Functional properties and biscuit making potential of soybean and cassava flour blends. P.I. AKUBOR. â and M.U. UKWURU. Department of Food science and ...
Plant Foods for Human Nutrition 58: 1–12, 2003. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.
Functional properties and biscuit making potential of soybean and cassava flour blends P.I. AKUBOR∗ and M.U. UKWURU Department of Food science and Technology, Federal Polytechnic, P.M.B. 1037, Idah, Kogi State, Nigeria (∗ author for correspondence)
Abstract. Blends of soybean flour (SF) and cassava flour (CF) were prepared on a replacement basis (CF/SF, 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 0:100). Functional properties of the blends were determined. Biscuits were produced from the blends and evaluated for their protein and fat contents, and physical and sensory properties. The SF had a greater capacity to absorb water and oil than the blends which increased with increasing levels of SF. The bulk densities of the blends were low which would be an advantage in the formulation of supplementary foods. The flour blends also exhibited low emulsifying properties, thus, would not be useful in products where emulsion activity is of prime importance. The foam capacity of the blends was low, but foams prepared from them were moderately stable. All the flours showed good gel forming capacity. The protein and fat contents of the flour blend biscuits increased with increasing levels of SF. The width, thickness and spread ratio were not significantly (p > 0.05) different among the flour blend biscuits. Biscuits weights, however, decreased with increased SF substitution. Sensory evaluation indicated that there were no significant differences in color, texture, flavor, taste and overall acceptability of the flour blend biscuits. At 50% level of SF incorporation, biscuits had higher scores for all the sensory attributes evaluated. Above this level, biscuits received lower sensory scores. Key words: Biscuit making, Cassava, Flour blend, Functional properties, Quality acceptance, Soybean
Introduction In the tropics, cassava (Manihot esculenta crantz) is the most productive crop and the cheapest source of calories for man [1]. Cultivation of cassava in Nigeria by farmers has recently increased tremendously [2]. The rapid expansion of cassava production is due to its adaptation to shorter periods of fallow (land left uncultivated for sometime). It is able to thrive without irrigation in areas where the dry season ranges from 1 to 5 months and as increase in demand in the quest for cheaper staple foods in urban centers [3]. In Nigeria, cassava is processed into lafun, gari, achicha, akpu and puraka [4]. These products are well liked and consumed daily. However, because cassava has a low protein content (1–2%), populations which eat a lot of it do
GSB/Prepr: XPS103081 QUAL 3728-DISK / Pipsnr. 5090202 / JM.KLUTEX2K (qualkap:bio1fam) v.1.2 qual3728.tex; 9/02/2004; 15:36; p.1
2 not receive an adequate intake of good quality protein [5]. Such populations are prone to malnutrition. Earlier efforts to increase the protein quality and quantity of cassava include crossing of different cassava dones and growing micro- organisms on the peeled tubers [6, 7]. A more effective approach to avoid nutritional problems in populations consuming a large amount of cassava is protein enrichment of cassava flour used in the preparation of cassava products. Soybeans contain 40% high quality protein with excellent digestibility [8]. The use of soybean protein is increasing because of its functional properties and being an economic source of dietary protein. However, soybeans are rich in lysine but low in sulphur amino acids [8]. On the other hand, cassava is poor in lysine and has a moderate content of sulphur amino acids [4]. Therefore, on the basis of complementarity’s, the combination of cassava and soybean flours in food formulations could potentially provide most of the nutrients needed in human diets. Bread made from cassava and soybeans flour blends [9] and tapioca macaroni [10] have been some of the most promising protein enriched products prepared from cassava tubers. Protein enrichment of gari, a cassava product, has been reported [11]. Fish protein has been added to cassava flour to prepare wafers [12]. Acceptable biscuits have been produced from 100% cassava flour. However, such products had low protein contents and poor textural characteristics. The proteins of soybean and cassava flours are non-gluten forming; such flours would make good biscuits [13]. The economic impact of the use of soybean/cassava flour blends in making biscuits lies in the replacement of imported wheat flour with locally grown crops. However, supplementing non-wheat flours involves technological difficulties and impairment of baking quality. There is also a dearth of information on the functional properties of soybeans/cassava flour blends and that information is essential in determining potential uses of these blends in food formulations. This study was, therefore, undertaken to determine the functional properties of soybean and cassava flour blends, and to evaluate the performance of the blends in a baked products, biscuits.
Materials and methods Source of raw materials Soybean seeds (white variety) were purchased from a local market while the freshly harvested sweet cultivar of cassava root (White variety 11–12 months old) were purchased from a local farmer, all in Idah town, Kogi State, Nigeria.
