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Original article
Impact of several variables on the microwave extraction of
Chenopodium Quinoa willd saponins
Vicente Gianna,1,2 Juan Manuel Montes,1 Edgardo Luis Calandri1,2 & Carlos Alberto Guzman2,3
1 School of Chemical Engineering. FCEFyN. UNC, Velez Sarsfield Av. 1611., 5015 Cordoba, Argentina
2 Institute of Science and Food Technology. FCEFyN. UNC, Velez Sarsfield Av. 1611., 5015 Cordoba, Argentina
3 National Council of Scientific and Technical Research (CONICET), Velez Sarsfield Av. 1611., 5015 Cordoba, Argentina
(Received 25 August 2011; Accepted in revised form 23 February 2012)
Summary Despite their possible applications in diverse fields, saponins are still considered to be industrial waste. The
use of saponins, however, would make seed processing more profitable and reduce the pollution of
watercourses. In this work, the microwave extraction method of Chenopodium quinoa Willd saponins was
investigated. The effects of variables such as temperature, time of microwave application, solvent
composition and solvent ⁄mass seed ratio were investigated. Solvent mixtures (ethanol–water and
isopropanol–water) were used for the extraction. The Taguchi design methodology was employed to
determine the number of experiments and the optimal conditions for different extractions. The efficiency of
each assay was determined and the results agreed with the best conditions provided by the Taguchi
experimental design for both solvent mixtures. The isopropanol–water mixture efficiency was 91.8% in one
extraction step, and for ethanol–water mixture, it was 57.1%, clearly showing the advantage of the first one.
Keywords Extraction, microwave, quinoa, saponins.
Introduction
Quinoa is an annual plant that is native to the Andes(South America), with Bolivia and Peru, providing 80%of world production. In Argentina, the production istargeted at domestic consumption, such as in seed orflour (Vilche et al., 2003).For the seed to be used for human consumption, the
saponins content must be removed because they impartbitter taste and are considered to be the main anti-nutrient of the quinoa. Saponins are known to causebreakdown in the human small intestine cell membranesand also negatively affect the assimilation of someproteins (Moges Woldemichael & Wink, 2001). Sapo-nins are found in quinoa grain pericarp (Taylor &Parker, 2002), and their presence in the fruits seems toplay a role in defence against pests such as birds andinsects, during physiological maturation of the plant(Cabieses, 2005).Quinoa saponins are triterpenoidal glycosides, which
are soluble in methanol and water (Ruales & Nair,1992). The maximum acceptable level of saponin inquinoa for human consumption varies between 0.06%and 0.12% (Bacigalupo & Tapia, 1990). This is consistent
with the results of sensory tests conducted at theUniversity of Ambato, Ecuador, where it was deter-mined that the maximum tolerance of saponin contentin the cooked grain was 0.1% (Nieto & Soria, 1991).Saponins also produce foaming in aqueous solutions.
This foam is stable even at very low concentrations (0.1%)and can be used as a natural emulsifier in beverages,shampoos and soaps, as well as in fire extinguishers,photography and the cosmetics industry. Furthermore,saponins have been used in the pharmaceutical industryand agriculture (San Martın & Briones, 1999).Another important property of saponins is their
antifungal activity. It has been shown that saponinsinhibit the growth of Candida albicans (Moges Wolde-michael & Wink, 2001) and (Reilly et al., 2004) and thatsaponins treated with alkali have a significant antifungalactivity against Botrytis cinerea (Stuardo & San Martin,2008). In Canada, a commercial product composedmainly of quinoa saponins called HeadsUp PlantProtectant� has been developed (HeadsUp Plant Pro-tectant Ltd, Kamsack, Canada).Saponins also have anticarcinogenic properties and
stimulate the immune system (Li et al., 2002). Oleanolicacid, one of the five major components of the saponinsfrom quinoa, showed significant antitumor activitywhen tested in colon cells (Estrada et al., 1998).*Correspondent: E-mail: [email protected]
International Journal of Food Science and Technology 2012 1
doi:10.1111/j.1365-2621.2012.03008.x
� 2012 The Authors. International Journal of Food Science and Technology � 2012 Institute of Food Science and Technology
The effect of water deficit level on saponin composi-tion of quinoa was determinate in a field experimentconducted in Mexico. The experiment took place duringthe development of Sajama and Chucara cultivars. Thesaponin content increases during branching, panicleinitiation and in blooming, followed by a decreaseduring the grain filling stage, when the plants undermedium water deficit recorded the highest saponincontent (Soliz-Guerrero et al., 2002).The microwave-assisted extraction (MAE) is a rela-
