While use of synthetic antioxidants (such as butylated hydroxytoluene and butylated hydroxyanisole) to maintain the quality of ready-to-eat food products has become commonplace, consumer concern regarding their safety has motivated the food industry to seek natural alternatives. Phenolic antioxidants can inhibit free radical formation and/or interrupt propagation of autoxidation. Fat-soluble vitamin E (α-tocopherol) and water-soluble vitamin C (L-ascorbic acid) are both effective in the appropriate matrix. Plant extracts, generally used for their flavoring characteristics, often have strong H-donating activity thus making them extremely effective antioxidants. This antioxidant activity is most often due to phenolic acids (gallic, protocatechuic, caffeic, and rosmarinic acids), phenolic diterpenes (carnosol, carnosic acid, rosmanol, and rosmadial), flavonoids (quercetin, catechin, naringenin, and kaempferol), and volatile oils (eugenol, carvacrol, thymol, and menthol). Some plant pigments (anthocyanin and anthocyanidin) can chelate metals and donate H to oxygen radicals thus slowing oxidation via 2 mechanisms. Tea and extracts of grape seeds and skins contain catechins, epicatechins, phenolic acids, proanthocyanidins, and resveratrol, all of which contribute to their antioxidative activity. The objective of this article is to provide an overview of natural antioxidants, their mechanisms of action, and potential applications.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1541-4337.2011.00156.x

Natural antioxidants: sources, compounds, mechanisms of action, and potential applications

In recent years, consumers have developed an ever-increasing interest in natural products as alternatives for artificial additives or pharmacologically relevant agents. Among them, essential oils have gained great popularity in the food, cosmetic, as well as the pharmaceutical industries. Constituting an array of many lipophilic and highly volatile components derived from a great range of different chemical classes, essential oils are known to be susceptible to conversion and degradation reactions. Oxidative and polymerization processes may result in a loss of quality and pharmacological properties. Despite their relevance for consumers, there is a paucity of information available addressing this issue. Therefore, the present review provides a comprehensive summary on possible changes in essential oils and factors affecting their stability. Focusing on individual essential oils, the various paths of degradation upon exposure to extrinsic parameters are outlined. Especially temperature, light, and oxygen availability are recognized to have a crucial impact on essential oil integrity. Finally, analytical methods to assess both genuine as well as altered essential oil profiles are evaluated with respect to their suitability to track chemical alterations. It is believed that only a careful inspection of essential oils by a set of convenient methods allows profound quality assessment that is relevant to producers and consumers alike.

Stability of Essential Oils: A Review

A review of the dietary flavonoid, kaempferol on human health and cancer chemoprevention

Evaluating the antioxidant capacity of natural products: a review on chemical and cellular-based assays.

Enzyme-assisted extraction of bioactives from plants

Antioxidative activity of Rosmarinus officinalis L. essential oil compared to its main components.

Chemical composition and antimicrobial activity of the essential oil of Rosemary.

Ten essential oils, namely, mint (Mentha spicata L., Lamiaceae), ginger (Zingiber officinale Rosc., Zingiberaceae), lemon (Citrus limon Burm.f., Rutaceae), grapefruit (Citrus paradisi Macf., Rutaceae), jasmine (Jasminum grandiflora L., Oleaceae), lavender (Mill., Lamiaceae), chamomile (Matricaria chamomilla L., Compositae), thyme (Thymus vulgaris L., Lamiaceae), rose (Rosa damascena Mill., Rosaceae) and cinnamon (Cinnamomum zeylanicum N. Lauraceae) were tested for their antibacterial activities towards Propionibacterium acnes and in vitro toxicology against three human cancer cell lines. Thyme, cinnamon and rose essential oils exhibited the best antibacterial activities towards P. acnes, with inhibition diameters of 40 +/- 1.2 mm, 33.5 +/- 1.5 mm and 16.5 +/- 0.7 mm, and minimal inhibitory concentrations of 0.016% (v/v), 0.016% (v/v) and 0.031% (v/v), respectively. Time-kill dynamic procedures showed that thyme, cinnamon, rose, and lavender essential oils exhibited the strongest bactericidal activities at a concentration of 0.25% (v/v), and P. acnes was completely killed after 5 min. The thyme essential oil exhibited the strongest cytotoxicity towards three human cancer cells. Its inhibition concentration 50% (IC(50)) values on PC-3, A549 and MCF-7 tumor cell lines were 0.010% (v/v), 0.011% (v/v) and 0.030% (v/v), respectively. The cytotoxicity of 10 essential oils on human prostate carcinoma cell (PC-3) was significantly stronger than on human lung carcinoma (A549) and human breast cancer (MCF-7) cell lines.

/pdf/activities-of-ten-essential-oils-towards-propionibacterium-47lkwqgmaj.pdf

Activities of Ten Essential Oils towards Propionibacterium acnes and PC-3, A-549 and MCF-7 Cancer Cells

Antioxidant activities of the aqueous and ethanol extracts of pigeonpea [Cajanus cajan (L.) Millsp.] leaves, as well as petroleum ether, ethyl acetate, n-butanol and water fractions and the four main compounds separated from the ethanol extract, i.e. cajaninstilbene acid (3-hydroxy-4-prenylmethoxystilbene-2-carboxylic acid), pinostrobin, vitexin and orientin, were examined by a DPPH radical-scavenging assay and a beta-carotene-linoleic acid test. In the DPPH system, the antioxidant activity of the ethanol extracts was superior to that of the aqueous extracts, with IC(50) values were 242.01 and 404.91 microg/mL, respectively. Among the four fractions, the ethyl acetate one showed the highest scavenging activity, with an IC(50) value of 194.98 microg/mL. Cajaninstilbene acid (302.12 microg/mL) and orientin (316.21 microg/mL) showed more efficient radical-scavenging abilities than pinostrobin and vitexin. In the beta-carotene-linoleic acid test, the inhibition ratio (%) of the ethyl acetate fraction (94.13%+/-3.41%) was found to be the highest, being almost equal to the inhibition capacity of the positive control BHT (93.89%+/-1.45%) at 4 mg/mL. Pinostrobin (>500 microg/mL) and vitexin (>500 microg/mL) showed insignificant antioxidant activities compared with cajaninstilbene (321.53 microg/mL) and orientin (444.61 microg/mL). In general, the ethyl acetate fraction of the ethanol extract showed greater activity than the main compounds in both systems, such results might be attributed to the synergistic effects of the components. The antioxidant activities of all the tested samples were concentration-dependent. Based on the results obtained, we can conclude that the pigeonpea leaf extracts may be valuable natural antioxidant sources and are potentially applicable in both medicine and the healthy food industry.

https://www.mdpi.com/1420-3049/14/3/1032/pdf

Nan Wu

Papers

Antioxidative activity of Rosmarinus officinalis L. essential oil compared to its main components.

Chemical composition and antimicrobial activity of the essential oil of Rosemary.

Activities of Ten Essential Oils towards Propionibacterium acnes and PC-3, A-549 and MCF-7 Cancer Cells

Antioxidant activities of extracts and main components of Pigeonpea [Cajanus cajan (L.) Millsp.] leaves.

Supercritical carbon dioxide extraction of seed oil from Opuntia dillenii Haw. and its antioxidant activity