Modification of starch digestibility and phenolic bioaccessibility in phenolic-rich flours by physical treatments with ferulic acid followed by vacuum oven and freeze-drying

Consumer demand for healthy snack products has led to increased efforts to modify glycemic responses of these products. The formation of starch-ferulic acid (FA) complexes through acidified water steeping leads to an increase in RS content and reduction of glycemic responses in animal models. However, the application of these methodologies to commercially relevant phenolic-rich flours (black rice, BR; purple maize, PM) and their impacts on starch digestibility and phenolic bioaccessbility remain unclear. Using an acidified water steeping method previously reported in pure starch, potato starch (PS), BR and PM flour slurries were prepared with FA at a 20:1 and 8:1 ratio in HCl-acidified water (pH 2). The steeping process reduced phenolic content (similar to 75%) and increased starch digestibility. Ferulic acid loading capacity on PS (22-124 mg/g starch) was greater than for PM and BR flours (8-40 mg/g starch). Ferulic acid bioaccessibility decreased with an increase in its amount in PS and flours. Steeping enhances cyanidin 3-O-glucoside bioaccessibility, while addition of FA decreases its bioaccessibility. The increase in starch digestibility of phenolic-rich flours after steeping with and without FA can be attributed to the limited loading capacity of FA and loss of native phenolics during the steeping process.