tively new technique but has been growing rapidly inrecent times. Compounds present in the matrix caninteract with a suitable solvent assisted by microwaveenergy, which heats the system and allows for betterextraction. Microwaves have advantages over the rate ofheating of the sample and prevent overheating, avoidingthermolabile substances denaturation. Therefore, withthis method, can achieve good yields in short time.As mentioned earlier, the objectives of this research
were to evaluate the extraction efficiency of saponinsfrom quinoa seed by solvent extraction, employingmicrowaves through an appropriate combination of theoperating variables (% alcohol, time, temperature,volume solvent ⁄gram seeds)
Materials and methods
The grains were harvested during 2009 in the place ‘LaPoma’, located between 65� 56 ‘and 66� 33¢ westlongitude and between 23� 20¢ and 24� 55¢ southlatitude, Province of Salta, Argentina.The tested solvent mixtures were as follows: a-
ethanol–water mixtures, b- isopropanol–water mixtures.Four variables were studied for the extraction process:1- temperature, 2- solvent composition, 3 - contact timeand 4- the ratio volume of solvent ⁄gram of fruit.The temperature was varied between 50 and 110 �C,
and care was taken not to exceed the moleculardegradation limit for saponins (Chen et al., 2007).The Taguchi experimental design was employed to
determine the optimal conditions with a minimal num-ber of experiments, for saponins extraction from etha-nol–water and isopropanol–water mixtures in amicrowave oven. For the orthogonal array, the de-
sign-easy 7.1 software for Windows and a Taguchimatrix of L16 – four factors of four levels each – wereused (Montgomery, 2004) and (Anderson & Witcomb,2007). anova tests were performed using InfoStat, 2010(statistical software) to analyse the statistical signifi-cance of the results.To carry out the extractions, a 50 mL glass reactor
(Schott� SCHOTT Argentina S.A., Buenos Aires,Argentina) with a Teflon� (DUPONT., Buenos Aires,Argentina) cap was used. It is fitted with seals made ofsilicone and viton to prevent leakage. A temperaturesensor was fixed to the reactor by rubber bands. A
900 W Litton BGH 16650 microwave (Argentine indus-try) with a temperature sensor was used during theexperiments.The extractions in Soxhlet device were performed with
20% ethanol–water or isopropanol–water mixtures inboth cases, in a ratio of 20 mLof solvent per gramof seed.
Extraction procedure with microwave equipment
The extraction was performed as follows: 1.0000 g ofwhole seeds was put into the reactor with the chosensolvent, and this was weighed and closed. The temper-ature probe was fixed and the reactor is introduced intothe MW oven and started. When the required temper-ature was reached, the timer was started. At the end, theoven was stopped and the reactor is cooled with coldwater, opened, weighed at room temperature, and theextract was recovered, filtering through a 0.2 lm mem-brane, employing a pressure filtration syringe.
Quantification of saponins
Saponins in the extracts were derivatised by the Liber-mann–Burchard reaction, mainly based on Monje et al.(2006) although it was taken into account (Hostettmann& Marston, 2005) and (Abisch & Reichstein, 1960). Theabsorbances were measured at 528 nm with a PerkinElmer Lambda 25 spectrophotometer. Calibrationcurves were determined with oleanolic acid. Linearregression of data followed the expression:
A ¼ 4:5725� ½S� þ 0:0164 ð1ÞR2 = 0.9998
A: measured absorbance, [S]: saponin concentration(mg ⁄mL) and R2: the square correlation coefficient ofthe calibration curve.The low quantification limit for eqn (1) is
0.05 mg ⁄mL and its linearity limit is 0.65 mg ⁄mL.All measurements were performed at least five times,
and the ‘Q’ acceptance criteria applied. The confidenceinterval was established by the Student’s ‘t’ test with aprobability of 95%, resulting ±0.011 for extractionswith ethanol and ±0.010 for isopropanol.For the extraction efficiency (E), the following equa-
tion was used:E = 100 · total mass of saponins [g] ⁄mass of seed [g]
Results and discussion
Four basic variables were analysed, each one at fourlevels, to find how we can use each variable in acombination to reach the optimum conditions. Table 1shows the Taguchi experimental matrix design with thefactors and levels mentioned before. Table 2 showsTaguchi experimental matrix applied. It was made afactorial design and found that 44 = 256 assays should
Microwave extraction V. Gianna et al.2
International Journal of Food Science and Technology 2012 � 2012 The Authors
International Journal of Food Science and Technology � 2012 Institute of Food Science and Technology
be necessary, whereas with Taguchi method, onlysixteen experiments must be done to establish the bestextraction condition.The anova testing for both ethanol–water and
isopropanol–water mixtures has shown that both, fac-tors and model, are significant with a ‘P’ value less than0.05. Values for ‘F’ have shown results in the samedirection.
