An environmentally-friendly cling film alternative could slow down how quickly avocados turn brown.

       Harvard University academics created a spray in a lab which covers the surface of the much-loved stoned fruit favoured by millennials and bourgeois cafes.

       Their proof-of-concept is the first time a team has managed to produce a one-step method where antimicrobial fibres can be spun and coated directly onto a fruit.

       The fibres are made of pullulan, a naturally-occurring sugar, and enriched with antimicrobial agents, such as thyme oil and citric acid.

       Dr Demokritou, associate professor at Harvard School of Public Health, said: “We knew we needed to get rid of the petroleum-based food packaging that is out there and replace it with something more sustainable, biodegradable and non-toxic.

       “And we asked ourselves at the same time, ‘Can we design food packaging with a functionality to extend shelf life and reduce food waste while enhancing food safety?’

       “What we have come up with is a scalable technology, which enables us to turn biopolymers, which can be derived as part of a circular economy from food waste, into smart fibres that can wrap food directly.

       “This is part of a new generation of ‘smart’ and ‘green’ food packaging.”

       40 per cent improvement

       Lab tests on avocados showed that those wrapped in the special antimicrobial wrap are only 50 per cent “off” after seven days. In contrast, non-wrapped or cling-filmed fruits are 90 per cent rotten by that time.

       The coating can be rinsed off with water and degrades in soil within three days, according to the study authors.

       Prof Demokritou said: “I’m not against plastics, I’m against petroleum-based plastics that we keep throwing out there because only a tiny portion of them can be recycled.

       “Over the past 50 to 60 years, during the Age of Plastic, we’ve placed six billion metric tons of plastic waste into our environment.

       “They are out there degrading slowly. And these tiny fragments are making it into the water we drink, the food we eat and the air we breathe.”

       The findings are published in the journal Nature Food.