| Abstract: | The origin of resistant starch (RS) in distiller's dried grains with solubles (DDGS) of triticale, wheat, barley, and corn from dry‐grind ethanol production was studied. A considerable portion of starch (up to 18% in DDGS) escaped from either granular starch hydrolysis or conventional jet‐cooking and fermentation processes. Confocal laser scanning microscopy revealed that some starch granules were still encapsulated in cells of grain kernel or embedded in protein matrix after milling and were thus physically inaccessible to amylases (type RS1). The crystalline structures of native starch granules were not completely degraded by amylases, retaining the skeletal structures in residual starch during granular starch hydrolysis or leaving residue granules and fragments with layered structures after jet‐cooking followed by the liquefaction and saccharification process, indicating the presence of RS2. Moreover, retrograded starch molecules (mainly amylose) as RS3, complexes of starch with other nonfermentable components as RS4, and starch–lipid complexes as RS5 were also present in DDGS. In general, the RS that escaped from the granular starch hydrolysis process was mainly RS1 and RS2, whereas that from the jet‐cooking process contained all types of RS (RS1 to RS5). Thus, the starch conversion efficiency and ethanol yield could be potentially affected by the presence of various RS in DDGS. |
