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Factors Affecting Stability of Rennin^1,2,

Department of Food Science and Industries, University of Wisconsin, Madison

ABSTRACT

The effects of temperature, pH, ionic strength, and ionic species on the stability of rennin were studied. Stability was determined by measuring decreases in clotting activity during 96 hr of incubation. Above pH 6.0, activity losses increased with pH, and were highly temperature dependent. They were accompanied by a precipitation of protein and appeared to be the result of pH denaturation. Maximum stability was maintained from pH 5.0 to 6.0. A region of instability was observed between pH 3.0 and 4.9 in buffers of 0.03 ionic strength. An instability maximum at pH 3.8 resulted in a loss of 35% of initial activity at 30 C over 96 hr. When the ionic strength was increased from 0.03 to 1.0 with NaCl, with other conditions constant, activity losses increased from 35 to 70%. Under the same conditions of pH, ionic strength, and temperature, rennin was more stable in sodium citrate, sodium lactate, and ammonium sulfate than in sodium chloride or potassium chloride. Below pH 4.5, activity losses were accompanied by an increase in the amount of Ruhemann's purple formed by the action of ninhydrin on the rennin mixture. This suggested that activity losses were due in part to self-digestion.

¹ Published with the approval of the Director, Wisconsin Agricultural Experiment Station.

² This study was supported in part by a research grant from Dairyland Food Laboratories, Inc., Waukesha, Wisconsin.

³ Present address: Department of Dairy and Poultry Science, Kansas State University, Manhattan, Kansas.

⁴ Present address: Department of Dairy Science, Utah State University, Logan, Utah.

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