Functional and Nutritional Properties
of Extruded Whole Pinto Bean Meal
(Phaseolus Vulgaris L.)
R.R. BALANDRÁN-QUINTANA, G.V. BARBOSA-CÁNOVAS, J.J. ZAZUETA-MORALES,
A. ANZALDÚA-MORALES, and A. QUINTERO-RAMOS
MATERIALS & METHODS
Pinto bean meals with 18, 20, and 22% moisture were ex-
truded at 140, 160 and 180 C, using screw speeds of 150, 200
and 250 rpm in a single-screw laboratory extruded. Expan-
Pinto beans (Phaseolus vulgaris L.) Were obtained from Central
sion index, bulk density, water absorption and solubility indi-
Bean Co., Inc. (Quincy, WA). Whole beans were ground in a hammer
ces, in vitro protein digestibility, and trypsin inhibitor activity
mill (Weber Bros. Metal Works, Chicago, IL) to pass a 40-mesh
in extrudate were measured. Temperature and feed moisture
screen. The pinto bean flour was hydrated with sufficient water to
influenced (p<0.05) expansion index, bulk density, water ab-
provide feed moisture, 18, 20 or 22% (w.b.), and kept at 3 C for 24h.
sorption index and in vitro protein digestibility. Water solubil-
The moisture content of the blends was again determined and when
ity index was affected by temperature only. Trypsin inhibitors
necessary water was added to the flour in a mixer model C-100T (The
were inactivated completely for all conditions. Screw speed
Hobart Manufacturing Co., Troy, OH) to produce the required mois-
had no effect on any dependent variable. Best product was
ture level. The hydrated pinto bean flours were kept in a refrigerator
produced with 22% feed moisture at 160 C.
overnight in sealed plastic pails, and extruded the following day. The
Key Words: pinto bean, extrusion, expansion, solubility
whole bean flour was analyzed for moisture, ash, lipid, protein, carbo-
index, protein digestibility
hydrate and fiber according to AOAC (1980).
The extrusion experiments were carried out on a single-screw
LEGUMES ARE IMPORTANT CONSTITUENTS OF THE DIET AND PRO-
laboratory cooking extruder (19 mm screw-diameter; length-to-dia
vide economical sources of proteins and energy (Phillips and Baker,
20:1; nominal compression ratio 2:1; and die opening 2.4 mm), (mod-
1987; Peace et al., 1988). They have also been indicated to show
el 2003-GR-8, C.W. Brabender Instruments Inc., New Jersey). The
apparent benefits of soluble fiber in preventing heart disease (Mor-
inner barrel was provided with a grooved surface to ensure zero slip at
row, 1991). However, the long cooking time required and presence of
the wall. The barrel was divided into independent electrically heated
anti-nutritional substances in the whole bean limit their use (Fleming,
zones (feed end and central zone) cooled by air. A third zone, at the die
1981; Deshpande and Damodaran, 1989; Borejszo and Khan, 1992).
barrel, also was electrically heated but not air cooled. The temperature
Among the antinutritional factors, trypsin inhibitors are important
gradient along the three barrel zones was 20 C. A screw operated feed
(Laskowski and Kato, 1980). Moreover, bean proteins have low bio-
hopper fed the extruded at 30 rpm. Extrusion parameters as indepen-
logical value because of their low digestibility (Sgarbieri and Whitak-
dent variables were: temperature at die end of barrel (140, 160, 180 C);
er, 1982; Marletta et al., 1992). Treatments to overcome such limiting
feed moisture content (18, 20, 22%, w.b.); and screw speed (150, 200,
factors, such as direct thermal processing, precooking, and formulat-
ed products containing legumes are not readily adaptable because of
Before extrusion, experimental blends were brought to about room
requirements for large equipment and high operational costs (Aguil-
temperature (22 C) and mixed manually to assure even moisture dis-
era et al., 1984; Estevez and Luh, 1985; Deshpande and Cheryan,
tribution. The order of processing was chosen by randomizing feed
1986; Uebersax et al., 1991).
