- Email: [email protected]
Effect of dilute lactic acid hydrolysis on the cooked viscosity of a fermented white wheat flour–yogurt mixture
Journal of Food Engineering 64 (2004) 343–346 www.elsevier.com/locate/jfoodeng
Effect of dilute lactic acid hydrolysis on the cooked viscosity of a fermented white wheat flour–yogurt mixture _ S glu ß enol Ibano
*
Engineering Faculty, Department of Food Engineering, Gaziantep University, 27310 Gaziantep, Turkey Received 24 April 2003; accepted 3 November 2003
Abstract A fermented wheat flour–yogurt mixture was hydrolyzed using dilute lactic acid solution to obtain low viscosities at high dry matters. The effect of acid concentration (0.2–1.0 N), time (2–6 h), and temperature (30–60 C) on the cooked viscosity of the soup was investigated using response surface methodology. A second order polynomial equation for predicting soup viscosity was developed. Acid concentration had the most pronounced effect on the viscosity, followed by temperature and time of hydrolysis. It is suggested that the regression equation can be used to find optimum hydrolysis conditions for the desired viscosity of the soup. 2003 Elsevier Ltd. All rights reserved. Keywords: Dilute acid hydrolysis; Wheat flour–yogurt mixture; Cooked viscosity; Response surface methodology
1. Introduction Fermented cereal–yogurt mixtures play an important role in the diets of many people in the Middle East, Asia, Africa and some parts in Europe (Economidou & Steinkrauss, 1983). Methods for preparation for such mixtures may vary from one place to another, but cereals, mostly wheat, and yogurt are always the two major components (Damir, Salama, & Mohamed, 1992). Some common examples of such products are tarhana in Turkey and Greece, kishk in Iraq and Egypt, and tahonya/talkuna in Hungary and Finland (Economidou & Steinkrauss, 1983). The practical nutritional importance of cereal–yogurt mixtures is their improvements of the basic protein diet by adding animal protein in a highly acceptable form. The dry matters of cereal–yogurt mixtures as soup is about 10%, which indicates that energy value may be as low as 100 kJ/100 g (Kocßt€ urk, 1966). Although higher energy values can be achieved by increasing the percentage of solids content, the consistency of such a soup would be too high making it unacceptable, especially for the infants. Therefore, the bulkiness caused by starch gelatinization is a major problem in the formulation of
infant cereal foods since these foods should have a lower viscosity (i.e. easy to swallow consistency) while higher energy and nutrient densities are desirable (i.e. high solids content) (Nout, 1993). Model systems to produce instant cereal–yogurt _ mixture powders by extrusion cooking (Ibano glu, Ainsworth, Wilson, & Hayes, 1995) and spray drying _ (Ibano glu, 1999) have been described. There is a growing commercial interest in producing instant cereal– yogurt mixture powders, which would involve the use of heat exchangers and pumps. Therefore, low viscosities at high dry solids concentrations would be desirable for the efficiency and economics of the process. The effect of dilute HCl hydrolysis on the cooked viscosity of a wheat flour–yogurt mixture has been _ _ studied (Ibano glu, Ibano glu, & Ainsworth, 1998). The purpose of this study was to investigate the effects of dilute lactic acid hydrolysis on the cooked viscosity of a wheat flour–yogurt mixture using response surface methodology.
2. Materials and methods 2.1. Materials
*
Tel.: +90-342-3601200; fax: +90-342-3601100. _ E-mail address: [email protected] (S glu). ß . Ibano
0260-8774/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2003.11.001
The wheat flour used was regular commercial wheat _ flour (Pnar Un, Izmir, Turkey) with a moisture content
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
344
of 12.5% (w/w) and a protein content of 11.6% (N · 5.7, w/w) (Egan, Kirk, & Sawyer, 1981). Yogurt was made from cow’s milk and had a fat content of 3.5% determined by the Soxhlet method using petroleum ether as the solvent. The lactic acid and NaOH used were of analytical purity.
