a comparison of the protein nutritive value and composition of four cultivars of faba beans (vicia...
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J. Sci. Fd Agric. 1975, 26, 1577-1583
A Comparison of the Protein Nutritive Value and Composition of Four Cultivars of Faba beans (Vicia faba L.) Grown and Harvested under Controlled Conditions
Robert Palmer and Reginald Thompson
Ro wett Research Institute, Bucksburn, Aberdeen, AB2 9S3, Scotland and Scottish Hovticultural Research Institute, Invergowrie, Din?dee, OD2 5 DA, Scotland
(Manuscript received 9 December 1974 and accepted 12 Jiiiiz 1975)
Faba beans (Vicia ,faba L.) of f a r cultivars, one of which was harvested in batches during the 2 months prior to normal harvesting time, and for com- parison, a sample of kidney beans (Phaseolus vulgaris L.) had similar amino acid compositions with sulphur amino acids limiting in all samples. Chemical scores ranged from 45-52 and all the faba beans, when fed to rats, gave biological values in close agreement with the chemical score. Diets containing two of the cultivars were supplemented with 0.1 % methionine and in both instances an increase in biological value of 22 units was obtained. Kidney beans fed to rats at the same level of crude protein resulted in the death of animals in 7-9 days. The haemagglutinin content of the faba bean samples was 8-16 times lower than in kidney beans. Early harvesting did not affect the nutritive value of the faba beans and no differences were observed between the different cultivars, none of which showed any evidence of toxicity.
.
1. Introduction
The protein content of different samples of faba beans (Viciafaba L.) has been shown to vary considerably, spring beans having a higher protein content than winter beans1 and different cultivars having different protein contents.2 The nutrition of the mother plant has also been shown to affect the amino acid composition.3 Differences in protein content and amino acid composition and the presence in the beans of anti-nutritional components are important factors in the evaluation of faba beans as protein sources for animals. The constituents most frequently implicated as the anti-nutritional factors in both kidney beans (Plzaseolus vulgaris L.) and faba beans are the trypsin inhibitors4 and the haemagglutinins ( lect in~) .~ Recent work with kidney beans suggests that the haemagglutinins are more likely to be the major anti-nutritional factors.6-8 Whereas in kidney beans the toxic effect is pronounced, producing severe weight loss followed in some cases by death,5,7*8 the poor performance of faba beans appears to be less acute and best described as a failure to produce, in various animal species, growth rates as high as those anticipated from criteria such as the amino acid c0ntent.~-13
I577
1578 R. Palmer and R. Thompson
The haemagglutinin content of V. faba has been shown to be considerably lower than in P. vulgaris14 and this observation can be considered as one explanation for the difference in toxicity between the two kinds of bean. The demonstration of the produc- tion of fungal toxins on beans of various Phaseolus species in conditions simulating poor storage and transport15 suggests that additional, extrinsic factors may add to the toxicity of the feedstuff.
In general faba beans ripen later in Scotland than further south and are therefore likely to be harvested whilst still immature. No information was available on the effect of growing different cultivars, in the conditions existing in Scotland, on the protein content and nutritional properties of faba beans. Thus the aims of the present work were to examine the differences between protein, amino acid and haemagglutinin content and nutritive value of faba beans at different stages of maturity and of different cultivars, and to compare the values obtained with those for a sample of kidney beans known to be toxic to rats. It was also possible to control the storage and subse- quent treatment of the faba bean samples from the date of harvesting in such a way as to minimise the destruction of heat labile toxins and to inhibit the growth of micro- organisms.
The term faba beans has been used to describe the different cultivars of Vicia faba because no other term seemed appropriate to describe the four cultivars, which included two field beans (V. faba minor), one horse bean (V. faba equiBa) and one broad bean (V. faba major).
2. Experimental 2.1. Beans Samples of field beans from two experiments were used for assessing the protein content and nutritive value. For both trials, beans were sown on 7 March 1973 to give a plant population density of about 50 plants/m2. Prior to sowing, fertilisers were incorporated into the soil at rates indicated by soil analysis to be appropriate viz: 39 kg N, 39 kg P and 225 kg K/ha and effective weed control was obtained with a pre-emergence application of simazine.
