Diego Durango

Thymol and carvacrol: biotransformation and antifungal activity against the plant pathogenic fungi Colletotrichum acutatum and Botryodiplodia theobromae

Fungal growth in fruits may cause spoilage and result in a reduction of their quality and quantity. The aim of the current study was to investigate the antifungal activity and the metabolism of thymol and carvacrol by Colletotrichum acutatum and Botryodiplodia theobromae. The results showed that both compounds provided relatively good control against these plant pathogenic fungi. Mycelial growth of C. acutatum and B. theobromae was inhibited at 50 µg/mL and above. At 150 µg/mL, thymol and carvacrol inhibited the radial growth of fungi completely and this effect remained for 240 h. Furthermore, thymol and carvacrol were metabolized by the plant pathogenic fungi in low proportion to several compounds, including thymoquinone, thymohydroquinone, thymyl- and carvacryl acetate, thymyl- and carvacryl methyl ether. The transformations affect the structural requirements of thymol and carvacrol related to their antimicrobial activity and mode of action. The relatively high antifungal activity of thymol and carvacrol against C. acutatum and B. theobromae and the low levels of microbial transformation indicate that both compounds could be an alternative to traditional chemical fungicides for control of pre- and postharvest phytopathogenic fungi on fruits or vegetables.

Antifungal activity against postharvest fungi by extracts from Colombian propolis

including papaya (Carica papaya L.), avocado (Persea americana) and mango (Mangifera indica L.). The use of synthetic chemicals as fungicides is the primary method of control of postharvest fungal decay caused by both diseases. However, several fungicides are not used for postharvest treatment or have been removed from the market due to possible toxicological risks. 3 Therefore, there is a need to develop new and acceptable post- and pre-harvest disinfestation methods. In this way, the use of natural products, either directly as crude preparations, or as pure compounds, can be a very attractive method for postharvest disease control of mango, papaya and avocado fruits. Propolis (or bee glue) is a natural resinous substance produced by Apis mellifera bees made up from parts of the plants, buds and exudates. In the beehive, propolis is thought to be used to seal holes, exclude draught and protect against external invaders. Its main function, however, is to prevent the decomposition of organic matter (i.e. creatures that have been killed by bees after an invasion) within the hive by inhibiting microbial growth. 4 Therefore, the presence of propolis may provide an environment not suitable for the growth of fungi and other microorganisms, and consequently to keep the hive environment aseptic. 5 In this way, one of the most frequent applications of bee glue is its antimicrobial activity against many gram-positive and gram-negative bacteria, yeasts and fungi, most of them associated with varying degrees of pathogenicity in humans. 6,7

Isoflavonoid composition and biological activity of extracts from soybean seedlings treated by different elicitors

Time-course and dose-response experiments were carried out to establish the ability for synthesizing isoflavonoids of soybean seedlings (cv. Soyica P34) treated with salicylic (SA) and isonicotinic acids (INA). Then, 25 structurally-related compounds were evaluated for their isoflavonoid-eliciting activity. Next, the antimicrobial and antioxidant activities of EtOAc-soluble fraction from soybean seedlings treated with some synthetic elicitors were determined. Results showed that the concentration of isoflavonoids in soybean seedlings was significantly increased by the application of SA and INA. The major isoflavonoids detected were the malonyl-glycosidic isoflavones, followed by genistin and daidzin. The isoflavone aglycones (genistein, daidzein, and formononetin), coumestrol and glyceollins were found in lower concentrations. Maximum accumulation of glyceollins was detected after 48 and 144 h in soybean seedlings treated with 1.6 mM INA and SA, respectively. EtOAc-extracts from soybean seedlings treated with two structurally-related compounds to INA displayed a significant antimicrobial and antioxidant activity. Therefore, INA, SA and structurally-related compounds can be used to increase the amounts of natural antioxidant or antimicrobial compounds in soybean, either to protect the plant directly against pathogens or as a natural source for subsequent isolation of isoflavonoids or bioactive extracts, which have potential application in functional foods or pharmaceutical and personal care products.