Effect of the use of starches of three new Ghanaian cassava varieties as a thickener on the physicochemical, rheological and sensory properties of yoghurt

Abstract

Yoghurt is a popular probiotic food rich in micronutrients but suffers from a thickness loss referred to as syneresis, which is caused by liquid expulsion from the gel during storage. To reduce this adverse sensory effect, the starches of three new cassava varieties, Abrabopa, AGRA and Bankye hemaa, were used as thickening agents in the production of yoghurt and its physicochemical, functional and sensory properties evaluated. The starches were extracted by wet gravimetric method and initially characterised by assessing their pH, colour, water binding capacity, swelling power, Solubility index and pasting characteristics. Each of these three starch samples were incorporated at a rate of 2.5, 5.0 and 7.5%, to prepare yoghurt, from fully-skimmed, partially-skimmed and whole milk. The pH, viscosity, syneresis, textural and sensory properties of the yoghurt samples stored at 6 ± 1 °C were monitored over 14 days. Whilst there were significant differences (p < 0.05) in the swelling power and indices, the water binding capacity of the starch samples were comparable. Their cooked paste viscosity were 512.5 BU (Bankye hemaa), 550 BU (Abrabopa) and 620 BU (AGRA) . When used in preparing the yoghurt, the whole milk yoghurt, with Abrabopa starch at 5.0% inclusion, gave the highest consistency (28.7 N.s) and cohesiveness (-2.1 N), whilst fully-skimmed milk yoghurt with AGRA starch, at 7.5%, gave the lowest consistency (7.5 N.s) and cohesiveness (-0.4 N). These results correlated well with those of the sensory scores, which gave the best taste, mouthfeel and sourness scores to yoghurt made from whole milk in which Abrabopa cassava starch at 7.5% had been incorporated and stored for 14 days. The starch of Abrabopa cassava variety therefore adequately prevented syneresis in yoghurt.