Food Chemistry 48 (1993) 137-143
Saponins, phytic acid, tannins and protease
inhibitors in qulnoa (Chenopodium qumoa,
Willd) seeds
Jenny Ruales a'b & Baboo M. Nair a
"Department of Applied Nutrition and Food Chemistry, Chemical Centre, University of Lund, PO Box 124, S-221 O0 Lund, Sweden
blnstituto de Investigaciones Tecnol6gicas, Escuela Politbcnica Nacional, Apartado Postal 17 O1 2759, Quito, Ecuador
(Received 1 July 1992; revised version received and accepted 5 January 1993)
The seeds of quinoa (Chenopodium quinoa, Willd), a food crop of the Andean
region of Latin America, contain protein of good quality and high amounts of
carbohydrates, fat, vitamins, and minerals. An industrial process for manufacturing infant food using quinoa as a basic raw material is being developed. The
presence of antinutrients are of importance in this context, and this paper deals
with saponins, phytic acid, tannins and protease inhibitors in quinoa seeds.
The samples of quinoa analysed in this experiment contained two main types
of saponins. The amount of saponin A (fl-D-glucopyranosyl-[/3-D-glucopyranosyl(1 ~ 3)-a-L-arabino-pyranosyl-(1 -~ 3)]-3-fl-23-dihydroxy-12-en-28-oate methyl
ester) was 0.7% of the dry weight and that of the saponin B (fl-o-glucopyranosyl-[fl-D-glucopyranosyl-(1 --~ 3)-a-L-arabino-pyranosyl-(1 --~ 3)]-3-fl-23-dihydroxyolean-12-en-28-oate was 0-2% of the dry weight. These were the major
saponins found in the quinoa bran collected while polishing the seeds.
After scrubbing and washing, the level of saponin-A remaining in the seeds
decreased to 0.31% of the dry weight, and saponin-B was completely removed
by this process.
The content of phytic acid in the quinoa seeds was about 1% of the dry matter,
and scrubbing and washing reduced the phytic acid content of the seeds by about
30%. Neither protease inhibitor nor tannins were detected in the quinoa seeds.
INTRODUCTION
pentose glycoside units joined to the sapogenin aglycone,
which can be a steroidal or a triterpenoid aglycone.
Quinoa saponins are soluble in methanol or water.
They produce stable foams in aqueous solutions, and
haemolyse red blood cells (Ruiz & Amaya, 1979; Birk
& Peri, 1980; Oakenfull, 1981; Price et al., 1987, 1989).
Saponins are reported to be toxic for cold-blooded
animals and they were used as fish poison by the inhabitants of South America. Some saponins form chemical
complexes with iron and reduce its absorption (West &
Greger, 1978; West et al., 1978; Southon et al., 1988;
Price et al., 1989). However, no evidence of formation
of complexes of saponin with vitamin A, E or D3 was
found by West & Greger (1978). Saponins are located
on the outer layers of the seeds, and can be removed by
polishing and washing with water.
Phytic acid (myoinositol hexaphosphoric acid) reduces
the availability of many minerals like iron, zinc, calcium
and magnesium. The formation of iron-phytate complexes of low solubility, in the small intestine is considered to be the basis for the interference of phytate
with iron absorption (Davies & Reid, 1979; Hallberg,
1984; Hallberg & Rossander, 1984; Hallberg et al.,
1987; Brune, 1989). Although the iron content in
Quinoa (Chenopodium quinoa, Willd) has been an indigenous crop of the Andean region of South America
since ancient times. Quinoa can be used as flour for
making bread or as whole grain in gruels, porridge or
soups. The protein content in quinoa (15% dry basis) is
much higher than that found in cereals such as wheat,
barley, oats, rice and sorghum (Ruales & Nair, 1992a;
Kent, 1984). The results of animal feeding experiments
showed high net protein utilization for raw whole (76)
and polished and washed quinoa (74) (Ruales & Nair,
1992a). Quinoa also contains more carotene, riboflavin,
tocopherols and folic acid than wheat, rice, oats and
maize, and can supply the daily requirements of certain
vitamins and several minerals for children between 1
and 3 years (Ruales & Nair, 1992b).
One of the factors which limit the widespread utilization of quinoa is its bitter taste caused by the presence
of saponins. Saponins are triterpene glucosides that
consist of a linear arrangement of one to six hexose or
Food Chem&trv 0308-8146/93/$06.00 © 1993 Elsevier Science
Publishers Ltd, England. Printed in Great Britain
137
138
J. Ruales, B. M. Nair
cereals is usually high, the iron absorption from them
is often poor due to the presence of high amounts of
phytates (Brune, 1989; Sandberg & Svanberg, 1991).
