Effect of saponin on the surface properties of quinoa proteins

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1 International Journal of Food Properties ISSN: (Print) (Online) Journal homepage: Effect of saponin on the surface properties of quinoa proteins G. S. Chauhan, W. Cui & N. A. M. Eskin To cite this article: G. S. Chauhan, W. Cui & N. A. M. Eskin (1999) Effect of saponin on the surface properties of quinoa proteins, International Journal of Food Properties, 2:1, 13-22, DOI: / To link to this article: Copyright Taylor and Francis Group, LLC Published online: 02 Sep Submit your article to this journal Article views: 153 View related articles Citing articles: 9 View citing articles Full Terms & Conditions of access and use can be found at

2 INTERNATIONAL JOURNAL OF FOOD PROPERTIES, 2(1), (1999) EFFECT OF SAPONIN ON THE SURFACE PROPERTIES OF QUINOA PROTEINS G. S. Chauhan 1 *, W. Cui 2, and N. A. M. Eskin 2 1 Dept. of Food Science and Technology G.B. Pant University of Agriculture and Technology Pantnagar , U.P. India 2 Dept. of Food and Nutrition, Faculty of Human Ecology University of Manitoba,Winnipeg R3T 2N2, Canada; 'Corresponding author ABSTRACT Quinoa seeds were cleaned, ground, and defatted using hexane. The defatted flour was dispersed and stirred in alkali to extract the proteins, one half of which was desaponized with methanol. The whole seed flour, protein, and desaponized protein fractions were compared for their functional properties. Removal of saponins increased water hydration capacity and lowered the fat binding capacity. The emulsion capacity was also reduced in the desaponized protein although emulsion the stability increased markedly. A slight decrease in buffer capacity was observed which was attributed to the removal of saponins. The foaming capacity and foam stability were affected in the similar manner to that of the emulsifying properties. The removal of saponins also lowered the total nitrogen solubility of quinoa proteins. INTRODUCTION Quinoa (chenopodium quinoa Wild.) a cereal crop grown in the Andes is receiving considerable attention as a food source because of its high protein content and nutritional value compared to other major cereals (Gonzalez et al., 1989). The nutritional quality of quinoa proteins has been evaluated by a number of research workers (White et al., 1955; Felipe and Conrad, 1957; Mahoney et al., 1975; Gross 13 Copyright 1999 by Marcel Dekker, Inc.

3 14 CHAUHAN, CUI, AND ESKIN et al., 1989; Gonzalez et al., 1989; Chauhan et al., 1992; Chauhan et al., 1998). Acceptability of proteins as food sources, however, depends on their functional as well as nutritional properties. The functional properties of a number of plant proteins have been studied extensively (Yasumatsu et al, 1972; Satterlee et al, 1975; Satterlee et al., 1976; McWatters and Cherry, 1977; Torgersen and Toledo, 1970; Akoiet al., 1980; Manak et al, 1980; Sathe and Salunkhe, 1981a,1981b; Ma, 1983). However, negligible information is available on the functional properties of quinoa proteins and how the presence of saponins affect these properties. The present investingation was undertaken to determine the surface properties of quinoa proteins as affected by saponins. MATERIALS Quinoa seeds of chltivar, D-407 Colorado Semi-Dwarf, grown in Rossburn, Manitoba were provided by Mr. H. Hrubeneniuk. The seeds were cleaned manually to remove any foreign materials present. METHODS Isolation of Proteins Quinoa seeds were ground in a Wiley Mill and passed through a 40 mesh sieve. The ground material was defatted and then suspended in alkali solution (0.015N NaOH, solid to solvent ratio of 1:10 which provided maximum protein recovery during preliminary trials) and stirred on a mechanical shaker for 2 hr at 25 C. The slurry was filtered through a double layer of cheese cloth to remove the hulls and then centrifuged at 4000xG for 20 min. The ph of the supernatant was adjusted to 4.7 using 10% HC1 to precipitate the proteins. The precipitated proteins separated out by centrifugation were then neutralized and freeze-dried. One half, of the dried protein material was extracted with methanol to remove the saponins. Both samples of proteins (original and desaponized) were stored under refrigeration until analyzed. Moisture and Protein Analysis The proximate composition of the quinoa seed has been reported by Chauhan et al. (1992). Both samples of protein were analyzed for moisture and protein content using AOAC (1984) standard methods. A factor of 5.7 was used to convert nitrogen to protein. Hydration and Surface Properties Water hydration capacity was determined according to the method of Quin and Paton(1979). Weighed quantity (5 g) of sample was transferred to a centrifuge tube (50 ml) and weighed the tube and sample. Then distilled water was added in

