Comprehensive reutilization of herbal waste: Coproduction of magnolol, honokiol, and β-amyrin from Magnolia officinalis residue

Herbal extraction residues (HERs) cause serious environmental pollution and resource waste. In this study, a novel green route was designed for the comprehensive reutilization of all components in HERs, taking Magnolia officinalis residues (MOR) as an example. The reluctant structure of MOR was first destroyed by alkali pretreatment to release the functional ingredients (magnolol and honokiol) originally remaining in MOR and to make MOR more accessible for hydrolysis. A metal–organic frame material MIL-101(Cr) with a maximum absorption capacity of 255.64 mg g−1 was synthesized to absorb the released honokiol and magnolol from the pretreated MOR solutions, and 40 g L−1 reducing sugars were obtained with 81.8% enzymatic hydrolysis rate at 10% MOR solid loading. Finally, 382 mg L−1 β-amyrin was produced from MOR hydrolysates by an engineered yeast strain. In total, 1 kg honokiol, 8 kg magnolol, and 7.64 kg β-amyrin could produce from 1 ton MOR by this cleaner process with a total economic output of 170,700 RMB.