Effect of pH on the Stability of Rennin-Porcine Pepsin Blends

Abstract

Stabilities of pepsin-free rennin and porcine pepsin enzymes were studied when mixtures of the two were held up to 72 hr at 30C, at pH 3.0 to 6.5. Milk clotting activity of rennin in the mixtures was determined by differential assay based on the relative stability of each enzyme at pH 6.3 and 7.3. At pH 7.3 porcine was deactivated completely and rapidly whereas rennin was only slightly affected.Below pH 5.5, rennin stability was impaired by pepsin. Although rennin alone was not stable at pH 3.0, with 25% or more pepsin, rennin was rapidly and completely destroyed in 48 hours. Rennin activity losses also were accelerated by pepsin at pH 3.8 and 4.8, in proportion to amounts of pepsin. Rennin was most stable in rennin-pepsin blends between pH 5.5 and 6.5.Greatest stability of pepsin in rennin-pepsin blends was between pH 3.8 and 5.5. Substantial losses of pepsin activity occurred at pH 6.0, with greater losses at pH 6.5. This was attributed to instability of porcine pepsin, and not to any effect of rennin. If anything, rennin had a slight stabilizing effect on pepsin at pH 6.5.