Impact of low-voltage Atmospheric Cold Plasma (ACP) on food-grade papain

Abstract The influence of pin-to-plate atmospheric cold plasma (ACP) on the enzyme activity and conformation of papain was investigated from 170 V- 230 V for 5–20 min. The maximum activity was obtained at pH 8, 85°C after 60 min by using 3% substrate concentration for both untreated and treated papain. A decrease in residual activity, Vmax, and Km of treated papain in comparison with untread papain was mainly due to the effect of reactive plasma species generated during the exposure of low-voltage ACP. The decrease in the intensity of the amide I, II, and III group of treated papain was observed in Raman spectra, FTIR spectra with increasing voltages. The decrease in α-helix, turns, random coils and an increase in β-sheet alters the secondary structural elements. The change in intrinsic fluorescence and a slight decrease in the surface hydrophobicity of treated papain were mainly due to the oxidation of amino acids leading to breakage of hydrogen bonds, hydrophobic bonds, ionic interaction, electrostatic interactions, and Van der Waal forces by exposure to plasma. In addition, a decrease in the free sulfhydryl group and S-S vibrations of the disulfide bond leads to partial denaturation and misfolding. A low-voltage ACP negatively influences the conformation of papain resulting in loss of activity.