ABSTRACT

This study was carried out to determine the effect of variety and particle size on the quality characteristics of water yam flour and bread. Three mature improved varieties of water yam (TDa 11/00316, TDa 11/00201, and TDa 11/00432) were obtained from the Yam Programme of National Root Crops Research Institute (NRCRI), Umudike, Nigeria. Each of the yam varieties was processed into flour by peeling with knife, washing with clean water, slicing (0.1 inch thickness), sun drying (37 – 40⁰C, for 16 h at 55% RH), milling (coarse and fine milling) and sieving into 150 microns and 300 microns particle sizes.  The flours were analyzed for functional, anti-nutrients, antioxidants, and pasting properties. They were then processed into gluten-free bread using xanthan gum and stevia to replace gluten and sugar respectively. The bread samples were analyzed for in vitro starch digestibility, physical properties, proximate composition, and sensory evaluation. Results showed that variety and particle size were significant factors affecting the quality characteristics of D. alata flour and bread. Functional properties ranged from 0.61 – 0.68 g/ml, 0.38 – 0.46 g/ml, 2.25 – 3.25 g/g, 1.39 – 1.64 g/g, 56.50 – 167.50 s, and 65.25 – 78.50⁰C for tapped bulk density, loose bulk density, water absorption capacity, oil absorption capacity, wettability and gelatinization temperature respectively. Anti-nutrients ranged from 1.37 – 1.74 %, 0.12 – 0.16 %, 0.12 – 0.15 mg/100g, and 16.93 – 23.41 mg GAE/100g for tannin, phytate, oxalate and total phenol respectively. Antioxidants ranged from 1.23 – 3.76 % and 12.11 – 45.36 % for DPPH and FRAP respectively. Pasting properties were reported as follows: pasting temperature: 84.40 – 86.90⁰C, peak time: 4.80 – 5.47 min, peak viscosity: 181.96 – 434.08 RVU, minimum viscosity: 142.21 – 351.79 RVU, breakdown viscosity: 32.29 – 171.84 RVU, final viscosity: 200.13 – 463.63 RVU, and setback viscosity: 56.46 – 167.50 RVU. In vitro starch digestibility was reported as follows: rapidly digestible starch (RDS): 0.59 – 2.59 g/100g, rapidly available glucose (RAG): 1.37 – 8.89 g/100g, slowly digestible starch (SDS): 0.23 – 6.49 g/100g, and resistant starch: 1.71 – 3.10 g/100g. Physical properties ranged from 175.50 – 190.50 cm³, 70.15 – 83.75 g, and 0.37 – 0.48 g/cm³ for loaf volume, weight and density respectively. Proximate composition were reported as follows: moisture content: 29.82 – 36.73 %, protein: 8.92 – 10.37 %, crude fibre: 0.53 – 0.95 %, fat: 1.33 – 5.46 %, ash: 2.32 – 2.92 %, and carbohydrate: 47.72 – 52.75 %. Sensory scores were reported as follows: appearance: 5.76 – 6.69, texture: 5.20 – 6.28, flavour: 5.20 – 6.32, taste: 4.92 – 6.52, aroma: 5.04 – 6.60, and general acceptability: 5.76 – 7.12. Bread made from coarser flour from TDa 11/00201 (WWP) was mostly accepted by the panelists. It was observed that interaction between variety and particle size had significant effect (p<0.05) on the anti-nutrient, antioxidant, pasting, physical and sensory properties of the flour and bread samples. It was concluded that smaller particle sizes enhance antioxidant properties of D. alata flour; however, coarser particle sizes are recommended for slower release of glucose especially that of the TDa 11/00201 variety.