510. Reactivation of milk phosphatase following heat treatment. I

Abstract

1. Commercial samples of milk of Swiss origin, sterilized by rapid heating to high temperatures, developed a positive phosphatase reaction on storage.2. The optimum temperatures of storage for the development of this positive phosphatase reaction was 30° C.3. These commercial samples were sterile when received and remained sterile during storage.4. The developed phosphatase is apparently identical with the normal alkaline phosphatase of raw milk as judged by (a) heat stability, (b) pH optimum and rate of hydrolysis at different pHs, (c) comparison of results by Kay-Graham and Aschaffenburg & Mullen tests.

Indigenous enzymes in milk: Overview and historical aspects—Part 2

“…Much work has been focussed on a phenomenon known as 'phosphatase reactivation', first recognised by Wright and Tramer (1953a, 1953b, 1954, who observed that UHT-treated milk was phosphatase-negative immediately after processing but became positive on storage; microbial phosphatase was shown not to be responsible. HTSTpasteurised bulk milk does not show reactivation, although some samples from individual cows may.…”

Fluorometric Detection of Active Alkaline Phosphatase and Gamma-Glutamyl Transferase in Fluid Dairy Products from Multiple Species

“…H ow ever, these m ethods have problem s w ith reproducibility, accuracy, and time needed to produce results (20, 21,30). Reactivation of ALP can occur in products that have been ultrapasteurized (138°C for 2 s), leading to false-positives results (10, 17,18,[27][28][29]. To date, reactivation has not been observed with GGT under ultrapasteurization conditions (10, 16).…”

Microbiological and enzymatic activity of bovine whole milk treated by pulsed electric fields

“…In the case of thermally treated milk, the activity of alkaline phosphatase decreased after treatment and then remained constant for 21 days during storage at 4 °C. This suggests that there was no biochemical reactivation of bovine alkaline phosphatase throughout the storage at 4 °C, unlike for heat‐treated milk stored above 22 °C (Wright and Tramer ; Lyster and Aschaffenburg ; Murthy et al . ; Rankin et al .…”

“…In the case of thermally treated milk, the activity of alkaline phosphatase decreased after treatment and then remained constant for 21 days during storage at 4°C. This suggests that there was no biochemical reactivation of bovine alkaline phosphatase throughout the storage at 4°C, unlike for heat-treated milk stored above 22°C (Wright and Tramer 1953;Lyster and Aschaffenburg 1962;Murthy et al 1976;Rankin et al 2010). Typically, alkaline phosphatase reactivates at temperature ranging from 22 to 37°C, and it has been reported that the presence of metal ions (Mg and Zn) stimulates the alkaline phosphatase activity reactivation (Rankin et al 2010).…”