Dr. Devin J. Rose
Date of this Version
Smith, C. (2019). Effect of Processing on Microbiota Accessible Carbohydrates in Whole Grains. (Master Thesis, University of Nebraska- Lincoln, Lincoln, NE, United States).
There is potential to increase microbiota accessible carbohydrates (MAC) in whole grains through food processing. Therefore, different processing conditions for boiling and extrusion of whole wheat flour were studied for their effect on MAC. Processing conditions had a minimal effect on fermentation response using 2 fecal samples of disparate composition. However, the processing method had an impact on the fermentation of non-digestible carbohydrates and subsequent short chain fatty acids production, but only for a microbiome with high diversity and a predominance of microbes associated with dietary fiber intake. Subsequently, five processing methods: boiling, extrusion, unleavened bread, yeast bread, and sourdough bread, were studied for their effects on in vitro fermentation of whole wheat flour using the fecal microbiota from 10 subjects. Different grain processing operations caused varying shifts in microbiota composition and activity. Notably, sourdough bread supported a diverse microbial community that produced more butyrate and propionate. Conversely, extrusion led to decreases in diversity and butyrate and propionate production, but enabled increase carbohydrate fermentation. These differences were attributed to changes in the microstructure of the grains. In order to better understand the effects of grain processing on host health, two microbiomes that ranged in diversity and were from subjects who habitually consumed high and low levels of dietary fiber and whole grains, were inoculated into germ free mice. These mice were then fed isocaloric western diets supplemented with cellulose (control), boiled whole wheat, extruded whole wheat, or extruded
brown rice. The mice harboring the microbiome from the low dietary fiber consumer had increases in diversity due to whole grains and the whole grain source and processing had differential effects. The mice harboring the microbiome from the high dietary fiber consumer was more diverse and was minimally affected by treatment. These mice had reduced body fat and body weight gain with boiled whole wheat compared to extruded whole wheat while there was no difference between brown rice and whole wheat. Both microbiomes had reduced glucose tolerance with extruded grains. Thus, both the digestion and fermentation are important factors of the effect of whole grains and food processing on host health.
Advisor: Devin J. Rose