Effect of Doping Natural Zeolite with Copper and Zinc Cations on Ethylene Removal and Postharvest Tomato Fruit Quality

Abstract

Tomatoes (Solanum lycopersicum L.), one of the most consumed vegetables worldwide, are climacteric fruit in which ripening is accompanied by quickly increased respiration and ethylene production. Ethylene stimulates ripening and senescence that finally may result in detrimental effects by promoting unwanted softening, grainy structure, accelerated pigment synthesis and chlorophyll loss in tomatoes. Therefore, most postharvest technology strategies are focused on the minimization of ethylene production, inhibition of its action and removal of ethylene from storage facilities. The aim of the present work was to study the ethylene adsorption capacity of a novel copper-zinc-based ethylene scavenger supported on natural zeolite and the effects of ethylene scavenging on quality attributes of tomatoes during their postharvest shelf life. Tomatoes (control, natural zeolite, zeolite doped with copper and zinc) were stored in hermetically sealed glass desiccators, in darkness at 20 °C and a relative humidity of 88 %. Production rates of ethylene and carbon dioxide were determined during 15 days of storage of tomato fruit by monitoring their headspace concentrations as a function of time using gas chromatography. Physical parameters, such as size, weight, colour and texture, and chemical attributes, including moisture, soluble solids, titratable acidity, reducing sugars and lycopene, were determined at the start of the experiment and after 8 and 15 days of tomato storage. Ethylene production diminished in 50 % for modified zeolite and in 7 % for natural zeolite during the first week, while major concentration peaks appeared for both zeolite treatments at 9.5 days. Moreover, modified zeolite delayed tomato respiration during the first six days. This adsorbent was able to shift the respiration peak compared to control treatment in time due to the incorporation of copper and zinc. Increased respiration and ethylene production rates in presence of both zeolites after 1 week of tomato storage trigger the decay of organic acids and part of the soluble solids. In addition, natural zeolite significantly reduced Young’s modulus at the end of storage, which can be attributed to the increased ethylene accumulation of about 40 % compared to control tomatoes. Furthermore, red colour evolution was promoted by natural zeolite, while modified zeolite induced the greatest delay of colour development in tomatoes. Additionally, the use of natural zeolite results to significantly higher increase of lycopene synthesis compared to tomatoes stored in presence of modified zeolite. Natural zeolite doped with copper and zinc cations favours ethylene removal and delays tomato fruit ripening. However, the single use of natural zeolite should be reconsidered due to its ripening promoting effects in tomatoes. Finally, the incorporation of copper and zinc cations to a zeolite support is a new, emergent postharvest technology to slow down fruit ripening that may create new commercial opportunities for fresh-market tomatoes.