Abstract
Natural antioxidants have drawn growing interest for use in animal feed and the food industry. In the current study, essential oils (EOs) obtained from hydrodistillation of three mentha species, including Mentha piperita (peppermint), Mentha spicata (native spearmint) and Mentha gracilis (Scotch spearmint), harvested in the Midwest region in the United States, were analyzed for their chemical composition using gas chromatography-mass spectrometry, and their antioxidant properties were assessed through chemical assays, in vitro cell culture modeling and in Caenorhabditis elegans (C. elegans). The activity of ferric iron reduction and free-radical scavenging capacity were assessed through chemical-based assays, including the reducing power assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, and Trolox equivalent antioxidant capacity assay (TEAC). Subsequently, the capacity of EOs to mitigate lipid peroxidation was analyzed at various doses using fresh liver homogenates from pigs. A porcine jejunum epithelial cell line (IPEC-J2) was employed as in vitro model to study the cellular antioxidant activity of the mint EOs. Finally, the effectiveness of mint EOs to alleviate acute systemic oxidative damage were evaluated in vivo using C. elegans. Data were analyzed by the MIXED procedure of SAS. Contrast statement was performed to assess linear or quadratic effects of mint EOs given at various doses. All three EOs are mostly composed of monoterpenes and their derivatives (76–90%), but differed in the major compounds, which are menthol and menthone (50%) in peppermint EO and carvone (70%) in spearmint EOs. Three mint EOs demonstrated prominent radical scavenging and Fe3+ reducing activity in chemical-based assays. In comparison with native and Scotch spearmint EOs, peppermint EO had the lowest (p < 0.05) half maximal effective concentration (EC50) in DPPH and TEAC assays and higher efficacy in the reducing power assay. All three EOs exhibited equivalent activity in mitigation of chemical-induced lipid peroxidation in liver tissues in a dose-dependent manner (linear, p < 0.001). The maximal cellular antioxidant activity (CAA) was observed at 5 µg/mL for peppermint, and 100 µg/mL for native and Scotch spearmint EOs. The addition of 25 µg/mL of both spearmint EOs increased (p < 0.05) cellular concentrations of glutathione in H2O2-treated IPEC-J2 cells, suggesting enhanced endogenous antioxidant defense. Supplementation of 100 µg/mL of peppermint or Scotch spearmint EO significantly increased (p < 0.05) the survival rate of C. elegans in response to H2O2-induced oxidative stress. The protective effect is comparable to that of supplementation of 10 µg/mL of ascorbic acid. However native spearmint EO failed to reduce the death rate within the same supplementation dose (10–200 μg/mL).
Highlights
Intracellular reactive oxygen species (ROS) are normally present at low concentrations as byproducts of mitochondrial respiration and have beneficial effects on cellular processes
This study aimed to thoroughly evaluate antioxidant properties of essential oils (EOs) collected from peppermint, native spearmint and Scotch spearmint using 3-tiered analyses, namely chemical assays, in vitro cell culture modeling and in vivo animal modeling in Caenorhabditis elegans
Substantial differences in chemical composition and abundance were observed between peppermint and the two spearmint EOs (Table 1)
Summary
Intracellular reactive oxygen species (ROS) are normally present at low concentrations as byproducts of mitochondrial respiration and have beneficial effects on cellular processes. Excessive ROS exposure causes oxidative damage to the lipid membrane, protein and DNA, which may lead to cell death and tissue injury [1,2]. The epithelial layer of the gastrointestinal tract is susceptible to oxidative damage as it is frequently exposed to noxious environmental factors (e.g., oxidized dietary constituents and pathogens). A large number of resident immune cells aligned with the gut epithelium is another significant source of ROS. The insults from environmental stress factors (i.e., heat-stress) heighten the production of ROS in enterocytes and compromises barrier function of gut epithelium in animals and humans [3,4,5,6]. Feed use antioxidants is an effective approach to prevent autoxidation of dietary constituents and a promising strategy to mitigate enteric oxidative stress in animals. Due to the consumer resistance to synthetic antioxidants (i.e., butylated hydroxytoluene, butylated hydroxyanisole and ethoxyquin) [9,10,11], identification of natural antioxidants has drawn growing interest
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