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3 Soybean flour The soybean seeds were cleaned of dust and other extraneouss materials, washed in tap water and boiled (100 ◦ C, 30min) in a plain aluminum pot with a lid. The parboiled seeds were dehulled manually, washed in tap water and then sun dried (32 ± 2 ◦ C, 48–72 h). The kernels were milled in a hammer mill (Model RLA 201-80014, UK) and screened through a 40 mesh sieve (British Standard). The flour was packed in high density polyethylene bags (0.77 mm thickness) and heat-sealed (Hulme-Martin H-M 1800 Model). Cassava flour The cassava roots were cleaned of sand, peeled manually, washed in tap water and cut into uniform-sized slices (3 cm × 1 cm) of 0.4 cm thickness with a sharp stainless knife. The slices were incubated in sterile distilled water contained in a sterile covered basin for 48h at 30± 2 ◦ C. During the wild fermentation, the water was poured off the slices at 24 h intervals. The fermented slices were sun- dried (32 ± 2 ◦ C, 48–72 h), milled in a hammer mill (Model RLA 201-80014,UK) and screened through a 40 mesh sieve (British standard). The flour was packed in high density polyethylene bags (0.77 mm thickness), heat sealed (Hulme-Martin H-M 1800 Model) and then stored in a freezer until used. Flour blending Soybean flour samples (10, 20, 30, 40, 50, 60, 70 and 80%) were mixed with cassava flour on a replacement basis and blended in an electrical blender (Model L 2B, Waterside, UK) for 2–3 min at full speed. The flour samples were packed in high density polyethylene bags and heat-sealed (Hulme-Martin H-M 1800 Model). Proximate analyses The crude protein (KjeIdahl, NX 6.25), fat (Solvent extraction), ash and moisture were determined according to the AOAC [14] methods (47.021, 14.018, 14.006 and 14.004, respectively). Total carbohydrate was obtained by difference (100-%moisture +%crude protein +% crude fat +% ash +%fiber). The calorie value was calculated using Atwater factors (4 × protein, 9 × fat and 4 × total carbohydrate).
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4 Evaluation of functional properties Packed bulk density was determined as described by Okaka & Potter [15] and expressed as g/km3 . The least gelation concentration was determined by a modification of the method of Coffman and Garcia [16] as described by Sathe et al. [17]. Foam capacity (FC) and foam stability (FS) were determined as described by Narayana & Narasinga Rao [18]. The volume of foam at 60 sec after whipping was expressed as FC. The foam volume was recorded 1 h after whipping to determine the FS as percent of the initial foam volume. The emulsion activity and stability were determined as described by Yassumatsu et al. [19]. The water and oil absorption capacities were determined by the method of Sosulski, et al. [20] and values expressed as ml/g flour. Preparation of biscuits Biscuits were prepared according to the formula of Niishibori and Kawashiki [21] with slight modifications. Sucrose and margarine were used in place of glucose and butter in the original formula [22]. The basis formulation used was 49.5% flour, 20% margarine, 10% beaten whole egg, 20% sucrose and 0.5% baking powder. The amounts of soybean flour which replaced cassava flour were 10, 20, 30, 40, 50, 60, 70, and 80%. The dry ingredients were mixed thoroughly. Margarine was added and rubbed in until uniform. The egg was added and the dough thoroughly kneaded on a flat clean stainless metal table for 5 min. The dough was thinly rolled on a sheeting board to 19 mm thickness, cut to 69 mm width and baked on greased pans for 15 min at 160 ◦ C in an air oven (F1 Foem, Model 4BF, Germany). The biscuits were cooled at 30 ± 2 ◦ C and heat-sealed (Hulme-Martin H-M 1800 Model) in high density polyethylene bags (0.77 mm thickness). Eight replicates of biscuits were baked for each experimental treatment. Physical evaluation of biscuits Biscuit width (W) and thickness (T) were measured with a vernier caliper. Weights were determined using a Mettler digital top loading balance (Mettler, PC 400, Switzerland). Spread ratio (SR) was calculated by the method of Ordorica- Falomir and Paredes – Lopez [23] as SR = W/T. Sensory evaluation Biscuit samples including the 100% cassava flour (Control) were evaluated by a panel of ten untrained judges for the sensory attributes of color, flavor, and texture using a six point structured hedonic scale [8]. Key to biscuit score was 6 = excellent, 5 = very good, 4 = good, 3 = fair, 2 = poor and 1 = very
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5 Table 1. Proximate composition of soybean and cassava flours∗ Property (%)
Soybean flour
Cassava flour
Moisture Crude fat Total carbohydrate Crude fiber Ash Crude protein
8.0 ± 0.72 25.0 ± 0.38 23.8 ± 0.09 4.0 ± 0.89 6.0 ± 1.04 38.2 ± 0.31
8.5 ± 0.94 0.3 ± 1.90 189.2 ± 0.41 1.2 ± 0.94 1.0 ± 0.49 1.0 ± 1.41
∗ , Means ± SD of 3 determinations.
