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

Department of Dairy and Poultry Sciences, Kansas State University, Manhattan 66502
and Department of Food Science and Industries, Utah State University, Logan 84321

ABSTRACT

Stabilities of pepsin-free rennin and porcine pepsin enzymes were studied when mixtures of the two were held up to 72 hr at 30 C, 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.

¹ Contribution 822.

² Contribution 1187.