Preparation and characterization of sorghum flour with increased resistant starch content

Authors: Vu, Thanh Hien; Bean, Scott; HSIEH, C - Kansas State University; SHI, YONG-CHENG - Kansas State University

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2017
Publication Date: 4/3/2017
Citation: Vu, T.T., Bean, S.R., Hsieh, C.F., Shi, Y. 2017. Preparation and characterization of sorghum flour with increased resistant starch content. Journal of the Science of Food and Agriculture. https://doi.org/10.1002/jsfa.8346.
DOI: https://doi.org/10.1002/jsfa.8346

Interpretive Summary: The objectives of this study were to develop a hydrothermal treatment to increase the resistant starch content of sorghum flour without gelatinizing the starch, to investigate the effect of treatment conditions on sorghum protein properties, and to understand how changes in protein properties impacts starch digestibility. Flour at 20% moisture that was heat treated for 4 h had the highest resistant starch content (22.1% compared with 5.6% in the untreated flour) of all conditions tested. Minimal starch gelatinization was found in the flour treated under these conditions. Thus, heat-moisture treatments were successful in increasing resistant starch content of sorghum flour without gelatinizing the starch which would retain starch functionality in food product applications. The increase in resistant starch of sorghum flour after heat-moisture treatment was most likely due to heat induced changes in sorghum proteins.

Technical Abstract: The primary objective of this research was to develop an effective process to increase the resistant starch content of sorghum flour. A secondary objective was to investigate the role of the sorghum proteins on starch digestibility. Samples of white sorghum flour (28.9% amylose content) with different moisture contents (0%, 12.5%, 20%, and 30%) were treated at different temperatures (100, 120, and 140 oC) for different times (1, 2, and 4 h). Samples after heat treatments were tested for starch digestibility and protein digestibility. The flour treated with 20% moisture at 100 oC for 4 h had the highest resistant starch (RS) content (22.1% compared with 5.6% of the untreated flour) and the lowest protein digestibility (8.4% compared with 68.3% of the untreated flour). The same heat-moisture treatment on isolated sorghum starch showed no significant change in RS content. Differential scanning calorimetry showed a very low degree of gelatinization for samples treated at moisture contents of 20% and below. X-ray diffraction also suggested minimal change in starch crystallinity after heat treatment at low moisture contents (20% and below). As expected, sorghum protein solubility decreased after heat treatment, suggesting that protein structure was altered during the heat treatments. Heat-moisture treatments were successful in increasing resistant starch content of sorghum flour without gelatinizing the starch which would retain starch functionality in food product applications. The increase in resistant starch of sorghum flour after heat-moisture treatment was most likely due to heat induced changes in sorghum proteins.