Extraction with MW
The matrix of experiments is shown in Table 2, whichincludes their respective average yields for both theethanol–water and isopropanol–water mixtures.
Experiment number seven showed the maximumextraction yields for both solvent mixtures (1.65% forethanol 20%, and 2.66% for isopropanol 20%). Thenumerical analysis of the results following the Taguchiprocedure (Montgomery, 2004) revealed that the opti-mal extraction conditions for the mixtures of ethanol–water and isopropanol–water were the same, namelyvolume of solvent ⁄gram of seeds: 20 mL ⁄g; time:20 min; temperature: 90 �C; alcohol concentrations:20%.The above results show that: (i) The best extractant
solvent was a mixture of isopropanol–water 20%; (ii)The higher temperature facilitated the diffusion of thesolute from the solid to the solvent.
Test for trend
To determine whether the above values corresponded tothose giving the best yields, a new series of experimentswere performed at the best experimental conditionskeeping all the variables constant except one, which wasregularly changed. The results for the isopropanol–water mixtures and ethanol–water mixtures are shownin Fig. 1a–d.Regarding the effect of solvent composition on
extraction efficiency, the tests showed that maximumextraction of saponins took place at a rather high
Table 1 Experimental design matrix
Level
Factor A
Vol. Solvent/g seed
Factor B
Time (min)
Factor C
T (�C)
Factor D
% alcohol
I 15 5 50 20
II 20 15 60 60
III 25 20 70 80
IV 30 30 90 95
Factors A, B, C and D are independent variables with four levels (levels
can be seen in the table). A: is the volume of solvent (alcohol–water
mixture) ⁄ g of seeds; B: time to apply microwave; C: the temperature at
which extraction takes place and D: % of alcohol in the solvent.
Table 2 Taguchi L16 experimental design (44)
Experiment
Factor A
Vol. Solvent/g seed
Factor B
Time (min)
Factor C
T (�C)
Factor D
% alcohol Vacancy
Experimental results(*)
Average efficiency: g saponins/100 g of
seed
Ethanol–water
mixtures
Isopropanol–water
mixtures
1 I(15) I(5) I(50) I(20) 1 0.765 ± 0.011 0.804 ± 0.010
2 I II(15) II(60) II(60) 2 0.797 ± 0.011 1.008 ± 0.010
3 I III(20) III(70) III(80) 3 1.070 ± 0.011 0.477 ± 0.010
4 I IV(30) IV(90) IV(95) 4 0.339 ± 0.011 0.012 ± 0.010
5 II(20) I II III 4 0.502 ± 0.011 0.196 ± 0.010
6 II II I IV 3 0.107 ± 0.011 0.015 ± 0.010
7 II III IV I 2 1.555 ± 0.011 2.663 ± 0.010
8 II IV III II 1 1.236 ± 0.011 1.380 ± 0.010
9 III(25) I III IV 2 0.065 ± 0.011 0.002 ± 0.010
10 III II IV III 1 0.749 ± 0.011 0.387 ± 0.010
11 III III I II 4 0.877 ± 0.011 0.898 ± 0.010
12 III IV II I 3 0.933 ± 0.011 1.568 ± 0.010
13 IV(30) I IV II 3 0.742 ± 0.011 0.921 ± 0.010
14 IV II III I 4 0.890 ± 0.011 1.565 ± 0.010
15 IV III II IV 1 0.073 ± 0.011 0.000 ± 0.010
16 IV IV I III 2 0.722 ± 0.011 0.385 ± 0.010
*Each experiment was performed with factors at the corresponding levels, indicated in roman numbers (see Table 1) and following the proceeding
explained in Materials and Methods.
This table provided the following conditions in the experiment. For example, for the experiment 1: solvent volume is 15 mL ⁄ g of seeds, applied 5 min
time, temperature 50 �C and the percentage of alcohol 20%. The experimentally measured efficiency is 0.804. This value is the average of the efficiencies
of five experiments performed in the same conditions.
