Sample collection & organization

Thirty-three samples of commercial plant-based protein powders were purchased either from amazon.ca or store shelves (supermarket/health/drug stores), representing an array of the main sources of protein — yellow pea protein (Pisum sativum), brown rice protein (Oryza sativa), soybean protein (Glycine max), hemp seed protein (Cannabis sativa), quinoa protein (Chenopodium quinoa), chia seed protein (Salvia hispanica), and pumpkin seed protein (Cucurbita sp.) — in both single and multi-ingredient products, from multiple companies. About 60 g of each powder was placed into a sterile plastic bag and assigned a random sample number before conducting a blind experiment for the following reported analyses. Thirteen voucher specimens representing the main protein sources as well as potential adulterants were obtained and morphologically identified by a botanist to serve as reference samples. An additional Bos taurus protein reference (milk) was obtained from the Elora Research Farms Rso (University of Guelph affiliated). All references are listed in Supplementary Table ^S2.