American Journal of Food Science and Nutrition Research 2015; 2(5): 138-144 Published online August 30, 2015 (http://www.openscienceonline.com/journal/fsnr)

Effect of Methods of Extraction on Physicochemical Properties of Soy Proteins (Tofu) John Dzikunoo*, George S. Ayernor, Firibu K. Saalia Department of Nutrition and Food Science, University of Ghana, Accra, Ghana

Email address [email protected] (J. Dzikunoo), [email protected] (G. S. Ayernor), [email protected] (F. K. Saalia)

To cite this article John Dzikunoo, George S. Ayernor, Firibu K. Saalia. Effect of Methods of Extraction on Physicochemical Properties of Soy Proteins (Tofu). American Journal of Food Science and Nutrition Research. Vol. 2, No. 5, 2015, pp. 138-144.

Abstract Soy proteins can be extracted using different protein coagulants. This study focused on the modifications of soy proteins from soymilk brought about by using citric acid, alkalined citric acid and the salt magnesium sulphate. The objective of this investigation was to determine the suitable levels of the extractive coagulants for production of a soy protein food (tofu); thus three different types of tofu were produced. Tofu properties evaluated were: yield, protein concentration, moisture, texture and colour with respect to the levels of coagulants. The main results showed that the yield of fresh tofu from magnesium sulphate at 10.4% produced the highest yield followed by citric acid and alkaline treated citric acid at concentration of 3% with no significant difference between the two acidic methods. On dry weight basis there were no significant variations in the protein yield of tofu with respect to the coagulants. The moisture content of the various coagulates varied significantly. Tofu from magnesium sulphate coagulation had the highest moisture content. The texture of tofu varied with the method of protein isolation. The salt precipitated proteins showed the highest textural indices such as softness, chewiness and springiness as compared to the acidic methods which also produced lighter tofu in colour. It can be seen that the three methods produced tofu with different physicochemical properties.

Keywords Soy Protein, Magnesium Sulphate, Citric Acid, Tofu and Texture

1. Introduction Proteins are essential food nutrients obtained from animal or vegetable sources and are known to influence texture and flavour of foods [1], [2]. Vegetable proteins can most extensively be found in legumes and cereals. The legume proteins are first important class of vegetable proteins and come second only to animal proteins; and a typical example is soy proteins [1]. It is well known that soy proteins contain well-balanced amino acids and they are applied in various food products such as soy sausages, tofu, tempeh, meat extenders, soy sauce, natto and miso. Soy proteins consist basically of glycinin and β-conglycinin proteins [3]. To study their physicochemical properties which affect their functionality in acidic and ionic environments, the proteins must be isolated. Soy protein isolation and precipitation has several uses in the food industry, ingredients and meat analogues [4]. According to [4], gel is a three-dimensional network in

which water is entrapped. It is visco-elastic making it solid at short time and a fluid at a long time. Gel formation according to [5] as cited by [4] involves several reactions such as denaturation, dissociation-association and aggregation. Reference [6] observed that protein particle rearrangement via the intramolecular interactions as a result of protein unfolding during heating creates negative charges which results in protein particle repulsion. The use of coagulants neutralizes the charges resulting in decrease in electrostatic repulsion between protein particles followed by aggregation via hydrophobic interactions resulting in the formation of tofu [6]. The coagulation has been observed by [7] and [8] to depend on: soybean variety and chemical composition, soymilk cooking temperature, soymilk volume, pH, coagulant type and concentration, method of adding and mixing coagulants into soymilk and coagulation time. A number of researches have been conducted in this area of tofu gel formation. At the 3rd IC-ISLAB conference, [9] characterized tofu using different coagulants: magnesium chloride, calcium chloride, lactic acid, acetic acid and rice

American Journal of Food Science and Nutrition Research 2015; 2(5): 138-144

vinegar. Reference [10] also analysed soy protein coagulation by magnesium chloride. However in this research, the characteristics of soy proteins were studied using magnesium sulphate and citric acid coagulants at different concentrations. The ability of soy proteins to form gels is the main property which is applied in this study to formulate tofu which is a widely known soy protein gel. Thus the objective of this research was to determine the suitable levels of coagulants used for the production of soy proteins (tofu).

