Effects of various oil extraction methods on the structural and functional properties of starches isolated from tigernut (Cyperus esculentus) tuber meals

Abstract Complete utilization of tigernut tubers, including their use in oil production and use of the meal as a byproduct, is an important aspect in improving their industrial value. However, there are few studies on the use of starch isolated from tiger tuber meals and cakes remaining after oil extraction. In this investigation, starches were isolated from tigernut tubers before and after various oil extraction processes and their structural and functional properties were comparatively investigated. A typical C-type X-ray diffraction pattern was observed for all of the isolated starches. Noticeable decreases in relative crystallinity by XRD and solid state 13C NMR were observed for starches from the cakes of tigernut tubers remaining after oil extraction utilizing a mechanical expeller. The proportion of amorphous phase (PPA) in the starches isolated from meals and cakes was relatively low compared with that of starch isolated from raw tigernut tuber. The branch-chain length distribution of the starches isolated from meals and cakes exhibited a low average chain length of amylopectin. These changes reflect a disruption in the ordered structure of starch granules caused by the various oil extraction processes, which led to significant variability in their functional properties, including paste clarity, freeze-thaw characteristics, thermal transition temperatures, texture, solubility, and swelling power. This investigation provides important information for the complete utilization of tigernut tubers.