poor. A 6-point structured hedonic scale (1 = disliked extremely, 6 = liked extremely) was also used to score overall acceptability of the biscuits. The judges consisted of students and staff of the polytechnic community familiar with favorable and unfavorable biscuit quality characteristics. Biscuit sample were tested in triplicate. Each quality was evaluated separately at 30 min intervals in the mid morning. The assessments were conducted under fluorescent light in a special room for sensory evaluation. At each session, each panelist judged six coded biscuit samples presented on white plates. The order of presentation of the samples to the panel was randomized. Tap water was provided for the judges to rinse their mouths between evaluations. Statistical analysis Data were statistically analyzed using Analysis of Variance [24]. Means were separated by least significant difference (LSD). Significance was accepted at p ≤ 0.05.
Results and discussion Proximate composition Soybean flour had considerably higher protein (38.2%) than the cassava flour (1.0%). Fat, ash and crude fiber were also higher in soybean flour than in cassava flour. The proximate compositions obtained in this study were similar to literature values for soybean flour [25] and cassava flour [26]. The high protein content of soybean flour makes it a useful protein supplement in cassava flour (Table 1).
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CF: SF Blends 50:50 40:60 0.50 ± 0.4 0.55± 0.3 129 ± 0.2 132 ± 0.1 123 ± 0.2 125 ± 0.3 6.00 ± 0.2 6.70 ± 0.1 60 ± 0.3 42.8 ± 0.1 8.40 ± 0.1 8.40 ± 0.1 3.90 ± 0.4 4.20 ± 0.2
30:70 0.58 ± 0.5 135 ± 0.2 129 ± 0.8 7.23 ± 0.2 52.3 ± 0.1 8.70 ± 01 5.0 ± 0.1
0.50± 0.1 103 ± 0.4 112 ± 0.3 5.60 ± 0.2 33 ± 0.4 5.0± 0.1 2.50 ± 0.1
0.63 ± 0.1 80 ± 0.9 109 ± 0.8 3.80 ± 0.4 25 ± 0.8 4.30 ± 0.7 2.30 ± 0.8
0.64 ± 0.5 100 ± 0.3 110 ± 0.1 4.50 ± 0.3 33 ± 0.4 4.44 ± 0.2 2.50 ± 0.3
80:20
CF: SF Blends 100:0 90:10
∗ Means ± SD of 3 determinations.
Bulk density (g/cm) Water absorption capacity (%) Oil absorption capacity (%) Foam capacity (%) Foam stability(%) Emulsion activity (%) Emulsion stability (%)
Functional property∗
Bulk density (g/cm) Water absorption capacity (%) Oil absorption capacity (%) Foam capacity (%) Foam stability(%) Emulsion activity (%) Emulsion stability (%)
Functional property∗
20:80 0.56 ± 0.8 138 ± 0.2 202 ± 0.4 7.89 ± 0.6 25.00 ± 0.5 8.90 ± 0.1 7.90 ± 0.2
0.67 ± 0.2 107 ± 0.5 116 ± 0.6 5.70 ± 0.3 50 ± 0.1 6.60 ± 0.2 2.60 ± 0.1
70:30
Table 2. Functional properties of cassava flour (CF), Soybean flour (SF) and their blends
0:100 0.58 ± 0.30 142 ± 0.2 208 ± 0.4 7.20 ± 0.1 50 ± 0.3 9.70 ± 0.1 8.30 ± 0.4
0.53 ± 0.2 125 ± 0.3 120 ± 0.7 5.78 ± 0.1 35 ± 0.2 6.80 ± 0.3 2.68 ± 0.5
60:40
6
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7 Functional properties The functional properties of soybean flour (SF) cassava flour (CF) and their blends shown in Table 2 indicated that SF absorbed more oil than water. The oil absorption capacity of SF was about twice its water absorption capacity. The CF had less capacity to bind and retain water as well as oil than SF. Protein absorbs water up to 200% its weight whereas carbohydrate absorbs only 15% of its weight [27]. The high protein content of SF explains its ability to absorb more water than CF. The water and oil absorption capacities of the SF/CF blends increased with increasing levels of SF. The blends had greater water and oil absorption capacities than the CF. These properties may give an advantage to the blends relative to CF in baked doughs where hydration to improve handling characteristics is required and in products such as ground meat formulations, doughnuts and pancakes, where oil holding property is an important consideration [28]. The bulk density of SF and CF were 0.063 g/cm3 and 0.058 g/cm3 , respectively, and ranged from 0.50 to 0.67 g/cm3 for the blends (Table 2). The bulk density of the blends which describes the degree of compactness of the matrices did not appear to be related to the level of soybean flour as no definite trend was observed in the values obtained with increasing soybean flour substitution. The low bulk density of the blends is an advantage in the formulation of supplementary foods. The emulsion activity of SF was 2-fold that of CF (Table 2). The presence of SF increased the emulsion activity of the SF/CF