3. Results and discussion Starches from different sources have been hydrolyzed using dilute acids in applications requiring a lower viscosity and higher concentration than is possible with unmodified starches (Rapaille, 1995). It is considered as an economic advantage to have a higher concentration and yet maintain fluidity in pumping (Raheem, 1995). Therefore acid treatment would lower the viscosity thus making it possible to increase the solids content of the soup without loosing its flowability. Acid concentration, hydrolysis time and temperature are the main variables affecting the viscosity of the hydrolyzed product (Shildneck & Smith, 1967). It was observed that acid concentration is the most significant factor affecting the cooked viscosity of the soup, followed by temperature and time of hydrolysis. Interaction of temperature with time was also found to be significant (Table 2). Similar results were found in our _ previous studies using dilute HCl solutions (Ibano glu et al., 1998). The effect of lactic acid concentration and temperature on the cooked viscosity of the soup at 4 h is given in Fig. 1. The viscosity decreases with increase in the acid concentration and increase in temperature. Similar trends were obtained for other reaction times (data not shown). The effect of changes in acid concentration and time on the viscosity at 45 C is given in Fig. 2. The increase in acid concentration and time result in a decrease while this decrease is less dramatic for the time.
2.2. Preparation of wheat flour–yogurt mixture Wheat flour (500 g) and yogurt (250 g) were kneaded by hand for 10 min after the addition of 100 ml tap water. The resulting batter was spread over a stainless steel tray to a depth of approximately 10 mm, incubated at 30 C for 48 h to ferment, dried in an air oven (10% m.c., w.b.) at 55 C for 48 h and ground to a particle size of <1 mm.
2.3. Experimental design and statistical analysis A central composite design with six replicates at the center point (Gacula & Singh, 1984) was used with lactic acid concentration (0.5–1.5 N), hydrolysis time (2.0–6.0 h), and temperature (30–60 C) being the hydrolysis variables. Response surface methodology was applied to the experimental data using a commercial statistical package, Design-Expert version 6.0 (Statease Inc., Minneapolis, USA). A second order polynomial was fitted to the data to obtain a regression equation. Statistical significance of the terms in the regression equation was examined. Response surface plots were generated with the same software.
Table 2 Regression equation coefficients for cooked viscosity of 10% (w/w) acid hydrolyzed soup in terms of actual variables
2.4. Dilute lactic acid hydrolysis and viscosity Wheat flour–yogurt mixture powder was subjected to dilute acid hydrolysis using lactic acid. For this purpose, the powder was mixed with lactic acid solution (40% dry matter) and incubated in a shaking water-bath according to the experimental design used (Table 1). After hydrolysis, the pH of the slurry was adjusted to the original pH of the slurry prior to hydrolysis (i.e. pH 5.5) using 50% w/w NaOH solution. The resulting slurry was simmered for 10 min and viscosity measured using a Brookfield viscometer (Brookfiled RTV, spindle no. 1) at 60 C.
Variablesa
Coefficients
R2
Constant X1 X2 X3 X12 X22 X32 X12 X13 X23
+2006 )2435 )5426 )2654 )76 (NS) +4376 +526 (NS) +2369 (NS) +3627 +2569 (NS)
0.92
Significant at P < 0:05. NS ¼ not significant. a X1 ¼ lactic acid concentration (N); X2 ¼ time (h); X3 ¼ temperature (C).
Table 1 Independent variables and experimental design levels used (LAC: Lactic Acid Concentration) Variables
Code
)1.68
)1
0
+1
+1.68
LAC (N) Time (h) Temperature (C)
X1 X2 X3
0.20 2.0 30
0.36 2.8 36
0.60 4.0 45
0.84 5.2 54
1.00 6.0 60
18079
16291
13559
12218
9039
8146
Viscosity (cP)
Viscosity (cP)
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
4520 0
345
4073 0
54
0.8 54
0.7
5.2
49
4.6
49 0.6
LAC (N)
45
45 0.5
Temp. (˚C)
40
Temp. (˚C)
4.0 40
3.4 36
0.4 36
Fig. 1. Effect of acid concentration and temperature on the cooked viscosity of acid-hydrolyzed soup at 4 h.
