Abstract Protein degradation of two cereals (wheat and maize) was studied by two different methods, a laboratory method using a proteolytic bacterial enzyme extracted from Streptomyces griseus and an in situ method. Results were very similar: 73% and 76% degradation for wheat and 38% and 41% degradation for maize with enzymatic and in situ incubation, respectively. Two separation procedures, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and fractionation procedures by precipitation/redissolution techniques were used to study the degradation of protein components after enzymatic and in situ incubation. Wheat storage proteins (gliadins, glutenins) were degraded more rapidly than those of maize (zein and glutelins). The electrophoretic profiles showed that protein components were less degraded after enzymatic than in situ incubation. Wheat protein components (glutelins) were not completely degraded 24 h after enzymatic incubation but were completely degraded after in situ incubation; in contrast, maize protein components were not degraded completely at 24 h neither after enzymatic nor in situ degradation. These observations agree with the results of separation procedures. Among the solubilized forms of nitrogen in the supernatant after enzymatic hydrolysis (ammonia, α amino nitrogen, protein, peptides), protein and peptides were in large concentration, and after 8 h of incubation, proteins were degraded more to peptides than to ammonia or α amino nitrogen.