This invention refers to a procedure for reducing inorganic (heavy metals) and organic (aflatoxins, moulds, etc.) contaminants in high-protein vegetable matter, mainly originating from rice. Applying said procedure to raw vegetable matter results in the obtainment of derivatives presenting levels of these contaminants significantly lower than the legal limits set by health authorities. Following the procedure set out in this invention, high-quality protein derivatives are obtained usable for vitamin and nutritional supplements, milk formula for babies, sports nutrition, clinical nutrition, animal feed ingredients, etc.