2.8
Time (h)
Fig. 3. Effect of temperature and time on the cooked viscosity of acidhydrolysed soup at 0.6 N lactic acid solution.
the viscosity within the range of conditions applied in this study. 16291 12218
4. Conclusions
Viscosity (cP)
8146 4073 0
0.8 5.2
0.7
4.6 0.6
LAC (N)
4.0 0.5
3.4 0.4
2.8
Time (h)
The results showed that acid concentration had the most pronounced effect on the cooked viscosity of the wheat flour–yogurt soup studied. Temperature and time of hydrolysis were found to affect the viscosity to a lesser extent. The regression equation obtained in this study can be used to find optimum acid hydrolysis conditions for the desired viscosity of the soup. The reduction of the soup viscosity at relatively higher concentrations would be desirable to increase the energy and nutrient density of the soup for infant feeding.
Fig. 2. Effect of acid concentration and time on the cooked viscosity of acid-hydrolyzed soup at 45 C.
References Similar results were obtained for other temperatures (data not shown). Finally, the effect of temperature and time on viscosity at 0.6 N lactic acid concentration is given in Fig. 3. The decrease in viscosity is more dramatic for increased temperature than time. The action of acid would reduce the molecular size of the starch molecules present in the wheat flour by hydrolyzing the glycosidic bonds between starch molecules which would result in reduced viscosity (Shildneck & Smith, 1967). The results suggest that the acid concentration is the driving force for the changes in the cooked viscosity of the soup followed by temperature. Time of hydrolysis was found to have the least effect on
Damir, A., Salama, A., & Mohamed, M. (1992). Acidity, microbial, organic and free amino acids development during fermentation of skimmed milk. Food Chemistry, 43, 265–269. Economidou, P., & Steinkrauss, K. (1983). Acid-fermented milk and milk/cereal foods. In K. Steinktauss (Ed.), Handbook of indigeneous fermented foods (pp. 271–297). New York: Marcel Dekker. Egan, H., Kirk, R. S., & Sawyer, R. (1981). Pearson’s chemical analysis of foods. London: Churchill Livingstone. Gacula, M., & Singh, J. (1984). Statistical methods in food and consumer research. New York: Academic Press, pp. 99–122. _ Ibano glu, S ß (1999). Spray drying of tarhana. Drying Technology, 17, 327–334. _ Ibano glu, S ß ., Ainsworth, P., Wilson, G., & Hayes, G. (1995). Effect of formulation on protein breakdown, in vitro digestibility, rheological properties and acceptability of tarhana, a traditional Turkish cereal food. Food Chemistry, 53, 143–147.
346
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
_ _ Ibano glu, S glu, E., & Ainsworth, P. (1998). Effect of dilute acid ß ., Ibano hydrolysis on the viscosity of tarhana, a traditional Turkish soup. International Journal of Food Science and Nutrition, 49, 463–466. Kocßt€ urk, O. (1966). Fortification of an old Turkish soup (tarhana) with soybean proteins. Vitalstoffe, 2, 77–79. Nout, M. (1993). Processed weaning foods for tropical climates. International Journal of Food Science and Nutrition, 43, 213– 221.
Raheem, D. (1995). Effect of amylase treatment on the consistency of cooked, fermented oat bran porridge. International Journal of Food Science and Nutrition, 46, 189–193. Rapaille, A. (1995). Use of starches in heat processed foods. Food Technology International Europe, 9, 73–76. Shildneck, P., & Smith, C. (1967). Production and use of acid-modified starch. In R. Whistler & E. Paschall (Eds.), Starch, chemistry and technology (pp. 403–420). New York: Academic Press.
