Rosemary (Salvia rosmarinus; formerly referred as Rosmarinus officinalis Linn) is an aromatic plant native to the Mediterranean region known to be rich in a variety of phytochemicals with anti-oxidant and anti-inflammatory properties. This perennial plant possesses a shrub shape reaching up to two meters high with a characteristic fragrance with uses including a spice for cooking, a medicinal plant, and a food preservative. 1 The health promoting properties of rosemary include hepatoprotective properties, therapeutic potential for Alzheimer’s, and anti-cancer properties. 2345 Spain, and more specifically, the province of Murcia (Southeast Spain), is a major processor and importer of rosemary, and the development of the commercial market has allowed for the use of rosemary to expand to the rest of Europe and the United States.6

The development of rosemary extract (RE) can generate a variety of unique formulations rich in compounds including rosmarinic acid (RA), carnosol (CL), and carnosic acid (CA). As with any other extract, the solvent and extraction method that is used will determine the resulting phytochemical composition, thereby impacting the physical and chemical properties of the extract. In the case of rosemary, a water soluble extract, which is typically rich in RA, will be effective in a water or polar matrix, while an oil soluble extract rich in diterpenes will be of value in an non-polar matrix such as a lipid formulation.7 Due to the variability in phytochemical composition that occurs from each extraction, the characterization of the phytochemical content of different extracts and essential oils is critical to report.

A more recent application of RE has been food preservation due to the ability to prevent oxidation and microbial contamination. 8910 This rationale has provided a consumer and industry interest in replacing or decreasing synthetic antioxidants in foods. The European Food Safety Authority (EFSA) has reviewed the safety of RE for use as food additives, and the panel found that the No Observable Adverse Effects Level (NOAEL) of rosemary extracts in 90-day rat studies was 180-400 mg RE/kg/day, which equates to 20-60 mg/kg/day of CL plus CA.11 These values translate to mean intake estimates of 500-1500 mg/kg/day of CL and CA in human adults. The panel concluded through several toxicology studies that these margins do not pose any safety risks in humans. As a result, RE can be added to food and beverages at levels of up to 400 mg/kg (as the sum of CA and CL) in the European Union.

Due to the growing interest on the medicinal properties of Salvia rosmarinus, our objective is to present the role of RE as a food preservative with beneficial properties for gastrointestinal health. Therefore, this manuscript builds a literature gathering on rosemary to identify main bioactive compounds, extracts and essential oils and to characterize their application. The anti-oxidant and anti-microbial properties of various REs are described along with specific food preservation studies. Finally, in vivo studies that show the impact of REs on GI health are outlined with significant findings. The goal of this review is to highlight the potential of REs to be used as natural food preservatives and to provide the benefit of improved GI health.

Rosemary has been extensively studied for its anti-microbial activity against both Gram-negative and Gram-positive bacteria. Oliveira et al. investigated the anti-microbial activity of RE (200 mg/mL in propylene glycol) against C. albicans, S. aureus, E. faecalis, S. mutans, and P. aeruginosa in planktonic cultures and against biofilm formation 18. RE showed the strongest activity against C. albicans with a MIC and a minimum microbicidal concentration (MMC) of 0.78 mg/mL and 3.13 mg/mL, respectively. Additionally, RE showed strong activity against P. aeruginosa with both an MIC and MMC of 6.25 mg/mL. S. aureus, S. mutans, and E. faecalis growths were inhibited at >25 mg/mL, but a microbicidal concentration was not reached. The study also revealed that RE was effective against biofilm formation of C. albicans, P. aeruginosa, S. aureus, and S. mutans. In poly-microbial films, C. albicans was cultured with the other four bacteria for 48 hours in this study and treated with 200 mg/mL RE for 5 minutes. The most significant reduction in microbial growth with RE occurred in C. albicans plus E. faecalis and C. albicans plus P. aeruginosa (P ≤ 0.0001).

Methanol and ethanol RE were also evaluated against eight different bacterial strains grown on agar, including E. coli, S. aureus, P. aeruginosa, B. cereus, E. faecalis, C. albicans, V. fluvialis, and V. damsel1. The methanol extract showed a higher degree of inhibition against bacterial growth compared to the ethanol extract. The authors noted that the presence of CA in the methanol extract was likely the reason for the increased anti-microbial activity. In fact, several studies have associated the concentration of CA in RE with its effectiveness against microbial growth 192021.

In a separate study, REO was evaluated against 60 clinical samples of multi-drug resistant E. coli 22. The chemical composition of REO was determined by GC-MS, and the major phytochemicals were 1,8-cineole (46.4%), camphor (11.4%), and α-pinene (11.0%). The MIC of REO against the clinical samples ranged from 18.0 to 20.0 µL/mL, although these values were less effective than basil essential oil tested in the same study (8.0 to 11.5 µL/mL). Jardak et al. also evaluated the anti-microbial effects of REO against S. aureus and S. epidermidis by microdilution method 7. The REO had a greater effect against S. epidermidis with an MIC of 0.312-0.625 µL/mL and MMC of 2.5 µL/mL versus an MIC and MMC of 1.25-2.5 µL/mL and 5 µL/mL, respectively, for S. aureus.

