Annealled purple yam (Dioscorea alata var. purpurea) flour improved gelatinisation profile, but increased glycemic index of substituted bread

Yam starch and flour has been explored for its functional properties including textural, antioxidative, hypoglycemic, and hypolipidemic characteristics. Our previous study showed that subtitution of 20% purple yam flour retained bread volume and sensory characteristic, as well as decreased glycemic index of bread by about 20 points. This work aimed to strengthen purple yam flour textural characteristics by improving gelatinisation profile using annealing at various times (1, 6, 12, 18, 24 hours), and temperatures (40, 45, 50, 55, 60°C). Annealed purple yam flour was then incorporated into bread making, to substitute wheat flour by 50%. In vivo study on blood glucose level was carried out using a commercial kit, in which result was used to calculate glycemic index. Result showed that annealing decreased peak viscosity (191 cP) and final viscosity (355 cP), as well as improved peak time (13 min). Temperature and time during annealing significantly (P 0.05) affected viscosity. Bread with 50% subtitution of annealed yam flour showed higher hardness (22 N), and lower bread volume (532 cm³). The use of arabic gum reduced hardness of substituted bread. Blood glucose level profile of volunteers after consumption of substituted bread did not substantially differ from that of normal bread, and this led to glycemic index of 93.19. Annealing did not seem to be a sufficient method to improve hypoglycemic effect of purple yam flour, which may correlate to its starch nature.