Production of Medium Chain Length Polyhydroxyalkanoate from Waste Cannabis sativa Biomass

Abstract

This works aims to evaluate a process to convert residual medical Cannabis sativa stalks into medium chain length polyhydroxyalkanoate (mcl-PHA), using chemical pretreatment and enzymatic hydrolysis to obtain sugars as a carbon source for a fermentation process with Pseudomonas aeruginosa. Chemical composition analysis revealed a content of structural polysaccharides of 57.64%. Thermochemical pretreatments with 2% sulfuric acid or 2% sodium hydroxide were capable of partially removing hemicellulose and lignin, as well as increasing cellulose crystallinity. Pretreated biomass was subjected to hydrolysis using commercial cellulase cocktails Celluclast® 1.5 L and Cellic® CTec3. Acid pretreatment showed an adverse effect on hydrolysis yield of holocellulose, decreasing to 39.5%; compared to 44.4% of untreated biomass. Alkaline pretreatment increased degree of hydrolysis up to 73.3%. Shake flask fermentation of hydrolysate with Pseudomonas aeruginosa produced cell growth of 1.65 g/L and a mcl-PHA titer of 0.41 g/L. Extracted polymer presented characteristic FTIR bands for PHAs, glass transition temperature of − 50.8 °C, melting temperature of 48.9 °C, possibly allowing its use in the biomedical industry. The developed process represents a potential way to valorize Cannabis waste stalks, using alkaline pretreatment, enzymatic hydrolysis with Celluclast® 1.5 L and fermentation with Pseudomonas aeruginosa. Further work should focus on improving yield of the obtained polyhydroxyalkanoate in fermentation, in order to improve industrial feasibility of the entire process and, in turn, increasing revenue of the medical Cannabis industry. Graphical Abstract