The accumulation of Stevia rebaudiana UGT proteins transiently expressed in Nicotiana benthamiana leaves was quantified using a label-free protein quantification method. Experiment 1 (exp1) involved a series of samples expressing only UGT91D, while exp2 involved a series of samples co-expressing UGT85C2, UGT74G1, UGT76G1, and UGT91D2.