In one trial, designed to study the growth of the cultivar Herz Freya, plants were harvested for the work described here on 30 August, 11 September, 26 September and 23 October 1973.
In the second trial comparisons were made between the cultivars Herz Freya and Maris Bead (V. faba minor) and Ostlers (V. faba equinu), each harvested at a similar stage of maturity, between 4 and 17 October 1973.
In addition to material from these sources, a sample of broad bean (V. faba major) cv. Primo was harvested on 18 September from a single unreplicated plot.
Immediately upon harvest all sub-samples for analysis and nutritional trials were stored at -20°C.
Beans of cv. Herz Freya harvested on the earliest date in the first experiment were of two distinct stages of maturity and were sub-divided accordingly into immature “Green” and more mature “Brown” fractions before further treatment. All the samples were ground in an 8 in Christy and Norris Mill fitted with a 1 mm pore
Protein nutritive value of faba beans 1579
diameter grid, spread in shallow trays and freeze-dried at a temperature not exceeding 20°C.
Kidney beans (Phaseolus vulgaris L.) cv. Processor, obtained from Hurst Gunson Cooper Taber Ltd, Witham, Essex, were ground as above.
2.2. Nitrogen All nitrogen estimations were carried out on a Technicon Auto Analyser after macro- digestion.16
2.3. Haemagglutination tests Haemagglutinin activity was determined by the method described by Pusztai and Watt,l7 all samples being serially diluted with 0.9 % NaCl.
2.4. Amino acid analysis Samples for amino acid analysis were hydrolysed under reflux in 5.6 N HC1 for 24 h at 1O5-11O0C, using a minimum volume of 10 ml acid per mg of material. Samples were dried in vucuo and analysed on a Locarte amino acid analyser.l* Methionine and cystine were determined from hydrolysates of performic acid oxidised material.19
2.5. Nutritional experiments with rats Net protein utilisation (n.p.u.) true N digestibility and biological value (b.v.) of the beans were determined using Barrier Maintained Hooded Rats of the Rowett colony, The technique of Miller and Bender20 was used with the modifications to diets and methods described previously.7 All the bean samples were incorporated into diets at a level to provide 10 % crude protein (N x 6.25). In addition to the group (four animals) fed the non-protein control diet a second group in each experiment was fed a “positive” control diet containing casein to provide 10% crude protein.
3. Results and discussion 3.1. Yield Yields of beans, tonnes/hectare (t/ha), corrected to 15 % moisture content from the serially harvested Herz Freya reached a maximum during early September (Table I). The lower yield at the first harvest date was a result of immaturity and that at the final harvest was due to losses through the shedding of beans from the pods before harvest. Crude protein content remained virtually constant throughout the period of the four harvests resulting in yields of 1.75, 1.97, 1.89 and 1.48 t/ha of crude protein for the four harvests in chronological order. Therefore, assuming adequate storage facilities, for example, on-farm drying or propionic acid treatment, are available, earlier harvesting appears to be preferable in respect of both protein and seed yield.
In the comparison of three faba bean cultivars, Ostlers and Herz Freya gave higher yields of beans than Maris Bead. However, in terms of crude protein Maris Bead and Herz Freya gave similar yields (1.55 and 1.57 t/ha respectively) while Ostlers out- yielded both with 1.86 t/ha.
