Coating Eggs with a Membrane for Preservation
As the Lunar New Year approaches, the festive atmosphere is becoming more pronounced. Many people like to gift eggs during the holiday season. Recently, some consumers have noticed that the eggs they purchased are coated with a thin membrane.
What exactly is this membrane? Does it pose any food safety risks? To answer these questions, a reporter from Science and Technology Daily interviewed relevant experts.
The Membrane’s Main Component is Liquid Paraffin
“Coating the eggs is part of the egg cleaning process. Workers clean and disinfect the surface of eggs from farms, then apply a coating to the fresh eggs. After these procedures, the eggs are ready for market,” explained Professor Li Liunan from the College of Animal Science and Veterinary Medicine at Tianjin Agricultural University. The main purpose of coating eggs is to preserve their freshness.
“Eggshells are not impenetrable; they have thousands of tiny pores,” Li further explained. Over time, eggs lose freshness because bacteria and mold can enter through these pores. Additionally, moisture and gases inside the egg can escape, affecting the egg’s freshness and taste.
By applying a coating, a protective film forms on the surface of the egg, sealing the pores. This inhibits the growth of microorganisms on the shell, prevents them from entering the egg, and reduces moisture loss, ultimately extending the egg’s shelf life.
Li noted that coating eggs is a simple operation. At room temperature, it can extend the egg’s freshness (eggs stored at 25°C remain edible after seven weeks), making it convenient for long-distance transportation. This method is more cost-effective compared to traditional refrigeration or modified atmosphere storage used in countries like the United States and Australia.
Is the Membrane Safe?
Is this membrane safe for food consumption? Do we need to take special precautions when eating these eggs?
“Preservative coatings that meet national standards are safe food additives, so consumers don’t need to worry. If you’re still concerned, you can wash it off with saltwater,” Li explained. The primary component of the preservative coating on eggshells is food-grade liquid paraffin. Besides liquid paraffin, other common food-grade coating materials include monoglycerides, vegetable oil, petroleum jelly, chitosan, polyvinyl alcohol, and propolis.
“Liquid paraffin is cost-effective and forms an effective film. It is non-toxic and harmless, and in small doses can be used to treat constipation. It is widely used in the food processing industry,” Li said. According to the National Food Safety Standard for Food Additives, liquid paraffin is a legal food additive with a maximum usage limit of 5 grams per kilogram.
Various Methods of Food Preservation
Coating for preservation is one of the main methods used for food preservation. This technique is applied not only to eggs but also to fruits and vegetables (such as citrus, apples, lemons, cucumbers) and meat products (such as fresh meat and ham).
“For fruit coatings, materials like edible chitosan, fruit wax, animal oil, and vegetable oil are often chosen. These are applied to the fruit’s surface by dipping or spraying to achieve preservation,” Li said.
Besides coating, other common preservation methods include modified atmosphere storage, heat treatment, low-temperature storage, and radiation preservation.
Modified atmosphere storage involves adjusting the proportions of oxygen, nitrogen, and carbon dioxide in sealed packaging, reducing oxygen levels and increasing carbon dioxide levels. “Lowering the oxygen content can effectively inhibit microbial growth, thus extending the shelf life,” Li said.
Heat treatment preservation is often used in canned food production. This method physically heats the cans to a certain temperature to kill microorganisms.
Low-temperature storage includes refrigeration and freezing. Refrigerators and freezers use this method to preserve food. Low temperatures can slow the growth of microorganisms in food. Below 10°C, the reproduction of most microorganisms and spoilage bacteria is greatly reduced; below 0°C, microbial activity nearly stops; and below -10°C, most microorganisms cannot survive. Low temperatures also reduce the activity of some enzymes in food and microorganisms.
Additionally, there is radiation preservation. This method uses the energy from radioactive elements to sterilize and de-insect fresh meat and its products, grains, fruits, vegetables, and seasonings, thereby maximizing the extension of food shelf life.
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