Effect of operational conditions on photocatalytic ethylene degradation applied to control tomato ripening

Abstract

Ethylene is a phytohormone that promotes the ripening of climacteric fruits. When present in the transport and storage environments of fruits and vegetables, ethylene can cause the acceleration of maturation and senescence, leading to the need to dispose of the products. Thus, the elimination of this gas in storage chambers has been studied as an efficient way to improve the shelf-life of climacteric fruits and vegetables. The main objective of this study was to investigate the effect of the operating conditions on the photocatalytic degradation of ethylene in a continuous flow reactor using TiO2 under UV-A light in the absence or presence of tomato fruits. The results for the catalyst deposition showed a linear increase in the photocatalytic degradation of ethylene with increasing thickness of the catalyst deposited on the inner wall of the reactor, up to a constant degradation value. The dependence of the reaction rate was linear with high values for the flow rate, which is associated with the surface reaction. However, at a low flow rate, mass transfer limitations can affect the ethylene reaction rate. Under a kinetic regime, the Langmuir-Hinshelwood model was able to describe the effect of the ethylene gas concentration on its degradation rate. Increasing incident irradiance led to a linear increase in the ethylene conversion over the range studied. A continuous rate of ethylene gas production during tomato ripening of 0.3182 μmol kg−1 h−1 was observed. In a real application, the reactor with a TiO2 film thickness of 0.419 μm under an incident irradiance of 5.18 W m−2 was able to maintain the ethylene concentration in the gas phase close to zero and a lower value for the carbon dioxide in the gas phase was achieved. This is related to a decrease in the respiration rate, indicating that this is an efficient technology for improving the shelf life of cherry tomatoes.