Effect of Pre-treatments on Cooking Time of Soya Flakes

ARTICLE IN PRESS Biosystems Engineering (2005) 94 (2), 311–315 doi:10.1016/j.biosystemseng.2005.06.005 PH—Postharvest Technology

RESEARCH NOTE

Effect of Pre-treatments on Cooking Time of Soya Flakes S.D. Deshpande1; S. Bal2 1

Central Institute of Agricultural Engineering, Nabi Bagh, Berasia Road, Bhopal 462 038 MP, India; e-mail of corresponding author: [email protected] 2 Post Harvest Technology Centre, Indian Institute of Technology, Kharagpur, WB, India; e-mail: [email protected] (Received 22 November 2004; accepted in revised form 20 June 2005; published online 13 December 2005)

Experiments on cooking characteristics of full-fat and defatted soya flakes were performed using different cooking treatments, viz., normal boiling, cooking with additive salts, pressure cooking to explore the feasibility of using such flakes in the preparation of broth. The results indicated that the optimum cooking time of soya flakes can be successfully reduced from 142 min by normal boiling to 69 min by pre-heating and boiling in 1% sodium bicarbonate (NaHCO3) and 11 min by pre-heating and pressure cooking in 1% NaHCO3 for the preparation of good-quality broth thus reducing time and energy in cooking considerably. r 2005 IAgrE. All rights reserved Published by Elsevier Ltd

1. Introduction Protein in the Indian diet is mainly derived from pulses. These are normally consumed by making a viscous broth, from the whole or pearled grains which is then consumed alongside wheat and rice products. Readily available pulses such as redgram or pigeonpea (Cajanus cajan), Bengal gram (Cicer arietinum), green gram (Phaseolus aureus Roxb) and black gram (Phaseolus mungo) are popular for this purpose. Soya bean, contains about 40% good-quality protein and 20% cholesterol-free oil, however, the use of this as an ingredient has been negligible due to its poor water absorption capacity and dispersibility and very long cooking time. In order to popularise soya bean as food in India, it is essential to incorporate it in the popular form of Indian foods, i.e. broth. Earlier studies on cooking aspects of soya bean have indicated that the soyadal (split soya bean) normally takes about 300 min for complete cooking by open atmospheric boiling to obtain broth (Deshpande, 1990). The addition of 1% (w/v) alkaline salts such as sodium bicarbonate (NaHCO3) and sodium citrate reduces the cooking time to 75 and 60 min, respectively (Gandhi et al., 1985). Chavan et al. (1983) reported the effect of pre-soaking treatments on the cooking quality of split legume. Pre-soaking treatments of different split 1537-5110/$32.00

legumes in water or soaking solution at 25 1C decreased the cooking time substantially. Paredes-Lopez and Carabez-Trelo (1991) reported that drying of soaked seeds increases the cooking time in grain legumes. Singh and Rao (1995) studied the cooking of split legume using NaHCO3 and found this to significantly reduce the cooking time. Agarwal et al. (1999) reported that different pre-milling treatments such as water spray, oil treatment, enzyme treatment caused significant loss of protein content except NaHCO3 treatment. Singh et al. (2000) observed maximum reduction in cooking time of chickpea pulse when it was soaked in NaHCO3 sodium bicarbonate solution. Singh et al. (2003) revealed that cooking time of pulses including soya bean linearly increased with storage time. Use of soya flake for food uses has great potential. Considering the use of homogenous broth (from split legumes) is very common in daily Indian preparations, hence the use of soya flakes in this form (broth) will be helpful in popularising the consumption of soya bean/ soya flake in India to eliminate protein malnutrition. The present investigation was therefore mainly focused on conducting the cooking studies on soya flakes for determining the possibility of preparation of homogeneous broth. Efforts were also made to reduce the cooking time of soya flakes for preparation of broth by using NaHCO3. 311

r 2005 IAgrE. All rights reserved Published by Elsevier Ltd

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S.D. DESHPANDE; S. BAL

where k1 and k2 are regression coefficients given in Table 1 along with the values of correlation coefficient.