Effect of dilute lactic acid hydrolysis on the cooked viscosity of a fermented white wheat flour–yogurt mixture _ S glu ß enol Ibano
*
Engineering Faculty, Department of Food Engineering, Gaziantep University, 27310 Gaziantep, Turkey Received 24 April 2003; accepted 3 November 2003
Abstract A fermented wheat flour–yogurt mixture was hydrolyzed using dilute lactic acid solution to obtain low viscosities at high dry matters. The effect of acid concentration (0.2–1.0 N), time (2–6 h), and temperature (30–60 C) on the cooked viscosity of the soup was investigated using response surface methodology. A second order polynomial equation for predicting soup viscosity was developed. Acid concentration had the most pronounced effect on the viscosity, followed by temperature and time of hydrolysis. It is suggested that the regression equation can be used to find optimum hydrolysis conditions for the desired viscosity of the soup. 2003 Elsevier Ltd. All rights reserved. Keywords: Dilute acid hydrolysis; Wheat flour–yogurt mixture; Cooked viscosity; Response surface methodology
1. Introduction Fermented cereal–yogurt mixtures play an important role in the diets of many people in the Middle East, Asia, Africa and some parts in Europe (Economidou & Steinkrauss, 1983). Methods for preparation for such mixtures may vary from one place to another, but cereals, mostly wheat, and yogurt are always the two major components (Damir, Salama, & Mohamed, 1992). Some common examples of such products are tarhana in Turkey and Greece, kishk in Iraq and Egypt, and tahonya/talkuna in Hungary and Finland (Economidou & Steinkrauss, 1983). The practical nutritional importance of cereal–yogurt mixtures is their improvements of the basic protein diet by adding animal protein in a highly acceptable form. The dry matters of cereal–yogurt mixtures as soup is about 10%, which indicates that energy value may be as low as 100 kJ/100 g (Kocßt€ urk, 1966). Although higher energy values can be achieved by increasing the percentage of solids content, the consistency of such a soup would be too high making it unacceptable, especially for the infants. Therefore, the bulkiness caused by starch gelatinization is a major problem in the formulation of
infant cereal foods since these foods should have a lower viscosity (i.e. easy to swallow consistency) while higher energy and nutrient densities are desirable (i.e. high solids content) (Nout, 1993). Model systems to produce instant cereal–yogurt _ mixture powders by extrusion cooking (Ibano glu, Ainsworth, Wilson, & Hayes, 1995) and spray drying _ (Ibano glu, 1999) have been described. There is a growing commercial interest in producing instant cereal– yogurt mixture powders, which would involve the use of heat exchangers and pumps. Therefore, low viscosities at high dry solids concentrations would be desirable for the efficiency and economics of the process. The effect of dilute HCl hydrolysis on the cooked viscosity of a wheat flour–yogurt mixture has been _ _ studied (Ibano glu, Ibano glu, & Ainsworth, 1998). The purpose of this study was to investigate the effects of dilute lactic acid hydrolysis on the cooked viscosity of a wheat flour–yogurt mixture using response surface methodology.
2. Materials and methods 2.1. Materials
*
Tel.: +90-342-3601200; fax: +90-342-3601100. _ E-mail address: [email protected] (S glu). ß . Ibano
0260-8774/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2003.11.001
The wheat flour used was regular commercial wheat _ flour (Pnar Un, Izmir, Turkey) with a moisture content
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
344
of 12.5% (w/w) and a protein content of 11.6% (N · 5.7, w/w) (Egan, Kirk, & Sawyer, 1981). Yogurt was made from cow’s milk and had a fat content of 3.5% determined by the Soxhlet method using petroleum ether as the solvent. The lactic acid and NaOH used were of analytical purity.
