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Nutrient retention of dehulled cowpea (Vigna unguiculata) at varying temperatures and time in soaking water
Bioresource Technology 57 (1996) 87-89 Copyright © 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0960-8524/96 $15.00+0.00 ELSEVIER
PII:SO960-8524(96)OOO2S-4
Short Communication Nutrient Retention of Dehulled Cowpea (Vigna unguiculata) at Varying Temperatures and Time in Soaking Water of cowpea seeds for direct consumption or for use in formulations. Soaking, therefore, aids easy removal of the seed coat and enhances the appearance, the nutritional quality and acceptance of the final product (Akpapunam, 1985; Okaka & Isieh, 1990). The literature is replete with research on cowpea (Onwueme, 1979; Akpapunam & Markakis, 1979; Ogun et al., 1989; Adewusi et al., 1991; Kon, 1979; Buescher & Chang, 1983) and similar legumes (Wang et al., 1979), but a common observation is the varying application of time and temperature of soaking either for the purpose of laboratory investigations or product development. The present work was therefore undertaken to identify optimum soaking conditions for the common variety of cowpea (V/gna unguiculata, white, black-eyed). Only critical amounts of valuable nutrients need be lost during the extraction of anti-nutrients into the soak water. Also, from an economic standpoint, reduction in time, cost of electricity, and labour in analysis or processing would be an asset.
Abstract The residual total solids, carbohydrate, and protein contents of dehulled cowpea were determined after soaking at varied combinations of temperature and time; 32°C, 45°C, 60~C, 75°C, 90~C and30, rain, 60 rain, 120 min. The loss of total solids was more dependent on time rather than temperature. Optimum retention of total solids (62.5%) was at 60°C/60 min, 90~C/60 min, for protein (69.6%) and 45°C/60 min, for carbohydrate (21.4% as sucrose) 6tTC/60 min. However, the 1.5% and 0.6% losses of protein and carbohydrate, respectively, at 600C/60 min, were considered insignificant. Hence, 60~C/60 min was recommended for processing cowpea, during which period enzymes are inactivated and gelatinization delayed. Copyright © 1996 Elsevier Science Ltd.
Key words: Soaked cowpea, nutrient varied temperature/time.
retention,
INTRODUCTION
METHODS
Legumes are widely cultivated in tropical subregions of the world. As a cheap source compared to animal protein, legumes are commonly consumed in the diet of many households in West Africa. Such legumes include cowpea (V/gna species). Different varieties of cowpea seeds are distinguished by the size and shape of the pods and colour and texture of the testa (Onwueme, 1979). A representative sample of cowpea seeds contained 90% dry matter, of which carbohydrate, protein, and ash constituted 52, 22, and 3.0%, respectively (Akpapunam & Markakis, 1979), but seeds are also known to contain toxic factors, such as tannins, trypsin inhibitors, phytate, cyanogenic glycosides, glucosinolates and flatus-inducing oligosaccharides (Adewusi & Osuntogun, 1991). Certain proportions of the valuable nutrients and the antinutrients are lost in water soaking and dehulling operations that usually precede the main processing
Sample collection and treatment The white, black-eyed variety of cowpea seeds (Vigna unguiculata) was purchased from a local market at Idah, Kogi State. The cowpea seeds were cleaned manually and sorted from weevil-infested seeds. Beans (10 g) were on each occasion soaked in 100 ml of distilled water contained in a beaker which was preheated in a regulated waterbath. The soaking was done at 20 temperature-time conditions of 32°C, 45°C, 60°C, 75°C, 90°C, and 30 min, 60 min, 90 min, 120 min. The soaked beans were removed, drained for 2 min, dehulled manually, and mashed in a mortar. Reference samples of beans were dehulled manually without pre-soaking, and ground. The recorded room temperature was 28°C. Chemical and statistical analysis Total solids, and crude protein (macrokjeldahl method) were determined according to AOAC
87
Short communication
88
Table 1. Two-way analysis of variance on percentage mean of some residual components of soaked and dehulled cowpea seed (Vigna unguiculata)
Property
Total solids Carbohydrate (as sucrose) Crude protein
Time (min) b
Temperature (°C) a
32
45
60
75
90
53.8 abcd 16.3 a 13.0 bcd
58.0 a 8.8 b 15.4 abc
57.3 ab 6.7 bc 19.4 a
56.2 abc 4.1 bcd 17.7 ab
48.6 d 1.3 d 15.2 abcd
LSD 7.12 4.96 5.57
30
60
90
120
59.2 a 11.1 a 14.7 a
54.5 ab 7.4 ab 16.1 a
54.2 abe 4.4 bc 16.3 a
51.2 bc 6.8 bc 17.5 a
LSD 5.94 4.13 4.63
Means along the same row with the same letters are not significantly different at 5% probability level. abDenote means of four and five variations of time and temperature, respectively. Control values at 28°C ambient and zero minute are 88.4% total solids, 35.6 carbohydrate, and 23.6% protein for a dehulled cowpea sample. Only 19.4% and 23.6% (control) are not significantly different at 5% probability level using the t-test.
