Calcium-Rich Pigeonpea Seed Coat: A Potential Byproduct for Food and Pharmaceutical Industries

Abstract

Pigeonpea is a protein-rich legume which is consumed worldwide in a variety of forms (whole seed, dhal, and as a green vegetable). In India, pigeonpea is milled to yield dhal (cotyledon) and this process generates 25–35% waste byproducts. The hull (seed coat) which accounts for 10% of the byproduct is disposed of either as waste or low-cost cattle feed. To recycle the waste byproducts into the food value chain, this study was conducted with the objectives: (i) to estimate nutrient accumulation in the major seed fractions (cotyledon and seed coat), (ii) to estimate the percentage of nutrient contribution by major seed fractions, (iii) to assess the percentage of nutrient loss due to dehulling, and (iv) to determine the scope of seed coat in nutritional value addition. For this, a subset of 60 diverse pigeonpea accessions selected from 600 pigeonpea accessions raised during the 2019 and 2020 rainy seasons at ICRISAT, Patancheru, India, was subjected to a cotyledon and seed coat nutrient analysis. The three-way analysis of variance revealed the significant influence of cropping years, seed fractions, genotypes, and their interactions on nutrient accumulation. The nutrients, namely protein (32.28 ± 2.29%), P (476.51 ± 39.05 mg/100 g), K (1557.73 ± 66.82 mg/100 g), Fe (4.42 ± 0.41 mg/100 g), Zn (2.25 ± 0.21 mg/100 g), and Cu (0.95 ± 0.07 mg/100 g) were enriched in cotyledon. Mn was equally enriched in both the cotyledon and seed coat (1.02 ± 0.12 mg/100 g and 0.97 ± 0.34 mg/100 g, respectively). The seed coat had a high concentration of Ca (652.02 ± 114.82 mg/100 g), and Mg (249.19 ± 34.12 mg/100 g) with wide variability for Fe (2.74–5.61 mg/100 g), Zn (0.88–3.95 mg/100 g), Cu (0.38–1.44 mg/100 g), and Mn (0.58–2.18 mg/100 g). It is noteworthy that the protein and P contents in the cotyledon were 7 and 18 times higher than that in the seed coat, respectively, and the Ca content in the seed coat was 12 times higher than that in the cotyledon. A correlation study revealed that for overall nutrient improvement in dhal, selection for a small seed size was desirable. On an average, the percentage of nutrient contribution by major seed fractions revealed that the cotyledon portion contributed around 95% protein and P; 90% K and Zn; 85% Fe, Cu, and Mn; and 75% Mg, while the seed coat portion contributed nearly 65% Ca to the whole grain. The findings of high Fe and protein concentrations in the cotyledon and high Ca accumulation in the seed coat can serve as a new guide for improved technological fractionation of these components to serve as a novel functional food ingredient and as a dietary supplement that can address malnutrition.

Grain Nutrients Variability in Pigeonpea Genebank Collection and Its Potential for Promoting Nutritional Security in Dryland Ecologies

“…The variability observed for whole-grain protein in the present study (23.35-29.50%) was higher than the protein content (16.76-26.82%) reported in previous studies (Amarteifio et al, 2002;Sekhon et al, 2017;Obala, 2018;Cheboi et al, 2019;Choi et al, 2020;Jawalekar et al, 2020) and is comparable with the dhal protein content of high protein lines (27-29%; Saxena et al, 1987). The protein content in dhal is higher than that in the whole grain (Susmitha et al, 2022), signifying that dhal nutritional analysis of the superior accessions in this study may still have higher protein than the high protein lines reported by Saxena et al (1987). This indicated the availability of superior parental sources for protein biofortification.…”

“…The pigeonpea is found to be rich in calcium (Saxena et al, 2010;Susmitha et al, 2022), and the results of this study inferred that the Ca content in pigeonpea (154. 28 mg/100 g) was found to be higher than many staple cereals (7.49-39.36 mg/100 g), such as rice, wheat, maize, pearl millet, sorghum, and barley but lesser to Ca-dense finger millet (364 mg/100 g).…”

“…Pigeonpea offers an affordable source of protein to the marginalized populations surviving in several developing countries of Asia and Africa. Other than protein, pigeonpea is rich in a few minerals too, and, more interestingly, the accumulation of Fe and Zn in the cotyledons benefits by overcoming the dehulling nutrient loss, which is common in cereals like wheat and rice ( Susmitha et al, 2022 ). Identification of nutrient-rich germplasm can further enrich the breeders’ crossing blocks for developing high-yielding and nutrient-rich varieties.…”

“…Furthermore, a good amount of K (15,000 mg/kg) and Mg (1,530.20 mg/kg) is accumulated in the pigeonpea whole grain, which can reduce the risk of cardiovascular diseases and diabetes when included in the diet ( Schulze et al, 2007 ; Cherbuin, 2016 ; Stone et al, 2016 ). In pigeonpea, the Fe and Zn content in cotyledon is indifferentiable from the whole-grain Fe and Zn ( Susmitha et al, 2022 ). This indicates that the Fe and Zn content reported in this study not only represents the whole grain but also the cotyledon.…”

“…Furthermore, the nutrient accumulation varied with the seed developmental stage, Fe and Zn are rich at the green stage, whereas protein, starch, Mn, and Ca are high at the grain stage ( Singh et al, 1984 ). Unlike cereals, the Fe and Zn are enriched in the cotyledons; thus the processing does not affect the availability of these minerals ( Susmitha et al, 2022 ). Nutrient improvement in pigeonpea was done utilizing few wild species.…”