Sesame residue melanoidins: Isolation, structure, and the role of alleviating cellular oxidative damage by modulating mitochondrial function

The traditional aqueous extraction of sesame oil yields abundant wet sesame residues rich in melanoidins. Melanoidins were isolated by Pronase E and ultrafiltration, in which the fraction >20 kDa (MELs) presented a higher melanoidin content of 75.52 % and the highest DPPH· scavenging rate of 83.83 %. The TEM, UV-VIS, FTIR and PY-GC‒MS results revealed that the MELs were disordered, amorphous, and rich in nitrogen oxide heterocyclic and carbonyl structures. The antioxidative mechanism of MELs was studied using a H2O2-induced oxidative damage model in LO2 cells. The TEM, Western blot and immunofluorescence results revealed that MELs reduced the influx of Ca2+ into mitochondria and alleviated mitochondrial Ca2+ overload by inhibiting the expression of transient receptor potential vanilloid 1 (TRPV1) on the mitochondrial membrane. The balance of mitochondrial dynamics was improved by reducing the expression of mitochondrial fission factor protein (MFF) and increasing the expression of mitochondrial fusion protein (MFN2), which inhibited the expression of proteins related to the PINK1/Parkin pathway and reduced the level of autophagy in mitochondria. Additionally, by upregulating Bcl-2 and inhibiting Bax, Cyt C, Caspase 3, Caspase 8, and Caspase 9 protein expression, cellular apoptosis was reduced by MELs. These results demonstrate that protease assisted ultrafiltration can effectively isolate melanoidins from sesame residues generated during the traditional process of sesame oil by aqueous extraction, and these melanoidins exhibit significant antioxidant activity, which provides a theoretical basis for the development of melanoidins from sesame residues.