Fermentative Production of Poly(β-L-malic Acid) from Renewable Feedstocks: Process Advances and Bamboo Shoot Shell Hydrolysate as an Emerging Case Study

Poly(β-L-malic acid) (PMLA) is a water-soluble, biodegradable aliphatic polyester whose pendant carboxyl groups support chemical functionalization for biomedical, packaging, and materials applications. Microbial fermentation can use pure sugars and biomass-derived carbon sources under mild conditions, but industrial translation remains constrained by feedstock cost and variability, strain performance, oxygen and pH control, pretreatment-derived inhibitors, and downstream recovery. This review therefore focuses on the fermentative production of PMLA from refined and renewable carbon sources, the microorganisms and metabolic routes involved, and the process variables that govern titer, yield, productivity, molecular weight, and purification. Agricultural and forestry feedstocks are compared according to their actual carbohydrate class and processing requirements. Bamboo shoot shell hydrolysate is treated as an emerging case study rather than an established production platform: one accepted shake-flask study directly demonstrated PMLA production by Aureobasidium pullulans NRRL Y-2311-1, but controlled bioreactor validation, reproducibility, techno-economic analysis, and application-specific product qualification remain to be further investigated. The review also examines autohydrolysis, low-molecular-weight PMLA for biomedical use, furan inhibition, membrane and ion-exchange purification, and the limits of current economic comparisons. This evidence-based framing identifies where bamboo-processing residues may contribute to renewable PMLA production while distinguishing laboratory feasibility from industrial readiness.