Food processing can improve the value of insoluble dietary fiber by boosting butyrogenic fermentation

Insoluble dietary fibers are traditionally known to be poorly fermented in the large intestine. Still their value may be high, as evidence shows that some groups of important butyrogenic bacteria preferentially utilize insoluble substrates to support their energy needs. The objective of this study was to increase fermentability of an insoluble bran fiber (pearl millet) through microwave and enzymatic treatments while keeping its mostly insoluble characteristic to possibly increase butyrate production. Combined microwave and enzymatic processing increased the amount of insoluble fiber fermented in vitro from 36 to 59%, with a minor increase in fiber solubility (8%). Processing doubled butyrate production at 6 h fermentation compared to the native fiber. 16S rRNA gene sequencing results showed that processing targeted the promotion of Firmicutes bacteria with a significant increase in Firmicutes/Bacteroidetes ratio compared to the native fiber. Overall, these data show that processing techniques can be used to increase the value of insoluble fiber, presumably by increasing accessibility of the fiber to degrading bacteria, and to support butyrogenic Firmicutes that preferentially compete on insoluble fibers. Increasing insoluble fiber fermentability enhances whole grain value of dietary fiber.