4 EFFECT OF SAPONIN ON QUINOA PROTEINS 15 unmeasured increments till a paste consistency was achieved. It was followed by centrifugation at 4000 rpm for 10 min. Supernatant, if any was discarded and the tube was again weighed. Water hydration capacity was calculated as ml of water absorbed/gm of protein material. Whipping and emulsifying properties were measured by the method of Yasumatsu et al. (1972). Whipping properties include foam expansion and foam stability. Foam expansion was measured by shaking 50 ml aqueous suspension (1%) of protein horizontally (6 cycles per second with 5 cm amplitude of shaking) for 1 min in 100 ml measuring cylinder. The resulting foam volume was measured and expressed as foam expansion (%). Foam stability was measured by measuring the foam volume after allowing the foam to stand for varying period of time. Emulsifying properties were evaluted in terms of emulsion capacity and emulsion activity. For emulsion capacity, a known quantity (7 g) of protein preparation was suspended in 100 ml water and then added 100 ml soybean oil followed by emulsification of mixer in a homogenizer at rpm for 1 min. The emulsion obtained was centrifuged at 1300xG for 5 min. The emulsion activity was calculated as the ratio of height of emulsified layer to the total emulsion layer and expressed as percent. Emulsion stability was measured as emulsion activity but after heating emulsion at 80 C for 30 min. The ratio of remaining emulsion to total height of emulsion expressed as per cent represents emulsion stability. The method described by Lin et al. (1974) was used to measure fat binding capacity. For its determination, weighed quantity (0.5 g) of sample was thoroughly mixed with 3 gm of corn oil in centrifuge tube (15 ml) and allowed to stand for 30 min followed by centrifugation at 1610xG for 25 min. The volume of free oil was measured. Fat absorption was expressed as the amount of corn oil bound by 100 g sample. Buffering capacity was estimated as described by Sathe and Salunkhe (1981). Sample was dispersed in 100 ml distilled water to form 0.5% protein dispersion. Initial ph was recorded and then dispersion was titrated to a desired ph by using 0.1 N HC1 or 0.1 N NaOH. Buffering capacity = (mg of titrant)/[weight of protein x A(pH)] (1) Nitrogen solubility was obtained using the method described by MA (1983). For this, 1% dispersion of protein was stirred for 20 min at room temperature and adjusted ph to 1.5 to 11.0 using 1 N NaOH or 1 N HC1 and centrifuged at looooxg for 30 min & estimated N 2 content in supernatant. Water hybration capacity and fat binding capacity denote the maximum amount of water and fat, respectively that a protein material can take up/bind and retain under food formulation conditions. Emulsifying properties consist of emulsion capacity and emulsion stability of protein dispersion. Emulsion capacity is the ability of a protein dispersion to emulsify oil whereas emulsion stability is the ability of the enulsion to remain stable and unchanged. Buffering capacity is defined as the capacity of proteins to resist any change in ph and mainly depends on the number of ionized -NH2 and -COOH groups. Whipping properties of a protein dispersion are measured in terms of foaming capacity and foaming stability. Foaming capacity or expansion is defined as percent of volume

5 16 CHAUHAN, CUI, AND ESKIN increase of a dispersion due to whipping and is the function of protein dispersibity, whereas foam stability is retention of foam volume over a definite period of time and is a reflection of film integrity, permeability to gas and film mechanical strength. RESULTS AND DISCUSSION The moisture and protein content of protein preparation (A), desaponized protein (B) and whole quinoa flour were 5.3, 7.3, 12.4% and 52.4, 72.1 and 13.7%, respectively. Water Hydration (WHC) and Fat Binding Capacity (FBC) The results shown in Table 1 revealed that desaponized protein (B) had the maximum water holding capacity (7.2 g/g) and lowest fat binding capacity (72.1%)comared to the other protein preparation (A) and flour. On protein basis, however, the differences in WHC of sample A and whole flour did not vary much. The WHC of quinoa proteins obtained in this investigation is quite high comared to the values reported by MA (1983) for oat, soybean and wheat proteins. As expected from the values for WHC, quinoa proteins exhibited lower values for FBC than reported for other plant proteins. Emulsifying Properties The emulsifying properties defined as emulsion activity (EA) and emulsion stability (ES), are presented in Table 1. The EA was much lower and ES was much higher for desaponized proteins compared to proteins with saponins. This suggested that saponins have an important influence on emulsifying properties of guinoa proteins. Much higher EA and ES values were found for quinoa proteins compared to the values reported for soybean protein products by Yasumatsu et al. (1972). Buffering Capacity (BC) Based on results for BC presented in Table 2, all samples exhibited a high buffer capacity below ph 4.0 and above ph However, the desaponized protein showed the lowest buffer capacity in the ph range of 4-11 compared to protein and flour. All samples registered the highest BC at ph 2.0. The BC of quinoa proteins was higher in the acidic range with the lowest BC values recorded at phs 4.0 and 9.0 for all samples except for whole seed flour in the acidic ph range. In the latter case the BC minimum shifted to ph 6.0 which probably reflects the more complex system of the flour as compared to protein preparations. Studies by Sathe and Salunkhe (1981) with Great Northern bean proteins and Canella et al. (1979) with a sunflower protein isolate reported similar trends in the buffer capacity.

