Effect of ph and clarified ruminal fluid on the stability of an exogenous fibrolityc enzyme product

Exogenous fibrolytic enzymes are not synthesized by the ruminal microorganisms, so they are added to feed in order to increase fiber degradation. The objective of this study was to evaluate in vitro xilanase, cellulose and laccase activity, as well as xylanase and cellulose enzymatic stability of an enzymatic fibrolytic product (Fibrozyme Alltech, Inc.). The experimental design was completely randomized and treatments were: buffer pH 6.0, buffer pH 7.0 and clarified ruminal fluid pH 6.5. Data were analyzed using the SAS Mixed procedure and the Tukey test (p≤0.05). The exogenous enzyme product contained 292 IU xylanase g ^-1 and 36 IU cellulase g ^-1, without laccase activity. In buffer with pH 6 cellulases were more stable than the xylanases, and both enzymes showed activity until 46 h. The speed constants of enzymatic inactivation (k) were -0.054 h ^-1 in xylanases and -0.008 h ^-1 in cellulases, and half life time (t _1/2) of 12.8 and 87.7 h. In buffer pH 7 cellulases remained more stable and the xylanases lost their activity at 32 h; values of k were -0.07 h ^-1 and -0.009 h ^-1, and t _1/2 of 9.9 and 77 h for xylanases and cellulases. In the medium with clarified ruminal fluid, cellulases maintained more stable their activity and xylanases lost it in 4 h (k-1.815 h ^-1 and -0.026 h ^-1; t _1/2=0.38 and 26.87 h for xylanases and cellulases). It is concluded that in vitro pH and enzymes contained in the clarified ruminal fluid affect the stability of the exogenous fibrolytic enzyme product.