2. Materials and Methods Mature grain soybeans (Glycine max L. Merr.) were obtained from Madina Market, Accra. Matured grain soybeans obtained were sorted out of debris and stored at 25oC for further use. Food grade coagulants; citric acid and magnesium sulphate were obtained from reputed sources. 2.1. Coagulant Concentration Coagulant concentration was very necessary to determine the suitable concentration for tofu production. Table 1 shows the variation of concentration for each coagulant used.

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2.2. Soymilk and Tofu Production Preparation of soymilk was done using the method described by [11] with modifications. 500g of soybean samples were rinsed and soaked in water overnight (16 hours) at 25oC. Hydrated soybeans were drained, rinsed and dehulled using Straub Model 4E grinding mill. Soybean samples were grounded with Elbee blender (LB-1222) on high speed with water for 2 min. The ratio of hydrated soybeans to water was 1:3 (solid/solvent) on weight basis. The slurry was filtered through 2 layers cheesecloth to separate insoluble materials (okara). The soymilk obtained was again filtered through 4 layers cheesecloth. Soymilk was heated to average temperature of 85-88oC using LPG gas cylinder. Percentage concentrations of each coagulant (citric acid and Magnesium sulphate) were added at 85-88oC and stirred for 3 s. The coagulated soymilk was left for 8 min and the soybean curd formed was transferred into a plastic strainer lined with 4 layers of cheesecloth. The cheesecloth with soy protein (tofu) samples was pressed for 30 min under a screw press to separate whey from the soy proteins. Soy protein gel was transferred into stomacher bags, sealed and stored in the refrigerator at 4oC. Figure 1 shows the flow diagram for the extraction of three different types of soy proteins (tofu) used in this study.

Fig. 1. Flow diagram for methods used in this study for the extraction of soy proteins (tofu).

2.3. Physicochemical Analyses of Soy Proteins 2.3.1. Moisture Content The moisture content of the various types of soy protein modifications was determined according to the [12] method with modifications. Soy protein gel (Tofu) samples were shredded and about 2g was weighed in moisture dishes of

known weight. These were placed in air oven at 45oC for 9 hours after which the temperature was increased to 105oC for 7 hours. Samples were then removed from the oven and cooled in the desiccator. The weight of the can and the samples were taken and the moisture content calculated. 2.3.2. Colour (L, a, b) Method The base of cylinder accompanying the Minolta CR- 310

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John Dzikunoo et al.: Effect of Methods of Extraction on Physicochemical Properties of Soy Proteins (Tofu)

Tristimulus Colour meter (Minolta Camera Co. Ltd, Osaka, Japan) was filled with samples to the brim. The colorimeter was fixed to the cylinder and the colour space parameters: Lightness (L), redness (a), and yellowness (b) were measured in triplicate. 2.3.3. Yield Calculation It was carried out according to the formula cited in the 3rd IC-ISLAB presentation [9]. i. Yield of fresh tofu ( )×

= ii.

Yield of tofu solid (%) ( )×

= = iii.

(1)

( )

(1)

( ) %

×

( )×

%

×

(2)

( )

Yield of protein ( )×

= =

(1)

( ) % %

×

( )× ×

( )

(2)

db: Dry matter basis 2.3.4. Protein Concentration Protein concentration of modified proteins was determined according to the Kjeldahl [12] method. 2.3.5. Textural Properties Instrumental texture profile analysis was carried out by TA.XT2i Texture Analyser (Stable Micro Systems) to determine hardness, fracturability, springiness and chewiness of tofu samples. Tofu samples were removed from the refrigerator and allowed to attain room temperature (25oC) before texture analysis. Samples were cut with stainless steel blade into uniform dimensions: 1cm diameter ×1.2cm height. Readings were taken in duplicate with one sample measured 10 times. All measurements were recorded as force (N). The settings for the texture analyser are: compression plate (35mm diameter), Pre-test speed (2mm/s), Test speed (1mm/s), Post-test speed (2mm/s), Distance (17mm), Load cell (25kg), Temperature (25oC) and Force (0.1N) 2.4. Statistical Analysis Using Statgraphics Centurion Version 15 and Microsoft Office Excel 2010 software, analysis of variance and multiple range tests of the data were studied. Statistical significance was set at p≤0.05.