moisture levels and die end temperatures at increasing levels of screw
Extrusion cooking has advantages, including versatility, high pro-
speed. Each extrusion run was brought to steady state as indicated by
ductivity, low operating costs, energy efficiency, and shorter cooking
constant torque and melt temperatures before sampling and data col-
times (Harper, 1981). Several legumes have been treated by extrusion
lection. Measurements of extrudate diameters for expansion index
and good expansion was reported (Camire et al., 1990; Gujska and
determination were made just after collecting fresh extrudates at the
Khan, 1990, 1991c; Borejszo and Khan, 1992; Avin et al., 1992).
die exit, then extrudates were ground in a hammer mill to pass a 40-
Trypsin inhibitors in beans were reduced by 80–90% or more by
mesh screen, sealed in plastic bags and refrigerated at 4–5 C for 2 mo.
extrusion (Hadad-Mansouri, 1983; Myer et al., 1981; Myer and
Froseth, 1983; Pham and del Rosario, 1988). In most previous stud-
ies, either high-protein or high-carbohydrate, bean fractions were ex-
Bulk density was determined by pouring the ground extrudate (40/
truded but little has been reported on extrusion cooking of whole seed
60-mesh) into a cylindrical container, scraping off excess and divid-
ing net weight of the powder by the volume of the container (Moreyra
Our objective was to examine the effects of extrusion conditions
and Peleg, 1981).
(temperature, feed moisture content and screw speed) on some func-
tional and nutritional properties of whole pinto bean meal.
Expansion, water absorption (WAI) and water solubility
Expansion index was reported as the ratio of extruded product
Authors Balandrán-Quintana, Anzaldúa-Morales, and Quintero-Ramos, are with
the Universidad Antónoma de Chihuahua, Faculty of Chemistry, Postgraduate Stud-
diameter and the diameter of the die hole (Gujska and Khan, 1990).
ies Dept., P.O. Box 1542-C, Chihuahua, Chih., Mexico. Author Quintero-Ramos is
Values reported were means of five measurements. WAI and WSI
presently on leave at the Institute of Food Science, Cornell University, New York State
were measured by the method of Anderson et al. (1969a).
Agricultural Experiment Station, Geneva NY 14456. Author Barbosa-Cánovas, is
with the Biological Systems Engineering Dept., Washington State Univ., Pullman,
WA 99164-6120. Author Zazueta-Morales is with the Universidad Autóbnoma de
In vitro protein digestibility and trypsin inhibitor (TI)
Sinaloa, Faculty of Chemistry & Biology, P.O. Box 1354, Culiacán, Sin., Mexico.
A multienzyme method was used according to Hsu et al. (1977).
Address inquiries to Dr. A. Quintero-Ramos.
Sample suspensions containing equal nitrogen content (6.25 mg pro-
Volume 63, No. 1, 1998—JOURNAL OF FOOD SCIENCE
Properties of Extruded Pinto Beans . . .
tein/mL) were incubated at pH 8.0 with a mixture of trypsin, chymot-
Table 1–Summary of analysis of variance of the effects of extrusion
rypsin and peptidase enzymes at 37°C for 10 min. Changes in pH
conditions on some properties of whole pinto bean meal extrudates
during hydrolysis were recorded at 1 min intervals. Digestibility was
calculated according to linear regression equation Y = 210.46 - 18.10X,
where Y = protein digestibility (%) and X = pH at 10 min hydrolysis.
TI content was determined by the procedure described by Hammer-
strand et al. (1981).
T ? M
T ? rpm
m ? rpm
A three variable, three level factorial design was used (Montgom-
aWater absorption index.
ery, 1991), where feed moisture was examined at 18, 20 and 22%, die
bWater solubility index.
end temperature was examined at 140, 160 and 180 C, and screw
**Significant at p<0.05; NS, not significant.
speed was examined at 150, 200 and 250 rpm. Extrusion experiments
(54 total) were performed consisting of 27 different combinations of
Kokini et al., 1992). Gujska and Khan (1990) found a similar behav-
the three variables, which were made in duplicate.
ior in navy bean extrudates. They also reported that screw speed did
not affect expansion index.
