Effects of microwave irradiation on ruminal protein and starch degradation of corn grain

This study was designed to evaluate effects of 800 W microwave irradiation for 3, 5 and 7 min on ruminal dry matter (DM), crude protein (CP) and starch degradation parameters of corn grain. Nylon bags of untreated or microwave treated corn were suspended in the rumen of three Holstein steers for 0–48 h, and resulting data were fitted to a non-linear degradation model to calculate effective rumen degradation (ERD). Microwave treatments decreased (P<0.05) the water soluble fraction and increased the potentially degradable fraction of CP, except for 7 min processing time that decreased (P<0.05) the potentially degradable fraction. Processing for 3 and 5 min had no effect, but for 7 min it decreased (P<0.05) ERD of CP. Microwave irradiation for 3 and 5 min increased (P<0.05) the water soluble fraction and decreased the potentially degradable fraction of starch. The degradation rate of the latter fraction increased (P<0.05) with 3 and 5 min processing times. Microwave irradiation for 7 min decreased (P<0.05) the water soluble fraction and the potentially degradable fraction of starch. Processing for 3 and 5 min increased (P<0.05), but for 7 min decreased (P<0.05) ERD of starch. From SDS-PAGE patterns, four major protein components in corn containing prolamin (i.e., zein), albumin, globulin and glutelin fractions were observed. Electrophoretic analysis of protein residues revealed that microwave processing decreased degradation of corn true protein. SDS-PAGE indicated that the bulk of the rumen undegradable protein for untreated corn was zein, while for 5 and 7 min microwave treated corn it was zein and other proteins. In this study, the optimal processing time with 800 W microwave power was judged to be 5 min.