Comparative Evaluation of Antioxidant, Phenolic, Flavonoid, Protein, And Isoflavone Profiles in Commercial Soy Products: A Multi-Methodological Approach

Soybeans are recognized for their high-quality protein, antioxidant activity, and bioactive phytochemicals. This study evaluated five commercial soy products–soy milk, soy cheese, soy flour, soy ground meat, and soybean sprouts–using spectrophotometric assays (CUPRAC, ABTS, Folin-Ciocalteu, AlCl3/NaNO2) and HPLC, with protein quantified by Lowry and Cu(II)-neocuproine (Nc) methods. Marked variations were found across products. Total antioxidant capacities ranged from 11.54 ± 0.03 to 18.18 ± 0.16 mmol TE 100 g-1 (CUPRAC) and 14.95 ± 0.46 to 21.53 ± 0.10 mmol TE 100 g-1 (ABTS), with soy milk exhibiting the highest ABTS and CUPRAC activities. Phenolic contents varied between 10.51 ± 0.08 and 18.27 ± 0.03 mmol GA 100 g-1, while flavonoids ranged from 5.10 ± 0.11 to 8.85 ± 0.14 mmol CAT 100 g-1. Protein levels were greatest in soy flour (63.02 ± 0.95 g 100 g-1) and soy ground meat (59.40 ± 1.46 g 100 g-1). HPLC revealed product-specific isoflavone distributions: genistin dominated in soy milk and flour, genistein in soy cheese and sprouts, and daidzein in soy ground meat. The main phenolic compound was 4-hydroxybenzoic acid, while rutin predominated in sprouts. This integrated methodology offers a rigorous analytical framework for assessing phytochemical and nutritional diversity in plant-based foods.