Adverse effects on zinc utilization when the diet contains large amounts of phytates were also reported by
Sandberg (1990). They are also found to inhibit the
proteases and amylases (Vaintraub & Bulmaga, 1991)
of the intestinal tract. Quinoa contains many essential
minerals like calcium (874 mg/kg), phosphorus (5.3 g/kg),
iron (5.3 g/kg) and zinc (36 mg/kg) and their availability is of importance in relation to its use as a basic
source of nutrients in an infant food.
Polyphenolic compounds like tannins are known to
interfere with digestion and absorption in monogastric
animals (Eggum et al., 1983; Bach Knudsen et al.,
1988). Polyphenols bind proteins, and those which
precipitate protein from aqueous solutions are usually
called tannins (Makkar et al., 1988). They form
complexes, not only with dietary proteins, but also with
digestive enzymes, thus reducing the digestibility of
protein in foods (Singh & Eggum, 1984).
Many plant foods contain substances which inhibit
the activity of certain proteolytic enzymes, reducing, in
this way, the digestibility of dietary proteins (Liener &
Kakade, 1980). Some protease inhibitors like the heatlabile trypsin inhibitor found in raw soybeans are,
however, inactivated by heat treatment. In infant foods
the factors which affect the digestibility of the protein
are especially important.
The present paper deals with the determination of
saponins, phytic acid, tannins and protease inhibitors
present in quinoa seeds.
MATERIALS AND METHODS
Materials
Seeds of quinoa (Chenopodium quinoa, Willd) variety
Latinreco-40057, were from the experimental farm of
Latinreco, Nestl6 Research Centre in Quito, Ecuador,
where quinoa was grown under controlled conditions
of agriculture, harvesting and storage. The saponin
standards used in high-performance liquid chromatography (HPLC) analysis, saponin A and saponin B,
were isolated from quinoa seeds by Dr C. Borel, Nestl6
Research Centre, Vevey, Switzerland.
All other reagents were of analytical grade.
Methods
Sample preparation
Quinoa seeds were scrubbed and polished using a
pulper (model 5707, Langsenkamp, Indianapolis, IN,
USA) and, after removing the dust, they were washed
with running tap water for 20 min and finally dried
(Ruales & Nair, 1992a).
The material separated with a grain separator (model
100, Hance Corp., Westville, OH, USA) from the
seeds, after scrubbing and polishing the quinoa seeds,
was collected as quinoa bran.
The samples of clean dry quinoa were milled to a flour
in a sample mill (Cyclotec 1093, Tecator AB, HOganas,
Sweden) equipped with a sieve of 0-25 mm pore size.
Saponins
A modified HPLC method described by Kesselmeir et
al. (1981) was used for the determination of saponins.
The saponins were extracted from 15 g of flour with
150 ml of methanol for 24 h, using a Soxhlet apparatus, after the seeds were defatted with 150 ml of
petroleum ether for 16 h. After the extraction, the
methanol was evaporated at 35°C using vacuum, and
the residue was dissolved in 5 ml of methanol. Separation of the saponins was performed by injecting 20 /xl
of the sample into a high-performance liquid chromatograph (Varian Model 5000 Liquid Chromatograph,
Varian Associates, Sunnyvale, CA, USA) equipped with
a column (4 mm x 250 mm) packed with LiChrospher
100 CH-8/2 (5 /~m) a UV detector and an integrator
(Shimadzu C-R3A Chromatopac, Kyoto, Japan). The
detection wavelength was 200 nm. A gradient elution
was performed with 25 to 40% acetonitrile in water
during 15 min. The flow rate was 2.0 ml/min. Saponins
A and B isolated from quinoa seeds were used as
standards.
