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Agricultural Science Digest, volume 42 issue 1 (february 2022) : 80-83

Proximate Composition, In vitro Digestibility and Anti Nutritional Factors of Millets and Legume Grains

Neha Rana1,*, Saroj Dahiya1
1Department of Foods and Nutrition, Chaudhary Charan Singh Haryana Agricultural University, Hisar-125 004, Haryana, India.
Cite article:- Rana Neha, Dahiya Saroj (2022). Proximate Composition, In vitro Digestibility and Anti Nutritional Factors of Millets and Legume Grains . Agricultural Science Digest. 42(1): 80-83. doi: 10.18805/ag.D-5248.
Background: Whole grains serve as a preferred carbohydrate source in a modern Indian diet to achieve a balance of macronutrients, micronutrients, fibers and phytochemicals for optimal health promotion and prevent chronic diseases such as type 2 diabetes, cardiovascular disease (CVD) and obesity. The five most common ancient grains that have the potential to be used more in Indian cooking are amaranth, barley, pearl millet, finger millet and sorghum. These grains have higher fiber and protein content.

Methods: The study was conducted to investigate chemical composition, sugar content, in vitro protein and starch digestibility and antinutrient content of pearl millet, sorghum and mung bean. Effect of blanching and germination on chemical composition of pearl millet and mung bean, respectively were determined. 

Conclusion: The results of proximate composition of grains revealed that germinated mung bean had significantly highest amount of protein, total soluble sugar, non reducing sugar content, in vitro protein digestibility. Sorghum had significantly higher content of total carbohydrate, reducing sugar, starch and in vitro starch digestibility. Crude fat, phytic acid and polyphenol were highest in unprocessed pearl millet. Germination and blanching of seeds cause the significant reduction in anti-nutrient content of mung bean and pearl millet, respectively.
India is the largest producer of many kinds of coarse cereals/millets which includes pearl millet, sorghum, oat, finger millet, foxtail millet etc. Among these, pearl millet and sorghum are unique millets which are rich in dietary fiber, micronutrients and phytochemicals. Research shows that sorghum and pearl millet grains are nutritionally comparable or even superior to major cereals such as wheat and rice owing to higher levels of protein with more balanced amino acid profile, dietary energy, vitamins, several minerals (especially micronutrients such as iron and zinc), insoluble dietary fiber leading to lower glycemic index. In addition to their nutritive value, several potential health beneûts such as preventing cancer and cardiovascular diseases, reducing tumor incidence, lowering blood pressure, risk of heart disease, cholesterol and rate of fat absorption, delaying gastric emptying, and supplying gastrointestinal bulk have been reported for millet (Gupta et al., 2012; Patni and Agrawal 2017).
Legumes have been considered as a cheap source of protein to the people. They contain 2 to 3 times more protein than cereals. They have shown numerous health benefits due to their dietary fibre content such as lower glycemic index for people with diabetes increased satiation and cancer prevention as well as protection against cardiovascular diseases (Polak et al., 2015; Cakir et al., 2019). Mung bean (Vigna radiata), also called green gram is a tropical legume, widely grown in Asia, particularly in Thailand, India and Pakistan. Mung bean is 3rd most important crop of India, in terms of cultivated area and production, accounting for 9 per cent of total legumes production. Mung bean is rich source of protein and amino acid especially lysine and thus can supplement cereal based human diets. It is good source of thiamin, niacin, vitamin B6, pantothenic acid, iron, calcium, magnesium, phosphorus and potassium and very good source of dietary fiber, vitamin C, vitamin K, riboflavin, folate, copper and manganese (Dahiya et al., 2015; Yi-Shen et al., 2018).
Source of raw material
The samples of pearl millet (Pennisetumglaucum) (WH-901-445) were procured from Bajra section, sorghum [Sorghum bicolor (L.) Moench] (HC-125) from Forage section, mung bean (Vigna radiata) (MH-125) from Pulses section, Department of Genetics and Plant Breeding, College of Agriculture, Chaudhary Charan Singh Haryana Agricultural University, Hisar. The seeds were cleaned and made free of dust, dirt and foreign materials prior to processing and product development. Raw materials were stored in clean and hygienic condition for further use.
Preparation of sample
Blanching of pearl millet
Blanching of pearl millet was done by the process of Chavan and Kachare (1994). Distilled water was brought to boiling to 98°C in an aluminium container. The grains were subjected to boiling water (1:5 ratio of seeds to boiling water) for 30 seconds and dried at 50°C for 60 minutes.
Germination of mung bean
Mung bean grains were first cleaned and free from broken seeds, dust and other foreign materials and then soaked in tap water for 12 h at 37°C. Seed to water ratio of 1:5 (W/V) was used. The unimbibed water was discarded. The soaked seeds were germinated in sterile petri dishes lined with wet filter paper for 48 h at 37°C with frequent watering. The sprouts were rinsed in distilled water and dried at 50-55°C.
Unprocessed sample of pearl millet, sorghum, mung bean, blanched pearl millet and germinated mung bean were ground to fine powder.The resultant flours were packed in air tight plastic containers.
Nutritional evaluation of raw and processed sample of pearl millet, sorghum and mung bean
Proximate composition of sample was determined according to AOAC (2000) method. Total carbohydrate was calculated by difference method. Total soluble sugars were estimated by using the method of Yemm and Willis (1954). Reducing sugars were estimated by using Somogyi’s modified method (Somogyi, 1945). The amount of non-reducing sugar was calculated as the difference between total soluble sugars and reducing sugars. Starch from the sugar free pellet was estimated by using the method of Clegg (1956). In vitro protein digestibility was carried out by the modified method of Mertz et al., (1983). The nitrogen contents of the sample and the undigested residue were determined by the micro- kjeldhal method of AOAC, 2000. In vitro starch digestibility was assessed by employing pancreatic amylase (Singh et al., 1982). Total polyphenols were extracted by the method of Singh and Jambunathan (1981). The amount of polyphenolic compounds was estimated as tannic acid equivalent according to Folin-Danis procedure (Swain and Hills, 1959).
Statistical analysis
Data collected were subjected to analysis of variance (ANOVA) using the SPSS Statistical Package.
The data in respect to proximate composition of grains are presented in Table 1. Significant differences were observed in proximate composition of different grains analyzed in the present study. Moisture content of the different grains was in range of 9.48 - 10.96 per cent. As legumes are rich source of protein, significantly higher amount of crude protein was present in germinated mung bean (25.78%) and crude fiber in unprocessed mung bean (4.52%), respectively. These results are in agreement with the values reported earlier by various workers (Paul et al., 2011; Dahiya, et al., 2015: Fayyaz, et al., 2018). A non significant difference was observed for crude protein in soaked, dehulled and germinated mung bean by Tarun (2014). Pearl millet had the highest amount of crude fat (5.56%) as reported by Patni and Agrawal (2017). Among the different grains, sorghum had significantly higher content of total carbohydrates. These results are similar to that reported by Noha et al., (2011) and Ogbonna et al., (2012).

