Release of allergenic proteins from rice grains induced by high hydrostatic pressure

Protein release from rice grains during high-pressure treatment was investigated. When polished rice grains were immersed in distilled water and pressurized at 100-400 MPa, a considerable amount of proteins (0.2-0.5 mg per gram of grains) was released. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses, the major proteins released were identified as 16 kDa albumin, alpha-globulin, and 33 kDa globulin, which were known as major rice allergens. By scanning electron microscopic observation of rice grains pressurized at 300 MPa, partial morphological changes in endosperm cells but no apparent structural changes in protein bodies were detected. The content of these allergenic proteins decreased by pressurization and almost completely disappeared from rice grains by the pressurization in the presence of proteolytic enzyme. These results suggest that partial destruction of endosperm cells caused by pressurization enhances permeability of a surrounding solution into rice grains and that a part of the proteins are solubilized and subsequently released into a surrounding solution.