A novel method was developed and validated to detect immunoglobulin G (IgG) activity by analyzing ionizable amino acids (IACs) and charge interactions, offering safe and efficient assessment without direct antigen handling. Bovine colostrum samples were heated at 75 °C for 0, 5, 15, 30, and 60 min to evaluate the impact of thermal treatment on IgG functionality. IgG activity was assessed using four complementary approaches: UV–VIS spectroscopy 1, UV–VIS spectroscopy 2, precipitation weight, and colorimetry (with or without substrate indicators such as anthocyanins, carotenoids, curcumin, alizarin, betalains, chlorophylls, and phycocyanin, etc.). Our findings from precipitation assays and immunoassays (Rocket Immunoelectrophoresis and Radial Immunodiffusion) consistently show that IgG precipitation near its isoelectric point (pI) correlates with a loss of antigen-binding capacity. This method leverages IgG’s aggregation-dispersion behavior under specific pH and ionic conditions to infer activity based on changes in net charge and isoelectric point (pI). Amino acid analysis, structural assessment via SDS-PAGE, and Rocket Immunoelectrophoresis confirmed that the new method accurately detects IgG activity, even under heat-induced denaturation. Results indicate that IgG maintains stability up to 5 min of heating, with substantial activity loss beyond 15 min and near-total inactivation at 60 min. This charge-based method provides a reliable framework for monitoring IgG stability, with significant implications for immunological and diagnostic applications where functional IgG is essential.