Effect of Processing Methods on Mineral Contents of Selected Lentils (Lens Culinuris) Varieties (Derash and Alemaya) Grown in Ethiopia

Mineral contents of legumes showed significant reduction during the process of cooking due to leaching of minerals into cooking water. The aim of this study was to investigate the effects of various processing methods (autoclaving, boiling, dehulling, germinating and soaking) on mineral contents of the two selected lentil varieties (Alemaya and Derash). The present study revealed that processing methods affect the mineral contents of lentils. Germinating process was the least reduction of Zn, Fe and Ca by 4.52, 4.23 and 0.55%, however, dehulling process was the highest reduction by 25.91, 19.14 and 9.56%, respectively. Keywords: Lentil, Alemaya variety, Derash variety, Mineral contents, Processing methods DOI : 10.7176/FSQM/88-03 Publication date :July 31 st 2019


Sample Preparation
Samples of each of Derash and Alemaya lentil varieties were cleaned manually by removing any foreign material, damaged and broken seeds. The seeds were processed by dehulling, soaking, germination, boiling and autoclaving. The processed samples including the control sample were dried in an oven at 50°C for about 24 hr. All samples were milled by laboratory miller (cyclo sample mill model no: 3010-081p) and pass through 75 µm sieve. The flours were packed in moisture proof plastic bags and stored in airtight tin containers at 4 o C until required for analysis.

Processing Techniques 2.5.1. Direct grinding
Cleaned seed of 600 g each of Derash and Alemaya varieties were directly ground by mill.

Dehulling
A 600 g cleaned seed of each of Derash and Alemaya varieties were dehulled by pestle and mortar. The hull was separated using traditional tool (gundoo) from split seeds. The split lentil was milled as indicated above.

Soaking
The 600 g of clean seed each of the two lentil varieties were soaked in distilled water for 12 hr at room temperature (Osama et al., 1985). The soaked samples were drained and rinsed three times with 600 ml distilled water. The samples were oven dried at 50 o C for 24 hr. The dried samples were milled and passed through 75 µm sieve. The flours were packed in moisture proof plastic bags and stored in airtight tin containers at 4 o C until required for analysis.

Autoclaving
The 600 g cleaned seed each of the two lentil variety were soaked in distilled water (1:10, w/v) for 12 hr at room temperature (25 °C). The soaked samples were drained and rinsed three times with 600 ml distilled water. The rinsed soaked samples were autoclaved at 121°C under 15 lb pressure in distilled water (1:10, w/v) until they became soft when felt between the fingers (35 min) (Hefnawy, 2011) and immediately dried in oven drying at 50°C for 24 hr. The dried sample was milled and passes through 75 µm sieve. The flours were packed in moisture proof plastic bags and stored in airtight tin containers at 4 o C until required for analysis.

Germination
The 600 g seed of each of Derash and Alemaya varieties were cleaned and soaked in distilled water at room temperature for 12 hr. The soaked samples were drained and rinsed three times with 600 ml distilled water. The water was drained off and the samples covered in trays lined with absorbent paper and left to germinate for 72 hr (Mashair et al., 2008). At the end of the germination process, the samples were oven dried at 50 o C for 24 hr, milled and passed through 75 µm sieve. The flours were packed in moisture proof plastic bags and stored in airtight tin containers at 4 o C until required for analysis.

Boiling
The 600 g cleaned samples of each of the two varieties were soaked in distilled water (1:10, w/v) for 12 hr at room temperature (25°C). The soaked seeds were drained and rinsed three times with 600 ml distilled water. The samples were then boiled in distilled water in the ratio of 1:10 (w/v) until they became soft when felt between the fingers (90 min) (Hefnawy, 2011) and immediately dried in oven at 50°C for 24 hr. The dried samples were milled and passed through 75 µm sieve. The flours were packed in moisture proof plastic bags and stored in airtight tin containers at 4 o C until required for analysis.

Minerals Analysis 2.6.1. Calcium
The calcium content was determined by atomic absorption spectrophotometer (AACC, 2000). Calcium content was calculated with the following formula  Where: C is the concentration of the sample from plot of absorption in μg/ml and s sample mass (g).

