Effect of soaking and microwave pretreatments on

PAK. J. FOOD SCI., 24(4), 2014: 186-194 ISSN: 2226-5899

Effect of soaking and microwave pretreatments on nutritional profile and cooking quality of different lentil cultivars Hafiz Rizwan Sharif1, Fang Zhong1, Faqir Muhammad Anjum2, Muhammad Issa Khan2, Mian Kamran Sharif2, Muhammad Aslam Khan1, Junaid Haider1, Faiz-ul-Hassan Shah2 1

State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, P.R. China. 2

National Institute of Food Science and Technology, University of Agriculture Faisalabad, Pakistan. Corresponding author Email: [email protected]

ABSTRACT The present study was planned to apply various cooking pretreatments for improvement in nutritional profile and cooking quality of some Pakistani lentil cultivars. For this purpose, four lentil cultivars were analyzed for physicochemical properties. All lentil varieties were subjected to soaking (1.5, 3.0 and 4.5 h) and microwave roasting (10, 20 and 30 sec) before cooking to find out impact on cooking time, anti-nutritional factors (tannins, phytic acid and trypsin inhibitor), in-vitro protein digestibility and the level of different minerals in control and treated samples. Mean square of each parameter revealed significant difference among different lentil varieties and the treatments applied. Overall there was 54.16, 48.47, 51.93 and 99.82% reduction were noted for cooking time, tannins, phytic acid and trypsin inhibitors of lentils subjected to soaking followed by cooking, respectively along with 72.01% improvement in in-vitro protein digestibility. Whereas comparatively less reduction in tannins, phytic acid and trypsin inhibitors were recorded for microwave roasted lentils as 30.67, 45.39 and 97.82%, respectively. Microwave treatments imparted less influence on in-vitro protein digestibility and cooking time in relation to soaking. Mineral losses were observed in all treated samples. However, maximum losses were observed for Zn (43.98%) and minimum for Cu (7.75%). Conclusively, soaking before cooking was found better than microwave roasting. Key words: lentil, soaking, microwave roasting, in-vitro protein digestibility, anti-nutritional factors, cooking time INTRODUCTION Chickpea, lentil, mash, mung, field pea, pigeon pea and arhar are the main legumes grown in Pakistan (Habibullah et al., 2007). Lentil (Lens culinaris M.) is an old world legume and was probably one of the first plant species to be domesticated (Cubero, 1981). It is one of the major cool-season food legumes grown in many parts of the world (Erskine et al., 2011). It is the 2nd largest grown legume crop of Rabi (cool) season in Pakistan after chickpea (Cicer arietinum L.) both in quality and quantity (Ayub et al., 2001). In 2011, it was grown on an area of 24.0 thousand hectares with 10.6 thousand tons production (GOP, 2011). It is considered as one of the most important pulse crops in the world and has proven many health benefits due to its nutritional quality. It may also be used as meat substitute in vegetarian diets and considered as a ‘poor man's meat’, as it is equally liked by all socioeconomic groups in South East Asia (Iqbal et al., 2006).

Despite of excellent nutritional profile, legumes have limited food applications mainly due to the existence of objectionable beany ﬂavors, deﬁciency of sulfur amino acids, presence of anti-nutritional compounds (trypsin inhibitors, tannins and phytic acid) and longtime of preparation. Presence of these antinutritional compounds hampered the digestibility of legumes proteins up to 50% in the digestive tract (Gilani and Cockell, 2005). Tannins and trypsin inhibitors hinder the functionality of digestive enzymes by forming insoluble complexes with protein and divalent ions such as Fe2+ and Zn2+, whereas phytic acid forms complexes with protein and minerals and ultimately lower their absorption in the body (Erdman, 1999; Vasagam and Rajkumar, 2011). Different processing methods like soaking, boiling, microwave cooking, pressure cooking (autoclaving) and fermentation have been reported to decrease the

186 Pakistan Journal of Food Sciences (2014), Volume 24, Issue 4, Page(s): 186-194


level of anti-nutritional factors along with increment in protein digestibility (Khattab et al., 2009). Among processing techniques, soaking, microwave roasting and cooking are the important treatments that can reduce the time require for preparation along with increase in nutritional value (Zhen et al., 2011). Cooking time is a major characteristic to determine cooking quality. It is a genetic characteristic that varies extensively among legumes and even in their varieties. Most of the legumes cooked from 20 to 90 minutes and the variation in cooking time is possibly due to difference in their chemical composition. This study was, therefore, carried out to analyze the effect of soaking and microwave roasting followed by cooking on cooking time and nutritional profile of four Pakistani lentil varieties.