3. Results and discussion Starches from different sources have been hydrolyzed using dilute acids in applications requiring a lower viscosity and higher concentration than is possible with unmodified starches (Rapaille, 1995). It is considered as an economic advantage to have a higher concentration and yet maintain fluidity in pumping (Raheem, 1995). Therefore acid treatment would lower the viscosity thus making it possible to increase the solids content of the soup without loosing its flowability. Acid concentration, hydrolysis time and temperature are the main variables affecting the viscosity of the hydrolyzed product (Shildneck & Smith, 1967). It was observed that acid concentration is the most significant factor affecting the cooked viscosity of the soup, followed by temperature and time of hydrolysis. Interaction of temperature with time was also found to be significant (Table 2). Similar results were found in our _ previous studies using dilute HCl solutions (Ibano glu et al., 1998). The effect of lactic acid concentration and temperature on the cooked viscosity of the soup at 4 h is given in Fig. 1. The viscosity decreases with increase in the acid concentration and increase in temperature. Similar trends were obtained for other reaction times (data not shown). The effect of changes in acid concentration and time on the viscosity at 45 C is given in Fig. 2. The increase in acid concentration and time result in a decrease while this decrease is less dramatic for the time.
2.2. Preparation of wheat flour–yogurt mixture Wheat flour (500 g) and yogurt (250 g) were kneaded by hand for 10 min after the addition of 100 ml tap water. The resulting batter was spread over a stainless steel tray to a depth of approximately 10 mm, incubated at 30 C for 48 h to ferment, dried in an air oven (10% m.c., w.b.) at 55 C for 48 h and ground to a particle size of <1 mm.
2.3. Experimental design and statistical analysis A central composite design with six replicates at the center point (Gacula & Singh, 1984) was used with lactic acid concentration (0.5–1.5 N), hydrolysis time (2.0–6.0 h), and temperature (30–60 C) being the hydrolysis variables. Response surface methodology was applied to the experimental data using a commercial statistical package, Design-Expert version 6.0 (Statease Inc., Minneapolis, USA). A second order polynomial was fitted to the data to obtain a regression equation. Statistical significance of the terms in the regression equation was examined. Response surface plots were generated with the same software.
Table 2 Regression equation coefficients for cooked viscosity of 10% (w/w) acid hydrolyzed soup in terms of actual variables
2.4. Dilute lactic acid hydrolysis and viscosity Wheat flour–yogurt mixture powder was subjected to dilute acid hydrolysis using lactic acid. For this purpose, the powder was mixed with lactic acid solution (40% dry matter) and incubated in a shaking water-bath according to the experimental design used (Table 1). After hydrolysis, the pH of the slurry was adjusted to the original pH of the slurry prior to hydrolysis (i.e. pH 5.5) using 50% w/w NaOH solution. The resulting slurry was simmered for 10 min and viscosity measured using a Brookfield viscometer (Brookfiled RTV, spindle no. 1) at 60 C.
Variablesa
Coefficients
R2
Constant X1 X2 X3 X12 X22 X32 X12 X13 X23
+2006 )2435 )5426 )2654 )76 (NS) +4376 +526 (NS) +2369 (NS) +3627 +2569 (NS)
0.92
Significant at P < 0:05. NS ¼ not significant. a X1 ¼ lactic acid concentration (N); X2 ¼ time (h); X3 ¼ temperature (C).
Table 1 Independent variables and experimental design levels used (LAC: Lactic Acid Concentration) Variables
Code
)1.68
)1
0
+1
+1.68
LAC (N) Time (h) Temperature (C)
X1 X2 X3
0.20 2.0 30
0.36 2.8 36
0.60 4.0 45
0.84 5.2 54
1.00 6.0 60
18079
16291
13559
12218
9039
8146
Viscosity (cP)
Viscosity (cP)
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
4520 0
345
4073 0
54
0.8 54
0.7
5.2
49
4.6
49 0.6
LAC (N)
45
45 0.5
Temp. (˚C)
40
Temp. (˚C)
4.0 40
3.4 36
0.4 36
Fig. 1. Effect of acid concentration and temperature on the cooked viscosity of acid-hydrolyzed soup at 4 h.