The statistical analysis of data (ANOVA) was performed on SAS®
Bulk density (BD)
software (SAS Institute, Inc., 1987). Significance was defined at p 0.05.
Bulk density was influenced by moisture and temperature (Fig. 2)
and it decreased with increasing temperature for 18% and 20% mois-
RESULTS & DISCUSSION
ture feed. For 22% moisture the BD decreased between 140 C and
EXTRUSION CONDITIONS (P<0.05) AND INTERACTIONS AFFECTED
160 C and increased between 160°C and 180°C. If expansion in-
some properties of the pinto bean meal extrudates (Table 1). Both
creased (Fig. 1), it would be logical to assume that BD would de-
temperature and feed moisture had a significant influence on most
crease, under similar conditions; but BD increased abruptly at 22%
dependent variables, either counteracting each other or alone. Screw
feed moisture when temperature increased from 160 to 180 C (Fig. 2).
speed had no effects upon any of the properties measured. Similar
This could be due to the effect of high temperatures on viscosity and
results have been reported by Avin et al. (1992).
starch degradation resulting in less expansion (Colonna et al., 1989;
Kokini et al., 1992). Avin et al. (1992) reported that density of extrud-
Expansion index (EI)
ed red bean was not influenced by temperature, moisture, or rpm.
Temperature and feed moisture influenced EI. As both variables
increased, more expansion occurred. However, there was a sudden
Water absorption index (WAI)
drop in EI at 180 C and 22% feed moisture (Fig. 1). An increase in EI
Temperature and feed moisture affected WAI (Fig. 3) which in-
when feed moisture went from 18 to 20% may be due to a reduction in
creased (p<0.05) with increasing temperature. Low WAI values at
viscosity, which resulted in less mechanical damage to starch, thus
low temperatures indicate a restricted water availability for the starch
enabling dough to expand more and faster (Harper, 1986; Colonna et
granule due to a more compact structure. However, when tempera-
al., 1989). As temperature increased, starch became more fully cooked
tures increased, amylose and amylopectin chains separated, forming
and thus better able to expand. This confirmed similar results on bean
an expansible matrix which resulted in a higher water-holding ability
extrudates (Gujska and Khan, 1990; Chen et al., 1991; Avin et al.,
(Colonna et al., 1989; Kokini et al., 1992). If temperature increased
1992; Czarnecki et al., 1993). A high expansion is desirable in an
beyond a limit, WAI reached a maximum and then decreased as a
industry that produces snacks and ready-to-eat foods. At 180 C and
result of starch dextrinization, as reported by Anderson et al., (1969a,
22% moisture, expansion index decreased, probably because at high
b; Anderson, 1982). They found maximum values of WAI at 200 C
temperatures starch dextrinization occurred (Colonna et al., 1989;
for cereals during extrusion with 15–25% feed moisture, and attribut-
Fig. 1–Effect of extrusion temperature and feed moisture on expan-
Fig. 2–Effect of extrusion temperature and feed moisture on bulk
sion index of whole pinto bean meal extrudates (each point on the
density of whole pinto bean meal extrudates (each point on the
graph is a mean of screw speeds).
graph is a mean of screw speeds).
114—JOURNAL OF FOOD SCIENCE—Volume 63, No. 1, 1998
ed this to starch breakdown which was verified by the viscosity pro-
situations that involve water bonding (Aguilera et al., 1980).
files. They also found that WAI was higher at higher feed moistures.
It is not clear whether the high fiber content in our extrudates
Gujska and Khan (1990) studied the effect of temperature on WAI on
affected WAI because published reports on effects of fiber are not
high starch fractions of pinto and navy beans during extrusion. WAI
clear. Badrie and Mellowes (1992) studied the effects of addition of
increased from 3.0 (110 C) to 4.0 (132 C) for pinto beans but could
wheat bran to cassava flour and reported an increase in WAI in extru-
not be evaluated at 150 C because the extrudate burned. In the same
dates. Gujska and Khan (1991a) reported that addition of hull to the
study, navy beans exhibited a maximum WAI (4.0) at 132 C and
high starch protein fraction of pinto bean flour resulted in a significant
lower values (3.83) at 150 C.