Soaking

MATERIALS AND METHODS

Preparation of flour from treated lentil seeds

Four lentil varieties (Masoor-93, NIAB Lentil-06, Punjab Masoor-09 and Masoor Markaz-09) were procured from the Pulses Research Institute, Ayub Agricultural Research Institute (AARI) Faisalabad and National Agriculture Research Council (NARC) Islamabad. All used reagents (analytical grade) and standards were from Merck (Merck KGaA, Darmstadt, Germany) and Sigma- Aldrich (SigmaAldrich Tokyo, Japan).

After cooking, samples were ground into fine flour through electric grinder using a 60 mesh (British standard screen) nylon sieve and packed in air tight glass jars for further analysis.

Chemical composition

50 g lentil seeds were soaked in 500mL water (1:10, w/v) at room temperature (25°C) according to method followed by Hefnawy, (2011). Microwave roasting 50 g lentil seeds were roasted in microwave oven (DW-162H, Dawlance, Korea) at 2450 MHz frequency by following the method described by Lez and Rez (2002). Cooking Control and treated (soaked and microwave roasted) samples were subjected to cooking in water at 100°C according to method of Hefnawy (2011).

Assessment of cooking time Cooking time of pre-soaked and microwave roasted lentils were assessed by following the method of William et al. (1983). Mineral contents

Lentil samples were analyzed for moisture, ash, crude fat, crude fiber, crude protein and nitrogen free extract according to their respective protocols as described in AOAC (2006).

Mineral contents of control and treated samples were determined by the method described in AOAC (2006).

Physical characteristics

Anti-nutritional appraisal

Seed weight, seed volume, seed density, hydration capacity, hydration index, swelling capacity and swelling index, were determined by following the methods described by Zia-ul-Haq et al. (2007). Table 1: Treatments plan used in study

Anti-nutritional constituents such as tannins, phytate and trypsin inhibitor were determined by following their respective methods.

Description T0

Control (cooking without any treatment)

T1

1.5 hours soaking + cooking

T2


T3


T4 T5 T6

10 seconds microwave roasting + cooking 20 seconds microwave roasting + cooking 30 seconds microwave roasting + cooking

Tannins Tannins were determined by following the method of Chodak and Tarko (2007). Catechin was used as standard in tannins determination and absorbance was taken at 500nm by spectrophotometer (CE 72007000 series, Cecil, UK). Phytic acid Phytic acid contents were determined according to the method of Haug and Lantzsch (1983). Briefly, phytic acid was determined by extracting the sample (0.05g) in 0.2 N 25 mL HCl solution followed by shaking for 30 minutes. Then 0.5 mL clear extract, containing phytic acid, was heated with 1.0 mL acidic ammonium iron-III sulphate solution of known iron concentrations in boiling water for 30 minutes. The reduction in iron contents



