Effect of pigeon pea and sorghum flour supplementation on the physico-chemical, protein digestibility, sensory properties and shelf life of millet flour

Abstract

Malnutrition is a major health problem in many parts of the world. Protein-energy malnutrition (PEM) remains a significant health issue among children in many parts of Kenya. The aim of this study was to utilize locally available sorghum, pearl millet, and pigeon peas in the formulation of a protein-rich complementary flour to contribute to reduced PEM among children under 5 years in Tharaka Nithi, Kenya. This study adopted a nested design with two factors; pigeon pea level and sorghum level nested in pigeon pea level. For shelf life study an additional factor was introduced which was storage time in days. Preparation of the blends included 5 ratios of Pigeon peas (0, 15, 30, 45, 60% of the total flour blend), and 3 levels of sorghum (0, 20, 40% of the milletsorghum flour mix). These blends were then analysed for physicochemical properties, protein digestibility, sensory properties and shelf life. The sensory evaluation of flour blends was carried out with informed consent of the respondents who voluntarily participated in sample assessment. Data on physico-chemical properties, protein quality, titratable acidity, pH and sensory evaluation was subjected to analysis of variance (ANOVA) and significant means separated via Tukey’s Honest Significant Difference (HSD). Data on the willingness to buy the different blends was analysed using the Kruskal Wallis test. Microbial data was log transformed and subjected to ANOVA. All data was analysed using Minitab software at P < 0.05. The addition of pigeon peas to the millet-sorghum-pigeon peas composite blend significantly (P < 0.001) increased all functional properties except bulk density while sorghum significantly affected swelling capacity (P = 0.019), water holding capacity (P=0.001), gelling temperature (P < 0.001), and tapped density (P = 0.002). Addition of pigeon peas significantly (P < 0.001) increased the protein content from 11.845% to 16.016% and digestibility of the flour blends from 34.95% to 46.34%. Sensory evaluation revealed that the addition of pigeon peas significantly (P < 0.001) lowered the taste (3.862 to 3.420), flavour (3.908 to 3.299), viscosity (4.000 to 3.270) and texture (4.035 to 3.420) rating and general acceptability of porridge (3.690 to 3.339) prepared from the composite blends. Sorghum significantly (P < 0.001) increased colour (2.897 to 4.224), taste, flavour and overall acceptability of the flour blends. Sensory evaluation revealed that the samples containing 34% sorghum and 15% pigeon peas performed best in all sensory attributes as well as in overall acceptability. The average relative humidity and temperature during storage was 55.494% and 25.225 0C, respectively. The addition of pigeon peas to the blends significantly (P < 0.001) increased the Titratable acidity (0.1862 to 0.245g/l) of the composite blends which indicated a gradual deterioration of the flour over the storage period. The initial mean yeasts and mold counts were 2.252 Log CFU/g respectively which were below the East African Community recommended safety limit for yeast and Mold counts in millet flour (4 Log CFU/g). However. This number rose within the first 16 days to 2.628 log cfu/g, then began dropping to (0.492 log cfu/g. This can be explained by the increasing acidity of flour, change in the pH, reduced relative humidity and oxygen supply in the storage container. It is therefore possible to produce pigeon pea containing flour product that is safe for human consumption and that can last for two months and above. These outcomes demonstrate the potential of pigeon peas, sorghum, and millet in creating protein-rich porridge flour and hence improving protein intake for children under 5 years. This study encourages the utilization of pigeon peas to improve the protein content of energy dense cereal grains occasionally used in complementary diets.