Immunoglobulins, commonly known as antibodies, are large Y-shaped glycoproteins produced by B cells in the immune system. They consist of two heavy chains and two light chains linked by disulfide bonds, with variable regions that bind antigens and constant regions that mediate effector functions. Five main isotypes exist: IgG, IgA, IgM, IgD, and IgE, each with distinct roles in humoral immunity. In food science, they occur naturally in milk, colostrum, and eggs, contributing to passive immunity and gut health. They are heat-sensitive and denature above 60-70°C. Molecular weights range from 150 kDa (IgG) to 900 kDa (IgM). They function in antigen neutralization, opsonization, and complement activation. Research from peer-reviewed immunology sources confirms their role in food-derived bioactive compounds.