decrease of WAI, probably a result of reduction of starch in the start-
Avin et al. (1992) reported that WAI increased with increasing
extrusion temperature in extrusion of red beans. However, those val-
ues of WAI were different from ours. The lowest WAI for pinto bean
Water solubility index (WSI)
in our study (3.35) was found at 140 C and the highest (5.33) at
WSI increased significantly (Fig. 4) with increasing temperature,
180°C. The differences may be caused by the protein content (15.45%
which may be related to starch depolymerization at higher tempera-
in Gujska and Khan, 1990 study; 20.22% in ours). It has been estab-
tures, reducing molecular length of amylose and amylopectin chains.
lished (Pomeranz, 1991; Wolf and Conan, 1971) that proteins are the
These results confirmed those of Anderson (1982) and Anderson et al.
most reactant components in foods and some of their reactions are
(1969a, b) who had extruded corn and sorghum. Also Gujska and
essential for functionality. Among functional properties water-hold-
Khan (1990), reported a significant increase in WSI with increasing
ing capacity is important because of the hydrogen bonds formed be-
extrusion temperature. However, Gujska and Khan (1991b) found
tween water and polar residues of protein molecules. Gujska and
that WSI decreased significantly with increasing moisture in the ex-
Khan (1991c) reported that extrusion caused a significant decrease in
trusion of pinto bean flour from 35.3 at 20% feed moisture to 21.1 at
water and salt-extractable proteins from both navy and pinto beans
30% feed moisture. They indicated that this was caused by greater
compared to the raw material. Also Jeunink and Cheftel (1979) found
shear degradation of starch during extrusion at low moisture. Howev-
a pronounced decrease in protein solubility in field bean extrudates.
er, in changing moisture from 26 to 28% the WSI did not change
They concluded that low solubility was due mainly to noncovalent
significantly. In our results, feed moisture changed from 18 to 22%,
interactions between polypeptide chains and other constituents and
which was outside the range studied by Gujska and Khan (1991b).
also to the formation of new disulfide bonds. Note that for those
In our study WSI went from 17.2 at 140 C to 23.15 at 180 C,
studies the water-extractable protein fraction decreased significantly
values which were different from those reported by Gujska and Khan
as a function of extrusion temperature from 110 to 150 C. Because of
(1990) who reported 19.0 at 110 C to 21.7 at 132 C in extruded pinto
the high protein content (20.22%) in the raw material we used, pro-
beans. Such differences may be due to the higher protein content in
teins were probably involved in the increasing water absorption as a
our raw material (20.22%) as compared with 15.45% in their study. At
result of such interactions.
140 C we had a lower WSI than their extrudates at 110 C. The effect
Increasing feed moisture also increased WAI (Fig. 3) when the
of protein content on WSI was confirmed by Gujska and Khan (1991a):
temperature went from 140 to 160 C, but at 180 C WAI was practical-
when they added a protein fraction at 10% level to the high starch
ly the same at all feed moisture contents. This may be due to a lower
fraction of pinto bean flour a decrease was observed in WSI. Howev-
viscosity in the dough at higher feed moistures, which resulted in
er, increasing the protein fraction to 20 and 30%, WSI did not change.
higher expansion and thus a higher water absorption capacity in the
extrudate. However, at high temperatures starch dextrinization took
In vitro protein digestibility (PD)
place and WAI did not increase further although there was the high
The protein digestibility of raw pinto bean meal was 72.7%, but
feed moisture (Colonna et al., 1989). A function of extrusion moisture
extrusion processing increased it to 81% for all experimental condi-
content in WAI was reported by Anderson et al. (1969a), and Gujska
tions. This confirmed results on extrusion of several cereals and le-
and Khan (1991b). An increasing WAI is advantageous since this
gumes (Czarnecki et al., 1993; Srihara and Alexander, 1984). Interac-
parameter determines the suitability of extruded products for use in
tion of temperature and feed moisture content was significant. PD
Fig. 3–Effect of extrusion temperature and feed moisture on water
Fig. 4–Effect of extrusion temperature on water solubility index of
absorption index of whole pinto bean meal extrudates (each point on
whole pinto bean meal extrudates (each point on the graph is a mean
the graph is a mean of screw speeds).
of screw speeds and feed moistures).