Phytic acid
Phytate was quantified as hexaphosphate equivalents,
using the method described by Harland & Oberleas
(1986). The sample (2 g of quinoa flour) was mixed
with 40 ml of HC1 (2.4%) by shaking vigorously for 3 h
at 20°C. The suspension was filtered with vacuum
through a Whatman No. 1 paper. An aliquot (1 ml)
of the filtrate was mixed with 1 ml of EDTA/NaOH solution (0.11M NazEDTA and 0.75M NaOH in H20 ),
made up to 25 ml with water and placed on the ionexchange (anion-exchange resin AG1-X4, 100-200 mesh
chloride form, Bio-Rad Laboratories, Richmond, CA,
USA) column (0-7 cm × 15 cm). The column was
washed first with 15 ml of H20 and then with 15 ml of
0.1M NaC1 before it was eluted with 15 ml of 0"7M
NaCI. The eluate was collected in a digestion vessel. A
blank was prepared by mixing 1 ml of 2.4% HCI with
1 ml of Na2EDTA-NaOH reagent and diluting with
water to 25 ml. A mixture of concentrated HzSO4
(0.5 ml) and HNO3 (3.0 ml) was added to the eluate to
release the phosphorus by wet digestion in a Kjeldahl
rack over medium heat (about 150°C), until active
boiling ceased, and a cloud of thick yellow vapour
filled the neck of the flask. The content was then heated
for 5 min at about 150°C, followed by heating for
5 min at about 80°C. The samples were cooled to room
temperature and then H20 (10 ml) was added to dissolve the salts. They were again heated for 10 min
under low heat (about 80°C). After cooling, the
solutions were transferred to a 50 ml volumetric flask.
An aliquot (2 ml) of 2.5% ammonium molybdate solution in 1N H2SO4 was added and mixed well, and then
I ml of sulphonic acid reagent (0.16 g of 1-amino-2naphthol-4-sulphonic acid, 1.92 g of Na2SO3 and 9-6 g
Saponins, phytic acid, tannins and protease inhibitors in quinoa
of NaHSO 3 in 100 ml of H20 ) was added and mixed
well; thereafter, the volume of the solution was made
up with water to 50 ml. After mixing well, the solution
was allowed to stand 15 min before the absorbance at
640 nm was measured in a spectrophotometer. The
amount of phytate (phytate = 28.2% P) in the sample
was calculated as hexaphosphate equivalents. Sodium
phytate (Sigma P 5756) solutions were used as standards.
Tannins
Tannins were determined as flavanols as described by
Truelsen (1984). The flavanols from 0-3 g of quinoa
flour were extracted with 5 ml of 70% acetone in 10mM
HC1, at room temperature (20°C) during 2 h. The
suspension was centrifuged at 3000g for 5 min. The
supernatant was collected in a beaker and the residue
was treated again with 5 ml of 70% acetone in 10 mM
HC1, under the same conditions as before. The filtrates
from the two extractions were pooled together and
made up to 10 ml with the extraction solution. An
aliquot of 200 /zl was mixed with 3 ml of 4-dimethylaminocinnamaldehyde solution (140 ml of methanol
and 50 ml of conc. HCI were mixed at 20°C and 200
mg of 4-dimethylaminocinnamaldehyde(Sigma, D 4506)
was added and made up to 200 ml with methanol). The
absorbance was measured at 640 nm, 3 min after
ixing the reagents. Catechin (Sigma, C1788) was used
as standard.
Protease &hibitors
The presence of protease inhibitors was determined by a
method described by Tovar (1983). Quinoa flour (2 g)
was treated with distilled water (10 ml) with continuous
stirring for 16 h at 4°C. The insoluble material was
separated by centrifugation at 10 000g for 20 min and
discarded. A 0.8% agarose solution was prepared in
0"IM Tris-HCl buffer of pH 8.6. This solution was used
to cast 2 nm thick gels on standard microscopy slides.
After the gel was solidified, wells were punched in the
gels. After filling the wells with 5/xl of test solution the
slides were incubated in a chamber for 20 min at 37°C
to allow inhibitor diffusion. The gels were immersed in
0-1M Tris-HC1 buffer of pH 8.6 containing trypsin
(Sigma T 8253) (100 /xg/litre). The gels were then
washed three times with distilled water, and were incubated for 5 min at 37°C with excess of a substrate solution of 3 mg of N-acetyl-DL-phenylalanine 2-naphthyl
ester (Sigma A 7512) dissolved in 1.25 ml of N,Ndimethylformamide (Sigma D 8654) and mixed with
11 ml of 0.1M Tris-HC1 buffer of pH 8-6 containing
6 mg of tetrazotized o-dianisidine (Sigma D 3502).
Finally, the gels were transferred to 7-5°/,, acetic acid to
fix the colour.
Statistical analysis
The statistical evaluation of the results was done
by one-way ANOVA using Statgraphics (Statistical
Graphics Corp., MD, USA) software. Multiple comparison tests were performed adopting Tukey's test at
the 95% confidence level.