Rosemary has been studied extensively for a variety of biological properties including anti-oxidant and anti-microbial activities 23. These properties make rosemary of particular interest as a natural food preservative2 24. The EU approved RE as a food preservative after extensive toxicity studies and determining that the o observed adverse effect level (NOAEL) range was wide enough to not pose any safety concerns 1. Published reports have suggested that up to 90% of the anti-oxidant capacity of RE can be attributed to the CL and CA content 1822. Therefore, RE used in food preservation is most often defined by the CL and CA content to ensure consistent potency and safety. Additionally, the significant anti-microbial activity of RE and REO further enables food preservation through inhibition of bacterial or mold growth on food products 11.

Several food matrix models have also been used to evaluate the ability of RE and REO as a food preservative. In fattening lambs with diets supplemented with RE through the animal feed, packaged meat showed a greater degree of protection from oxidation and microbial growth with RE supplementation 7. Additionally, shelf life and sensory qualities such as odor and color were improved in lamb given RE, and these factors were improved with higher CL intake 18. Addition of RE to pork patties packaged in modified-atmosphere packaging (MAP) protected against protein and lipid oxidation greater than BHT, a common synthetic preservative 18. Addition of REO at 0.2% in combination with MAP had a positive effect in sensory qualities and decreased lipid oxidation in poultry fillets, although no significant effects on microbial growth were detected 11. Addition of RE at 2.0% (v/v) to edible gelatin coating significantly inhibited growth of Listeria monocytogenes inoculated on raw beef for 48 hours 1. Altogether, these studies show the potential for RE as a natural alternative to synthetic food preservatives, although optimization of the extract needs to be done to achieve the maximum benefits of RE.

In addition to being a natural food preservative, evidence suggests that rosemary extract may improve gastrointestinal health. Inflammatory bowel disease (IBD) is one area in particular that RE administration has been evaluated 7. Due to its anti-oxidant and anti-inflammatory properties, RE has been hypothesized to prevent or treat IBD. To test this hypothesis, several in vivo models of acute colitis have been developed to study the underlying mechanisms of IBD and to test the efficacy of various compounds against the disease (Table IV). These models evaluate parameters such as pro-inflammatory cytokine expression, myeloperoxidase activity, colonic weight and length, and histological assessment of colonic sections and crypt formation to determine the effectiveness of treatment 252627.

Rosemary has been evaluated in these in vivo models with positive results for preventing and treating colitis. In a study in rats given TNBS to induce colitis, RE and REO at doses above 100 mg/kg given 6 consecutive days were shown to reduce the weight per length ratio of the colon, which is increased in moderate to severe colitis 11. Treatments with RE and REO were also shown by histological analysis to significantly reduce inflammation, crypt damage, and total colonic index. This study attributed the majority of the effects of RE to RA due to its anti-oxidant properties and high lipid solubility. Analysis of REO by GC-MS revealed the most abundant component was α-pinene, which has significant anti-inflammatory activity through inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (Nf-κB) nuclear translocation 28.

In vitro, RE possesses anti-inflammatory properties that translate to being effective at treating in vivo colitis models. In RAW 264.7 macrophages stimulated with lipopolysaccharide (LPS) to induce inflammatory conditions, RE lowered expression levels of TNF-α, IL-6, and nitrite levels compared to LPS stimulation alone 4. The redox sensitive transcription factor Nf-κB nuclear translocation was also decreased, along with iNOS and COX-2 expression, when treated with 5 and 10 µg/mL RE. In mice induced with colitis by dextran sodium sulfate (DSS) administration, disease activity index, scored by stool consistency, body weight loss, and presence of blood in feces, improved with treatment of 50 and 100 mg/kg RE compared to DSS only. Mice given RE also had less apparent colonic damage and leukocyte infiltration. Analysis of intestinal proteins also revealed that mice treated with RE had lower expression of the inflammatory markers NF-kB, COX-2, and iNOS, similar to the in vitro results. The study also found that DSS treatment increased the expression of the mitogen-activated protein kinase (MAPK) proteins p38, ERK, and JNK. However, RE treatment was able to restore the expression of these proteins to control values. These results suggest the in vivo efficacy for RE to treat colitis through its anti-oxidant and anti-inflammatory function at doses that do not present toxicity risk.

This review summarizes food preservation properties and the health promoting properties to the gastrointestinal tract with rosemary extracts. Rosemary extracts and essential oils present promising methods of natural food preservation due to their bioactivities that prevent many types of food spoilage and microbial growth. Beyond food preservation, however, these herbs have also been shown to promote GI health. Studies performed in mice have shown positive effects of lowering GI inflammation and lessening the symptoms of DSS exposure. These studies suggest that health promoting properties specific to gastrointestinal health are an additional benefit to using rosemary extract as a natural food preservative.