Proteins of Plant Origin
Vegetable Proteins: Fresh vegetables are not considered to be a very good source of proteins. On fresh weight basis, the average protein content of some common vegetables are carrots and lettuce - 1%, white potatoes, asparagus and green beans - 2% and fresh peas - 6%.
Although protein content of potatoes is only 2%, quality is considered to be good to excellent due to relatively high content of the amino acids - lysine and tryptophan. Outer layers, the so called "cortex" of tubers contain most of the proteins. These layers also have a much higher content of essential amino acids than do the inner layers. The outer layer proteins can be increased by selective plant breeding.