Keeping food ripe with wood

Materials World magazine
3 Jun 2020

A wood-based catalyst could delay ripening and make fruit last longer.

A new way to slow down fruit degradation works by breaking down ethylene into water and carbon dioxide at room temperature. Researchers from Swiss companies Empa and ETH Zurich believe this could prevent excessive food waste. 

Dr Mirko Lukovic, Researcher at Empa, outlines how when fruits mature, they release ethylene in the form of a gas. A small amount of ethylene accelerates the ripening. To counteract the effects, the scientists have developed a material based on a delignified wood structure, enriched with a catalyst dispersed at an atomic level. 

Using an acid solution, the lignin and part of the hemicellulose components of wood are decomposed, leaving the remaining cellulose structure with a large surface area and extremely porous. At this stage, the structure is a compatible scaffold for a catalyst. 

The team coats the walls with a layer of titanium oxide xerogel with cerium doping to bind and stick platinum atoms to the walls of the hierarchical porous cellulose scaffold. The coating is made by submerging the sample into a precursor solution and applying vacuum impregnation – it is then left to dry for around two weeks.  

‘The base material is wood, which is a natural material that is readily available at a very low cost,’ Lukovic explains. ‘Furthermore, it already has the desirable properties, such as porosity and high surface-area, therefore there is no need for an extra manufacturing step/process. ‘It is an eco-friendly and renewable material. The entire product is non-toxic, therefore there is no risk involved when placed in contact with food.’

He adds, ‘It is...enough to put a sample of the modified wood, containing platinum, next to the fruits. Any ethylene that is released by the fruits will eventually diffuse into the pores and channels of the modified wood and therefore will come into contact with the platinum catalyst, where it will be decomposed into the water and carbon dioxide. In other words, the block of modified wood placed next to fruits will absorb and decompose any ethylene released into the atmosphere next to it.’

According to Lukovic, the process could be manufactured at large scale as the principle is the same. ‘The only limit to the scalability is the demand for the final product.’