Optimization of Millet Incorporated Mango Stirred Yoghurt Using Response Surface Methodology

Abstract

This study developed and optimised a millet-incorporated mango stirred yoghurt containing mango pulp, steamed little millet and popped amaranth. A three-factor face-centred central composite design comprising 20 experimental runs was used to assess the effects of mango pulp, steamed little millet and popped amaranth on colour and appearance, flavour, mouthfeel and consistency, sweetness, overall acceptability and viscosity. Quadratic models adequately described the measured responses, and numerical optimisation identified a formulation containing 16.0% mango pulp, 1.5% steamed little millet and 3.5% popped amaranth, with a desirability of 1.00. The optimised formulation was prepared and compared with mango stirred yoghurt produced without millet and amaranth. The millet-incorporated product contained 25.00% total solids, 2.80% fat, 3.24% protein, 0.87% ash and 18.07% carbohydrate. Its viscosity was 4558.42 cP at 20°C, compared with 2362.20 cP for the control. The optimised product also obtained higher scores for all evaluated sensory attributes. Degree of hydrolysis, tyrosine content, free fatty acid content and DPPH radical-scavenging activity were significantly higher in the millet-incorporated yoghurt. Lactic acid bacterial counts were comparable between the two products, while coliforms and yeasts and moulds were not detected at the time of analysis. The findings demonstrate that steamed little millet and popped amaranth can be incorporated into mango stirred yoghurt to obtain an acceptable fermented dairy product with modified compositional, physicochemical and biofunctional characteristics.