Non-invasive and real-time monitoring of polyhydroxyalkanoates production using two-dimensional fluorescence spectroscopy

Bioplastics are a sustainable and environmental-friendly alternative to the conventional petroleum-based plastics, namely due to their source (biobased) and due to their biodegradability or both. Polyhydroxyalkanoates (PHA) stand out among the bioplastics group by being intracellular biobased, biodegradable and biocompatible polymers. PHA production has been highly investigated during the last decades. However, to date, PHA production has been monitored through offline and time-consuming tools, involving hazardous solvents, not allowing a timely control of the bioprocesses, which often results in a loss of process productivity and hinders its implementation at full scale. Therefore, two-dimensional (2D) fluorescence spectroscopy was assessed for monitoring the PHA content at real-time, as it is a non-destructive, solvent-free and non-invasive technique. The complex information of the biological broth was captured within fluorescence excitation-emission matrices (EEMs), which were deconvoluted through projection to latent structures (PLS) modelling to estimate PHA production by an enriched PHA microbial culture, using fermented brewer's spent grain as feedstock. A good correlation for PHA prediction was achieved, with an average error of ca. 4.0% g_PHA/g_TS for new predictions. This work demonstrates the great potential of using 2D fluorescence spectroscopy to assess the intracellular PHA content without requiring staining agents. Moreover, it unlocks the possibility of an online and real-time monitoring of the biopolymer production processes, which will contribute towards the improvement of the PHA process productivity and, consequently, its implementation at full scale.