Table 2. Deduced optimum values
Property
Total solid Carbohydrate as sucrose Crude protein
Optimum temperature (°C)
Optimum time (min)
Optimum retention value (%)
60 45 90
60 60 60
62.2 21.4 69.6
(1980) using the mashed or ground samples. Carbohydrate was determined by the phenol-sulphuric acid method (Dubois et al., 1956) as the equivalent of sucrose content. A standard sucrose solution (10% w/v) was used in preparing the calibration curve. Analysis of variance and student's t-test were used as appropriate to indicate significant differences, while the means were separated by LSD method (Steele & Torrie, 1960).
general increase in protein retention with a maximum at 60°C which was associated with denaturation of protein systems, heat-induced Maillard reaction and protein-protein interaction (Adewusi et al., 1991). Minimum variations in residual crude protein content were observed from 45 to 90°C at 60 min. Based on these results, an optimum soaking condition of 60°C/60 min is advocated for maximum retention of nutrients for cowpea food processors.
RESULTS AND DISCUSSION The results of analyses are given in Table 1 as a twoway analysis of variance, while Table 2 shows the deduced optimum values of each parameter. The optimum soaking condition for total solids retention could be achieved at 60°C/60 min, when minimum and insignificant variations were rejected. Soaking in water at a shorter time than 30 min would promote nutrient retention, while soaking at 90°C for longer times led to continuous loss of total solids (Adewusi et al., 1991). The carbohydrate trend showed a correlation with that of total solids. The least variation in residual sucrose was at 45°C. The optimum soaking temperature and time for carbohydrate retention is 60°C/60 min (Table 1). This temperature recommendation is in agreement with Okechukwu et al. (1991), who reported gelatinization of carbohydrate at 67-78°C and gave a 35-39% loss effect on sugars (Akpapunam & Markakis, 1979). For the crude protein, temperature seemed to be the more critical factor affecting its retention, rather than time (P>0.05). At above 32°C, there was a
REFERENCES
Adewusi, S. R. A. & Osuntogun, B. A. (1991). Effects of cooking on tannin content, trypsin inhibitor activity and in vitro digestibility of some legume seeds in Nigeria. Nig. Food J., 9, 139-145. Adewusi, S. R. A., Osuntogun, B. A. & Oke, O. L. (1991). Available lysine and reducing sugar content of some legume seeds and products as estimated by chemical methods. Nig. Food J., 9, 146-153. Akpapunam, M. A. & Markakis, P. (1979). Oligosaccharides of 13 American cultivars of cowpeas (Vigna Sinensis). J. Food Sci., 44, 1317-1318. Akpapunam, M. A. (1985). Characteristics of moin-moin flour prepared from cowpea/maize blends. Nig. Food J., 3, 207-208. AOAC (1980). Official Methods of Analysis, 13th edn. Association of Official Analytical Chemists, Washington, DC. Buescher, R. W. & Chang, J. S. (1983). Quality improvement of canned mung bean (Vigna radiata) sprouts. J. Food Sci., 48(6), 1598--1603. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Anal Chem., 28,
Short communication 350-356. Kon, S. (1979). Effect of soaking temperature on cooking and nutritional quality of beans. J. Food Sci., 44, 1329-1340. Ogun, P. O., Markakis, P. & Chenoweth, W. (1989). Effect of processing on certain anti-nutrients in cowpeas. J. Food Sci., 54, 4. Okaka, J. C. & Isieh, M. I. (1990). Development and quality evaluation of cowpea-wheat biscuits. Nig. Food J., 8, 56--62. Okechukwu, P. E., Rao, M. A., Ngoddy, P. O. & McWatters, K. H. (1991). Rheology of sol-gel thermal transition in cowpea flour and starch slurry. J. Food Sci., 56(6), 1744-1748. Onwueme, I. C. (1979). Crop Science BK. 2. Cassell, New York, p. 56. Steele, R. G. D. & Torrie, J. H. (1960). Principles and
89
Procedures of Statistics. McGraw-Hill, New York. Wang, H. L., Swain, E. W., Hesseltine, C. W. & Heath, H. D. (1979). Hydration of whole soya beans affects solids losses and cooking quality. J. Food Sci., 44, 1510-1513.
S. S. Aroba, a V. I. E. Ajiwe, b* I. A. Ani, a & O. A. Awoleve a aDepartment of Food Technology, Federal Polytechnic PMB 1037, Idah, Kogi State, Nigeria bDepartment of Science Technology, Nnamdi Azikiwe University, PMB 5025, Awka, Nigeria (Received 25 August 1995; accepted 19 February 1996) *Author to whom correspondence should be addressed.