of supernatant were indicated as phytate contents using 2 mL of 2,2 bipyridines solution at wavelength 519 nm through spectrophotometer (CE 7200-7000 series, Cecil, UK), after calibration of instrument with standard phytic acid solution. Trypsin inhibitor The concentration of trypsin inhibitor was determined according to AACC (2000). Trypsin inhibitor was extracted from each sample by shaking 200 mg of fat free sample with 10 ml of 0.1 M phosphate buffer (pH 7.6) at room temperature for 1 hour. The extract was diluted four fold. The aliquots containing 0.2, 0.4, 0.6 and 0.8 ml were analyzed for trypsin inhibitor activity at 410 nm wavelength by spectrophotometer (Cecil CE-7200, UK). In-vitro protein digestibility In-vitro protein digestibility of all samples with known % N was determined by following the protocol of Monjula and John (1991), with minor modifications. A known weight of the sample containing 16 mg nitrogen was taken in triplicate and digested with 1 mg pepsin in 15 mL of 0.1 M HCL at 37˚C for 2 hours. The reaction was stopped by addition of 15 mL of 10% trichloroacetic acid (TCA), the mixture was then filtered through Whatman No. 1 filter paper. The TCA soluble fraction was assayed for nitrogen using the micro-kjeldhal method (AOAC, 2006). N in supernatant-enzyme N Protein digestibility %= ×100 N in sample Statistical analysis The data obtained for each parameter was subjected to statistical analysis using Statistix software 8.1 (Analytical Software, USA). LSD test was applied to determine significant differences among means and p value ≤0.05 was consider to be statistically significant. RESULTS AND DISCUSSION Proximate composition of lentil varieties The results of proximate composition of four lentil varieties (Table 2) revealed significant differences among the cultivars with respect to moisture, ash, crude fat, crude fiber, crude protein and nitrogen free extract (NFE). The lentil variety Masoor Markaz-09 possessed significantly highest moisture content as compared to other lentil varieties. The ash content, crude fat and crude fiber were found significantly highest in Masoor-93. The variety Masoor Markaz-09 yielded highest content of protein followed by Punjab Masoor-09, NIAB Lentil-06 and Masoor-93, in a descending order. The

amount of NFE was found highest in NIAB Lentil06, while Punjab Masoor-09 possessed lowest. The moisture, ash, crude fat, crude fiber, crude protein and NFE in lentils ranged from 8.63 to 9.73, 2.21 to 3.05, 1.18 to 1.82, 5.82 to 6.92, 26.22 to 29.14 and 51.90 to 53.71%, respectively. The results are in agreement with the findings of Iqbal et al. (2006) who found moisture (9.3%), crude protein (26.1%), crude fat (3.2%) and ash (2.8%) while Zia-ul-Haq et al. (2011) noted a range of crude protein, crude fat and ash from 28.80 to 30.60, 1.93 to 2.15 and 4.16 to 5.71%, respectively in different Pakistani lentil cultivars. In another study Wang and Daun (2006) reported 25.9 to 28.7% (crude protein), 1.0 to 1.2% (crude fat) and 2.6 to 3.0% (ash) in four Canadian varieties on dry weight basis whereas, Hefnawy (2011) found moisture (8.51%), crude protein (26.6%), crude fat (1.0%) and ash (3.4%) in Egyptian lentil. The variation in chemical composition was might be due to genetic and environmental factors (Wang and Daun, 2006). Physical parameters lentil varieties Seed weight and volume were found significantly high in Masoor Markaz-09. The lentil variety Masoor-93 possessed significantly highest seed density as compare to other lentil varieties. Hydration capacity was found significantly highest in Masoor-93, whereas swelling capacity in Masoor Markaz-09. The lentil variety NIAB Lentil-06 possessed the highest hydration index as compare to the other lentil varieties. The swelling capacity was not found significantly different in NIAB Lentil-06 and Masoor Markaz-09 but Masoor-93 possessed higher swelling capacity. The seed weight, seed volume, seed density, hydration capacity and swelling capacity in lentil flours ranged from 0.017 to 0.024 (g/seed), 0.018 to 0.024 (mL/seed), 0.928 to 1.043 (g/mL), 0.018 to 0.022 (g/seed), 0.017 to 0.022 (mL/seed), respectively (Table 3). The results of the present study are in line with the outcomes of Huma et al. (2008) who found 100 lentil’s seed weight (2.88g), volume (6.0mL), seed density (0.48g/mL), water absorption capacity (15.42g/100g) and swelling capacity (32.72g/100g). In an earlier study Jood et al. (1998) also reported a range of seed weight, seed volume, seed density, hydration capacity and swelling capacity from 0.022 to 0.026 (g/seed), 0.021 to 0.025 (mL/seed), 0.82 to 0.93 (g/mL), 0.019 to 0.026 (g/seed), 0.018 to 0.025 (mL/seed), respectively in three Indian lentil varieties. The differences in physical characteristics could be attributed to the differences in varietal and agronomic practices (Zia-ul-Haq et al. 2007).