Iron
Iron content was determined by Atomic Absorption Spectrophotometer (AACC, 2000).
Where: µg/mL is the absorbance reading concentration 2.6.3. Zinc Zinc content was determined by Atomic Absorption Spectrophotometer (AACC, 2000). Zinc content was calculated by the following formula: Zn ppm = μg/mL x100 Sample mass db 3 Where: µg/mL is the absorbance reading concentration

Statistical Analysis
Mineral content of the raw and processed samples were statistically analyzed using analysis of variance (ANOVA) and least significant difference (LSD). The statistical package used was (SAS Institute and Cary, NC). Significant differences were determined at the P ≤ 0.05 level using Fisher LSD to identify significant differences among mean effects of the varieties and processing methods.

Results and Discussions 3.1. Mineral contents in Raw Lentil Varieties
Zinc, iron and calcium contents of the two lentil varieties were significantly (P≤0.05) different from each other (

Effect of Processing Methods on Mineral Contents 3.2.1. Zinc
Processing methods resulted in significant (P≤0.05) effect on zinc content (Table 3.). The maximum (47.35 mg/kg) average value was found in the raw sample and the minimum (35.08 mg/kg) was found in dehulled sample. According to this finding, the zinc content reduced in dehulled, boiled, autoclaved, soaked and germinated samples by 25.91, 16.56, 13.79, 7.41 and 4.52%, respectively. These reductions may be due to the minerals leached from the lentils' seeds into the distilled water at different rates during soaking, boiling and autoclaving. The reduction of zinc in dehulled samples might be due to the removal of seed coat during processing. .49 Au = authoclaving, Bo = boiling, Dh = dehulling, Ge = germinating, Ra = raw, So = soaking CV = coefficient of variation; LSD = least significance difference; values are mean values followed by the same letter in column are not different at 5% level of significance.

Iron
The result of these finding showed that processing methods had significant (P≤0.05) effect on the iron contents of samples (Table 3). The average values of raw, autoclaved, boiled, dehulled, germinated and soaked samples were 60. 55, 52.21, 54.89, 48.96, 57.99 and 56.47 mg/kg, respectively. Processing reduced the content of iron by 19.14, 13.77, 9.35, 6.74 and 4.23% in dehulled, autoclaved, boiled, soaked and germinated samples, respectively. The reduction of iron content might be attributed to leaching during soaking, cooking after soaking and removal of seed coat of lentil samples. These finding agreed with the report of Mubarak, (2005) on the effect of dehulling, soaking, germinating, boiling, autoclaving and microwave cooking of mung bean seeds. However, El-Adawy et al. (2003) reported that germination of mung bean, pea and lentil increased the content of iron. Haytowitz and Matthews, (1983) reported that cooking in boiling water caused great losses of Fe (8%). Hatcher, (2009) reported that dehulling (removal of seed coat) resulted in a significant decrease in iron content.

Calcium
Processing method had significant (P≤0.05) effect on calcium content of lentils (Table 3.). Processing decreased the content of calcium from maximum (842.93 mg/kg) to a minimum (762.38 mg/kg) in raw and dehulled sample, respectively. Processing methods reduced the contents of calcium by 9.56, 4.75, 3.55, 1.27 and 0.55% in dehulled, boiled, autoclaved, soaked and germinated samples, respectively. The reduction of calcium due to germination disagreed with the finding of El-Adawy et al. (2003) on lentil, mung bean and pea which increased after germination. However, agreed with Mubarak, (2005) who reported on reduction of calcium content during dehulling, boiling, germinating, autoclaving, soaking and microwave cooking in mung bean seeds. The reduction of calcium during germination could be due to leaching during soaking that takes place prior to germination.

Conclusion and Recommendation 4.1. Conclusion
The mineral contents of the lentils' samples were reduced in varied degree by all processing methods indicated in this finding. Dehulling process was the highest reduction whereas germinating process was the least reduction of mineral contents.

Recommendation
The current study observed the effect of different processing methods on mineral contents. This finding recommends that:  Instead of dehulling, using germination during lentil processing to different end products.  Study on the effect of modern processing techniques on the mineral contents of lentil varieties in Ethiopia.