PII:SO960-8524(96)OOO2S-4
Short Communication Nutrient Retention of Dehulled Cowpea (Vigna unguiculata) at Varying Temperatures and Time in Soaking Water of cowpea seeds for direct consumption or for use in formulations. Soaking, therefore, aids easy removal of the seed coat and enhances the appearance, the nutritional quality and acceptance of the final product (Akpapunam, 1985; Okaka & Isieh, 1990). The literature is replete with research on cowpea (Onwueme, 1979; Akpapunam & Markakis, 1979; Ogun et al., 1989; Adewusi et al., 1991; Kon, 1979; Buescher & Chang, 1983) and similar legumes (Wang et al., 1979), but a common observation is the varying application of time and temperature of soaking either for the purpose of laboratory investigations or product development. The present work was therefore undertaken to identify optimum soaking conditions for the common variety of cowpea (V/gna unguiculata, white, black-eyed). Only critical amounts of valuable nutrients need be lost during the extraction of anti-nutrients into the soak water. Also, from an economic standpoint, reduction in time, cost of electricity, and labour in analysis or processing would be an asset.
Abstract The residual total solids, carbohydrate, and protein contents of dehulled cowpea were determined after soaking at varied combinations of temperature and time; 32°C, 45°C, 60~C, 75°C, 90~C and30, rain, 60 rain, 120 min. The loss of total solids was more dependent on time rather than temperature. Optimum retention of total solids (62.5%) was at 60°C/60 min, 90~C/60 min, for protein (69.6%) and 45°C/60 min, for carbohydrate (21.4% as sucrose) 6tTC/60 min. However, the 1.5% and 0.6% losses of protein and carbohydrate, respectively, at 600C/60 min, were considered insignificant. Hence, 60~C/60 min was recommended for processing cowpea, during which period enzymes are inactivated and gelatinization delayed. Copyright © 1996 Elsevier Science Ltd.
Key words: Soaked cowpea, nutrient varied temperature/time.
retention,
INTRODUCTION
METHODS
Legumes are widely cultivated in tropical subregions of the world. As a cheap source compared to animal protein, legumes are commonly consumed in the diet of many households in West Africa. Such legumes include cowpea (V/gna species). Different varieties of cowpea seeds are distinguished by the size and shape of the pods and colour and texture of the testa (Onwueme, 1979). A representative sample of cowpea seeds contained 90% dry matter, of which carbohydrate, protein, and ash constituted 52, 22, and 3.0%, respectively (Akpapunam & Markakis, 1979), but seeds are also known to contain toxic factors, such as tannins, trypsin inhibitors, phytate, cyanogenic glycosides, glucosinolates and flatus-inducing oligosaccharides (Adewusi & Osuntogun, 1991). Certain proportions of the valuable nutrients and the antinutrients are lost in water soaking and dehulling operations that usually precede the main processing
Sample collection and treatment The white, black-eyed variety of cowpea seeds (Vigna unguiculata) was purchased from a local market at Idah, Kogi State. The cowpea seeds were cleaned manually and sorted from weevil-infested seeds. Beans (10 g) were on each occasion soaked in 100 ml of distilled water contained in a beaker which was preheated in a regulated waterbath. The soaking was done at 20 temperature-time conditions of 32°C, 45°C, 60°C, 75°C, 90°C, and 30 min, 60 min, 90 min, 120 min. The soaked beans were removed, drained for 2 min, dehulled manually, and mashed in a mortar. Reference samples of beans were dehulled manually without pre-soaking, and ground. The recorded room temperature was 28°C. Chemical and statistical analysis Total solids, and crude protein (macrokjeldahl method) were determined according to AOAC
87
Short communication
88
Table 1. Two-way analysis of variance on percentage mean of some residual components of soaked and dehulled cowpea seed (Vigna unguiculata)
Property
Total solids Carbohydrate (as sucrose) Crude protein
Time (min) b
Temperature (°C) a
32
45
60
75
90
53.8 abcd 16.3 a 13.0 bcd
58.0 a 8.8 b 15.4 abc
57.3 ab 6.7 bc 19.4 a
56.2 abc 4.1 bcd 17.7 ab
48.6 d 1.3 d 15.2 abcd
LSD 7.12 4.96 5.57
30
60
90
120
59.2 a 11.1 a 14.7 a
54.5 ab 7.4 ab 16.1 a
54.2 abe 4.4 bc 16.3 a
51.2 bc 6.8 bc 17.5 a
LSD 5.94 4.13 4.63
Means along the same row with the same letters are not significantly different at 5% probability level. abDenote means of four and five variations of time and temperature, respectively. Control values at 28°C ambient and zero minute are 88.4% total solids, 35.6 carbohydrate, and 23.6% protein for a dehulled cowpea sample. Only 19.4% and 23.6% (control) are not significantly different at 5% probability level using the t-test.
