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Harnessing the benefits of sorghum: In vitro starch digestion, in vitro fermentation and processing of tannin and tannin-free sorghums

Nyambe Lisulo Mkandawire, University of Nebraska - Lincoln


Sorghum is an important grain mainly used for food and feed purposes. In most areas where sorghum has been used, it has had negative perceptions associated with its tannin contents, perceived low starch and protein digestibility and lack of functionality when compared to other grains such as wheat and maize. Therefore, sorghum related research and its use by the food industry has been limited and lags behind other cereals. The present dissertation discusses 4 research areas aimed at increasing utilization of tannin and non-tannin sorghums, and at improving their image when used as wholegrain flours. In vitro starch digestibility of raw and processed wholegrain sorghum flours did not correlate with condensed tannin content in each of the 15 flours tested. However, tannin extracts both reduced and enhanced amylase activity depending on conditions. This trend was clear in extracts but more complex in wholegrain flours. An in vitro fermentation model using human feces showed that tannin and non-tannin flours were efficiently degraded by fecal bacteria leading to higher production of acetate and propionate compared to inulin. After extensive fermentation, enhanced butyrate production was associated with non-tannin flour. Overall, all sorghums enriched for Bacteroidetes. RTE extruded breakfast cereals were processed from two sorghum varieties (tannin and non-tannin sorghums) with increasing wholegrain flour percentages (55, 62.5 and 70%). Consumer acceptability of the cereals did not significantly differ from an oat based control. Variety and percentage flour added influenced some physical and chemical characteristics. Extrusion increased in vitro starch digestibility but decreased protein digestibility of the cereals. Finally, frybreads were prepared from refined and wholegrain tannin and non-tannin sorghum composite fours (sorghum-wheat). Panelists rated frybreads with up to 50% sorghum flour as not significantly different from the control, 100% wheat flour frybreads. Interestingly, reduced oil absorption during frying was associated with wholegrain tannin sorghum but not with composite flour or non-tannin flours indicating that tannins could play a role in reduction of oil in fried foods.

Subject Area

Food Science

Recommended Citation

Mkandawire, Nyambe Lisulo, "Harnessing the benefits of sorghum: In vitro starch digestion, in vitro fermentation and processing of tannin and tannin-free sorghums" (2013). ETD collection for University of Nebraska - Lincoln. AAI3590985.