Effects of Black Rice Anthocyanin Enrichment on Bread Digestibility and Glycemic Index

By incorporating black rice anthocyanins into a carbohydrate-rich food matrix, this project aims to assess the changes in in-vitro carbohydrate digestibility, and the glycemic index (GI) of the enriched carbohydrate-rich food. We hypothesize that the bread enriched with black rice anthocyanins will retard carbohydrate digestibility, and have a lower GI. A simulated digestion model in-vitro was used to investigate the digestibility of bread enriched with black rice anthocyanin extract (BRAE). To assess the GI of the enriched bread, 24 healthy adults participated in a randomized, controlled crossover study with 3 intervention arms. Participants received 50-g glucose solutions as a reference; interventions included 50-g available carbohydrate (ACHO) servings of white bread (CON), bread enriched with 2% (BB-2) and 4% (BB-4) BRAE. In the simulated digestion model, the enrichment of BRAE was found to significantly reduce oral and intestinal digestion of bread. Relative to CON, the concentration of glucose released in the simulated oral digestion was reduced for BB-2 (P = 0.9529) and BB-4 (P = 0.0001). Relative to CON, the incremental area under the intestinal digestion curves (IAUC) were also reduced for BB-2 (P = 0.0001) and BB-4 (P < 0.0001). The rate constants of the modelled intestinal digestion profiles saw a dose-response reduction with BRAE enrichment. In the randomized controlled trial, there was up to a 27-point reduction in the GI of BRAE-enriched bread. Relative to CON, a significant difference in 2 h mean insulin concentration was also observed after BB-2 (P = 0.024). However, considerable inter-individual variation was also observed in postprandial measurements among the healthy participants. These findings suggest that the enrichment of BRAE in bread slows carbohydrate digestibility, reduces GI, and improves postprandial insulinemic responses. BRAE may thus be a viable food-sourced ingredient for the enrichment of some carbohydrate-rich foods, as a dietary strategy to manage postprandial hyperglycemia. This research was co-funded by National University Health System and National University of Singapore as part of the grant awarded to the Health Innovation Program (CF/SCL/16/178) led by Prof. E Shyong Tai.