Effect of hydroxypropyl methylcellulose, protein and fat on predicted glycemic index and antioxidant property of gluten-free bread from rice flour

Due to the lack of gluten, hydroxypropyl methylcellulose (HPMC), whey protein concentrate (WPC) and soy protein isolate (SPI) were fortified (4 g/100 g flour) into gluten-free bread made from rice flour. The heteropolymer structure of HPMC and protein covered starch granules, resulting in a decrease in predicted glycemic index (pGI) of bread from 84.08 to 67.20-71.04. Addition of butter reduced the pGI to 73.55. By changing the baking mode from hot air baking to microwave baking and microwave-hot air baking, the pGI was reduced from 73.55 to 70.51-70.81 (p <= 0.05). With addition of HPMC or/ and protein, the gluten-free bread exhibited stronger inhibition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals than the wheat bread. Therefore, starch digestibility of the gluten-free bread was mainly reduced by mixture of HPMC, proteins and butter in the dough recipe. Addition of HPMC and WPC further benefited the improvement of antioxidant activity by DPPH assay. Practical applications The finding of this research was the technique to manipulate GI and antioxidant activity in the rice-flour bread by microwave assisted baking process and addition of HPMC, WPC and butter. The outcome of this research could increase health benefit of gluten-free bread from rice flour, in terms of slow starch digestion and high antioxidant activity.