Abstract
Differences in the chemical and physical properties of dietary fibers are increasingly known to exert effects on their fermentation by gut microbiota. Here, we demonstrate that maize bran particle size fractions show metabolic output and microbial community differences similar to those we previously observed for wheat brans. As for wheat brans, maize bran particles varied in starch and protein content and in sugar composition with respect to size. We fermented maize bran particles varying in size in vitro with human fecal microbiota as inocula, measuring their metabolic fate [i.e., short-chain fatty acids (SCFAs)] and resulting community structure (via 16S rRNA gene amplicon sequencing). Metabolically, acetate, propionate and butyrate productions were size-dependent. 16S rRNA sequencing revealed that the size-dependent SCFA production was linked to divergent microbial community structures, which exerted effects at fine taxonomic resolution (the genus and species level). These results further suggest that the physical properties of bran particles, such as size, are important variables governing microbial community compositional and metabolic responses.
Highlights
The human gut houses trillions of microorganisms, and their physiological importance in human health is becoming increasingly understood
To test our hypothesis that the fermentation of maize bran is particle size-dependent, we performed in vitro fermentation with maize brans milled to a range of particle sizes
The other three sizes (250–300, 300–500, 500–850 μm) produced less than half the amount for all the short-chain fatty acids (SCFAs) compared to the smallest fraction
Summary
The human gut houses trillions of microorganisms, and their physiological importance in human health is becoming increasingly understood. Specificity in consumption of dietary fiber structures by microbial species is known to govern their population sizes in the gut (Dominianni et al, 2015). Modern refined flour is comprised mainly of fine endosperm particles, and germ and bran are removed during the milling process In some countries, such as the United States, production of “whole” flour typically involves brans being milled separately to small particle sizes and added back to refined flour. This reduction in the grain particle with westernization may, in part, explain microbiome differences among Western and nonWestern populations (Cordain et al, 2005). We demonstrate that particle size effects occur in in vitro fermentation of maize brans by fecal microbiota
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