The Impact of Streptomyces griseus Protease Reserved for Protein Evaluation of Ruminant Feed on Carbohydrase Activity during Co-Incubation

Abstract

For protein evaluation of feedstuffs for ruminants, the Streptomyces griseus protease test provides a solely enzymatic method for estimating ruminal protein degradation. Since plant proteins are often structured in carbohydrate complexes, the use of carbohydrase during the test might improve its accuracy. It is advisable to co-incubate protease and carbohydrase, risking that the carbohydrase activity is reduced under the influence of the protease. The present study was conducted to investigate this impact by using α-amylase or the multi-enzyme complex Viscozym® L as carbohydrase. The detection of active protease was determined fluorescence photometrically using internally quenched fluorogenic substrates (IQFS). Cellulose, pectin, and starch degradation were determined spectrophotometrically using 3,5-dinitro salicylic acid as a colorimetric agent. The Streptomyces griseus protease mixture proved to be active for the selected IQFS immediately after the start of measurements (p < 0.05). Starch hydrolysis catalyzed by α-amylase or Viscozym® L, respectively, was decreased by co-incubation with protease mixture by maximal 3% or 37%, respectively, at 5 h incubation time (p > 0.05). Pectin and cellulose hydrolysis catalyzed by Viscozym® L, respectively, was not significantly influenced by co-incubation with a protease mixture (p > 0.05). Although a decrease in carbohydrase activity during co-incubation with Streptomyces griseus protease occurred, it was only numerical and might be counteracted by an adapted carbohydrase activity.