Cooking parameters of lentil varieties The means for effect of cooking pretreatments (soaking and microwave roasting) on cooking time of four different lentil varieties (Table 5) showed that the maximum cooking time (17.42±1.02 min) was taken by Masoor Markaz-09 followed by Punjab Masoor-09 i.e. 16.57±1.52 min while the lowest time (13.28±1.09 min) was observed for Masoor-93. Soaking treatments showed significant effect on cooking time of all lentil varieties as compare to control (T0). A gradual decrease in cooking time was noted with gradual increase in soaking intervals as shown in Table 4. Maximum reduction (8.25±0.83 min) was observed in T3 followed by T2 (11.20±1.07) and T1 (12.00±1.41). On contrary gradual increase in microwave roasting time showed negative effect on cooking time. Maximum cooking time (21.25±1.75 min) was taken by T6 trailed by T5 (18.50±1.51) and T4 (18.00±1.30). Overall 54.16% reduction in cooking time for soaked and 18% increment for microwave roasted samples were witnessed as compared with T0 (control sample). Current results are in conformity with earlier findings of Huma et al. (2008) who found 50% reduction in cooking time for 2 to 6h soaked lentils. This was might be due to the reduction in hardness of legumes as a result of soaking in water. Seed size, seed hull and hydration capacity are the other factors that also influence on cooking time. Anti-nutritional factors in lentil varieties The means for effect of cooking pretreatments (soaking and microwave roasting) on tannin contents of four different lentil varieties (Table 5) showed that the maximum tannin contents (7.05±0.50 mg/g) were observed for Masoor-93 followed by NIAB Lentil-06 (6.31±0.41 mg/g), Punjab Masoor-09 (6.16±0.21) and Masoor Markaz-09 (5.62±0.18 mg/g). A gradual decrease was found in tannin contents of cooked lentils subjected to soaking with gradual increase in soaking intervals as compare to T0 i.e. 8.54±0.68 mg/g (Table 4). Maximum reduction (4.40±0.29 mg/g) was observed in T3 followed by T2 (5.03±0.39) and T1(5.24±0.39). Whereas less decrease in tannin contents was observed in lentils subjected to microwave roasting with increase in roasting time. The minimum tannins (5.92±0.31 mg/g) were noted for T6. Overall there was 48.47% and 30.67% reduction of tannins were witnessed in lentils subjected to soaking and microwave roasting, respectively as compare to T0. The results of the present study about the reduction in tannin contents are in harmony with the findings of Rehman and Shah, (2005) who reported 23.49% reduction in tannin contents. In various studies about

50% reduction of tannins in lentils after heat treatments were also illustrated by Moharram et al., 1986; Huma et al., 2008; Hefnawy 2011. Phytic acid The means for effect of cooking pretreatments (soaking and microwave roasting) and lentil varieties on phytic acid are cited in Table 4 and 5, respectively. Among lentil cultivars, maximum phytic acid 7.61±0.19 mg/g was noted for Punjab Masoor-09 followed by 7.26±0.31 mg/g for Masoor Markaz-09, 7.25±0.41 mg/g for NIAB Lentil-06, while lowest 6.74±0.23 mg/g for Masoor-93. As the time of soaking increased, there was more reduction in phytic acid contents were observed as compare to microwave treatment. Maximum reduction (5.59±0.47 mg/g) was observed in T3 and T6 (6.35±0.26 mg/g) among soaked and microwave treated samples. Conclusively there was 51.93% and 45.39% reduction of phytic acid were recorded in soaked and microwave roasted lentils, respectively as compare to T0. Both cooking pretreatments were found effective in dissociation of phytate complexes. The results of the present study about the reduction in phytate contents are in agreement with the findings of Rehman and Shah (2005) who observed 24% reduction of phytates. Studies carried out by Huma et al. (2008), Hefnawy (2011) and Qayyum et al. (2012) also testified more than 50% reduction of phytates in different legumes as a result of heat treatments. Trypsin inhibitor Mean values regarding the effect of cooking pretreatments (soaking and microwave roasting) and lentil varieties on trypsin inhibitors, correspondingly mentioned in table 4 and 5. Among four studied varieties, highest trypsin inhibitor activity (4.17±0.19 TIU/g) was found in Punjab Masoor-09 whilst lowest (3.09±0.12 TIU/g) in Masoor-93. Trend in reduction of trypsin inhibitor activity as a function of cooking pretreatments was noticed similar to tannins and phytic acid. Maximum reduction was evident in T3 (0.41±0.13 TIU/g) and T6 (0.42±0.02). Finally, 99.27% and 97.82% reduction in trypsin inhibitor activity was noticed for soaked and microwave roasted lentils, respectively as compare to T0. Results of current study are in resemblance with the findings of El-Adawy (2000) and Qayyum et al. (2012) who reported trypsin inhibitor reduction in different legumes as a function of heat treatments. More reduction in trypsin inhibitor activity as compare to the other antinutritional factors like tannins and phytic acid, might be due to its more sensitivity towards heat.