Table 2. Deduced optimum values
Property
Total solid Carbohydrate as sucrose Crude protein
Optimum temperature (°C)
Optimum time (min)
Optimum retention value (%)
60 45 90
60 60 60
62.2 21.4 69.6
(1980) using the mashed or ground samples. Carbohydrate was determined by the phenol-sulphuric acid method (Dubois et al., 1956) as the equivalent of sucrose content. A standard sucrose solution (10% w/v) was used in preparing the calibration curve. Analysis of variance and student's t-test were used as appropriate to indicate significant differences, while the means were separated by LSD method (Steele & Torrie, 1960).
general increase in protein retention with a maximum at 60°C which was associated with denaturation of protein systems, heat-induced Maillard reaction and protein-protein interaction (Adewusi et al., 1991). Minimum variations in residual crude protein content were observed from 45 to 90°C at 60 min. Based on these results, an optimum soaking condition of 60°C/60 min is advocated for maximum retention of nutrients for cowpea food processors.
RESULTS AND DISCUSSION The results of analyses are given in Table 1 as a twoway analysis of variance, while Table 2 shows the deduced optimum values of each parameter. The optimum soaking condition for total solids retention could be achieved at 60°C/60 min, when minimum and insignificant variations were rejected. Soaking in water at a shorter time than 30 min would promote nutrient retention, while soaking at 90°C for longer times led to continuous loss of total solids (Adewusi et al., 1991). The carbohydrate trend showed a correlation with that of total solids. The least variation in residual sucrose was at 45°C. The optimum soaking temperature and time for carbohydrate retention is 60°C/60 min (Table 1). This temperature recommendation is in agreement with Okechukwu et al. (1991), who reported gelatinization of carbohydrate at 67-78°C and gave a 35-39% loss effect on sugars (Akpapunam & Markakis, 1979). For the crude protein, temperature seemed to be the more critical factor affecting its retention, rather than time (P>0.05). At above 32°C, there was a
REFERENCES
Adewusi, S. R. A. & Osuntogun, B. A. (1991). Effects of cooking on tannin content, trypsin inhibitor activity and in vitro digestibility of some legume seeds in Nigeria. Nig. Food J., 9, 139-145. Adewusi, S. R. A., Osuntogun, B. A. & Oke, O. L. (1991). Available lysine and reducing sugar content of some legume seeds and products as estimated by chemical methods. Nig. Food J., 9, 146-153. Akpapunam, M. A. & Markakis, P. (1979). Oligosaccharides of 13 American cultivars of cowpeas (Vigna Sinensis). J. Food Sci., 44, 1317-1318. Akpapunam, M. A. (1985). Characteristics of moin-moin flour prepared from cowpea/maize blends. Nig. Food J., 3, 207-208. AOAC (1980). Official Methods of Analysis, 13th edn. Association of Official Analytical Chemists, Washington, DC. Buescher, R. W. & Chang, J. S. (1983). Quality improvement of canned mung bean (Vigna radiata) sprouts. J. Food Sci., 48(6), 1598--1603. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Anal Chem., 28,
Short communication 350-356. Kon, S. (1979). Effect of soaking temperature on cooking and nutritional quality of beans. J. Food Sci., 44, 1329-1340. Ogun, P. O., Markakis, P. & Chenoweth, W. (1989). Effect of processing on certain anti-nutrients in cowpeas. J. Food Sci., 54, 4. Okaka, J. C. & Isieh, M. I. (1990). Development and quality evaluation of cowpea-wheat biscuits. Nig. Food J., 8, 56--62. Okechukwu, P. E., Rao, M. A., Ngoddy, P. O. & McWatters, K. H. (1991). Rheology of sol-gel thermal transition in cowpea flour and starch slurry. J. Food Sci., 56(6), 1744-1748. Onwueme, I. C. (1979). Crop Science BK. 2. Cassell, New York, p. 56. Steele, R. G. D. & Torrie, J. H. (1960). Principles and
89
Procedures of Statistics. McGraw-Hill, New York. Wang, H. L., Swain, E. W., Hesseltine, C. W. & Heath, H. D. (1979). Hydration of whole soya beans affects solids losses and cooking quality. J. Food Sci., 44, 1510-1513.
S. S. Aroba, a V. I. E. Ajiwe, b* I. A. Ani, a & O. A. Awoleve a aDepartment of Food Technology, Federal Polytechnic PMB 1037, Idah, Kogi State, Nigeria bDepartment of Science Technology, Nnamdi Azikiwe University, PMB 5025, Awka, Nigeria (Received 25 August 1995; accepted 19 February 1996) *Author to whom correspondence should be addressed.