Utilisation of tuna condensate waste from the canning industry as a novel substrate for polyhydroxyalkanoate production

Abstract

Tuna condensate, an organic-rich by-product from the tuna canning industry, was assessed as a substrate for polyhydroxyalkanoate (PHA) production using Cupriavidus necator TISTR 1095. The effect of cultivation parameters on PHA accumulation was studied, including substrate concentration, carbon to nitrogen (C/N) ratio, initial pH-value control and fermentation strategies. For the bacterium, a biomass of 3.8 ± 0.1 g/L, PHA of 1.64 ± 0.1 g/L with PHA productivity of 0.027 g/L.h were obtained under batch cultivation using 100% tuna condensate with a C/N ratio of 88:1 and no control of pH. However, the PHA production was increased 1.3-fold when repeated-batch cultivation was applied. The highest biomass (7.5 ± 0.1 g/L) and PHA (3.8 ± 0.1 g/L) with 0.063 g/L.h of PHA productivity were achieved after the third cycle of repeated-batch cultivation. High chemical oxygen demand (COD) removal efficiency of 70% under the optimal condition was also demonstrated. The polymers generated by C. necator TISTR 1095 were characterised. The size of polymer granules was in the range of 0.7-0.8 μm. The polymer produced in the optimal medium under batch and repeated-batch cultivation was identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 20 mol% of 3-hydroxyvalerate. The molecular mass (Mn) and polydispersity of the polymer were 2 × 106 Da and 2.5, respectively. The results demonstrated that tuna condensate could be used as a cheap substrate for PHA production on an industrial scale.