Table 2: Proximate composition of different lentil varieties Components Masoor-93 NIAB Lentil-06

Punjab Masoor-09

Masoor Markaz-09

Moisture

8.63±0.18c

8.82±0.03bc

8.87±0.05b

9.73±0.05a

Ash

3.05±0.07a

2.69±0.04c

2.83±0.05b

2.21±0.05d

Crude fat

1.82±0.10a

1.48±0.04b

1.61±0.07b

1.18±0.02c

Crude fiber

6.92±0.11a

6.41±0.10c

6.59±0.08b

5.82±0.09d

Crude protein

26.22±0.34c

26.87±0.82bc

27.72±0.28b

29.14±0.57a

NFE

53.34±0.59ab

53.71±0.86a

52.35±0.29bc

51.90±0.55c

Means sharing similar letters are statistically non-significant (P>0.05)

Table 3: Physical properties of different lentil varieties Properties Masoor-93 NIAB Lentil-06

Punjab Masoor-09

Masoor Markaz-09

Seed weight (g/seed)

0.022±0.002a

0.017±0.001b

0.021±0.002ab

0.024±0.002a

Seed volume (mL/seed)

0.021±0.002ab

0.018±0.001c

0.020±0.001bc

0.024±0.001a

Seed density (g/mL)

1.043±0.208a

0.928±1.040a

1.040±0.173a

1.003±0.141a

Hydration capacity (g/seed)

0.022±0.002a

0.018±0.001c

0.019±0.002c

0.021±0.001b

Hydration index

1.016±0.078ab

1.062±0.103a

0.906±0.032ab

0.870±0.061b

Swelling capacity (mL/seed)

0.020±0.020ab

0.017±0.001b

0.018±0.001b

0.022±0.001a

Swelling index

0.958±0.022a

0.927±0.070a

0.908±0.115a

0.930±0.013a

Means sharing similar letters are statistically non-significant (P>0.05) T0 = (control), T1 = lentils cooked after 1.5 h soaking, T 2 = lentils cooked after 3.0 h soaking, T 3 = lentils cooked after 4.5 h soaking, T 4 = lentils cooked after 10 sec microwave roasting, T 5 = lentils cooked after 20 sec microwave roasting and T6 = lentils cooked after 30 sec microwave roasting



Table 4: Effect of different treatments on cooking time, In-vitro protein digestibility and Anti-nutritional factors in lentil varieties Anti-nutritional factors Cooking time (min)

In-vitro protein digestibility

T0

18.00±1.82b

T1

Phytic acid (mg/g)

Tannins (mg/g)

Trypsin inhibitors (TIU/g)

