Synergistic Effects of Plant Essential Oils and Extracts on Gut Microbiota in Rats

The application of essential oils and plant extracts as natural food preservatives has gained increasing interest; however, their potential impacts on gut health and host physiology remain unknown. This study evaluated the effects of synergistic combinations of peppermint essential oil (EO) + thyme EO and peppermint EO + feijoa peel extract on gut microbiota composition and colonic morphology in a rat model. Sprague–Dawley rats were orally given the synergistic combinations daily for 28 days, and their effects were assessed using 16S rRNA gene sequencing of the caecum microbiota and histological analysis of proximal colon tissues. Alpha diversity metrics showed no significant differences (p > 0.05) between treatment and control groups, and beta diversity indicated no treatment-related shift in the bacterial communities. Taxonomic profiling at the phylum, family, and genus levels showed comparable relative abundances of dominant microbial taxa across all treatments, with no evidence of dysbiosis. Histological examination of proximal colon tissues revealed no significant changes in crypt depth between treated and control groups, confirming the absence of adverse morphological effects on the intestinal epithelium. The results of this study indicate that synergistic combinations of peppermint EO, thyme EO, and feijoa peel extract do not adversely affect the gut microbiota composition and colonic morphology in rats, thereby supporting their application as preservatives in foods.