Caramel apples may not always turn out to be as delicious and fun to eat as you would like. The American Society for Microbiology reported, Listeria sometimes grows on caramel apples which are not refrigerated. According to a new study caramel apples which are punctured with dipping sticks and than not refrigerated over the course of a couple of weeks may harbor a bacterium which is called Listeria monocytogenes.
Researchers studied listeria growth on a group of Granny Smith apples which were dipped in caramel and stored at either room temperature or in the refrigerator. The researchers from the University of Wisconsin-Madison’s Food Research Institute observed that the average population of L. monocytogenes increased 1,000-fold on caramel apples which had sticks and which were stored at room temperature for three days. Listerial growth was delayed on caramel apples which did not have sticks and which were stored at room temperature. There was significantly less listerial growth in caramel apples which were stored in the refrigerator.
Lead study coauthor Kathleen Glass, PhD, said that inserting a stick into an apple causes a small bit of juice to migrate to the surface. That moisture is trapped under a layer of caramel and creates a microenvironment which facilitates growth of any L. monocytogenes cells which are already present on the apple surface. The transfer of moisture and microbial growth are accelerated at room temperature in comparison to refrigeration. Dr. Glass has suggested that to be on the safe side consumers should search for refrigerated caramel apples or eat them when they are fresh.
This study has been published in the journal mBio. In 2014 a multistate listeriosis outbreak was found to be associated with consumption of caramel-coated apples.This was an unexpected and previously unreported vehicle of transmission for Listeria monocytogenes. Symptoms of listeriosis include fever, stiff neck, headache, and gastrointestinal illness. The symptoms often do not appear for three to four weeks after eating foods which are infected. In the 2014 outbreak 35 people from 12 states were infected and seven people died. It’s therefore a good idea to be very careful about the freshness and refrigeration of caramel apples.
