Scientists develop new edible coatings for fresh fruits and vegetables
The scientist who turned fresh-cut apple slices into a popular convenience food has turned his attention to developing coatings for food that are invisible, edible, colourless, odorless and tasteless.
Attila E. Pavalath, PhD, a scientist with the US Department of Agriculture’s Western Regional Research Centre in Albany, California, presented his research at the September 2013 meeting of the American Chemical Society. He said the use of edible film had “grown dramatically” since the mid-1980s, when only 10 companies were in the business, to more than 1,000 companies with annual sales exceeding US$100 million.
According to Mr Pavalath, ready-to-eat fruits and vegetables now account for about 10 per cent of all produce sales in the US, with sales exceeding US$10 billion annually. He said the use of edible films is likely to expand dramatically in the future – especially for fruits and vegetables – as health-conscious consumers look for more foods that require minimal preparation, such as cut fruit and premixed salads.
“Fruits and vegetables have skins that provide natural protection against drying out, discolouration and other forms of spoilage,” Mr Pavlath said. “Cutting and peeling remove that natural protection, allowing deterioration and spoilage to begin. It’s visible within minutes for foods like apples and bananas, but occurs without any outward sign for other fruits and vegetables,” he said.
“Nature is a very good chemist and we are learning from that and sometimes improving on it with new edible coatings that protect the quality and nutritional value of food,” Mr Pavlath said.
Coatings mean food lasts longer
The edible coatings invented by Mr Pavlath and colleagues enabled schoolchildren and other consumers to enjoy a new apple treat – refrigerated, packaged apple slices that last two to three weeks without turning brown or losing crispness. Apples ordinarily begin to turn brown within 30 minutes of cutting or peeling.
Mr Pavlath’s process involved treating freshly cut apple slices with a form of Vitamin C, resulting in the first commercial product that retains the desirable characteristics of fresh apples without leaving a detectable residue.
Apples lose some of their natural wax coating during washing after harvest. Previously, this has been replaced with a thin layer of carnauba wax, obtained from the leaves of palm trees. The same wax also gives sugar-coated chocolate lollies their appealing gloss. Other common edible coatings include starch, alginate, carrageenan, gluten, whey and beeswax.
Edible films used throughout history
In his presentation to the American Chemical Society, Mr Pavlath said edible films were by no means a twenty-first century innovation.
According to Mr Pavlath, edible films were used at least as early as the 1100s, when merchants in citrus-growing regions of southern China used wax to preserve oranges shipped by caravan to the Emperor’s table in the North.
People in Europe for centuries preserved fresh fruit with “larding” a coating of the melted fat from hogs. The coatings sealed off the fruit, preventing the exchange of gasses with the air, which is essential for sustaining good quality.
Modern coatings allow gas exchange, protect food in other ways
According to Mr Pavlath, today’s edible films allow that exchange of gasses and have other features that maintain freshness, flavour, aroma, texture and nutritional value. He said they generally provide the same protection against bacteria as the natural skin, if the foods are handled under sterile conditions when they are cut in the factory. The foods are either sprayed with or immersed in the liquid coating after cutting. The finished fruits and vegetables then go to consumers in sealed containers.
The great 21st century challenges?
Mr Pavlath cited two major challenges in his presentation.
- Bananas have so far proved difficult to find an edible coating for that would make fresh-cut sliced bananas a commercial reality. Banana’s are America’s favourite fruit and are consumed in the US in greater quantities than apples and oranges combined.
- Avocados have also proved difficult to coat, because they are notorious for discolouring very quickly after peeling.