2. Materials and methods Experiments on cooking characteristics of full-fat and defatted soya flakes were performed using different cooking treatments to explore the possibility of using these flakes for the preparation of dal (broth). The treatments adopted were as follows: (1) (2) (3) (4) (5) (6) (7) (8)

normal boiling; pre-heating and boiling; boiling with 1% NaHCO3; pre-heating and boiling with 1% NaHCO3; pressure cooking; pre-heating and pressure cooking; pressure cooking with 1% NaHCO3 and pre-heating and pressure cooking with 1% NaHCO3.

2.1. Experimental arrangement It consisted of glass beakers of 250 ml capacity for keeping the samples, electrical hot plate, pressure cooker, distilled water, alkaline salt NaHCO3, 2 mm sieve and oven.

2.2. Experimental procedure Each test sample (10 g of soya flakes) was placed in a beaker and 100 ml of distilled water was added. Then this beaker was kept either on hot plate or in the pressure cooker according to the type of cooking test for a specified duration. The cooked material was stirred vigorously for about 1 min with a solid glass stirring rod and was passed through a 2
0 mm sieve; the fraction which remained on the sieve was washed with water (100 ml). Both fractions were dried to constant weight at 373 K i.e. 100 1C. The ratio of the weight of the fraction which passed through the sieve to the total weight of both fractions expressed as percentage was adopted as the index of cookability (Zarkadas et al., 1965; Gupta et al., 1976; Deshpande, 1990).

3. Results and discussion The index of cookability Ic was found to increase linearly with cooking time t in minutes (Fig. 1). The variation in Ic with t for different treatments of cooking may be represented by a regression equation: I c ¼ k1 þ k2 t

(1)

3.1. Determination of optimum cooking time for different cooking treatments For complete cooking of soya flakes, the cooking time was obtained from the cooking curves (Fig. 1) as the time required for obtaining 100% index of cookability and was termed as the optimum cooking time. For example, for full-fat soya flakes, under normal boiling conditions, the optimum cooking time required to attain 100% index of cookability was obtained from Fig. 1(a) as 140 and 142 min for defatted and full-fat soya flakes, respectively. In the similar way, the values of optimum cooking time required for obtaining 100% index of cookability for other cooking treatments for full-fat and defatted soyaflakes are presented in Table 2. Both types of soya flakes require very high optimum cooking time in open boiling compared to other treatments of cooking. The effect of addition of NaHCO3 to the cooking water in reducing the cooking time was more pronounced than the pre-heating of flakes. However, greater reduction in cooking time was noted when the flakes were subjected to the combination of pre-heating followed by cooking in the boiling water containing 1% NaHCO3 salt (Fig. 2). A considerable reduction in cooking time was noted when the flakes were subjected to pressure-cooking at 1
03 bar. The optimum cooking time was 21 min for fullfat flakes, which was further reduced to 11 min when the flakes were subjected to pre-heating and pressure cooked with NaHCO3. The slight reduction (about 1–3%) in optimum cooking time was observed in different cooking treatments for defatted flakes as compared to the full-fat flakes. The longer cooking time required for soya flakes is mainly due to the interference of divalent cations such as calcium, magnesium and phytate. The addition of NaHCO3 to the cooking medium brings the pH towards the alkaline and enhances the inactivation of lipoxygenase. This treatment minimises the beany flavour and replaces the divalent cations which interfere with the cooking of soya flakes. The bridging effect of divalent cations is lost by replacement with monovalent cations thereby improving the cooking quality (Gandhi et al., 1985; Deshpande, 1990). As soya flake contains a high content of these factors, it is the alkaline medium which is a significant factor in the reduction of the cooking times.

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100 Index of cookability Ic, %

Index of cookability Ic,%

EFFECT OF PRE-TREATMENT

90 80 70 60 70

(a)

90

110

130

150

100 95 90 40

50

(b)

Cooking time t, min

60

70

80

90

Cooking time t, min

95 90 Index of cookability Ic, %

Index of cookability Ic,%

100

85 80 75 70 40

(c)

50 60 70 80 Cooking time t, min

100

95

90 30

40 50 60 Cooking time t, min

(d)

70

Index of cookability Ic, %

100 Index of cookability Ic,%

100

95

90

95 90 85 80

85 14

(e)

16 18 20 22 Cooking time t, min

8

10

4

6 8 10 Cooking time t, min

(f)

