Quality characteristics and acceptability of 'amala' (yam-based thick paste) as influenced by particle size categorization of yam (Dioscorea rotundata) flour.

The study was essentially an investigation on the influence of size-categorized yam (Dioscorea rotundata) flour on the quality characteristics and acceptability of amala (yam-based thick paste). Yam flour was separated into three major particle size categories (i.e. 75-150 µm, 150-300 µm and whole meal [<300 µm]), while the physicochemical properties of each category were evaluated and flour samples finally used to prepare amala. Both the protein and ash contents of the yam flours were found to decrease with the decrease in the particle size giving 2.87% and 2.27% in 75-150 µm flour category, respectively. The loose bulk density and packed bulk density of the whole meal (<300 µm) were higher than that of others giving 0.50 g/cm(3) and 0.78 g/cm(3), respectively, while 150-300 µm flour category gave the highest value (2.88 g/g) in water absorption capacity. The colour characteristics of the flour samples showed that the whole meal (<300 µm) had the highest lightness index, L*-value (76.4). The 75-150 µm flour category had the highest chroma, C-value (19.2), while that of 150-300 µm had the lowest value (18.7) with no significant difference at p < 0.05. The pasting characteristics of the flour samples showed that 75-150 µm flour category exhibited highest peak viscosity (257.1 RVU), while the whole meal (<300 µm) exhibited highest breakdown viscosity (40.9 RVU), final viscosity (364.0 RVU) and setback viscosity (99.7 RVU). The amala prepared from 150-300 µm flour category gave the highest softness index (19.6 mm) while that obtained from 75-150 µm flour category gave the lowest value (16.6 mm). The sensory quality rating of amala prepared from the flour samples showed that amala from 150-300 µm flour category was rated the highest in terms of colour, texture (ease of mouldability), aroma and overall acceptability. Both positive and negative correlations were found between some properties of size-categorized yam flours and sensory quality characteristics of amala.