Total phenolic content and antioxidant capacity of lichen extracts

Background: Lichens are unique organisms consisting of a fungus and a photosynthetic partner growing in a symbiotic relationship [1]. Lichens have the ability to survive extreme conditions like low temperature, aridity or high UV radiation [2]. Recent data showed the resistance of the lichen symbiosis Aspicilia fruticulosa to space conditions: experiments with the European Biopan facility (a spaceflight on board of a Russian Foton retrievable satellite) revealed that space vacuum/cosmic radiation did not impair metabolic activity of lichens [3]. The effect was related to high amounts of antioxidant compounds [3] commonly equated with polyphenols.

Objective: We evaluated the in vitro antioxidant activity/phenolic content of different extracts (Ex) from 4 lichen's species collected in the Republic of Mari El in Russia: Cladonia ragiferina (CR), Cladonia sylvatica (CS), Evernia prunastri (EP) and Usnea barbata (UB).

Methods: Lichens were air-dried at RT and grounded to a uniform powder. The Soxhlet extraction of lichens using chloroform as a solvent or mechanochemical treatment with NaOH and further maceration with 40% ethanol were performed. The total antioxidant capacity of Ex and the total phenolics content were determined using the phosphomolybdenum method [4] and the Folin-Ciocalteau method, respectively.

Results: The highest total phenolic content was determined in the chloroform Ex of EP with 401 ± 18 mg-equivalent of GA/g extract. The standard of usnic acid equals to 378 ± 13 mg of GA/g. The highest antioxidant activity was measured in CR (chloroform Ex) and CS (NaOH with ethanol Ex): 298 ± 14 mg AA/g and 286 ± 34 mg AA/g, respectively (Table 1).

Conclusion: The phenolic content did not match the antioxidant capacity considering the applied methods. Further studies of lichen's antioxidant/radical scavenging activity in relation to responsible compounds are essential to identify natural compounds that can be used to reduce oxidative stress associated with many human diseases.

Table 1: Total phenolic and total antioxidant capacity of lichen's extracts (n = 3).

Sample	Total antioxidant activity, mg AA per g extract	Total phenolics content, mg GA per g extract
Usnic acid (standard)	148.9 ± 2.9	377.5 ± 13.2
CS (chloroform Ex)	170.8 ± 27.6	285.1 ± 1.0
CS (petroleum ether Ex)	161.7 ± 19.7	309.9 ± 3.0
CS (acetone Ex)	151.0 ± 19.0	301.4 ± 3.9
CS (NaOH with ethanol Ex)	285.6 ± 33.7	229.9 ± 2.5
CR (chloroform Ex)	298.4 ± 13.5	234.1 ± 7.7
UB (chloroform Ex)	206.5 ± 5.1	243.8 ± 2.0
EP (chloroform Ex)	172.6 ± 12.6	401.1 ± 18.1

AA – ascorbic acid, GA – gallic acid

References:

[1] Molnár K et al. Z Naturforsch C 2010; 65: 157 – 173

[2] de Vera JP. Fungal Ecology 2012; 5: 472 – 479

[3] Raggio J et al. Astrobiology 2011; 11: 281 – 292

[4] Manojlovic NT et al. Evid Based Complement Alternat Med 2012; 452431