6 m m n H O *1 Table 1. Effect of saponin on water hydration capacity (WHC), fat binding capacity (FBC), emulsion capacity (EC), and emulsion -a stability (ES) of quinoa proteins. Sample WHC, g/g FBC, % EC,% ES, % a o SB PB SB PB SB PB SB PB O >*a I A 3.0± ± ± ± ± ± z B ^ C ND 35'.0il.0 ND Note All the values are means of 2 replicates A - Protein preparation; B - Desaponized Proteins; C - Whole seed flour SB- Sample weight basis; PB- Protein weight basis ND- Not Determined

7 18 CHAUHAN, CUI, AND ESKIN Table 2. Buffering capacity of quinoa proteins at different ph. ph A Sample B Note All values are average of two replicates A - Protein preparation; C - Whole quinoa flour B - Desaponized proteins Table 3. Effect of saponin on foaming capacity (%)' and foaming stability (%) of quinoa proteins. PH A Sample B Note All values are average of two replicates x Values for zero hrs represent foaming capacity

8 EFFECT OF SAPONIN ON QUINOA PROTEINS Time (Hrs) 16 Figure 1. Effect of saponins on foaming stability of quinoa proteins. I whole seed flour, % protein with saponins, A desaponized protein. Whipping Properties The whipping properties of quinoa proteins in terms of foaming capacity, and stability are shown in Table 3 and depicted in Fig. 1. A marked effect of saponins on whipping properties was evident by the low foaming capacity of desaponized protein compared to the protein with saponins. The foaming capacity of the desaponized protein, however, was still higher than the whole seed flour. The reverse was found with respect to the foaming stability which was much higher in the absence of saponins. The rate of decrease in the foaming stability of the sample with saponins remained fairly constant during the first 4 hr, whereas the foaming stability of desaponied protein remained unchanged after 2 hrs. The foaming capacity as well as foaming stability of whole seed flour were much lower compared to the protein preparations. Nitrogen Solubility The effect of saponins on the nitrogen solubility of quinoa proteins is presented in table 4 and depicted in Figure 2. The minimum nitrogen solubility in both protein

9 20 CHAUHAN, CUI, AND ESKIN Table 4. Effect of saponin on nitrogen solubility (%) of quinoa proteins at different ph. PH Sample Note All values are average of two replicates A - Protein preparation; B - Desaponized proteins litroger) Solub ility PH Figure 2. Effect of saponins on nitrogen solubility of quinoa proteins, with saponins, desaponized protein. protein

10 EFFECT OF SAPONIN ON QUINOA PROTEINS 21 samples was observed at ph 4 and 5, with the lower value for the desaponized proteins. Total nitrogen sloubility was considerably reduced by the removal of saponins. The protein sample with saponins showed 98% of nitrogen solubility at ph 10 whereas the corresponding value for desaponized protein was only 72.3%. In the acidic range the maximum nitrogen solubility value for the protein sample was 90.7% at ph 2.0 compared to 38.4% for desaponized protein at ph 1.5. CONCLUSIONS Saponins have a marked effect on the surface properties of quinoa proteins. However, emulsifying properties and whipping properties were affected to a great extent as compared to fat binding and water hydration capacity. The effect on nitrogen solubility was inter mediate. ACKNOWLEDGMENT The authors are grateful to the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian International Development Agency (CIDA) for supporting Dr.G.S. Chauhan as an NSERC/CIDA research associate which permitted this work to be carried out. REFERENCES AOAC "Official Methods of Analysis". Association of official Analytical Chemists, Washington, D.C. Aoki, H., Taneyama, O., and Inami, M Emulsifying properties of soy protein: Characteristics of 7S and 11S proteins. Journal of Food Science. 5: Canella, M., Castriotta, G., and Bernardi, A Functional and physicochemical properties of succinylaed and acetylated sunflower proteins. Ledensm. Wiss. u-technol. 12: Chauhan, G. S., Eskin, N. A. M., and Tkachuk, R Distribution of nutrients and antinutrients in quinoa seed fractions. Cereal Chemistry. 69: Chauhan, G. S., Cui, W., and Eskin, N. A. M Effect of saponins extraction on the nutritional quality of quinoa proteins. Journal of Food Science and Technology (Submitted). Felipe, Q. P., and conrad, A. E Nutritive value of quinoa proteins. Journal of Agriculture and Food Chemistry. 5: Gonzalez, J. A., Roldan, A., Gallardo, M., Escudero, T., and Prado, F. E Quantitative determinations of chemical compounds with nutritional value from Inca crops: Chenopodiumquinoa. Journal of Plant Foods for Human Nutrition. 39:

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