Maltodextrin-Coated Peppermint and Caraway Essential Oils Effects on Soil Microbiota

Abstract

Essential oils exhibit strong antimicrobial effects that can serve as a substitute for synthetic pesticides. However, many reports mention the use of essential oils in protecting above-ground plant organs and storing raw materials and seeds, but only a few address the effects of treatments on soil microbiota. Regarding this, it is necessary to find a solution that will prevent the rapid degradation of oils in soil and extend the period of their action on the soil microbiota. The solution to this problem can be microencapsulation, where the choice of carrier plays a key role. In our experiment, maltodextrin was studied, often used in the microencapsulation of essential oils. It was examined independently in two doses (M1 and M2, with 50 and 200 g kg−1, respectively) and a combination with two essential oils known for their antimicrobial activity. We hypothesized that the selected microbial communities would react differently to the stress caused by maltodextrin-encapsulated essential oils. The serial dilution method assessed the number of colony-forming units (CFU) of bacteria, fungi, and actinomycetes. As the goal of microencapsulation was to prolong the effect of essential oils, their reaction was observed over a longer period. The soil microbial populations were examined in sandy and loamy soil at 1, 7, 14, and 78 days after encapsulated essential oils were mixed with the soil samples. In both types of soil, a significant increase in bacteria and actinomycetes was observed with maltodextrin in both doses. Encapsulated peppermint and caraway oils had different effects on microbes, both inhibitory and stimulatory. It is also important to note that peppermint with a smaller dose of maltodextrin significantly inhibited the growth of fungi in sandy soil in all measurements, as well as that caraway oil with a higher dose of maltodextrin significantly stimulated the growth of bacteria and actinomycetes in sandy soil. The higher dose of maltodextrin could explain this stimulation. Further research is recommended to test different doses of essential oils and maltodextrin, which would lead to the optimal dose of both wall and core materials.