Volume 63, No. 1, 1998—JOURNAL OF FOOD SCIENCE—115
Properties of Extruded Pinto Beans . . .
increased (Fig. 5) with extrusion temperature up to 160 C, and then
Camire, M.E., Camire, A., and Krumchar, K. 1990. Chemical and nutritional changes in
foods during extrusion. Crit. Rev. Food Sci. & Nutr. 29: 35-57.
decreased slightly at 180 C. This was not expected since thermal
Chen, J., Serafin, F.L., Pandya, R.N., and Daun, H. 1991. Effects of extrusion conditions
processing usually improves PD (Srihara and Alexander, 1984). How-
on sensory properties of corn meal extrudates. J. Food Sci. 56: 84-89.
Colonna, P., Tayeb, J., and Mercier, C. 1989. Extrusion cooking of starch and starchy
ever, Lanfer-Marquez and Lajolo (1991) stated that, under certain
products, in Extrusion Cooking, C. Mercier, P. Linko and J.M. Harper (Ed.), p. 247-
conditions, excessive cooking may reduce PD due to cross links for-
319. Am. Assoc. Cereal Chem., Inc., St. Paul, MN.
Czarnecki, Z., Gujska, E., and Khan, K. 1993. Extrusion of pinto bean high protein
mation between proteins.
fraction pretreated with papain and cellulase enzymes. J. Food Sci. 58: 395-398.
Deshpande, S.S. and Cheryan, M. 1986. Microstructure and water uptake of phaseolus
and winged beans. J. Food Sci. 51: 1218-1223.
Deshpande, S.S. and Damodaran, S. 1989. Structure-digestibility relationship of le-
No antitrypsin activity was found in extrudates under any experi-
gume 7S proteins. J. Food Sci. 54: 108-113.
Estevez, A.M. and Luh, B.S. 1985. Chemical and physical characteristics of ready-to-
mental conditions, which indicates that high temperature as well as
eat dry beans. J. Food Sci. 50: 777-781.
intense mechanical stress during extrusion processing completely in-
Fleming, S.E. 1981. A study of relationships between flatus potential and carbohy-
drate distribution in legume seeds. J. Food Sci. 46: 794-798.
activated such substances. Reported inhibition values after extrusion
Gujska, E. and Khan, K. 1990. Effect of temperature on properties of extrudates from
of beans (Mustakas et al., 1964; Harper and Jansen, 1985; Noguchi,
high starch fractions of navy, pinto and garbanzo beans. J. Food Sci. 55: 466-469.
Gujska, E. and Khan, K. 1991a. Functional properties of extrudates from high starch
1986) have usually been 95%, at extrusion temperatures of 120–
fractions of navy pinto beans and corn meal blended with legume high protein
150 C. The temperatures we used reached 180 C, which was a more
fractions. J. Food Sci. 56: 431-435.
Gujska, E. and Khan, K. 1991b. Feed moisture effects on functional properties, trypsin
severe process and destroyed the trypsin inhibitors completely. Ac-
inhibitor and hemagglutinating activities of extruded bean high starch fractions. J.
cording to Harper (1993), a reduction of 70% or more in antitrypsin
Food Sci. 56: 443-447.
Gujska, E. and Khan, K. 1991c. High temperature extrusion effects on protein solubil-
activity in beans is adequate for nutritive quality.
ity and distribution in navy and pinto beans. J. Food Sci. 56: 1013-1016.
Hadad-Mansouri, M. 1983. Effet des traitments thermiques sur les facteurs antitryp-
siques en la valeur alimentaire de 3 légumineuses: Phaseolus vulgaris, Cicer ariet-
inum, Lens esculenta. Thése de Magister, Université d’Alger, Algiers, Algeria. 65p.
