Bio-detoxification of Jatropha curcas L. cake by a soil-borne Mucor circinelloides strain using a zebrafish survival model and solid-state fermentation

Aims: The aims of the study were to (1) improve the evaluation criteria of detoxifying Jatropha curcas L. cake (JCC) (2) isolate and characterize a JCC tolerant strain (3) explore its JCC detoxifying potential.

Methods and results: The zebrafish was employed as a survival model to screen the strains capable of detoxifying JCC. A strain identified as Mucor circinelloides SCYA25, which is highly capable of degrading all toxic components, was isolated from soil. Different solid-state fermentation parameters were optimized by response surface methodology (RSM). The optimal values for inoculation amount, moisture content, temperature, and time were found to be 18% (1.8×10⁶ spores g^-1 cake), 66%, 26 ℃, and 36 d, respectively, to achieve maximum detoxification of the JCC (92%). Under optimal fermentation conditions, the protein content of JCC was increased, while the concentrations of ether extract, crude fiber, toxins, and anti-nutritional substances were all degraded considerably (P < 0.05). Scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FITR) analysis revealed that the fermentation process could disrupt the surface structure and improve the ratio of α-helix to β-folding in the JCC protein, which may improve the digestibility when the detoxified JCC is used as a feedstuff.

Conclusions: Our results indicate that M. circinelloides SCYA25 is able to detoxify JCC and improve its nutritional profile, which is beneficial to the safe utilization of JCC as a protein feedstuff.

Significance/ impact: The newly identified M. circinelloides SCYA25 detoxified JCC in a safe manner to provide a potential alternative to soybean meal for the feed industry. These results also provide a new perspective and method for the toxicity evaluation and utilization of JCC and similar toxic agricultural by-products.

Keywords: Mucor circinelloides; Detoxification; Jatropha curcas L. cake; Protein feed; Response surface methodology; Solid-state fermentation; Zebrafish.