41.17±1.05g

11.63±0.67a

8.54±0.68a

19.31±1.4a

12.00±1.41c

66.23±1.51c

6.59±0.37d

5.24±0.39e

1.25±0.13c

T2

11.20±1.07c

68.02±1.36b

6.09±0.34f

5.03±0.39e

0.94±0.12d

T3

8.25±0.83d

72.01±0.98a

5.59±0.47g

4.40±0.29f

0.41±0.13e

T4

18.00±1.30b

61.12±0.68f

7.43±0.23b

7.70±0.19b

1.51±0.16b

T5

18.50±1.51b

61.90±0.68e

6.83±0.24c

7.17±0.41c

1.19±0.14c

21.25±1.75a

63.46±1.57d

6.35±0.26e

5.92±0.31d

0.42±0.02e

Treatments

T6


Table 5: Effect of different lentil varieties on cooking time, in-vitro protein digestibility and Anti-nutritional factors Anti-nutritional factors Cooking time In-vitro protein Varieties Phytic acid Tannins Trypsin inhibitors (min) digestibility (mg/g) (mg/g) (TIU/g) Masoor-93

13.28±1.09b

61.57±2.02c

6.74±0.23c

7.05±0.50a

3.09±0.12d

NIAB Lentil06

14.00±1.15b

60.82±1.69d

7.25±0.41b

6.31±0s.41b

3.41±0.18c

Punjab Masoor-09

16.57±1.52a

62.38±1.52b

7.61±0.19a

6.16±0.21b

4.17±0.19a

Masoor Markaz-09

17.42±1.02a

63.18±2.03a

7.26±0.31b

5.62±0.18c

3.64±0.12b




Table 6: mineral profile of different treatments of lentil verities Treatments Na K Ca Mg

Fe

Cu

Zn

Mn

T0

72.91±3.86a

911.00±13.03a

114.92±9.20a

131.50±6.38a

4.33±0.23a

6.45±0.07a

3.66±0.07a

2.71±0.15a

T1

65.41±2.21c

660.42±10.36c

104.75±4.91c

124.42±6.80b

3.19±0.30c

6.07±0.04c

2.31±0.09c

2.49±0.13c

T2

61.33±4.34e

637.17±11.70e

97.58±3.81e

117.58±8.74d

3.08±0.26e

5.98±0.05e

2.20±0.10d

2.39±0.14e

T3

55.25±4.20g

582.25±15.69g

89.58±8.01g

111.67±8.33e

2.92±0.21g

5.88±0.06g

2.05±0.07f

2.28±0.12g

T4

68.66±3.23b

677.25±8.42b

106.83±5.32b

125.33±6.53b

3.24±0.34b

6.12±0.04b

2.39±0.13b

2.52±0.12b

T5

63.58±2.72d

651.50±4.70d

101.17±4.08d

120.92±8.15c

3.14±0.28d

6.03±0.05d

2.28±0.14c

2.44±0.13d

T6

57.50±3.89f

612.67±11.40f

93.33±5.73f

120.92±7.86c

3.02±0.24f

5.95±0.07f

2.15±0.13e

2.36±0.13f

Means sharing similar letters are statistically non-significant (P>0.05) T0 = (control), T1 = lentils cooked after 1.5 h soaking, T 2 = lentils cooked after 3.0 h soaking, T 3 = lentils cooked after 4.5 h soaking, T 4 = lentils cooked after 10 sec microwave roasting, T 5 = lentils cooked after 20 sec microwave roasting and T 6 = lentils cooked after 30 sec microwave roasting Table 7: Mineral profile of different lentil varieties Varities Na K

