Title: Research highlights
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00071929/00011
 Material Information
Title: Research highlights
Uniform Title: Research highlights (East Lansing, Mich.)
Physical Description: v. : ill. ; 28 cm.
Language: English
Creator: Bean/Cowpea Collaborative Research Support Program
Publisher: Michigan State University Bean/Cowpea CRSP
Place of Publication: East Lansing
Publication Date: 1984-
Subject: Beans -- Research -- Periodicals -- Africa   ( lcsh )
Beans -- Research -- Periodicals -- Latin America   ( lcsh )
Cowpea -- Research -- Periodicals -- Africa   ( lcsh )
Cowpea -- Research -- Periodicals -- Latin America   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
periodical   ( marcgt )
Statement of Responsibility: Michigan State University Bean/Cowpea CRSP.
Dates or Sequential Designation: Vol. 1, no. 1 (1984)-
General Note: Title from caption.
Funding: Electronic resources created as part of a prototype UF Institutional Repository and Faculty Papers project by the University of Florida.
 Record Information
Bibliographic ID: UF00071929
Volume ID: VID00011
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 13864898

Full Text

Michigan State University Bean/Cowpea CRSP

Vol. 2 No. 6 1985

INCAP/Washington State University/Swanson

Protein Quality and Nutritional
Value of Beans
Ricardo Bressani
Chief of the Division of
Food and Agricultural Sciences
Research Coordinator, INCAP
P.O. Box 1188
Guatemala, Guatemala, C. A.

Common beans (Phaseolus vulgaris L.) are the
main source of complementary protein in the
cereal and starchy food diets of large segments
of the Latin American population. Average con-
sumption varies between 20 and 75 grams per
person per day in Central America. Thus, pro-
duction, availability, acceptability, cooking
qualities and nutritive value of beans are of
great importance.
Research at the Institute of Nutrition for Cen-
tral America and Panama (INCAP) links bean
production-oriented research with scientific im-
provements in conservation, acceptability, cook-
ing quality and nutritive value. INCAP research
addresses factors responsible for decreased
bean availability in the diets of consumers, such
as microbial and insect attacks which cause post
harvest losses and the hard-to-cook condition
which renders beans unduly firm after cooking
and lowers their nutritive value. The research
programs also consider ways to increase the
utilization of nutrients in beans, and ways to in-
crease the consumption of beans through
development of non-traditional food products.
A number of such research efforts jointly spon-
sored by the CRSP, INCAP and other par-
ticipating institutions,1 are evolving important
findings critical in responding to these problems.
A preliminary study indicated that significant
losses of beans and nutrients occur during

'The Washington State University/INCAP project also
includes collaboration with Colorado State University,
Kansas State University, Michigan State University and the
University of Puerto Rico.

harvest, handling, shipping and processing.
Harvest losses of seeds due to threshing and
handling were from 0.7 percent to 21 percent.
Total bean losses, including storage and
marketing, varied from 3 to 69 percent. Poor
storage conditions are probably among the most
important factors in production losses and
underuse of beans due to poor consumer accep-
tance. Losses also occurred during transport, an
important consideration in the marketing
Hard-to-Cook Condition
A problem common to beans and some other
grain legumes is known as the hard-to-cook con-
dition. As the term suggests, these beans are
hard to cook and require more fuel for pro-
longed cooking to make them palatable. Pro-
longed cooking also reduces bean nutritive
value. One of our research objectives is to ex-
plain the biochemical and/or biophysical
mechanisms which cause beans to become hard
to cook.
INCAP research shows that two processing
treatments could minimize or control bean
hardening. One is the use of a moist, high-
temperature treatment for a relatively short
time. This process apparently alters some
biochemical and/or physical functions of the
grain, prolonging the storage time before the
hard-to-cook condition is induced. However, the
process is accompanied by a 60 percent loss in
The second treatment is more effective but
less practical and requires immersion of the seed

Funded Through USAID/BIFAD Grant No. AID/DSAN-XII-G-0261

in a 20 percent sodium chloride solution. The
sodium ion apparently penetrates cells of the
seed, causing changes that delay the hard-to-
cook condition from developing in storage. It
has previously been suggested by Louis
Rockland2'3 that an increase in the ratio of
monovalent to divalent ions is related to quick
In addition to these two technological ap-
proaches, research is also underway to increase
the content of monovalent ions in the seed by
soil or foliar fertilization.
New preliminary findings at INCAP have
shown significant interaction between en-
vironmental and genetic factors and the cook-
ing time of beans, with environmental factors
having the greater effect. In studies of these fac-
tors, within certain ranges, factors which were
associated with larger seed size were related
both to higher yields and to reduced cooking
Complementary Effect
The well-known complementary effect on
protein quality which occurs when beans and
cereals are eaten together has received much
attention. For example, a mixture of beans and

