Bioactive compounds inDiospyros mafiensis roots inhibit growth, sporulation and aflatoxin production byAspergillus flavus andAspergillus parasiticus

Abstract

Diospyros mafiensis F. White is a medicinal shrub or small tree (6 m tall) widely distributed in the Zanzibar-Inhambane regional mosaic and traditionally used to treat leprosy, diarrhoea, and skin fungal infections in Tanzania and Mozambique. Our objective was to determine the anti-aflatoxigenic properties of compounds from D. mafiensis root bark against vegetative growth, sporulation and aflatoxin production by Aspergillus flavus and Aspergillus parasiticus. Bioassay-guided extraction, fractionation, and isolation of bioactive compounds using A. parasiticus B62 were employed. The bioactive compounds were elucidated using 1H and 13CNMR and LC-MS. Growth inhibition was determined by measuring the colony diameter of A. flavus AF3357 and A. parasiticus SU-1 ATCC56775. Inhibitory effects on sporulation were estimated using a haemocytometer. Total aflatoxin was quantified by direct competitive enzyme-linked immunosorbent assay (ELISA). Bioactive compounds diosquinone (DQ) and 3-hydroxydiosquinone (3HDQ) were identified. DQ weakly inhibited A. flavus and A. parasiticus vegetative growth (MIC50 > 100 µg/ml) and 3HDQ strongly inhibited A. flavus (MIC50 = 14.9 µg/ml) and A. parasiticus (MIC50 = 39.1 µg/ml). DQ strongly reduced total aflatoxin production by A. flavus from 157 to 36 ng/plate, and by A. parasiticus from 1,145 ng/plate to 45 ng/plate at 100 µg/ml. 3HDQ reduced total aflatoxin production by A. parasiticus from 1,145 to 32 ng/plate; stimulated production by A. flavus from 157 to 872 ng/plate at 12.5 µg/ml but reduced to 45 ng/plate at 100 µg/ml. In summary, DQ and 3HDQ could be used as natural antifungal compounds to prevent mould growth and aflatoxin accumulation in food and feed.

Chemical Composition and Bioactive Potential of Extracts from Diospyros capricornuta F. White against Aspergillus flavus and Aspergillus parasiticus

“…Arguably, this sends the message that weak inhibition of vegetative growth of a certain fungal strain does not necessarily mean weak inhibition of aflatoxin formation. This is consistent with Mmongoyo et al (2017) who found out that although extracts and diosquinone from D. mafiensis weakly suppressed fungal growth, they inhibited aflatoxin production strongly even at lower doses. Similarly, the D. capricornuta stem-bark methanolic extracts strongly inhibit toxin production in A. flavus, particularly at the dose of 250 µg/mL by over 99% and A. parasiticus by 94%.…”

“…Similarly, the D. capricornuta stem-bark methanolic extracts strongly inhibit toxin production in A. flavus, particularly at the dose of 250 µg/mL by over 99% and A. parasiticus by 94%. This phenomenon of inhibitors from the herbal extracts strongly inhibiting fungal toxin production without severely inhibiting their mycelial growth has been reported (Bhatnagar and McCormick 1988, Jayashree and Subramanyam 1999, Mmongoyo et al 2017. Since the aflatoxigenic fungi produce aflatoxins via a complex biochemical system called aflatoxin biosynthesis (Yu et al 2004), the mode of action of the extracts to inhibit the fungi to produce aflatoxins is associated with their inherent abilities to block aflatoxin biosynthesis and stop aflatoxin production completely (Holmes et al 2008).…”

“…In this respect, the use for protecting food crops against aflatoxigenic fungi may be safe. Actually, the small-scale farmers may sustainably use chips or powders of leaves, stem-barks, and root-barks as cheap preservatives to preserve their cereal crops in storage (Bankole 1997, Mmongoyo et al 2017. According to Da Cruz Cabral et al (2013), the complex combination of compounds in the extracts interacting with the fungi may be helpful to offset the issue of fungal resistance against synthetic fungicides.…”

The Genus Diospyros: A Review of Novel Insights into the Biological Activity and Species of Mozambican Flora

“…Several studies have reported the potential antifungal activity of the root and root bark of most Diospyros species [42,54,92]. However, the antifungal activity of a leaf extract of D. mespiliformis has also been confirmed [47,93].…”

“…The antiaflatoxigenic activity of D. mafiensis root, another Mozambican medicinal plant, has been linked to the presence of diosquione and 3-hydroxydioquinone, making this herbal drug also an important natural antifungal for preventing fungal growth and aflatoxin accumulation in food [42]. In addition, this species has also been found to have analgesic, antidiabetic, anti-inflammatory, and antioxidant effects, likely correlated with the presence of these kind of constituents.…”