Ca

Mg

Fe

Cu

Zn

Mn

Masoor-93

66.95±5.92a

687.24±10.34a

106.71±7.04a

132.33±4.91a

3.66±0.20a

6.13±0.18a

2.55±0.02a

2.63±0.03a

NIAB Lentil-06

61.47±3.24c

672.05±9.54c

100.71±6.23c

116.29±6.06c

3.03±0.01d

6.00±0.17d

2.39±0.05c

2.40±0.03c

Punjab Masoor-09

65.76±4.12b

679.86±12.03b

103.81±6.60b

121.52±7.46b

3.22±0.01b

6.10±0.18b

2.49±0.04b

2.49±0.14b

Masoor Markaz-09

59.90±5.27d

665.00±11.23d

93.43±4.44d

116.90±7.04c

3.19±0.02c

6.06±0.19c

2.31±0.03d

2.31±0.13d




In-vitro protein digestibility (IVPD) of different lentil varieties Low digestibility of the legume protein is one of the main drawback that limits the nutritional quality of food legumes. The results for effect of cooking pretreatments (soaking and microwave roasting) on IVPD of four different lentil varieties (Table 5) showed that Masoor Markaz-09 possessed highest IVPD (63.18±2.03%) followed by (62.38±1.52%) for Punjab Masoor-09, (61.57±2.02%) for Masoor-93 whilst lowest (60.82±1.69%) for NIAB Lentil-06. Effect of soaking on IVPD was found more pronounced as compare to microwave roasting. IVPD values 72.01±0.98% (maximum) and 61.12±0.68% (minimum) were observed for T3 and T4, respectively as a function of cooking pretreatments. Generally, 72.01% and 54.14% improvement in IVPD was observed for soaked and microwave roasted lentils, respectively as compare to T 0. Jood et al. (1998); Hania and Niely (2007) reported IVPD of untreated lentil seeds 45 and 52%, respectively. Our results are coincide with the earlier conclusions of Khatoon and Prakash (2004) who reported more improvement in IVPD as a result of soaking before cooking as compare to microwave treatment. The improvement in IVPD might be credited to destruction of antinutritional factors like trypsin inhibitor, tannins and phytic acid which creates large spaces within matrix, increases susceptibility of enzyme’s attack that ultimately denatures the protein and enhances its digestibility (Rehman and Shah, 2005). Mineral profile of lentil varieties High concentrations of potassium, magnesium, calcium and sodium were found in all lentil cultivars whilst lesser concentrations of copper, iron, manganese and zinc were recorded (Table 7). Means for effect of cooking pretreatments (soaking and microwave roasting) on mineral contents of different lentil cultivars revealed that Na, K, Ca, Mg, Fe, Cu, Zn and Mn contents were ranged from 55.25±4.20 to 72.91±3.86, 582.25±15.69 to 911.00±13.03, 89.58±8.01 to 114.92±9.20, 111.67±8.33 to 131.50±6.38, 2.92±0.21 to 4.33±0.23, 5.88±0.06 to 6.45±0.07, 2.05±0.07 to 3.66±0.07, 2.28±0.12 to 2.71±0.15 mg/100g, respectively (Table 6). A prominent decrease in all minerals were observed in cooked lentils subjected to soaking and microwave roasting with gradual increase in treatment time intervals as compared with T0. Effect of soaking on mineral reduction were found more pronounce in relation to microwave roasting. Maximum decline

(43.98%) was observed for Zn in T3 whereas minimum for Cu (7.75%) in T 6. Overall there was 24.22, 36.08, 22.02, 15.07, 32.56, 8.83, 43.98 and 15.86% reduction was noted for Na, K, Ca, Mg, Fe, Cu, Zn and Mn in lentil samples subjected to soaking, whereas 21.13, 32.74, 18.78, 8.04, 30.25, 7.75, 41.25 and 12.91% reduction in microwave roasted lentils, respectively as compared with T 0. The results about the reduction in mineral contents are in accordance with the findings of Hefnawy (2011); Alajaji and ElAdawy (2006). Additionally, Wang et al. (2009) also observed the same trend in chickpea and lentil about mineral reduction as a function of heat treatment. The reduction in mineral contents was due to leaching of minerals. CONCLUSION Conclusively, cooking pretreatments (soaking and microwave roasting) imparted positive effect on improvement of lentil’s nutritional profile by lowering the anti-nutritional factors along with enhancement in in-vitro protein digestibility. In addition, reduction in cooking time was also witnessed as a result of soaking before cooking in contrary to microwave roasting. Despite, the negative effects of cooking pretreatments on mineral losses, it is recommended that soaking for 4.5 hours before cooking is good for reduction in cooking time as well as improvement in nutritional value of lentils. Acknowledgement The authors would like to acknowledge the support and assistance of China Scholarship Council (CSC) Program and National Institute of Food Science and Technology, University of Agriculture Faisalabad, Pakistan. REFERENCES 1.

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