Edible coatings for ready-to-eat foods

HOW apple slices sold ready-to-eat at grocery stores or fast-food restaurants stay looking fresh has to do with the edible film that prevents them from oxidising. Whilst doing an excellent job at maintaining freshness, this edible coating goes unnoticed because it is invisible, colourless, odourless, and tasteless. But these are characteristics that make the coating ideal for sliced fruits and salad greens.

Attila E. Pavlath, Ph.D, who is currently with the U.S. Department of Agriculture’s Western Regional Research Centre in Albany, California, takes credit for this edible film. At the 246th National Meeting & Exposition of the American Chemical Society (ACS), held in September, he announced advances in this product, which he said can be used on other foods to keep them safe, fresh and flavourful for a longer period of time.

Since the 1980s, the use of edible films has seen a significant growth, according to Mr Pavlath. He said that back then, only 10 companies were in the business, and now there are more than 1,000 companies with annual sales exceeding $100 million. Ready-to-eat fruits and vegetables now account for about 10% of all produce sales, with sales exceeding $10 billion annually.

Health consciousness amongst consumers is driving the growth of the edible film industry. The figures noted are expected to increase since demand is also increasing for healthy and fresh meals that require easy or no preparation. These include cut fruits and premixed salads, he said.

“Fruits and vegetables have skins that provide natural protection against drying out, discoloration and other forms of spoilage,” Mr Pavlath explained, during the ACS conference. “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. 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.”

Those coatings consist of a thin layer of edible material applied to the surface of a food product to preserve freshness. Apples, for instance, lose some of their natural wax coating during washing after harvest. The replacement is a thin layer of carnauba wax, obtained from the leaves of palm trees. That wax also gives sugar-coated chocolate candy an appealing gloss. Other common edible coatings include starch, alginate, carrageenan, gluten, whey and beeswax.

Mr Pavlath and his group invented the technology that enabled schoolchildren and other consumers in the U.S. 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 after cutting or peeling. Mr Pavlath’s process involves 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.

An old technology

Mr Pavlath said that edible films are not a product of the 21st century. 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. Those coatings sealed off the fruit, preventing the exchannike