Production and characterization of amaranth amyloid fibrils from food protein waste

Plant proteins self-assembly into amyloid fibrils is a promising modification to be introduced in emerging food and materials applications. Although the valorization of protein-rich side streams in amaranth oil production is completely missing, we show that double salt extraction provides the recovery of globulin fraction of amaranth seed from food waste with high purity and complete protein solubility at acidic pH. We demonstrate in silico the self-assembly propensity with a high density of amyloidogenic regions of the 11S seed storage globulin of Amaranthus hypochondriacus. We further show that the recovered amaranth proteins can self-assemble into amyloid fibrils under heat-induced acidic hydrolysis. The amyloid nature of the fibrils was studied by thiazole orange (TO) fluorescence, SDS-PAGE, FTIR, CD, TEM, and AFM. We systematically investigated how the tem-perature of fibrillization affected protein unfolding, peptide release, as well as its effect on tuning the formation, growth, and polymorphism of amaranth amyloid fibrils. The beta-sheet-rich structured proteins produced from the amaranth food waste exhibited mesoscopic polymorphism of the rigid amyloid fibrils with the manifestation of left-handed ribbons of varying polymorphism. We show that favourable conditions for extensive hydrolysis of the amaranth proteins promote the growth of well-ordered thick twisted ribbons with small-pitch and extraordinary rigidity and we interpret these finding based on structural mesoscopic models of amyloid fibrils. These results provide additional insight into the formation of plant amyloid fibrils as functional food and biocompatible materials, and introduce a pathway to convert amaranth food protein waste into amyloid nanofibrils.