12 14 16 18 Cooking time t, min

20

100 Index of cookability Ic, %

Index of cookability Ic,%

100 95 90 85 80

90

85

80

75 4 (g)

95

6 8 10 12 14 Cooking time t, min

16 (h)

12

Fig. 1. Effect of cooking time on index of cookability of full-fat flakes ( ) and defatted flakes ( ) for different cooking treatments: (a) normal boiling; (b) pre-heating and boiling; (c) boiling with 1% NaHCO3; (d) pre-heating and boiling with 1% NaHCO3 (e) pressure cooking; (f) pre-heating and pressure cooking; (g) pressure cooking with 1% NaHCO3; (h) pre-heating and pressure cooking with 1% NaHCO3; ‘‘gradients of the data lines within graph set (a) to (d) and within graph set (e) to (h) are visually comparable but not between graph sets’’

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S.D. DESHPANDE; S. BAL

Table 1 Regression coefficients for full-fat and defatted soya flakes with different cooking treatments Cooking treatment

Full-fat flakes Regression coefficient

(1) Normal boiling (2) Pre-heating and boiling (3) Boiling with 1% NaHCO3 (4) Pre-heating and boiling with 1% NaHCO3 (5) Pressure cooking (6) Pre-heating and pressure cooking (7) Pressure cooking with 1% NaHCO3 (8) Pre-heating and pressure cooking with 1% NaHCO3

Defatted flakes

Correlation Goodness of coefficient fit

k1

k2

43
53 89
69 42
61 86
82

0
40 0
12 0
75 0
19

0
98 0
97 0
98 0
99

63
93 65
31

1
70 2
07

67
45 72
68

Regression coefficient

Correlation Goodness of coefficient fit

k1

k2

0
96 0
95 0
97 0
98

52
09 90
85 45
65 88
14

0
34 0
11 0
71 0
18

0
97 0
96 0
98 0
97

0
94 0
93 0
95 0
93

0
99 0
97

0
99 0
94

64
94 64
89

1
69 2
11

0
98 0
96

0
97 0
93

2
19

0
98

0
95

68
85

2
13

0
98

0
95

2
49

0
96

0
93

73
10

2
46

0
96

0
93

Table 2 Optimum cooking time for full-fat and defatted soya flakes with different cooking treatments Cooking treatment

(1) (2) (3) (4) (5) (6) (7) (8)

Optimum cooking time, min

Normal boiling Pre-heating and boiling Boiling with 1% NaHCO3 Pre-heating and boiling with 1% NaHCO3 Pressure cooking Pre-heating and pressure cooking Pressure cooking with 1% NaHCO3 Pre-heating and pressure cooking with 1% NaHCO3

160

Defatted flakes

142
46 84
50 76
82 69
20 21
21 16
78 14
85 10
96

139
70 83
04 76
31 67
19 20
79 16
67 14
63 10
94

The results indicated that the optimum cooking time of soya flakes can be successfully reduced from 142 min by normal boiling to 69 min by pre-heating and boiling in 1% NaHCO3 and 11 min by pre-heating and pressure cooking in 1% NaHCO3 for the preparation of an homogeneous and good quality dal broth.

140 Optimum cooking time, min

Full-fat flakes

120 100 80 60 40

4. Conclusions

20 0

1

2

3

4

5

6

7

8

Cooking treatments Fig. 2. Effect of cooking treatments for full-fat flakes ( ) and defatted flakes ( ) on optimum cooking time: (1) normal boiling; (2) pre-heating and boiling; (3) boiling with 1% NaHCO3; (4) pre-heating and boiling with 1% NaHCO3 (5) pressure cooking; (6) pre-heating and pressure cooking; (7) pressure cooking with 1% NaHCO3; (8) pre-heating and pressure cooking with 1% NaHCO3

It was observed that the index of cookability increases linearly with time of cooking. Study further revealed that the soya flakes can be cooked for dal preparation by pressure cooking in 21 min compared to normal boiling in 142 min. The use of NaHCO3 further reduces the pressure-cooking time to about 11 min. The effect of defatting of soya flakes on cooking time was not significant with only a slight reduction (about 1–3%) in cooking time observed in different cooking treatments, compared to full-fat flakes.

ARTICLE IN PRESS EFFECT OF PRE-TREATMENT

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