Impact of atmospheric pressure cold plasma on the rheological and gelling properties of high methoxyl apple pectin

Cold plasma is an emerging sustainable method for modification of hydrocolloids. In the present study, atmospheric pressure pin-to-plate cold plasma was employed for modification of high-methoxyl apple pectin (DE similar to 68%). Chemical modifications are rigorous, and often require huge amounts of solvents and chemicals. Hence, the use of sustainable and "green" techniques such as cold plasma need to be investigated for their ability to impact the rheological and gelling properties of pectin. Intrinsic viscosity, apparent viscosity and viscoelastic properties of cold plasma-treated pectin dispersions and gels were studied. Kinetic studies were undertaken to evaluate the effect of cold plasma on the degradation and gelation of pectin. Improvement in rheological properties was observed for short plasma treatments at lower voltages (190 V|9 min and 210 V|6 min). Prolonged treatments at higher voltage treatments (210 and 230 V) had a negative impact on the rheological and gelling properties. The depolymerization, monitored by the intrinsic viscosity exhibited second-order degradation kinetics. The pseudoplastic pectin dispersions transitioned towards Newtonian-like behavior after plasma treatments. The thermal stability of the pectin dispersions decreased by 29% after a plasma treatment of 230 V for 15 min. A decline in gel strength and stability was confirmed by the decline in critical and cross-over strain during strain-sweep experiments. The gel formation of pectin in the presence of sucrose was a two-step process. The energy gap between the high-temperature and low-temperature region decreased as the plasma treatment progressed. To summarize, it is necessary to optimize the intensity of the plasma treatments to achieve the desired rheological properties.