Tab
le 1
. Y
ield
, dry
mat
ter,
N a
nd a
min
o ac
ids o
f fa
ba a
nd k
idne
y be
ans
Her
z H
erz
Frey
a Fr
eya
Dat
e ha
rves
ted
30 A
ug
11 S
ea
Yie
ld t/
ha a
t 15
% m
oist
ure c
onte
nt
6.8-
%
dry
mat
ter
at h
arve
st
47.4
F
-7
“G
reen
” “B
row
n”
N (
% o
f dr
y m
atte
r)
Ess
entia
l am
ino
acid
s (g
/16
g N
):
Thr
eoni
ne
Val
ine
Met
hion
ine
Cys
tine
Is0
Leu
cine
L
euci
ne
Tyr
osin
e Ph
eny l
alan
ine
Lys
ine
His
tidin
e A
rgin
ine
Tot
al e
ssen
tial a
min
o ac
ids
Prol
ine
Asp
artic
aci
d Se
rine
G
luta
mic
aci
d G
lyci
ne
Ala
nine
T
otal
C
hem
ical
scor
e
4.75
3.3
4.2
0.
9 1.
3 3.
8 7.
1 3
.2
3.7
6.0
2.4
8.5
44.4
4
.2
10.0
4.
3 14
.8
3.9
3.9
85.5
52
4.97
3.3
4.2
0.7
1.2
3.8
7.3
2.9
3.
7 6.
1 2.
4 8.
3 43
.9
4.4
10.3
4.
5 15
.1
3.9
3.8
85.9
45
7.i
76
.7
4.84
3.1
3.9
0.9
1.
3 3.
7 6.
9 3.
1 3.
5 5.
8 2.
4 7.
9 42
.5
4.9
9.5
4.2
13.9
3.
7 3.
6 82
.3
52
Her
z H
erz
Frey
a Fr
eya Cul
tivar
-
~
26 S
ep
7.6
76.8
4.68
3.1
4.0
0.
8 1.
2 3.
6 6.
6 2.
9 3.
3 5.
5 2.
2 7.
5 40
.7
4.0
9.6
4.1
14.1
3.
7 3.
5 79
.7
48
23 O
ct
5.9
74.6
4.73
3.2
3.9
0.8
1.1
3.7
7.0
3.
0 3.
4 5.
8 2.
2 7.
8 41
.9
5.1
9.5
4.2
14.2
3.
7 3.
6 82
.2
45
Rat
H
erz
Mar
is Pr
o-
requ
ire-
Fr
eya
Bea
d O
stle
rs
Prim
o ce
ssor
C
asei
n m
ents
4 O
ct
6.2
86.3
4.72
3.3
4.2
0.7
1.3
2.6
6.
8 3.
3 3.
8 5.
9 2.
4 8.
2 42
.5
4.3
10.3
4.
3 14
.8
3.9
3.7
83.8
48
17 O
ct
5.6
84
.8
5.30
3.2
4.1
0.
7 1.
3 3.
7 7.
0 3.
1 3.
6 5.
7 2.
4 8
.9
43.7
4.
0 9.
9 4.
1 14
.5
3.9
3.8
83.9
48
4Oct
18
Sep
6.
8 84
.2
5.13
4.
91
2.9
3.2
3.7
4.2
0.7
1.1
1.
3 1.
1 3.
8 3.
6 7.
1 6.
7 3
.0
3.1
3.
3 3.
5 5.
6 5.
9 2.
3 2.
3 8.
0 8.
4 41
.7
43.1
5.
1 4.
1 9.
2 9.
7 4
.0
4.1
13.5
14
.6
3.6
3.9
3.6
3.9
80.7
83
.4
48
52
3.61
4.2
4.6
1 .o
1.2
4.
1 6.
8 3.
1 4.
5 5.
9 2
.6
5.3
43.3
2.
4 11
.5
5.3
14.5
3.
6 3.
6 84
.2
52
13.1
4.1
4.3
6.2
5.3
2’6
1
4.2
0.4
/ 4.
9 5.
3 8.
8 6.
4
5’71
6.
9 5.0J
7.4
5.3
2.6
3.5
3.4
1.8
51.1
9
.4
6.9
5.4
20.6
1.
9 3.