139
RESULTS AND DISCUSSION
Saponins
The analysis of saponins has been done by different
methods. One method deals with the measurement of
the amount of foam produced after shaking the sample
with water. This afrosimetric method does not take into
account the presence of any other surfactants. Moreover, it is not particularly sensitive (Oakenfull, 1981).
The saponins present in quinoa differ in proportions
with the variety. Some saponins may form a stable and
compact foam. Koziol (1991) found, when using the
afrosimetric method, that the variety Porotok produced
an unstable foam described as larger air bubbles which
were easily collapsed making the determination of
saponins difficult. The accuracy and precision of the
afrosimetric method (Koziol, 1991) depends on the type
of saponins present in the seeds. However, this method
is satisfactory for screening different varieties and for
obtaining a rapid knowledge about the efficiency of the
process of removing saponins from the quinoa seeds.
Using a thin-layer chromatography technique, a water
extract of the sample was separated on a silica gel plate
using chloroform-acetic acid-methanol-water or nbutanol-acetic acid-water, and saponins were developed
with sulphuric acid (Ballon et al., 1976; Romero, 1981).
Saponins have also been determined by spectrophotometric methods, using oleanolic acid as reference (Elias
& Diaz, 1988). The spectrophotometric methods utilize
the colour produced by the reaction of saponins with
vanillin or anisaldehyde. These methods are not suitable for estimating saponins in plant extracts due to the
fact that the reactions are not specific, and coloured
products can be produced from other compounds such
as flavonoids (Oakenfull, 1981). Further, the capacity
of saponins to inhibit growth of the fungus Trichoderma viride on potato dextrose agar was used to quantify saponins (Birk & Peri, 1980). Good correlation
between the values from bioassay using red flour beetle
larve and a HPLC method were obtained by Bercker &
Hanners (1990). Quinoa saponins were isolated by
monitoring the fractions with brine shrimp lethality
and a taste for bitterness (Ma et al., 1989). The same
authors identified some quinoa saponins, using chemical
spectral and enzymatic methods. Quinoa saponins have
also been characterized, after acid hydrolysis producing
oleanic acid and hederagenin, and the saponins were
detected by using gas chromatography and by mass
spectrometry (Meyer et al., 1990). In addition, a gravimetric method (Junac, 1983), a method based on the
ability of saponins to cause haemolysis (Jones & Elliott,
1969; Reichert et al., 1986) and a gas chromatographic
method have also been developed for analysis of
saponins in quinoa (Ridout et al., 1991).
The HPLC method is suitable for the analysis of
saponins in crude extracts of plant tissues. It has the
advantage over other methods used in this study in
that it has high accuracy and precision. However, suitable standards of saponins are necessary for correct
140
J. Ruales, B. M. Nair
Quinoa
saponin
QuinoasaponinB
A
-.
" ~ ' ~
glc - ma - 0
.:..:+.
~-
/
~-
/
-
Table 1. Content of saponins and phytic acid in quinoa seeds
(g/lO0 g dry basis)"
COOCH 3
glc
- ara
-
Raw whole
quinoa
COOglc
"CH2OH
Saponin A
Saponin B
0-7 +_0.05b
0.2 + 0 " 0 2 b
0"0
Phytic a c i d
1.0
0"8
_
0'08
0.3 -+ 0.02"
+ 0.00"
~
4- 0 . 0 1
b
Bran
1.7 _+0.08d
0.6
_+ 0 . 0 3
d
--
" Means (n -- 3) + SD.
t,.,.a Means in the same row followed by the same letter are
not significantly different by Tukey's test at 95% confidence
limits.
Ara:~-L-Arabinopyranosyl
GIc:P -D-Glucopyranosyl
Polished and
washed quinoa
Fig. I. Proposed structure of quinoa saponins.
identification of the components and their quantitative
determination (Kesselmeir & Stuck, 1981; Ireland &
Dziedzic, 1987).
In the present study an HPLC method was used for
the determination of the saponin content in quinoa
seeds used for making an infant food. Two major
saponins were identified in quinoa seeds and also in
quinoa bran. These are present in relatively high
amounts. Known amounts of both standards (saponins
A and B) were separately spiked and coeluted with the
sample in HPLC.
Saponin A, with a retention time of 7.04 min,
corresponds to fl-D-glucopyranosyl-[fl-D-glucopyranosyl(1 -+ 3)-a-L-arabino-pyranosyl-(1 --~ 3)]-3-fl-23-dihydroxy12-en-28-oate-30 methyl ester, and saponin-B, with a
retention time of 12.53 min, corresponds to fl-D-glucopyranosyl-[/3-D-glucopyranosyl-(l --~ 3)-a-L-arabino-pyranosyl-(1 ---)3)]-3-/3-23 dihydroxyolean-12-en-28-oate (Fig.