Microwave extraction V. Gianna et al. 3
� 2012 The Authors International Journal of Food Science and Technology 2012
International Journal of Food Science and Technology � 2012 Institute of Food Science and Technology
polarity, but not the highest one, because pure waterexhibited a lower capacity. This fact could indicate thatthe solubility of the saponins does not depend only onthe ability of the solvents to form hydrogen bondsand ⁄or dipole–dipole interactions. Due to the fact thatispropanol gave the best performance, this may indicatethat the carbon chain also participated in the solubili-sation process.As a comparison with MAE, Soxhlet extractions were
performed. After refluxing for 310 min with ethanol20%, a 1.52% yield in saponins was obtained, whileisopropanol 20% gave 2.57% after 390 min of reflux. Itis evident that almost twenty times as much time wasnecessary to achieve the same results as with the MWmethod, indicating that microwaves had a decisiveparticipation in the solubilisation of saponins.It was previously reported that if the extraction
temperature exceeds 90 �C, the saponins may bedegraded (Chen et al., 2007). This seems to be confirmedin Fig. 1d, which shows a decrease in the extractionefficiency at temperatures higher than 90 �C.Figure 2 shows the efficiency of the extraction at
several stages, where the same grains were extracted
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35
E
ffic
ien
cy
(g o
f sa
po
nin
s p
er 1
00 g
of
seed
s)
t (min)
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35 40 45
E
ffic
incy
(g
of
sap
on
ins
per
100
g o
f se
eds)
% Alcohol
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30 35
Eff
icie
ncy
(g
of
sap
on
ins
per
100
g o
f se
eds)
Volume of solvent per gram of seed
0
0.5
1
1.5
2
2.5
3
50 60 70 80 90 100
E
ffic
ien
cy (
g o
f sa
po
nin
s p
er 1
00 g
of
seed
s)
Temperature °C
(a)
(b)
(c)
(d)
Figure 1 (a) Effect of duration of microwave radiation (—•—isopropanol; ethanol). In this figure, A: Volume solvent ⁄ gseed = 20 mL ⁄ g, C: Temperature = 90 �C, D: % alcohol = 20
remain constant. (b) Effect of alcohol concentration (—•— isopropa-
nol; ethanol). In this figure, A: Volume solvent ⁄ gseed = 20 mL ⁄ g, B: Time = 20 min, C: Temperature = 90 �C re-
main constant. (c) Effect of the variable volume of solvent ⁄ gram of
fruit (—•— isopropanol; ethanol). In this figure, B: Time = 20 -
min, C: Temperature = 90 �C, D: % alcohol = 20 remain constant.
(d) Effect of the temperature in the extraction (—•— isopropanol;
ethanol). In this figure, A: Volume solvent ⁄ g seed = 20 mL ⁄ g, B:Time = 20 min, D: % alcohol = 20 remain constant.
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
2.75
3
1 2 3
Eff
icie
nci
y (g
of
sap
on
in p
er 1
00 g
of
seed
s)
Stages
Efficiency of the extraction in stages
Figure 2 Efficiency of the extraction in stages (—•— isopropanol;
ethanol). The three successive extractions were performed in optimal
conditions (A: Volume solvent ⁄ g seed = 20 mL ⁄ g, B: Time = 20 min,
C: Temperature = 90 �C, D: % alcohol = 20) with the same seeds
and fresh solvent in each extraction.
Microwave extraction V. Gianna et al.4
International Journal of Food Science and Technology 2012 � 2012 The Authors
International Journal of Food Science and Technology � 2012 Institute of Food Science and Technology
with successive portions of fresh solvent, keeping theoptimal extractions conditions for each stage. Extrac-tion with the isopropanol mixture in the first stageremoved 2.663 g of saponins, 0.155 g in the second oneand in the third one, 0.082 g, all expressed by 100 g ofseeds. In the fourth step, the saponins level remainedunder quantification limit; therefore, the final concen-tration should be the sum of the first three; it is2.900 ± 0.010 (g of saponins ⁄100 g of seeds). Thisresult is within typical values for quinoa saponins(Repo-Carrasco et al., 2011). In the first extraction step,the yield was 91.8%; nevertheless, the extraction withethanol is shown lesser efficiency, reaching 57.2% yieldfor the first extraction step (Fig. 2).
Conclusion
The present study showed the Taguchi method to beuseful in determining the best saponin extraction con-ditions.The efficiency of the microwave extraction was
significantly higher than the Soxhlet extraction, andthe use of alcohol as a solvent enabled an easy saponinremoval.The MAE extraction time is considerably less than
with the Soxhlet method. Consequently, there is less riskof gelation of the starch, which makes filtering easierwhile avoiding charring by the concentrated sulphuricacid medium of the Lieberman–Burchard reagent.
Acknowledgments
The Science and Technology Ministry of the province ofCordoba, Argentina for its partial funding of thisresearch.
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International Journal of Food Science and Technology � 2012 Institute of Food Science and Technology