2.8
Time (h)
Fig. 3. Effect of temperature and time on the cooked viscosity of acidhydrolysed soup at 0.6 N lactic acid solution.
the viscosity within the range of conditions applied in this study. 16291 12218
4. Conclusions
Viscosity (cP)
8146 4073 0
0.8 5.2
0.7
4.6 0.6
LAC (N)
4.0 0.5
3.4 0.4
2.8
Time (h)
The results showed that acid concentration had the most pronounced effect on the cooked viscosity of the wheat flour–yogurt soup studied. Temperature and time of hydrolysis were found to affect the viscosity to a lesser extent. The regression equation obtained in this study can be used to find optimum acid hydrolysis conditions for the desired viscosity of the soup. The reduction of the soup viscosity at relatively higher concentrations would be desirable to increase the energy and nutrient density of the soup for infant feeding.
Fig. 2. Effect of acid concentration and time on the cooked viscosity of acid-hydrolyzed soup at 45 C.
References Similar results were obtained for other temperatures (data not shown). Finally, the effect of temperature and time on viscosity at 0.6 N lactic acid concentration is given in Fig. 3. The decrease in viscosity is more dramatic for increased temperature than time. The action of acid would reduce the molecular size of the starch molecules present in the wheat flour by hydrolyzing the glycosidic bonds between starch molecules which would result in reduced viscosity (Shildneck & Smith, 1967). The results suggest that the acid concentration is the driving force for the changes in the cooked viscosity of the soup followed by temperature. Time of hydrolysis was found to have the least effect on
Damir, A., Salama, A., & Mohamed, M. (1992). Acidity, microbial, organic and free amino acids development during fermentation of skimmed milk. Food Chemistry, 43, 265–269. Economidou, P., & Steinkrauss, K. (1983). Acid-fermented milk and milk/cereal foods. In K. Steinktauss (Ed.), Handbook of indigeneous fermented foods (pp. 271–297). New York: Marcel Dekker. Egan, H., Kirk, R. S., & Sawyer, R. (1981). Pearson’s chemical analysis of foods. London: Churchill Livingstone. Gacula, M., & Singh, J. (1984). Statistical methods in food and consumer research. New York: Academic Press, pp. 99–122. _ Ibano glu, S ß (1999). Spray drying of tarhana. Drying Technology, 17, 327–334. _ Ibano glu, S ß ., Ainsworth, P., Wilson, G., & Hayes, G. (1995). Effect of formulation on protein breakdown, in vitro digestibility, rheological properties and acceptability of tarhana, a traditional Turkish cereal food. Food Chemistry, 53, 143–147.
346
_ Sß . Ibano glu / Journal of Food Engineering 64 (2004) 343–346
_ _ Ibano glu, S glu, E., & Ainsworth, P. (1998). Effect of dilute acid ß ., Ibano hydrolysis on the viscosity of tarhana, a traditional Turkish soup. International Journal of Food Science and Nutrition, 49, 463–466. Kocßt€ urk, O. (1966). Fortification of an old Turkish soup (tarhana) with soybean proteins. Vitalstoffe, 2, 77–79. Nout, M. (1993). Processed weaning foods for tropical climates. International Journal of Food Science and Nutrition, 43, 213– 221.
Raheem, D. (1995). Effect of amylase treatment on the consistency of cooked, fermented oat bran porridge. International Journal of Food Science and Nutrition, 46, 189–193. Rapaille, A. (1995). Use of starches in heat processed foods. Food Technology International Europe, 9, 73–76. Shildneck, P., & Smith, C. (1967). Production and use of acid-modified starch. In R. Whistler & E. Paschall (Eds.), Starch, chemistry and technology (pp. 403–420). New York: Academic Press.