Exploring Lemon Industry By-Products for Polyhydroxyalkanoate Production: Comparative Performances of Haloferax mediterranei PHBV vs. Commercial PHBV

AbstractThis study investigates the valorisation of lemon industry by-products as carbon sourcesto produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) using the halophilicarchaeon Haloferax mediterranei. The resulting polymer (HFX PHBV) was supplementedwith nucleating agents (orotic acid, boron nitride, and theobromine) and compared with acommercial PHBV grade (Enmat Y1000) under identical conditions. Fermentation strategieswere optimised by varying the lemon by-product concentration, inoculum size, and nutrientstoichiometry (C:N:P ratios), followed by scaleup in a 2 L bioreactor. A 11% (v/v) lemonby-product combined with a 5% (v/v) inoculum yielded the highest productivity underminimal medium conditions (2.127 g/L PHBV), while enriched media further enhancedthe polymer accumulation (up to 3.250 g/L PHBV). A comparative characterisation of HFXPHBV and Enmat Y1000, using NMR, TGA, MFR, DSC, Raman spectroscopy, XRD, andDMA, revealed that HFX PHBV exhibited lower crystallinity, increased flexibility, and ahigh hydroxyvalerate content (27.4%), which conferred improved ductility. Investigationof nucleating agents demonstrated that orotic acid was the most effective at enhancingthe crystallisation kinetics. Overall, this study demonstrates an efficient PHBV productionprocess based on waste valorisation, yielding a biopolymer with competitive physicochemicalproperties relative to a commercial standard, and provides integrated solutions to theglobal challenges of plastic pollution and food waste.