0 98
.3
71
Tab
le 2
. N
et p
rote
in u
tilis
atio
n, tr
ue N
dig
estib
ility
and
bio
logi
cal v
alue
of
bean
s co
mpa
red
to th
e ha
emag
glut
inin
con
tent
and
che
mic
al s
core
Cul
tivar
Her
z H
erz
Her
z H
erz
Her
z M
aris
Fr
eya
Frey
a Fr
eya
Frey
a Fr
eya
Ost
lers
B
ead
Prim
o Pr
oces
sor
Cas
ein
Dat
e ha
rves
ted
Hae
mag
glut
inin
s“
n.p.
u.b
N d
iges
tibili
ty
Bio
logi
cal v
alue
C
hem
ical
sco
re
+O
.l%
L-M
et
n.p.
u.
Bio
logi
cal v
alue
30.8
11
.9
-
“Gre
en”
“Bro
wn”
80
0 80
0 80
0 40
39
42
(n
=2)
(n=2
) 81
81
83
49
48
51
52
45
52
26.9
23
.10
800
400
39
39
81
81
48
48
48
45
57
70
(n=
3)
4.10
4.
10
17.1
0 18
.9
400
800
$00
800
50
39
40
39
40
-c
-
82
83
87
85
48
48
45
47
48
48
48
52
49 -
58
67
70
(n=4
) 99
71
71
81
82
a Lo
wes
t dilu
tion
of b
ean
extr
act
(pgi
ml)
at w
hich
agg
lutin
atio
n of
rab
bit
r.b.c
. oc
curr
ed.
c -=
N
o in
form
atio
n du
e to
pre
mat
ure
deat
h of
rat
s.
Est
imat
ions
on
a si
ngle
gro
up o
f fo
ur r
ats (n
= 1)
unl
ess
othe
rwis
e in
dica
ted.
1582
3.2. Amino acid analysis Amino acid analysis of the samples (Table 1) showed the similarity in composition between the faba bean cultivars and also between the samples of Herz Freya harvested on different dates. Even the obviously unripe “Green” beans harvested on the earliest date showed no great differences from the later samples apart from the lower dry matter. The kidney bean Processor differed from the faba beans in having a higher content of threonine and phenylalanine and a lower arginine content but the values for the sulphur amino acids, methionine and cystine, were similar in all the samples and were the first limiting amino acids. The chemical scores ranged from 45-52.
3.3. Experiments with rats In experiments with rats (Table 2) the faba bean samples gave biological values ranging from 45-51, in close agreement with the values predicted from the chemical score. The digestibility of N was between 81-87 x. The agreement between chemical scores and biological values is an indication of the absence of anti-nutritional factors from the faba bean samples. Two of the samples were supplemented by the addition of 0.1 % L-methionine to the diet. At this level of supplementation 70 % of the sulphur amino acid requirement of the rat is satisfied and no other amino acids appear to be limiting since the biological value of both the samples increased by 22 units. This figure corresponded to the increase in chemical score based on the sulphur amino acids and ‘provides further evidence of the absence of anti-nutritional factors.
Rats fed on diets containing Phaseolus beans (Processor) lost weight rapidly and to a greater extent than the groups fed non-protein control diets. In each of three replicate groups of four rats one or more animals died between the seventh and ninth day of feeding. In earlier work with a less toxic haricot bean,7 rats survived for the 10 day experimental period but lost more weight than the respective control group, giving rise to a “negative” n.p.u.7 A third variety of Phaseolus vulguris (cv. Glamis) has been tested and found to have a similar haemagglutinin content to Processor and also resulted in the death of rats within the 10 day experimental period.
R. Palmer and R. Thompson
3.4. Haemagglutinin assay In the haemagglutinin assay (Table 2) an extract of the Phaseolus bean Processor, serially diluted to a concentration equivalent to 50 pg of original beans/ml, was capable of agglutinating rabbit red blood cells, when an equal volume of whole blood, diluted 1 : 12 with saline, was added to the extract. This agglutinating activity was between eight and 16 times greater than the value obtained with the faba bean extracts which were active only down to concentrations of 400-800 pg/ml.
