The influence of pasteurization temperatures, homogenization pressures and storage duration at 4C̊ on activity of milk xanthine oxidase

The influence of pasteurization temperatures : homogenization pressures and storage duration at 4°C on activity of milk xanthine oxidase was studied.

The activity of xanthine oxidase in raw milk was increased after milk was stored at 4°C for 24 hours but decreased upon further storage. Raw milk contained 0.2275 ± 0.0051 units per ml.

The activity of xanthine oxidase was increased when raw milk was heated to 55°C for 5 minutes. Milk heated at 55°C for 5 minutes had an activity of 0.2356 ± 0.0206 per ml and 0.2373 ± 0.0146 units per ml after storage at 4°C for 2 and 24 hours, respectively.

The activity of xanthine oxidase in milk was increased gradually as the homogenization pressures were increased from 1000 to 4000 pounds per square inch (psi). Milk homogenized at 4000 psi had 0.2559 ± 0.0056 units per ml after being stored at 4°C for 2 hours. Milk homogenized at 4000 psi had 0.2661 ± 0.0051 units per ml after storage at 4°C for 24 hours and lesser amounts when stored for longer periods.

The xanthine oxidase activity was greater in whipping cream than in skimmilk, homogenized milk or half and half. The whipping cream contained 0.2766 units per ml when analyzed on the day of purchase but decreased upon further storage. The skimmilk of different processors contained 0.0463 to 0.0680 units per ml when analyzed on the day of purchase but after 24 and 48 hours storage the activity decreased. The homogenized milk of different processors contained 0.0007 to 0.1202 units per ml when analyzed on the day of purchase but decreased upon further storage. Half and half contained 0.0094 units per ml when analyzed on the day of purchase and lesser amounts after 24 and 48 hours storage.