Umami From the Plant Kingdom

As fruits and vegetables mature, they develop a more intense taste. Ripe tomatoes and ripe green peas are especially good sources of glutamate, as are cabbage and mature potatoes that have been cooked. Of the plants that contain nucleotides, tomatoes and potatoes are again prominent and are joined on the list by green asparagus, lentils, and spinach. A particular plant extract, green tea, is also able to impart a strong umami taste.

Generally speaking, fruits have very little glutamate and are not able to contribute to umami in any significant way. Tomatoes are a spectacular exception to this statement, as their free glutamate content increases dramatically over time. When ripe, they have ten times more glutamate than when green. Without it, they taste tart, much like a tomatillo or a citrus fruit. As they ripen, their sugar substances and organic acids are also developing.