Patatin is one of the major storage proteins of the potato tuber, with a molecular weight of about 40 kDa and accounting for 30 to 40 percent of total soluble protein, stockpiling nitrogen for the sprouting plant. Beyond storage it exhibits esterase and lipase activity, hydrolysing lipid esters, which links it to the tuber’s defence and metabolism. Food scientists study it as a potential functional ingredient, since its emulsifying, foaming, and nutritional properties could add value to potato processing side streams such as fruit water from starch manufacture. Recovering patatin turns an effluent burden into a protein ingredient for food and feed, exemplifying the circular valorisation of processing residues.