3.1. Moisture Content As presented, Table 2 shows the mean moisture content of soy protein coagulates from the different coagulants. The moisture content of the modified soy proteins (tofu) affects the textural properties of tofu. It was therefore imperative to know the moisture contents of the tofu products. The results (Table 2) indicate significant differences among the moisture contents of the acid-based tofu and the salt-based product. Tofu gel from magnesium sulphate coagulant had the highest moisture content of 69.36%. Citric acid tofu recorded a moisture content of 62.70% and NaOH/citric acid tofu also had a moisture content of 64.98%. There was however no significant difference in the moisture content between the acidic methods. At the 3rd IC-ISLAB conference, [9] also presented a lower moisture content of tofu when acid coagulants were used as compared with salt coagulants. The presenters stated that the differences in moisture content might be as a result of the differences in molecular weight of coagulated protein fractions and the time required for tofu gel formation which also suggest that the salt precipitated product has a higher water holding capacity. Table 1. Variation of concentration for each coagulant used. Coagulant Citric acid Magnesium sulphate Citric acid & Sodium hydroxide

Concentration levels (%) 2.0, 2.5, 3.0 8.4, 10.4, 12.4 3.0

Table 2. Mean moisture content of soy protein (tofu) from different coagulants. Coagulant used Citric acid MgSO4 NaOH/citric acid

% Moisture content of tofu 62.70 ± 2.53a 69.36 ± 0.35b 64.98 ± 0.08a

Values with different superscripts within the same column are significantly different at p≤0.05

Acid coagulants used in tofu preparations tend to have a high affinity for 7S protein fractions in soymilk than 11S. Moreover the 11S fractions are heavier than 7S and hence trap a lot of water in its network during coagulation [9]. Gelation rate achieved by magnesium sulphate was observed to be slower than that of acid (citric acid) coagulant. This phenomenon was also observed by [13]. A further study, by [14] using diffusing wave spectroscopy also noted that the protein coagulation by acid is sudden and it was explained that it resulted from short-ranged interactions. The short time period of coagulation releases much whey from the bond thus trapping only a little amount of water in the protein network. 3.2. Yield of Soy Proteins (Tofu)

3. Results and Discussion The effect of extraction methods on the physicochemical properties of soy protein coagulates (tofu) are presented and discussed below:

The yields of soy proteins obtained using different concentrations of citric acid and magnesium sulphate are presented in Figures 2 and 3. Three different concentrations of citric acid (2.0%, 2.5%, 3.0%) and magnesium sulphate (8.4%, 10.4%, 12.4%) were considered. The third type of

American Journal of Food Science and Nutrition Research 2015; 2(5): 138-144

coagulation combines NaOH and citric acid at 3.0% (Table 4). Calculating the yields of fresh tofu and tofu solids was necessary to determine the amount of soy proteins (tofu) produced and also evaluating which of the concentrations gave the highest yield. The results as shown in Figures 2 and 3 indicate that increasing concentration of either citric acid or magnesium sulphate does not have any significant effect on the yield of fresh tofu and tofu solids. Protein coagulation either by acid or salt occurs at the isoelectric point (4-5) pH or at the ionic point respectively [15]. Tofu gel formation involves heating of soymilk proteins and causing the proteins to unfold exposing disulphide bonds and hydrophobic interactions which are mostly negatively charged and subsequent neutralization of these charges by the addition of the coagulants resulting in protein aggregation [16]. The neutralization of charges occurs at the isoelectric or ionic point. Addition of the different concentrations of citric acid and magnesium sulphate did not shown any significant effect in the yield of tofu because the aggregation of soy proteins will only occur at the isoelectric or ionic point. Since all the concentrations used will only coagulate and precipitate proteins at these points, there was no significant differences in the yield of tofu obtained.

Figure 2. Yield of Fresh and Total Solids of Soy proteins (Tofu) from soybean using concentrations of citric acid.

Figure 3. Yield of Fresh and Total Solids of Soy protein (Tofu) from soybean using concentrations of magnesium sulphate.