The recent work of Pusztai et a1.* demonstrates the growth inhibitory effect of partially purified proteins from the Phaseolus bean Processor and shows that the growth depression is related to the haemagglutinin content of the various fractions. The poor nutritional performance which other workers have observed on feeding raw faba beans99 11-13 has not been linked conclusively to either the haemagglutinins or the trypsin inhibitors. In the present work faba beans were included at a level to provide 10 % crude protein (N x 6.25) in the diets, i.e. about 30 % by weight, which corresponds to the levels at which poor performance has been observed.9~ 1% 13
Protein nutritive value of faba beans 1583
However, all of the samples gave biological values which corresponded well with the chemical score and both the samples tested with supplementary methionine gave good improvements in biological values.
The faba beans used in this work were subjected to immediate low temperature storage after harvesting and were subsequently freeze-dried. These precautions were designed to prevent destruction of the heat labile toxins in the bean and also to minimise the growth of microorganisms. Thus it is unlikely that the toxicity of our samples was lower than that of normal commercially available faba beans. However, the samples tested have been shown to be nutritionally of good quality and apparently free of any anti-nutritional properties. It therefore seems possible that poor storage conditions giving rise to fungal and bacterial growth may be a contributory cause of the poor nutritive value often attributed to faba beans.
Acknowledgements
The authors are grateful to Dr R. H. Smith and Dr A. Pusztai for their help and advice, to Mr A. D. McIntosh for the amino acid analyses and to the Department of Chemical and Physical Analysis, Rowett Institute, for the N estimations.
References 1. 2. 3. 4.
5.
6. 7. 8. 9.
10. 11.
12. 13. 14. 15. 16. 17. 18. 19. 20.
Clarke, H. E. Proc. Nutr. SOC. 1970, 29, 64. Bond, D. A. Proc. Nutr. SOC. 1970, 29, 74. Eppendorfer, W. H. J. Sci. Fd Agric. 1971, 22, 501. Liener, I. E.; Kakade, M. L. In Toxic Constituents of Plant Foodstuffs 1969, p. 8 (Liener, 1. E., Ed.), New York, Academic Press. Jaffe, W. G. In Toxic Constituents of Plant Foodsfufls 1969, p. 69 (Liener, I. E., Ed.), New York, Academic Press. Evans, R. J.; Pusztai, A.; Watt, W. B.; Bauer, D. H. Biochim. biophys. Acta 1973, 303, 175. Palmer, R. ; McIntosh, A.; Pusztai, A. J. Sci. Fd Agric. 1973, 24, 937. Pusztai, A.; Grant, G.; Palmer, R. J. Sci. Fd Agric. 1975, 26, 149. Wilson, B. J.; McNab, J. M.; Bentley, H. Br. Poult. Sci. 1972, 13, 521. Wilson, B. J.; McNab, J. M.; Bentley, H. J. Sci. Fd Agric. 1972, 23, 679. Marquardt, R. R.; Campbell, L. D.; Stothers, S. C. ; McKirdy, J. A. Can. J. Anim. Sci. 1974, 54, 177. Fowler, V. R.; Livingstone, R. M. Proc. Br. SOC. Anim. Prod. 1972, p. 138. Livingstone, R. M.; Fowler, V. R.; Woodham, A. A. Proc. Nutr. SOC. 1970,29, 46A. Makela, 0. Studies in Haemagglutinins of Leguminosae Seeds 1957, Weilin and Goos, Helsinki. Beuchat, L. R.; Lechowich, R. V. J. Milk Fd Technoi. 1970,33, 373. Davidson, J.; Mathieson, J.; Boyne, A, W. Analyst, Lond. 1970, 95, 181. Pusztai, A.; Watt, W. B. Biochim. Biophys. Acta 1970, 207, 413. Spackman, D. H.; Stein, W. H.; Moore, S. Analyt. Chem. 1958, 30, 1190. Moore, S. J . Biol. Chem. 1963, 238,235. Miller, D. S.; Bender, A. E. Br. J. Nutr. 1955, 9, 382.
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