Nutritional and Anti-nutritional Evaluation of Selected Sorghum Varieties and Sorghum – Pigeon Pea Flour Blends for Ready to Eat Complementary Food Product Development

Abstract

Sorghum and pigeon peas are important crops in semi-arid regions of Kenya. Improved varieties of these crops that are adapted to these regions have been developed, however a study to determine the nutritional value has not been done. These crops are good sources of protein and minerals but they have some limitations, the presence of anti-nutrients in the grains reduces the bioavailability of these nutrients to the human body. These limitations have been overcome by processing with fermentation and malting the most common. The nutritional composition of two improved sorghum varieties (Seredo and Gadam), two improved pigeon pea varieties (KAT 60/8 and Mbaazi II) and three local varieties of each crop were determined. The effects of fermentation, germination and dehulling techniques on nutritional composition of the food were determined. Malted sorghum, fermented sorghum and steam cooked dehulled pigeon pea flours were prepared by appropriate processes. The flours were blended at three different ratios of 1:1, 2:1 and 5:1 (w/w, sorghum: pigeon pea). Untreated flour of both crops was also prepared and blended at the same ratios and used as control. The nutritional composition varied among the varieties. Seredo exhibited higher levels of anti-nutrient (phytates and tannins) than Gadam and the local variety while local variety exhibited the highest levels of phytates among pigeon peas varieties. The phytates content ranged from 237.4 mg/100 g – 318.8 mg/100 g in sorghum varieties and 149.4 mg/100 g – 208 mg/100 g in pigeon pea varieties. The tannin content ranged from 3.18 mg/100 g – 5.36 mg/100 g in sorghum varieties and 5.11 mg/100 g – 6.05 mg/100 g in pigeon pea varieties. The macro elements (Ca and mg) were generally high while the microelements (Cu and Zn) contents were low for both crops, Seredo and local variety of pigeon pea showed high levels of Fe. From the study KAT 60/8 variety of pigeon pea had the highest protein content and was recommended for improving protein quality of the three sorghum varieties. Results also indicated that Seredo, Gadam and local varieties of sorghum from Tharaka Nithi, Machakos and Makueni Counties respectively had the highest crude protein value hence were recommended for product development. Ready to eat complementary food product was developed by blending flours from the three sorghum varieties and the pigeon pea variety. Fermentation and malting increased the crude protein content of the ready to eat complementary food significantly (p<0.05) compared to control. xivFermented sorghum flour blend exhibited the highest levels of crude protein. Crude protein content differed significantly (p<0.05) among the formulations, flour blended at the ratio of 1:1 had the highest with 14.91%. The anti-nutrients content of the ready to eat complementary food was significantly reduced by fermentation and malting. The tannin and phytate content was least in fermented and malted food which had 2.25 mg/100 g and 207.5 mg/100 g respectively. Blending flours at the ratio of 1:1 had the anti-nutrients content compared to flour ratios of 2:1 and 5:1. The macro elements (Ca and mg) were found to be highest in formulation 1:1 which had 29.81 mg/100 g and 44.86 mg/100 g respectively. Micro element (Fe) Iron was found to be highest in food formulated at the ratio of 5:1 which had 11.87 mg/100 g. The results suggest that fermentation, as a processing technique and blending sorghum and pigeon pea flours at the ratio of 1:1 using Gadam variety, can be used to effectively enhance the nutritional value of sorghum- pigeon pea ready to eat complementary food with concomitant reduction of its anti-nutritional factors. This may be recommended as desirable for solving the problem of protein deficiency among infant in developing countries.