Proteolysis and lipolysis induced by acidification of sesame seeds

Vinegar-soaked seeds can be consumed as functional foods, and the acidification of vacuoles during seed germination is key for protein mobilization. Inspired by these, sesame seeds, containing proteases with peak activity at pH 4.5, were soaked in a 2 % acetic acid solution at 25 °C. Transmission electron microscopy showed that the acidic sesame proteases localized in protein storage vacuoles (PSVs), while liquid chromatography tandem mass spectrometry identified nine lipases. The seeds were acidified to pH 4.5 within 9 h, and the proteases were fully activated to hydrolyze the storage proteins and tonoplast of PSVs. The proteases were released and attacked almost all organelles. Oil body membrane proteins were degraded, causing the inner oil accessible to lipases. By 7 days of soaking, the protein components in the soaking system consisted of 39 % small peptides and 31 % free amino acids, while the oil was hydrolyzed into 26 % free fatty acids and 13 % diacylglycerols.