Table 1: Proximate composition of grains (%, dry weight basis).

Data in respect of total soluble sugar, reducing sugar and non- reducing sugar content of grains are presented in (Table 2). Among the grains, germinated mung bean had significantly higher content of total soluble and non-reducing sugars.  These results are in agreement with those reported by earlier workers in legume (Kakati et al., 2010; Tarun, 2014). Germination (24h) also caused significant increase in sugar contents. The increase in sugars contents might be due to enzymatic hydrolysis of starch in to simple sugars. Hydrolysis of starch to monosaccharide, results in increased concentration of sugars in pulses. Observations of Kakati et al., (2010) that germination caused significant increase in sugar content in green gram and black gram. Sorghum exhibited significantly highest amount of reducing sugar and starch content. These results are in agreement with the earlier results reported by Elkonin et al., (2013) and Souilah et al., (2014).

Table 2: Sugar and starch content of grains (g/100 g, dry weight basis).

In vitro digestibility
Data in respect of In vitro protein and starch digestibility of grains are presented in Table 3. Maximum In vitro protein digestibility (87.22%) was observed in germinated mung bean and sorghum (70.02%) and In vitro starch digestibility (32.96 mg maltose released/g) was highest in sorghum. Similar results were also reported in sorghum by Badubi (2012) and Elkonin et al., (2013). Similarly, Uppal and Bains (2012) found that In vitro protein digestibility in mung bean was highest after germination (89.1%). Other workers also reported improvement in protein digestibility after gemination (Olu et al., 2013). The hydrolysis of seed proteins, protease inhibitors, phytic acid and polyphenols during germination may account for considerably increase protein digestibility in legumes (Chitra et al., 1997).

Table 3: In vitro digestibility of grains.

Anti-nutritional factors
The data regarding phytic acid and polyphenol of grains are presented in Table 4. Anti-nutritional factors are compounds found in most food substances which are poisonous to humans or in some ways limit the nutrient availability to the body thus preventing optimal exploitation of the nutrients present in food and decreasing its nutritive value. For example phytic acid, lectins, tannins, saponins, amylase inhibitors and protease inhibitors have been shown to reduce the availability of nutrients and cause growth inhibition. Most of the toxic and anti-nutrient effects of these compounds in plant foods can be removed by several processing methods such as soaking, germination, boiling, autoclaving, fermentation, genetic manipulation and other processing methods without altering the nutritional value of food (Thakur and Kumar, 2017).

Table 4: Anti-nutrient contents of grains (mg/100g, dry weight basis).

Phytic acid was highest in unprocessed mung bean followed by unprocessed pearl millet, germinated mung bean, blanched pearl millet and sorghum. The polyphenol content of all grains ranged from 203.42 to 739.43 mg/100 g. The results of phytic acid content in present study in mung bean (758.40 mg/100 g) and pearl millet (754.19 mg/100 g) are in agreement with those reported by Tarun (2014) and Kulthe et al., (2016), respectively. Pearl millet had the highest amount of polyphenol (739.43 mg/100 g). Polyphenol content of pearl millet varieties ranged from 502.78 to 658.30 mg/100 g as reported by Anju (2005). Germination of mung bean and blanching of pearl millet cause the significant reduction in phytic acid (487.84 mg/100 g) and polyphenol content (546.50 mg/100 g), respectively. The blanching of pearl millet was found to reduce phytic acid and polyphenol contents from 34-39 and 14-29%, respectively (Bhati et al., 2016: Demissew and Meresa, 2017; Krishnan and Meera, 2018). Singh et al., 2014 reported that phytic acid and polyphenol content reduced in germinated mung bean.
In conclusion, processing i.e. blanching of pearl millet and germination of mung bean improve the nutrition quality of food grains. Germinated mung bean had higher content of protein, total soluble sugar, non-reducing sugar and in vitro protein digestibility and lower content of phytic acid and polyphenol. Blenching of pearl millet reduces the phytic acid and polyphenol content and improves the starch digestibility. Sorghum was good in terms of total carbohydrate, starch, In vitro starch digestibility and lower amount of phytic acid.

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