blends, values ranged from 4.4 to 8.9%. All the flours had emulsion activities which were lower than the 18% reported for fluted pumpkin [29], 18–20% for African bread-fruit kernel and sweet-potato flour blends [30] and 12–36.6% for African breadfruit kernel and maize flour blends [31]. The emulsion stability of the blends showed a similar trend to the emulsion activity (Table2). The high proportion of carbohydrate in cassava flour (89.2%) may have adversely affected their ability to form and stabilize an emulsion. A similar observation was made for peanut flour [32]. The SF,CF and SF/CF blends would not be useful in milk, mayonnaise, salad dressing and spread formulations because of the high emulsion requirements of these products. The foam capacity was 3.8% for CF, 7.7% for SF and ranged from 4.5– 7.5% for the blends. All the flours had low foam capacity. Okaka & Potter [15] have reported that the superiority of soybean flour over cowpea flour in foaming properly was due to the higher protein content of soybean flour. In the present study, the foam capacity of the blends agreed with this report; values increased with increasing levels of soybean flour in the blends. However, the foam stability, defined as how quickly the foam collapsed once formed, failed to do the same as the foam capacity (Table 2). The blend (SF:CF 80:20)
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8 Table 3. Gelation properties of soybean flour (SF), cassava flour (CF) and their blends CF:SF Flour concentration (%, w/v) 2 4 6 8 10 12
14
16
18
20
100:0 90:10 80:20 70:30 60:40 50:50 40:60 30:70 20:80 0:100
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
– – – – – – – – – ±
+ ± ± ± ± – ± ± ± +
+ ± ± ± ± ± ± + + +
+ + ± ± ± + + + + +
+ + ± + + + + + + +
+ + + + + + + + + +
– not gelled, ± slightly gelled, + gelled.
with the highest protein content had lower foam stability than the blend with the least soybean flour (SF:CF, 90:10). It appeared that not only the amount of native protein but probably also the nature of the protein influenced the foam stability of the blends. According to Kitabatake & Doi [33], carbohydrates have a stabilizing effect on foams because their hydrophilic nature serves to increase the viscosity of the colloidal solution, thereby, preventing the collapse of the gas bubble. The high carbohydrate content of cassava flour with respect to soybean flour may explain the observed trend in the foam stability of the blends. Table 3 information shows that the least gelatin concentration of SF and CF were 4 and 10% (w/r), respectively, whereas those of the blends varied between 6 and 8% (w/v). Gelatin is an important functional property as it affects texture and mouthfeel of foods. The SF, CF and their blends would be good gel forming or firming agents and would be useful in custard type puddings and sauces/soups which require thickening and gelling. Physicochemical properties of biscuits The SF biscuit had higher protein and fat contents than the CF biscuit (Table 4). The protein and fat contents of the flour blend biscuits increased with increasing incorporation of SF, thus improving the nutritive value of the biscuits. The 100% CF biscuit contained 1.6% protein and 10.7% fat. These values increased to 32.2% protein and 30.5% fat„ respectively, for the 20:80 (CF:SF) biscuit which had the highest level of SF incorporation. Although this re-
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9 Table 4. Protein and fat contents, and physical properties of biscuits prepared form Biscuit Physical properties CF:SF Protein Fat (%) (%) 100:0 90:10 80:20 70:30 60:40 50:50 40:60 30:70 20:80
1.6±0.34a 5.8±0.43ai 9.2±0.81h 12.8±0.25g 16.4±0.30f 20.0±0.41e 24.0±0.93d 27.8±0.87c 31.2±0.76b
10.7±1.04a 13.2±0.41ai 15.8±1.41h 18.4±0.94g 20.9±0.81f 23.1±0.14e 25.8±0.04d 27.4±0.09c 30.5±0.34b
Thickness (mm)
Width (mm)
Weight (g)
Spread ratio
22.5±0.15a 20.6±0.12ab 22.6±0.15a 22.5±0.07a 21.5±0.07a 21.3±0.07a 20.6±0.07db 20.6±0.07ab 20.6±0.06b
71±0.12a 71±0.06a 71±0.14a 70.5±0.07a 70.5±0.07a 70.5±0.07a 70.5±0.14a 71±0.06a 71±0.06b
72.49±2.80a 12.3±2.19a 11.72±2.20b 11.32±2.43b 11.23±1.50b 11.80±1.46b 9.93±1.14c 9.93±1.14c 9.18±0.85c
3.16a 3.45a 3.14a 3.13a 3.28a 3.31a 3.42a 3.45a 3.45a
+, Means ± SD of 3 determinations. Means within a column with the same superscript were not significantly (p >0.05) different.