2Rockland, L.B. and E.A. Metzler. 1967. Quick-Cooking
Lima and Other Dry Beans. Food Technology 21:344-348.
'Varriano-Marsten, E. and E. de Omana. 1979. The Effects
of Sodium Salt Solutions on the Chemical Composition
and Morphology of Black Beans (Phaeseolus vulgaris L.).
Journal of Food Science 44:531-536.

maize in a 70/30 ratio (by weight) has a protein
value 1.9 times that of beans alone and 1.8 times
that of maize consumed alone. Similar effects
have been noted at INCAP when beans are
blended with rice, sorghum or wheat. The main
reason for this is the apparently complementary
effect that bean protein, high in lysine relative
to that of cereals, has on the total protein
An even higher bean/cereal protein value
would occur if the sulfur-containing amino acids
(methionine and cystine) of beans could be in-
creased modestly by 33 percent from present
levels. Beans with this enhanced methionine
content would also be of high value in diets
based on root crops such as cassava as a staple.
Various research indicated that bean strains
vary in amounts of sulfur-containing amino
acids. This suggests that methionine and cystine
levels could be increased through breeding and
selection of varieties with higher sulfur contents.
Screening is relatively easy because the content
of sulfur-containing amino acids can be deter-
mined by analyzing for elemental sulfur. Sulfur
and sulfur-containing amino acids have been
shown to be significantly related at the 1 per-
cent probability level.
Sulfur-content studies show a significant in-
teraction between variety and locality, however
variety has the greatest effect on content.

2. Bean harvest by traditional methods is one phase of
post-harvest losses.

1. Dr. Bressani (right), CRSP Co-Principal Investigator from
INCAP, conversing at a CRSP workshop with CRSP
researcher Dr. Tony Hall of the Senegal/University of
California-Riverside project.

3. Maize is the staple of most Central American diets.

Low Protein Digestibility
Heat applied in cooking destroys antinutri-
tional factors such as trypsin inhibitors and
hemaglutinin compounds present in seeds of
most food legumes. Still, research indicates that
humans digest only 55 percent of the protein in
beans, or only about 13 percent of the usual 24
percent crude protein available. The reasons for
this are being studied. It is known that
polyphenolic compounds present in the seed
coat affect protein digestibility of cooked beans.
White beans contain very little or no
polyphenols in the seed coats and thus have a
higher protein digestibility than red or black
beans. Even after protein digestibility data are
corrected for the effect of seed phenolics,
digestibility values are still low compared with
other food components such as casein and egg
Protein Fraction
There is recent evidence that a fraction of the
bean protein, representing 15-20 percent of the
total protein, has a digestibility below 20 per-
cent. If allowances are made for this low value
and the quantity of the fraction present, overall
protein digestibility in beans is comparable to
that of other vegetables.
The challenge is to determine if the undigest-
ible protein fraction exists in the original seed
or if it develops during storage or cooking. If
the fraction is present in raw beans, it may be
possible for breeders to eliminate it. However,
if it comes about as part of the normal changes
which occur during storage or cooking, new
technology will be needed to reduce its

Bean-Cooking Broth
The liquid from cooked beans is sometimes
consumed separately, especially by young peo-
ple and infants. Nutritionally, this broth contains
around 1 percent protein with an amino acid
pattern reflecting that of bean protein. It con-
tains high levels of polyphenols and potassium
which reduce the quality of the protein. When
fed to rats, the broth causes a decrease in weight
gain and in protein digestibility in amounts cor-
related with the quantity consumed.
The effect on digestibility was expected due
to the polyphenols present, however, the
decrease in protein quality was not. The
decrease in protein quality continued even when
beans were supplemented with methionine, the
essential amino acid which controls the
biological utilization of bean protein.
Research under this project is continuing to
determine whether some polyphenols are being
hydrolyzed and absorbed, thus decreasing the
utilization of the absorbed amino acid by
unknown mechanisms.
Future INCAPICRSP Research
Further CRSP-supported research will build on
the above findings and will provide a clearer
picture of the mechanisms which act to impair
the nutritive value of beans. This information
will be an invaluable.aid to plant breeders in
choosing traits to select and strategies to use
in improving bean nutrition.

1W IrJ3

I4 nr. a froL) 'i, ashir'n L',gton' -p.State University.p P
Investigator from Washington State University.

5. A granular-heated-bed dry cooker for beans developed by
workers at Colorado State University.

For further information contact:
Bean/Cowpea CRSP
200 Center for International Programs
Michigan State University
East Lansing, Michigan 48824-1035

Telephone: (517) 355-4693
Telex: 810-251-0737

An international community of persons, institutions,
agencies and governments committed to collectively
strengthening health and nutrition in developing
countries by improving the availability
and utilization of beans and cowpeas

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