Exploitation of wasted bread as substrate for polyhydroxyalkanoates production through the use of Haloferax mediterranei and seawater.

The use of biotechnology to produce bioplastic was widely investigated considering the interest to find sustainable ways for the production of disposable products. Different biotechnologies were exploited evaluating the use of low-cost raw materials and selected microorganisms. The halophile microorganism Haloferax mediterranei, able to synthesize poly(hydroxybutyrate-hydroxyvalerate) (PHBV), is a promising strain for the industrial production of bioplastic from carbohydrates and minerals rich substrates through bioprocessing. Wasted bread was used as substrate for bioplastic production by microbial fermentation by using microfiltered seawater and wasted bread-derived substrate instead of expensive media and minerals supplement required for Hfx. mediterranei DSM1411 growth. The best ratio of wasted bread homogenate and seawater was evaluated and 40:60 was the optimum for microbial growth. Protease and amylaseadditions to the bread homogenate stimulated microbial growth, but without significantly increasing bioplastic production, which reached 1.53 g/L under experimental conditions in a 3-liter bioreactor. Instead of using the traditional extraction method for PHBV recovery with chloroform, a process based on repeated washing with water, followed or not by a purification using ethanol precipitation, was used. Yield of PHBV obtained using the different extraction methods were 21.6 ± 3.6 (standard extraction/purification procedure with CHCl3:H2O mixture), 24.8 ± 3.0 (water-based extraction), and 19.8 ± 3.3 mg PHAs/g of wasted bread (water-based extraction followed by ethanol purification). The PHBV produced using the water-based extraction had a slightly greater hydroxyvalerate concentration (12.95 vs. 10.78%, w/w) than the traditional one without affecting the purity of the recovered biopolymer which reached 100% (w/w). This research demonstrated the possibility of using unexpensive substrates, as bread and saltwater, for fermentation-based bioplastic manufacture. Moreover, the set up of green bioplastic recovery, based on osmotic shock by using water, was an efficient operation for obtaining high quality PHBV with comparable concentration compared to conventional solvent extraction.