1). Thirteen saponins from quinoa bran, have been
isolated using preparative methods and their structures
were identified. Seven of them were oleanane (Mizui et
al., 1988, 1990). The chromatogram of the quinoa bran
showed a pattern of saponin content similar to that of
raw whole quinoa seeds.
After quinoa had been polished and washed with
water, saponin A was decreased by 56% of the original
content, while saponin B was not detectable in the processed samples (Table 1), i.e. <50 ng/100 g. A linearity
response was seen up to 10 p~g (Fig. 2). As quinoa had
no bitter taste, after final washing, assayed by an informal panel composed of researchers who were taking
Raw Quinoa
part in the processing, it can be assumed that the bitter
taste most probably is the contribution of saponin B.
The amount of remaining saponins in the seeds after
scrubbing and washing was much lower than the lethal
doses of saponins by oral intake reported by George
(1965), which were 3 to 1000 times higher than that by
intravenous injections. The lethal dose by oral digestion in rodents varies from 1.9 to 6000 mg saponins/kg
body weight. On the other hand, the bran obtained
from quinoa seeds could be a source of saponins. Its
potential toxicity to various organisms makes it an
attractive insecticide (Price et al., 1987). Saponins are
used, as natural detergents, for flavouring, in health
foods, in tonics, etc. (Birk & Peri, 1980; Oakenfull,
1981; Merk, 1983; Price et al., 1987). Saponins are also
of interest from the pharmacological point of view as
they have been shown to modify the permeability of
the small intestine, which may help the absorption of
specific drugs (Oakenfull & Sidhu, 1990). The addition
of saponins is found to lower the level of cholesterol
in the plasma by increasing the faecal bile excretion
(Oakenfull & Fenwich, 1978; Topping et al., 1980;
Southon et al., 1988).
Phytic acid
The content of phytates present in the unpolished seeds
was 1.04 + 0.08 g/100 g and for polished and washed
seeds it was 0-78 + 0.01 g of dry matter. Relative
standard deviations for repeatability ranging from 2.5
to 10°/,), and for reproducibility from 4.5 to 11.0%, have
Quinoa Bran
r~
Washed Quinoa
<
t~
=
7-
o
4
s
12
Time(rain)
lo
o
(
s
i~
Time(rain)
~s
o
4
e
12
Tilnc0 n i n )
16
Fig. 2. Separation of saponins from quinoa seeds after methanol extraction. The separation was done on a LiChrosorb I00
CH-8/2 (5 p,m) column (125 m × 4 ram) by 15 min gradient elution from 25 to 40% acetonitrile in water; flow rate, 2 ml/min;
injection, 20/zl; detection (A = 200 nm).
Saponins, phytic acid, tannins and protease inhibitors in quinoa
been reported for the contents of phytic acid in food
samples (Harland & Oberleas, 1986). The process of
removing the bitter taste from quinoa seeds was carried
out by first scrubbing and then washing, leading to a
significant decrease (about 30%) in the recovery of
phytic acid. The phytic acid concentration in processed
quinoa seeds was comparable with those values for
whole grain rye flour (7.7 mg/g), whole grain wheat
flour (8.7 mg/g), lentils (8.4 mg/g) and faba bean
(8.0 mg/g) (Torelm & Bruce, 1982; Lombardi-Boccia et
al., 1991).
However, this shows that phytic acid is present not
only in the outer layers of quinoa seeds as is the case in
rye and wheat (Kent, 1984; Hallberg et al., 1987) but
also evenly distributed in the quinoa endosperm. The
amounts of phytic acid obtained in this study are in
concordance with the values reported by Koziol (1992)
for five different varieties of quinoa, which ranged from
10.5 to 13.1 mg/g. However, the content of phytic acid
obtained in this study are higher than the values
reported by Chauhan et al. (1992).
A study (Allred et al., 1976) carried out in rats
showed that the availability of iron from polished and
washed quinoa was at least equal to the availability of
iron from FeSO4. When the diets of the rates were
supplemented with 30% of quinoa, the iron gained as
haemoglobin per mg of iron intake was 0.74. When
diets had 50% of quinoa, the efficiency diminished to
0.51, compared to an efficiency of 0.55 for FeSO4
added to the wheat based diet. Moreover, Allred et al.
