Heat Sensitivity of Pectinesterase Activity in Papaya Purée and of Catalase‐Like Activity in Passion Fruit Juice

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Abstract
SUMMARY: Passion fruit juice catalyzed hydrogen per‐oxide decomposition as a first‐order reaction with a rate constant equal to 0.009/min/ml of juice at 77°F. The activity was destroyed by mild heat and did not regenerate after storage. It was affected only slightly by increasing juice pH from 3.0 to 6.8, although the fresh juice inactivated commercial catalase. Pectinesterase (PE) activity in ripe papaya flesh averaged 0.013 meq/min/g at 86°F. Rate of destruction for PE in acidified purée was determined in the range 169–186°F, giving a z value of 11°F from the thermal inactivation curve and a D180= 10 min. Further experiments on heat‐processed acidified purée in No. 2 cans indicated a residual activity more heat resistant than that predicted by extrapolation of the thermal‐in‐activation curve.