As seen from Table 3, the highest yield of tofu obtained from the three different treatments of soymilk is apparent. The results show significant differences in the fresh yield of tofu. Magnesium sulphate coagulation of soy proteins (tofu) gave the highest yield of 135.90% followed by the other citric acid treatments which showed no significant changes in yield. A study conducted by [17] and [9] also reported the same trend in the yield of tofu when acid and salt coagulants were used. The longer time period required by the salt

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coagulant as stated by [13] precipitated more proteins because it might have interacted better than the organo-acidic methods. Reference [9] further explained that the higher fresh tofu yield by salt coagulation might be as a result of the 11S fractions of soy proteins that they tend to coagulate mostly. These 11S proteins have a heavier molecular weight (about 350 kDa) as compared to 7S (170kDa) proteins coagulated mostly by acid (citric acid) coagulants. In this study there was however no significant differences in the solid yield of the various tofu treatments. Table 3. Maximum yield of fresh tofu and tofu solids obtained from the concentrations of different coagulants. Coagulant Citric acid MgSO4 NaOH/citric acid

Concentration (%) 3.0 10.4 3.0

Yield of fresh tofu (%) 104.95a 135.90b 104.23a

Yield of tofu solids (%) 40.83a 43.84a 37.20a

Values with different superscripts within the same column are significantly different at p≤0.05

3.3. Protein Content Tofu gel is basically an aggregation of soy proteins. It was therefore important to determine protein content and protein yield of the tofu obtained. The protein contents and yields of tofu in this study are presented in Table 4. The results in the table indicate no significant differences in the protein content and yield of the different concentrations of coagulants used. Citric acid coagulation of soy proteins is dependent on the isoelectric pH in the system. Reference [15] pointed out that food proteins exhibit minimum solubility at pH between 4 and 5 and maximum solubility at alkaline or more acidic pH. The effect of pH in coagulation is evident in the table 4. As pH decreased from 4.00 to 3.93 with respect to the different concentrations, it can be seen that protein concentration also decreased from 58.97% to 47.14% respectively. As pH decreased below 4.00, proteins gained net positive charge. The charge on the protein increases electrostatic repulsion and hydration of charged residues, promoting solubilisation of the protein [15] hence the decrease in protein content at 3% concentration of citric acid (pH 3.93) in this study. The protein content and yield of tofu from the salt was however not significantly different among the various concentrations. Comparing the protein contents and yields from the three coagulants, there were no significant differences. This indicates the efficacy of protein coagulation either by salt or acid. Reference [8] explained that the protein content in tofu obtained from the same variety of soybean was approximately the same. 3.4. Colour of Soy Protein Gel (Tofu) The effect of coagulant concentration on the colour of tofu is shown in Table 5. The results indicate significant differences among the colour indices measured with respect to the different concentrations of the coagulants used. As the concentration of MgSO4 is increased from 8.4% to 12.4%,

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the lightness of tofu decreased from 70.54 to 68.84 respectively. As lightness reduces, redness of tofu also decreases from -0.89 to -0.20. Tofu however becomes more yellow with increasing magnesium sulphate concentration. At

the lowest concentration of 8.4% of the salt yellowness was 16.32 and increased to 16.46 at the concentration of 12.4% of the salt. The variations in colour may be attributed to redox effects.

Table 4. Protein content and yield obtained from tofu using various concentrations of different coagulants. Coagulant Citric acid

MgSO4

NaOH/Citric acid

Concentration (%) 2.0 2.5 3.0 8.4 10.4 12.4 3.0

pH of coagulation (Isoelectric point) 4.00 3.99 3.93 4.65 4.68 4.66 4.04

Protein (%db) 58.97a 56.79a 47.14b 54.23c 54.44c 53.99c 56.31d

Protein Yield (%) 70.99a 67.98a 57.85a 56.16b 55.67b 54.61b 65.35c

Values bearing the same superscript letters in the same column are not significantly different at p≥0.05 Protein content of soybean flour (%db) =31.92 db= dry matter basis Table 5. Instrumental colour measurement of tofu obtained from concentrations of different coagulants. Coagulant

Concentration (%) 8.4 10.4 12.4

Colour indices L (Lightness) 70.54a 69.48± 0.01b 68.84± 0.03c

MgSO4

a (Redness) -0.89± 0.04a -0.48± 0.02b -0.20± 0.05c

b (Yellowness) +16.32± 0.02a +15.58± 0.03b +16.46± 0.04c

Citric acid

2 2.5 3

70.73± 0.08a 70.51± 0.04b 71.24± 0.03c

-0.18± 0.02a -0.23± 0.03b -0.81± 0.01c

+15.00± 0.06a +15.22± 0.02b +17.80± 0.03c

NaOH/Citric acid

3

70.02± 0.06d

-23± 0.01d

+15.47± 0.01d

Values with different superscripts within the same column are significantly different at p≤0.05 Soymilk: L (79.48), a (-1.47), b (+9.04), White board calibration: L (97.95), a (-0.12), b (+1.64)