EXTRUSION OF WHOLE PINTO BEAN MEAL, UNDER CONDITIONS USED,
[Cited by Cheftel, J.C. 1989. Extrusion cooking and food safety, in Extrusion Cook-
ing, C. Mercier, P. Linko, J.M. Harper (Ed.), p. 435-461. Am. Assoc. Cereal Chem., St.
was highly effective for inactivation of trypsin inhibitors and increas-
ing in vitro digestibility of the protein. Extrusion temperature and feed
Hamerstrand, G.E., Black, L.Y., and Glover, J.D. 1981. Trypsin inhibitors in soy prod-
ucts: Modification of the standard analytical procedure. Cereal Chem. 58: 42-45.
moisture were the most important variables affecting dependent vari-
Harper, J.M. 1981. Extrusion of Foods, Vol. 2. CRC Press, Inc., Boca Raton, FL.
ables. Expansion index, bulk density, water absorption and solubility
Harper, J.M. and Jansen, G.R. 1985. Production of nutritious precooked foods in de-
veloping countries by low-cost extrusion technology. Food rev. Int. 1: 27-97.
indexes, could be controlled by appropriate processing conditions.
Harper, J.M. 1986. Extrusion texturization of food. Food technol. 40(3): 70-76.
The 160 C extrusion temperature and 22% feed moisture yielded the best
Harper, J.M. 1993. Personal communication. Chihuahua, Chihuahua, México.
Hsu, H.W., Vavak, D.L., Satterlee, L.D., and Miller, G.A. 1977. A multienzyme technique
products overall but an optimization study is needed to confirm this.
for estimating protein digestibility. J. Food Sci. 42: 1260-1273.
Jeunink, J. and Cheftel, J.C. 1979. Chemical and physicochemical changes in field
bean and soybean proteins texturized by extrusion. J. Food Sci. 44: 1322-1325.
Kokini, J.L., Lai, L., and Chedid, L.L. 1992. Effect of starch structure on starch rheolog-
Aguilera, J.M., Rossi, F., Hiche, E., and Chichester, C.O. 1980. Development and eval-
ical properties. Food technol. 46(6): 124-139.
uation of an extrusion-texturized peanut protein. J. Food Sci. 45: 246-250, 254.
Lanfer-Marquez, V.M. and Lajolo, F.M. 1991. In vivo digestibility of bean (Phaseolus
Aguilera, J.M., Crisafulli, E.B., Lusas, E.W., Uebersax, M.A., and Zabik, M.E. 1984. Air
vulgaris L.) Proteins: The role of endogenous protein. J. Agric. Food Chem. 39:
classification and extrusion of navy bean fractions. J. Food Sci. 49: 543-546.
Anderson, R.A. 1982. Water absorption and solubility and amylograph characteristics
Laskowski, M. Jr. and Kato, I. 1980. Protein inhibitor of proteinases. Ann. Rev. Bio-
on roll-cooked small grain products. Cereal Chem. 59: 265-269.
chem. 49: 593-626.
Anderson, R.A., Conway, H.F., Pfeifer, V.F., and Griffin, E.L. Jr. 1969a. Gelatinization of
Marletta, L., Carbonaro, M., and Carnovale, E. 1992. In vitro protein and sulphur ami-
corn grits by roll- and extrusion-cooking. Cereal Sci. Today 14: 4-7, 11-12.
noacid availability as a measure of bean protein quality. J. Food Sci. Agric. 59: 497-
Anderson, R.A., Conway, H.F., Pfeifer, V.F., and Griffin, E.L. Jr. 1969b. Roll and extru-
sion-cooking of grain sorghum grits. Cereal Sci. Today 14: 372-375, 381.
Montgomery, D.C. 1991. Diseño y Análisis de Experimentos, Grupo editorial,
AOAC. 1980. Official Methods of Analysis. Association of Official Analytical Chem-
Iberoamérica, México City.
ists, Washington, DC.
Moreyra, R. and Peleg, M. 1981. Effect of equilibrium water activity on the bulk prop-
Avin, D., Kim, C-H., and Maga, J.A. 1992. Effect of extrusion variables on the physical
erties of selected food powders. J. Food Sci. 46: 1918-1922.
characteristics of red bean (Phaseolus vulgaris) flour extrudates. J. Food Proc. Pres.
