Food grade waxes are applied to a number of products prior to storage and distribution to control post harvest rot and extend shelf life. While products such as apples and oranges receive a single wax, lemons receive both storage and finishing wax treatments. But little is known about the impact of different waxes and the waxing step on microbial food safety. Luxin Wang, PhD, associate professor at University of California, Davis, wished to fill these knowledge gaps through its research project entitled: “Waxing of whole products and their implication and impact on the microbial safety of food”. Wang’s co-principal investigators are colleagues at UC Davis, Linda Harris, PhD, and Lena Sheng, PhD.
“We hope to provide the industry with information on how waxes contribute to the microbial safety of fresh produce by using lemons and oranges as model products,” she said. Additionally, Wang said, the results could be used by individual packaging factories to support the development of their food safety plans or risk assessments.
The project has three objectives, two of which will be carried out in the laboratory, while the final objective will start in the laboratory and end with validation in the pilot packaging plant. Two microbial cocktails with five strains composed of Listeria monocytogenes and Salmonella spp. will be used for this study. The cultures are from the Harris co-PI culture collection and are isolates from previous outbreaks of the products.
For objective one, four storage waxes and 15 finishing waxes were obtained from industry collaborators. The researchers evaluated the chemical and microbial characteristics of these waxes as well as their impact on the survival of pathogens.
“The waxes had a wide pH range of 8 to 13 and varying compositions,” Wang said. “Of these, two storage waxes and one finishing wax had background populations of microorganisms.”
The team observed that the behavior of pathogens inoculated into waxes depended on the type of pathogen, the type of wax, and the storage temperature.
“In fgeneral, Listeria better survived than Salmonella, and both pathogens survived 4 ° C better than 22 ° C and in dilute waxes than in undiluted waxes, ”she said. “As storage waxes are used in diluted form, the information obtained from Objective 1 will help industry decide how best to store their unused or used storage and finishing waxes. “
For the second objective, storage waxes will be applied to lemons inoculated with pathogens and then stored at 4 ° C or 22 ° C for specific periods mimicking the storage conditions in lemon packaging plants.
“For the first two objectives, we would like to mimic two scenarios. The first is to assess what happens if the fruit is exposed to contaminated waxes, ”Wang said. “In the second scenario, the fruit arrives at the packing station already contaminated on the surface before the application of the wax.”
The team is just getting started on goal two. In the latter part of their research, which has not yet started, the researchers plan to evaluate the pathogen control effectiveness of finishing waxes and heat-drying steps in pilot packing station trials. . A non-pathogenic surrogate organism will be used for this study.