Contrary to what was observed in the lightness and redness of tofu made from the salt, the lightness and redness of tofu from citric acid increases from 70.73 to 71.24 and -0.18 to 0.81 respectively. Just like Magnesium sulphate, citric acid tofu yellowness also increased with increasing concentration. The increasing lightness with increasing citric acid concentration might be due to bleaching properties of acids.

Table 6 compares the colour of whey obtained from magnesium sulphate tofu and the two citric acid treatments. The lightness in colour of whey appeared to relate to the efficacy of protein extraction. The more protein extracted the lighter the whey as evident in the three methods of protein extraction.

Table 6. Instrumental colour measurement of whey obtained from tofu using different coagulants. Coagulant

Concentration (%)

MgSO4 Citric acid NaOH/citric acid

10.4 3 3

Colour indices L 90.73± 0.03a 93.14± 0.16b 93.06 ± 0.09b

a -3.35± 0.04a -2.75± 0.08b -5.02± 0.07c

b 11.09± 0.09a 9.87± 0.11b 15.72± 0.15c

Values with different superscripts within the same column are significantly different at p≤0.05

3.5. Instrumental Textural Properties of Tofu Texture profile analysis (TPA) of tofu is necessary to understand the rheological quality of tofu. This research focused on the objective textural studies of instrumental indices of hardness, fracturability, springiness and chewiness of tofu samples as transcribed by the texturometor (See Table 7). Comparing the types of tofu made from the different

coagulants, there were significant textural differences between and among the tofu samples. The hardness of tofu indicates its resistance to compressive forces. The hardness of tofu from the two acid treatments shows no significant differences. However, the hardness of tofu products from the acid treatments was higher than tofu made from that of salt precipitation. The softness of salt precipitated tofu is due to the higher moisture content of the products (see also table 2 for moisture content). Furthermore the high moisture content

American Journal of Food Science and Nutrition Research 2015; 2(5): 138-144

of tofu made from magnesium sulphate also had an effect on the solid contents of the tofu which ultimately affected the hardness also. High solid content of acid-based-tofu implies increasing soy protein concentration [18]. The increased soy

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protein concentration may increase compactness of the tofu thus increasing the hardness.

Table 7. Texture profile of tofu made from different coagulants. Tofu type

Texture profile of tofu Hardness (N) a

Fracturability (N) a

Acid-based tofu

17.93

Alkaline-acid-based tofu

20.29a

6.53a

b

b

Salt-based tofu

12.48

a

8.38

1.32

Springiness 1.36 1.5a 1.92

Chewiness 13.25a 15.8ab

b

17.21b

Values with different superscripts within the same column are significantly different at p≤0.05

Fracturability according to [19] refers to the force with which a material fractures and a product of high degree of hardness and low degree of cohesiveness. Fracturability signifies the first break in the force-deformation curve as the food sample crumbles, cracks or shatters. In this study (table 7), it can be observed that fracturability followed the trend of hardness that is less moisture give rise to more hardness and higher fracturability. Tofu samples show some degree of springiness among them. Springiness shows how the tofu samples return to their original shape once they have been compressed and the deforming force is removed [19]. High springiness products possess a higher elasticity [19]. The results in Table 7 show that salt-based tofu was highly springy and therefore more elastic than acid-based tofu which may be due to higher hydrogen bonding which affords elasticity as a result of moisture content. The same trend in apparent in the textural index of chewiness of tofu.

providing me the moral support throughout this research.

References [1]

van Vliet, T., Martin, A.H. and Bos, M.A. Gelation and interfacial behaviour of vegetable proteins; Current Opinion in Colloid & Interface Science. Elsevier Science Ltd, 2002; 7:462-468.

[2]

Kinsella, J. E. Functional Properties of Food Proteins: A review. Critical Reviews in Food Science and Nutrition, 1976; 7, 219-280.