Morrow, B. 1991. The rebirth of legumes. Food Technol. 45(9): 96, 121.
Mustakas, G.C., Griffin, E.L., Allen, L.E., and Smith, O.B. 1964. Production and nutri-
Badrie, N. and Mellowes, W.A. 1992. Soybean flour/oil and wheat bran effects on char-
tional evaluation of extrusion-cooked full-fat soybean flour. J. Am. Oil Chem. Soc.
acteristics of cassave (Manihot esculenta crantz) flour extrudate. J. Food Sci. 57:
Myer, R.O., Coon, c.N., and Froseth, J.A. 1981. The nutritional value of extruded beans
Borejszo, Z. And Khan, K. 1992. Reduction of flatulence-causing sugars by high tem-
and extruded mixtures of beans and soybeans in chick diets. Poult. Sci. 61: 2117-
perature extrusion of pinto bean high starch fractions. J. Food Sci. 57: 771-772.
Myer, R.O. and Froseth, J.A. 1983. Extruded mixtures of beans (Phaseolus vulgaris)
and soy beans as protein sources in barley-based swine diets. J. Animal Sci. 57: 296,
Noguchi, A. 1986. Food processing activities in Japan on the use of twin-screw extrud-
ers. Report of the National Food Research Institute, Tsukuba, Japan, p. 40.
Peace, R.W., Keith, M.O., Sarwar, G., and Botting, H.G. 1988. Effects of storage on pro-
tein nutritional quality of grain legumes. J. Food Sci. 53: 439-441.
Pham, C.B. and Del Rosario, R.R. 1988. Inactivation of trypsin inhibitors using the
extrusion process. [Cited by Cheftel, J.C. 1989. Extrusion cooking and food safety
in Extrusion Cooking, C. Mercier, P. Linko, and J.M. Har-per (Ed.), p. 435-461. Am.
Assoc. Cereal Chem., St. Paul, MN.]
Phillips, R.D. and Baker, E.A. 1987. Protein nutritional quality of traditional and
novel cowpea products measured by in vivo and in vitro methods. J. Food Sci. 52:
Pomeranz, Y. 1991. Functional Properties of Food Components. Academic Press, Inc.,
San Francisco, CA.
SAS Institute, Inc. 1987. Statistical Analysis System, Version 6.0. SAS Institute, Inc.,
Sgarbieri, V.C. and Whitaker, J.R. 1982. Physical, chemical and nutritional properties
of common beans (Phaseolus) protein. Adv. Food res. 28: 93-166.
Srihara, P. and Alexander, J.C. 1984. Effect of heat treatment on nutritive quality of
plant protein blends. Can. Inst. Food Sci. Technol. J. 2: 237-240.
Uebersax, M.A., Ruengsakuirach, S., and Occeña, L.G. 1991. Strategies and procedures
for processing dry beans. Food Technol. 45(9): 104-108.
Wolf, W.J. and Cowan, J.C. 1971. Soybean as a Food Source. The Chemical Rubber Co.,
Ms received 12/12/96; revised 7/1/97; accepted 8/7/97.
We thank Frank Younce for technical assistance and we are also grateful to Prof. Mal-
colm C. Bourne (Cornell University) for advice and help. Thanks to Universidad
Autónoma de Chihuahua (Postgraduate Studies Division) for financial help.
This material was presented as a poster at the 1995 IFT Annual Meeting, Anaheim, CA, and is based
on author Rene Balandrán’s thesis for a M.S. degree. Studies and thesis were carried out at the
Universidad Autónoma de Chihuahua, Chih. Mex. And the Washington State University, Biological
Fig. 5–Effect of extrusion temperature and feed moisture on in vitro
Systems Engineering Dept., Pullman, WA, sponsored by CONACYT (National Board of Science &
digestibility of proteins (each point on the graph is a mean of screw
Technology) and the Universidad Autónoma de Chihuahua, Mexico.
116—JOURNAL OF FOOD SCIENCE—Volume 63, No. 1, 1998