Pre-drying treatment of plant related tissues using plasma processed air: Impact on enzyme activity and quality attributes of cut apple and potato

During post-harvest processing of fresh cut and dried fruits and vegetables, polyphenol oxidase (PPO) and peroxidase (POD) need to be inactivated or inhibited in order to avoid undesirable browning reactions and loss of sensorial or nutritional quality. To meet this goal, the application of plasma processed air (PPA) offers a promising “gentle” alternative to traditional methods, such as pasteurization or the addition of anti-browning compounds. Using ambient air as process gas instead of an expensive noble gas, such as argon, exhibits a substantial improvement for the development of large-scale plasmas at ambient pressure and allows the indirect treatment of larger goods within a remote exposure reactor. In this study the ability of PPA to inactivate PPO and POD in complex food matrices and its impact on quality parameters, such as color, texture and cell integrity directly after freshly cutting and during storage of warm air dried and freeze dried produce was evaluated.The study evidently shows that PPA processing is capable of reducing the activity of PPO and POD in the freshly cut tissue from both apple and potato. Following exposure to PPA for 10min the PPO activity was reduced by about 62% and 77% in fresh cut apple and potato tissue, respectively. POD, as the more temperature-stable enzyme, was even less stable upon PPA treatment for 10min and was reduced by about 65% and 89% in fresh cut apple and potato tissue, respectively. Blackening of the potato tissue could be completely prevented by plasma treatment while a browning different from the habitual nature of enzymatic browning occurred upon exposure of the apple tissue to PPA. In both cases, the pH value on the tissue surface dropped to 1.5 while cell integrity and dry matter content were not significantly affected.The quality and shelf life of freshly cut and dried fruits and vegetables greatly depend on the activity of naturally occurring enzymes which catalyze browning reactions at cut surfaces. This study shows that the application of PPA, as a promising nonthermal “pasteurization” technology, enables the inactivation of PPO and POD in complex food matrices. It further describes the impact of the PPA treatment on quality parameters of the freshly cut tissue from apple and potato and goes beyond on evaluating color, texture and enzyme activity in warm air dried and freeze dried tissue over a storage time of three weeks. The results contribute to the understanding and product-specificity of PPA-induced effects on quality and shelf life of fresh cut and dried fruit and vegetable produce and could be a basis for a possible industrial implementation.