[3]

Thanh, V. H. and Shibasaki, K. Beta-conglycinin from soybean proteins - isolation and immunological and physicochemical properties of monomeric forms. Biochimica Et Biophys Acta, 1977; 490(2):370-384.

[4]

Renkema, J. M. S. (2001). Formation, structure and rheological properties of soy protein gels. Ph. D. thesis, Wageningen University, The Netherlands.

[5]

Hermansson, A. M. Soy protein gelation. Journal of the American Oil Chemists' Society, 1986; 63, 658-666.

[6]

Guo, S., and Ono, T. The role of composition and content of protein particles in soymilk on tofu curding by glucono-dlactone or calcium sulfate. Journal of Food Science, 2005; 70(4), 258-262.

[7]

W. Shurtleff and A. Aoyagi. Tofu and Soymilk Production. Vol. 2. New-Age Foods Study Center, Lafayette, CA, 1979.

[8]

Cai, T. D. and Chang, K. C. Characteristics of productionscale tofu as affected by soymilk coagulation method: propeller blade size, mixing time and coagulant concentration. Food Research International, 1998; 31 (4), 289-295.

[9]

Sidar. A., Utami, I. S., Rahayu, S. and Rahayu, E. S. 3rd ICISLAB. Tofu characterization using acid and salt coagulants in industrial scale, 2012.

4. Conclusion The two main categories of soy protein coagulation (organo-acid and Epsom salt) influenced the physicochemical properties of soybean proteins. On the moisture contenttexture basis of soy protein coagulates, the product from citric acid coagulant was more compact as compared to the salt coagulated tofu. However the wet citric acid tofu was lower in yield than that of the salt based product. Based on product yield, 3% citric acid and 10.4% Epsom salt were recommended for tofu production. Though there were variations in colour of tofu this does not significantly affect product quality. On the textural properties of tofu, the method of soy protein coagulation significantly influenced the textural indices of tofu measured. Important scientific notification is that pH adjustment for acidic systems and ionic balance for the salt methods are necessary in maximizing the yield of tofu.

Acknowledgements The authors would like to thank Dr. L. Abbey and Charlotte Oduro-Yeboah for their assistance on texture studies of the manuscript. Thanks to Akorfa Fiave for

[10] Hsieh, J., Yu, C. and Tsai, T. Proteomic profiling of the coagulation of soymilk proteins induced by magnesium chloride. Food Hydrocolloids, 2012; 29, 219-225. [11] Lim, B.T., Deman, J.M., Deman, L. and Buzzell, R.I. Yield and quality of tofu as affected by soybean and soymilk characteristics. Calcium Sulfate Coagulant. J. Food Sci. 55, 1990; 1088-1092, 1111. [12] AOAC. Official Methods of Analysis. Association of Official Analytical Chemist. 15th edition, Washington, D.C. 1990.

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John Dzikunoo et al.: Effect of Methods of Extraction on Physicochemical Properties of Soy Proteins (Tofu)

[13] Perera, C. O., Prabhakaran, M. P., and Valiyaveettil, S. Effect of Different Coagulants on the Isoflavone Levels and Physical Properties of Prepared Firm Tofu. Food Chemistry, 2006; 99, 492–499.

[17] Parmar, J., Sharma, H. R. and Verma, R. (2007). Effect of Source and Coagulants on the Physicochemical and Organoleptic Evaluation of Soy Tofu. J. Dairying, Foods and H. S. 2007; 26 (2), 69-74.

[14] Malaki Nik, A., Alexander, M., Poysa, V., Woodrow, L., and Corredig, M. Effect of soy protein subunit composition on the rheological properties of soymilk during acidification. Food Biophysics, 2011; 6, 26-36.

[18] Lui, H. H., Chien, J. T. and Kuo, M. I. Ultra high pressure homogenized soy flour for tofu making. Food Hydrocolloids, 2013; 32, 278-285.

[15] O. R. Fennema (Ed). Food Chemistry. Marcel Dekker, Inc. New York. 1997. Pp. 356-365. [16] Prabhakaran, M. P., Perera, C. O., and Valiyaveettil, S. Effect of different coagulants on the isoflavone levels and physical properties of prepared firm tofu. Food Chemistry, 2006; 99, 492-499.

[19] Civille, G. V. and Szczesniak, A. S. Guidelines to training a texture profile panel. Journal of Texture Studies, 1973; 4, 204223.