Dear Mike,
Thank you for drawing our attention to these data. I had only seen figures
on raw oilseed soybeans (part of a study to determine whether they should
be ground and included in an animal feed formula). As I suspected, there
are important changes in the amino acid balance with cooking and processing
into tofu (What is Okara?).
I think your question, though, has to do with how to make sense out of
these figures, which don't seem to say much by themselves. One way of
thinking about protein quality is in terms of the proportions of amino
acids. Egg is considered close to ideal for humans-breast milk is
sometimes used instead and it is very similar. But to think of proportions
means ratios between the numbers. In your table the AA content is expressed
as g/100g of edible portion, i.e. as percentages of the whole food. In the
book "Diet for a Small Planet" (Francis Lappé) the author used a kind of
star graph to represent the proportions of the essential amino acids (the
ones we must get from our food because our bodies cannot synthesize them).
These are the first eight (some say ten) AA listed in your table, from
tryptophan to phenyalanine. The star graphs in Lappé's book represented the
proportion of EAA in the total EAA fraction. This allows one to easily
compare an EAA profile to the 'ideal', presumably egg protein.
For a quick idea, just eyeballing the figures, consider the ratio between
leucine and isoleucine. This is considered problematic; a high
leucine:isoleucine ration can be 'toxic' (e.g. it exacerbates pelagra, the
niacin deficiency associate with diets based on non-lime-treated maize as a
staple grain). Raw soybeans have a high leucine:isoleucine ratio (2.972:
1.770 according to the table, or 1.68:1, compared to eggs at 1.56:1. This
figure is lower than the data I worked with before which were for soybeans
used for oil production and forrage, not for human consumption-the ration
was almost 2:1. Perhaps this is one reason some vareities of soybeans are
preferred by humans) Cooking doesn't help, the ratio remains the same at
1.68, though notice that the numbers (g/100g) change. However, processing
into tofu does make a difference; the ratio drops to 1.53, below that of eggs.
It's actually interesting to look at the data just for the EAA fraction:
Tofu* Okara Soybeans** Egg ***
NDB No: 16159 16130 16108 16109 1123
Amino acids Raw Cooked
(g) in (100g edible)
Tryptophan 0.162 0.050 0.530 0.242 0.152
Threonine 0.425 0.131 1.585 0.723 0.600
Isoleucine 0.516 0.159 1.770 0.807 0.682
Leucine 0.791 0.244 2.972 1.355 1.067
Lysine 0.685 0.212 2.429 1.108 0.897
Methionine 0.133 0.041 0.492 0.224 0.390
Cystine 0.144 0.044 0.588 0.268 0.290
P.alanine 0.506 0.157 1.905 0.869 0.664
Total EAA 3.362 1.038 12.271 5.596 4.742
The last row gives the total EAA in 100 grams of edible portion. Note that
for eggs, about 4.7% is made of essential amino acids. But raw soybeans
have 12.3% EAA. It would be reasonable to assume that a higher percentage
of EAA means a higher quality protein, right? But, of course, nobody I
know eats raw soybeans. And what do we do when we process soybeans? Cooking
reduces total EAA to around 6% while tofu has 3.4%, less than eggs. One
purpose of processing soybeans seems to be to eliminate most of its
protein. I suspect that the reason for this is that its protein is largely
unedible. Its probably better to eat less of a protein whose EAA
proportions are out of balance.
Judged by this standard (i.e. EAA profile compared to eggs) all other beans
(that I have seen data for) are better than soybeans. I always assumed
this is why no one can convince Mexican farmers (who grow, collectively and
appreciate hundreds of varieties of beans) to eat "the food of the future."
I can't figure out how to do it on the computer, but if you take the last
table and convert the figures to percentages of the column totals, then
draw an eight pointed star with an axis (ray) for each essential amino acid
and locate each value on its axis. Then connect the points, you have a
visual way of comparing EAA fractions of these different foods.
Not eaxactly Nutrition 101, but, I hope, interesting.
PS. Dear Minelle. I don't care for soybeans in any form. Tofu is a fairly
'natural' process (compared to making industrial soy milk or soybean
hotdogs) and I find it edible when well disguised in spciy hot and sour
soup! Most other forms of soybeans make me sick. Which brings up another
aspect, re thryroid problems etc.: soybeans seem to be loaded with
phytohormones and other secondary compounds (a characteristic of legumes in
general) that don't sit well with some folks.
Ronald Nigh
Dana, A.C.
Mexico, D.F. & San Cristóbal de Las Casas, Chiapas
Tel. y FAX 525-666-73-66 (DF)
529-678-72-15 (Chiapas)
danamex@mail.internet.com.mx
To Unsubscribe: Email majordomo@ces.ncsu.edu with the command
"unsubscribe sanet-mg". If you receive the digest format, use the command
"unsubscribe sanet-mg-digest".
To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command
"subscribe sanet-mg-digest".
All messages to sanet-mg are archived at:
http://www.sare.org/htdocs/hypermail
This archive was generated by hypermail 2b29 : Sun Feb 06 2000 - 12:00:24 EST