Effect of atmospheric pressure cold plasma (ACP) on activity and structure of alkaline phosphatase

• Atmospheric pressure cold plasma (ACP) treatments inactivate alkaline phosphatase (ALP) enzyme.
• The temperature never exceeds 30 °C and the pH of enzyme solution remain constant.
• The Weibull model best describes the enzyme inactivation kinetics.
• The inactivation is attributed to the loss of α-helical and β-sheet secondary structures of the protein.

Atmospheric cold plasma treatments (ACP) is a novel non-thermal processing technology with several emerging potential applications in food processing, including dairy. This study evaluates the effect of ACP on the activity and structure of alkaline phosphatase (ALP), an enzyme native to milk. ALP enzyme in solution was treated with ACP at three discreet high voltages (40, 50 and 60 kV) for durations ranging between 15 s and 5 min. Results demonstrated that the dielectric barrier discharge based plasma technology was able to inactivate the enzyme within a few seconds. Kinetic models, namely first order, Weibull and logistic models were fitted to the experimentally observed data and the model parameters were determined. The Weibull model was found to best describe the observed variance in residual activity for all the voltages applied. The dichroic spectra suggested that the enzyme was characterized by a predominance of α-helix structure, and the helical content showed a tendency to decrease with increase in treatment time and voltage. The maximum temperature recorded for most intense treatments was in the order of only 30 °C and no change in pH was noticed.