Best indicator of protein quality is:

The net protein utilization, or NPU, is the ratio of amino acid conveed to proteins to the ratio of amino acids supplied. It may be affected by the salvage of essential amino acids within the body, but is profoundly affected by the level of limiting amino acids within a foodstuff.This value can be determined by determining dietary protein intake and then measuring nitrogen excretion. One formula for NPU is:NPU = ((0.16 x (24 hour protein intake in grams)) - ((24 hour urinary urea nitrogen) + 2) - (0.1 x (ideal body weight in kilograms))) / (0.16 x (24 hour protein intake in grams))As a value, NPU can range from 1 to 0, with a value of 1 indicating 100% utilization of dietary nitrogen as protein and a value of 0 an indication that none of the nitrogen supplied was conveed to protein.