 • 5.2 d
25.4 • 3.6 d
29.4 • 3.5 d
5 9 . 6 • 6.9 c
110.2 • 10.0 b
90.6 • 3.1 d
87.8 • 5.9 d
78.0 • 3.0 d
85.4 • 2.9 d
1 8 9 . 8 • 21.9 c
258.2 • 21.5 b
aEach value represents the mean +- standard error
of five samples.
b'c'dMeans within a column with different superscripts are significantly different (P<.05).
479
release values from the different corn samples
at 1 and 5 hr are presented in table 4. Roasting
at 93, 104 and 116 C resulted in similar glucose
release values as that obtained from raw corn.
However, roasting at 127 C resulted in (P<.05)
higher glucose release values than was obtained
from raw corn. Roasting at 137 C further
increased (P<.05) glucose release above that
obtained at 127 C. Glucose release was also
determined on samples roasted at 137, 148 and
178 C. Results indicated that glucose release
continued to increase with increasing roasting
temperature, ttowever, only a small amount of
feed could be processed at temperatures above
137 C as the roaster would only operate for a
few minutes at these higher temperatures.
The enzymatic digestion of the corn samples
indicate that corn roasted at 127 C or higher
increased the availability of starch to enzymatic
attack. These findings on glucose release are
similar to those reported by Liang et al. (1970)
with sorghum and corn and by Erwin (1966)
with milo in that as the intensity o f " c o o k i n g "
is increased (roasting temperature in this case)
glucose release increased. McNeill et al. (1970)
also observed that carbohydrate susceptibility
to amyloglucosidase was greater for micron'i'zed
than dry or reconstituted sorghum grain.
A m i n o A c i d Content. Of the 16 amino acids
studied, only lysine and arginine levels were
reduced (P<.05) by roasting temperature. The
lysine content of raw corn and that roasted at
137, 148 and 176 C was .28, .23, .23 and .17%,
respectively. The arginine level was reduced
from .47 to .33% by roasting at 176 C. Costa et
al. (1972) reported depressed gains and feed
intakes of growing pigs from 7 to 20 kg when
fed corn roasted at a similar temperature (145
C). Emerick et al. (1961) has also reported
depressed gains in rats fed corn dried at high
temperatures.
Preference Study. After finding that the
higher roasting temperatures resulted in more
favorable changes in corn, a preference study
was conducted to examine the effects of higher
roasting temperatures on corn intake by steers.
The results are presented in table 5. A marked
difference (P<.01) in intake occurred as a result
of the type of corn. The largest intake occurred
on raw corn followed by the 137 C roasted
corn. The difference between intakes of raw
and 137 C roasted corn was nonsignificant even
though the difference in intake was 1.16
kg/day. Also present was a steer by type of
corn interaction. This was probably due to steer
FELSMAN
480
TABLE 5. MEAN DAILY FEED INTAKES DURING P R E F E R E N C E T R I A L
Daily feed intake (kg) a
Steer
Raw corn
137 C roasted corn
171 C roasted corn
1
2
3
x
3.80
4.04
2.27
3.37
1.85
2.02
2.77
2.21
.01
.07
.41
.16
-+ .28
-+ .21
+- .43
-+ .55 b
+ .35
-+ .29
+- .33
-+ .28 b
-+ .01
-+ .03
+- .19
-+ .12 c
a~_+ SE.
be
.
.
' Means within
the . same. hne wtth different superscripts are significantly different (P<.05).
3 which consumed more 137 C roasted corn
t h a n r a w c o r n . T h i s s t e e r also c o n s u m e d g r e a t e r
q u a n t i t i e s o f t h e 171 C r o a s t e d c o r n t h a n t h e
o t h e r s t e e r s . In f e e d i n g t r i a l s w i t h c a t t l e ,
H a r v e y e t al. ( 1 9 7 4 ) o b s e r v e d s i g n i f i c a n t inc r e a s e s in p e r f o r m a n c e w h e n c o r n w a s r o a s t e d
a t a t e m p e r a t u r e o f 1 3 8 C. P e r r y e t al. ( 1 9 7 4 )
also r e p o r t e d t h a t c a t t l e f e d c o r n r o a s t e d a t 1 3 5
C and then rolled while hot or fed corn roasted
a t 1 4 8 C r e q u i r e d 1 7 % less f e e d p e r u n i t o f g a i n
than those fed raw corn.
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