Research Progress in Biotransformation of Plant and Phytochemicals by Aspergillus: Active Metabolites and Industrial Applications

Plant-derived bioactive compounds, such as polyphenols and saponins, possess significant pharmacological value. However, conventional extraction methods often suffer from low efficiency, poor bioavailability, and environmental burdens. Aspergillus-based biotransformation has emerged as a superior platform for overcoming these limitations due to their robust secretomes, versatile metabolic networks, and the GRAS (Generally Recognized as Safe) status of specific industrially relevant species (e.g., A. oryzae and A. niger). Existing literature frequently focuses on isolated compounds or general fungal processes. To fill this gap, this review systematically links specific Aspergillus enzymatic systems to an “enzymatic hydrolysis–transformation–synthesis” closed-loop framework, which is essential for industrial-scale valorization. In this review, we summarize recent advances in the biotransformation of phytochemicals by A. niger, A. oryzae, and A. nidulans. These fungi utilize specialized enzymes—including β-glucosidases, cellulases, and glycosidases—to enable precise hydrolysis, deglycosylation, and detoxification under mild conditions. We highlight representative transformations that demonstrate markedly enhanced bioactivity and solubility. Key examples include the conversion of polydatin to resveratrol (>90% yield) and ginsenoside Rb1 to ginsenoside compound K (94.4% conversion rate). Although industrial applications span the food, pharmaceutical, and cosmetic sectors, significant challenges persist in solid-state fermentation (SSF) scale-up, strain stability, target compound over-degradation, and downstream purification. Genetic engineering, process optimization and hybrid bioprocessing are highlighted as promising strategies to overcome these limitations and realize sustainable, high-value production of natural bioactive metabolites.