Effect of cold plasma treatment on microbial load and quality of baby carrots

In the United States, about 80 percent of all food shipments and 91 percent of all temperature controlled freight shipments, including about 28.5 million tons of refrigerated fruit and vegetables, are transported by truck. In the complex food transportation system, microbial contamination is a problem, which may be introduced at earlier stages in the supply chain and can spread out to many distributors, retailers, and consumers. Baby carrots are consumed worldwide because of their nutritional benefits. However, in the past two decades, there has been an increase in foodborne diseases outbreaks caused by microorganisms associated with fresh produce. Cold plasma treatment of fresh produce, an emerging food preservation technology, is a fast and environmentally friendly method that disinfects the product at a low temperature (30-40°C). Cold plasma uses an ionized gas comprised of charged ions and free electrons for the treatment of the product and kills microorganisms by altering their metabolic pathways. Till date, very little research has been focused on the effect of cold plasma mist (micro meter size water droplets) on the quality and shelf life of fresh produce, and its efficacy in transportation. Therefore, the purpose of this study was to evaluate the efficacy of dielectric barrier discharge (DBD) cold plasma mist on the microbial load and quality of baby carrots in a refrigerated plasma chamber simulating a transportation truck. Conditions in transportation truck were simulated by installing cold plasma mist system in a 100 L volume refrigerator termed as plasma chamber. Baby carrots were inoculated with E. coli O157:H7 and treated with cold plasma mist for different treatment times. The effect of cold plasma on microbial load and quality (color values, texture, moisture content, total polyphenol content, [beta]-carotene) was evaluated at each treatment time. Carrots treated with tap water mist (no plasma) were used as controls. Complete inactivation of E. coli O157:H7 was achieved when baby carrots were treated with plasma mist for 30 min. At each treatment time, lower microbial load was observed for plasma mist treated carrots compared to tap water mist treated carrots. While no significant changes in color values (L*, a*, b*, chroma, hue, and browning index) were observed when baby carrots were treated with plasma mist for 30 minutes, browning index values decreased with an increase in treatment time but was not significantly different. Further, there was no significant difference between firmness values and moisture content (wet basis) of baby carrots treated with tap water mist or plasma mist. The change in total polyphenol content (TPC) of carrots was almost negligible in both tap water and plasma mist treatments. However, plasma mist treatment resulted in no significant difference in [beta]-carotene of baby carrots. This research demonstrated the potential of cold plasma system as an efficient disinfection system that may achieve complete inactivation of microorganisms with no noticeable negative effect on the quality.