Antioxidant compounds from microbial sources: A review

Lichens are complex symbiotic associations between fungi and algae which are important constituents of many ecosystems. The production of various unique extracellular secondary metabolites known as lichen substances is the result of this symbiosis. These compounds exist within the thalli and typically form crystals on the surface of the fungal hyphae. Thus far, more than 800 secondary metabolites of lichens have been discovered, most of them being exclusively present in lichens. In recent date, lichens have been taken up for many researches concerning the phytochemical and pharmaceutical applications. Lichens and their secondary metabolites have many pharmaceutical roles, primarily including antimicrobial, antioxidant, antiviral, anticancer, antigenotoxic, anti-inflammatory, analgesic and antipyretic activities. Hence, the present study was undertaken to explain the lichens as the important potential sources of bioactive secondary metabolites.

Lichens as a Potential Source of Bioactive Secondary Metabolites

Natural extracts are the source of many antioxidant substances. They have proven useful not only as supplements preventing diseases caused by oxidative stress and food additives preventing oxidation but also as system components for the production of metallic nanoparticles by the so-called green synthesis. This is important given the drastically increased demand for nanomaterials in biomedical fields. The source of ecological technology for producing nanoparticles can be plants or microorganisms (yeast, algae, cyanobacteria, fungi, and bacteria). This review presents recently published research on the green synthesis of nanoparticles. The conditions of biosynthesis and possible mechanisms of nanoparticle formation with the participation of bacteria are presented. The potential of natural extracts for biogenic synthesis depends on the content of reducing substances. The assessment of the antioxidant activity of extracts as multicomponent mixtures is still a challenge for analytical chemistry. There is still no universal test for measuring total antioxidant capacity (TAC). There are many in vitro chemical tests that quantify the antioxidant scavenging activity of free radicals and their ability to chelate metals and that reduce free radical damage. This paper presents the classification of antioxidants and non-enzymatic methods of testing antioxidant capacity in vitro, with particular emphasis on methods based on nanoparticles. Examples of recent studies on the antioxidant activity of natural extracts obtained from different species such as plants, fungi, bacteria, algae, lichens, actinomycetes were collected, giving evaluation methods, reference antioxidants, and details on the preparation of extracts.

https://www.mdpi.com/1996-1944/14/15/4135/pdf

Antioxidants: Classification, Natural Sources, Activity/Capacity Measurements, and Usefulness for the Synthesis of Nanoparticles.

Lichen secondary metabolites , Lichen secondary metabolites , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

Lichen secondary metabolites

Lichens are a form of symbiont between a fungus and an alga or cyanobacterium, which contains a wide variety of organic compounds with certain secondary metabolite classes typical of these organisms The Ramalina genus has approximately 246 species distributed around the World, of which in this review approximately 118 species with published chemical or biological activity studies of extracts or isolated compounds were cited From the 153 mentioned compounds, only 27 passed were tested for biological activity, being usnic acid the most studied compound and the one showing the best results in almost all in vitro tests performed, although other compounds also presented excellent results as antimicrobial, antitumor and anti-inflammatory agents, among others Extracts of several species also presented significant results in performed biological tests, demonstrating the potential that these organisms have, in particular, the gender Ramalina, to produce bioactive molecules that can be used as a model for the production of pharmaceuticals

https://www.mdpi.com/1420-3049/20/5/8952/pdf

M Geol

Papers

Antibacterial and antioxidant activity of lichen species Ramalina roesleri