(1976) reported quinoa as a better source of iron for
haemoglobin regeneration than wheat flour in anaemic
rats. Thus, animal experiments indicate a good bioavailability of iron in spite of the rather high phytate
content. Studies on human beings are needed to
explore this further.
The ability of the phytates to form complexes with
minerals like iron, zinc, calcium and magnesium
can make the mineral content of a food inadequate
especially for children. The Food and Nutrition Board
(National Academy of Science, Washington, DC
(NRC, 1989) recommends 10 mg of iron per day for
children between 1 to 10 years. Sandberg (1990)
reported that the minimum amounts of phytic acid to
avoid negative effects on iron and zinc absorption were
10 and 50 mg per meal, respectively. The reduction of
phytic acid in foods by processes like fermentation,
sprouting and scalding has been reported. The hydrolysis of phytate by endogenous and exogenous phytases
increased the availability of iron in rye, oats and wheat
bran (Sandberg & Svanberg, 1991; Snider & Liebman,
1992). Sandberg et al. (1987) found degradation of
inositol hexaphosphate to inositol penta- and tetraphosphates during extrusion of wheat bran, and the
phytase activity was lost. Reductions of phytic acid
content in doughs made from coarse meals are reported
to be small, but with increasing temperature up to 55°C
the phytic acid concentrations were less than 8 and 4%
of original concentrations for wheat and rye, respectively (Fretzdorff & Brtimmer, 1992).
141
Tannins
Tannins measured as flavonols were not present at detectable levels in raw whole quinoa or raw polished and
washed quinoa. Chauhan et al. (1992), on the other
hand, found 0.53 g of tannins in whole quinoa seeds,
0.28 g in manually dehulled (flour) and 0.23 g in water
dehulled (flour) per 100 g on a dry matter basis. The
compositions of nutrients and antinutrients in food
plants may vary, depending on the variety and growing
conditions. This may partly explain the difference
between our report and that of Chauhan et al. (1992).
Nevertheless, the values reported by Chauhan et al. are
appreciably lower than those of rice beans (1.3%),
green gram (1.1%) and black gram 1.1% (Kaur &
Kapoor, 1992), but higher than that of barley 0-12%
(Kent, 1984). The method applied in this study
presented a standard deviation of 0.0012% and a
coefficient of variation of 1.1% between 0.078 and
0.131% of the content of tannins in 80 barley samples
(Truelsen, 1984).
Proteaseinhibitors
Using the qualitative method for determination of
trypsin inhibitor, no protease inhibitor was detected
even when a concentrated extract from quinoa flour
was analysed (2 g sample in 10 ml of water). In any
case, protease inhibitors in quinoa seeds are below
50 ppm (0.97 TUI/100 g where TUI is Trypsin units
inhibited; Kakade et al., 1969), which is the detection
limit of the method. Romero (1981) analysed trypsin
inhibitors in eight varieties of quinoa and found values
ranging from 1.36 to 5.04 TUI/mg. These values are
much lower than those reported for soybean (Glycine
max) 24-5-41.5 TUI/mg, kidney beans (Phaseolus
vulgaris) 12.9-42.8 TUI/mg, and lentils (Lens esculenta)
17.8 TUI/mg (Romero, 1981). In addition, Romero
(1981) reported that trypsin inhibitors present in quinoa
are thermolabile, which means that cooking, autolaving and extrusion will inactivate these antinutrients.
Quinoa seeds were reported (Ruales & Nair, 1992a)
to have high digestibility and high biological value as
assayed by animal feeding experiments. This further
supports the conclusion that any protease inhibitor
activity in quinoa is too low to reduce the bioavailability
of quinoa protein.
CONCLUSIONS
Saponins and phytic acid are the two main antinutrients
present in quinoa seeds. The process of scrubbing
and washing quinoa seeds to remove the bitter taste
reduced the saponin A content by 56% and the phytate
content by 30%. Saponin B was completely removed.
The saponins appeared to be mainly, but not entirely,
in the outer layer of the seeds, whereas phytates seemed
more evenly distributed. No tannins or protease
inhibitors were detected in raw whole or polished and
washed quinoa seeds.
142
J. Ruales, B. M. Nair
ACKNOWLEDGEMENTS
We thank Gunilla Onning and Helena Ljlieberg of the
Department of Food Chemistry and Applied Nutrition
for the advice in running the H P L C and phytic acid
analysis, and Professor N.-G Asp for reviewing the
manuscript. The financial support from the International Program in the Chemical Sciences, Uppsala,
Sweden, and International Foundation for Science,
Stockholm, Sweden, is gratefully acknowledged.
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