search did not involve the evaluation of protein quality of the biscuits, the flour blend biscuits should have better protein quality than the 100% CF biscuit, because of the expected complementation between the proteins of SF and CF. The experimental baking studies showed that the different levels of SF in the blends did not affect the handling of the doughs. The doughs had the necessary tensile strength and extensibility for sheeting, though they are non-gluten forming. Little variation was observed in the thickness and width of the 100% CF biscuits (Table 4). The thickness of the 100% CF biscuit (control) was 22.5 mm and remained fairly uniform with the addition of SF. This was probably due to the fairly uniform width of the flour blend biscuits. Reducing the width (drawing together of dough) would increase biscuit thickness and vice verse. In general, spread ratio did not differ significantly (p >0.05) among the biscuits. Ordorica-Falomir and PeredesLopez [23] have reported that spread ratio of cookies made with high protein flour does not develop during baking, as non-wheat high protein flours used in biscuits exhibit greater water retention than those made from wheat flour. The water in the system was insufficient to dissolve the sugar during baking which increased the viscosity and the biscuits spread at a slower rate. The mean weight for the 100% CF biscuit (control) was 12.59 g; this value decreased significantly (p 0.05) different. 1 = very poor, 6 = excellent. Means ± SD of three determinations.
Sensory evaluation of cookies Table 5 data show that there were no significant (p >0.05) differences in color, flavor, taste and overall acceptability among the SF, CF and SF/CF composite biscuits. Similarly no significant (p > 0.05) differences were found in the texture of the biscuits. Dough prepared from CF was more viscous and dense than that from SF. These characteristics were manifested in the firmer texture(lower sensory scores) of biscuits made from CF. Addition of SF to CF led to more tender biscuits. The SF was higher in fat than CF. Fats have been associated with crispiness of baked foods. Since the SF/CF blends are not source of gluten forming protein, the fat impacted flavor and tenderness of the biscuits rather than having a shortening effect. The SF/CF composite biscuits were rated higher (higher overall acceptability score) than the 100% CF biscuits. Although not significantly different, at the 50% level of SF substitution, biscuits had higher scores for all the sensory quality attributes and overall acceptability evaluated than the other composite biscuits. Above this level, lower sensory scores were recorded for the quality attributes of the biscuits.
Conclusion This study has characterized the functional properties of soybean flour, cassava flour and their blends for the production of good quality biscuits. Al-
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11 though either soybean flour or cassava flour could produce acceptable biscuits, various blends of soybean and cassava flour would produce more acceptable biscuits. Soybean flour could substitute up to 50% for cassava flour in biscuits without adversely affecting product quality. At the 50% soybean flour substitution level, protein and fat contents increased from 1.6 to 20% and 10.7 to 23.1%, respectively. Higher substitution of soybean flour above this level increased the protein and fat contents, but sensory quality attributes and overall acceptability were reduced. Biscuit consumption is high in Nigeria, therefore, soybean / cassava flour blend biscuits will serve as a vehicle for increasing intake of protein and calories in Nigerian diets. This is an advantage in a non- traditional wheat producing country such as Nigeria. It is also of interest in child feeding programs and for low income groups. This study has opened new possibilities of application for soybean and cassava flours. However, evaluation of protein quality of the biscuits in future research would be desirable. Acknowledgment The authors wish to thank Miss Evangeline Chibugo Oforkansi, Department of Food Science and Technology, Federal Polytechnic, Idah for her technical assistance. References 1. 2. 3. 4. 5.
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