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

Abstract

The use of the halophile microorganism Haloferax mediterranei, able to synthesize poly(hydroxybutyrate-hydroxyvalerate) (PHBV), is considered as a promising tool for the industrial production of bioplastic through bioprocessing. A consistent supplementation of the growth substrate in carbohydrates and minerals is overall necessary to allow its PHBV production. In this work, wasted bread was used as substrate for bioplastic production by microbial fermentation. Instead of the consistent and expensive minerals supplement required for Hfx. mediterranei DSM1411 growth, microfiltered seawater was added to the wasted bread-derived substrate. The suitable ratio of wasted bread homogenate and seawater, corresponding to 40:60, was selected. The addition of proteases and amylase to the bread homogenate promoted the microbial growth but it did not correspond to the increase of bioplastic production by the microorganism, that reach, under the experimental conditions, 1.53 g/L. An extraction procedure of the PHBV from cells, based on repeated washing with water, followed or not by a purification through ethanol precipitation, was applied instead of the conventional extraction with chloroform. 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). Slightly higher hydroxyvalerate content (12.95 vs 10.78%, w/w) was found in PHBV obtained through the water-based extraction compared to the conventional one, moreover, the former was characterized by purity of 100% (w/w). Results demonstrated the suitability of wasted bread, supplemented with seawater, to be used as substrate for bioplastic production through fermentation. Results moreover demonstrated that a solvent-free extraction, exclusively based on osmotic shock, could be used to recover the bioplastic from cells.

Production of single-cell-protein (SCP) / poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrices through fermentation of archaeaHaloferax mediterranei

“…The composition of the resulting archaea SCP/PHBV matrix was determined by FTIR analysis, which revealed a PHBV content of 21.4 ± 1.1 % (w/w) and a protein content of 24.4 ± 1.2 % (w/w). Montemurro et al previously demonstrated the suitability of enzymatically hydrolyzed BW, supplemented with seawater, as a substrate for bioplastic production by fermenting H. mediterranei (Montemurro et al, 2022).…”

“…The global annual bread production is >100 million tonnes (Narisetty et al, 2021). Owing to a short shelf-life and the overproduction of bread, approximately 10% (∼ 10 million tonnes) of the bread produced globally is discarded; it amounts to around 24 million slices of bread every day, representing 27- 31% of the total food waste mass (Montemurro et al, 2022). In the UK, the largest bread consumer in Europe, approximately 0.3 million tonnes of bread is wasted annually (Jung et al, 2022).…”

“…Disposal of BW without its valorization could result in the loss of resources (Jung et al, 2022). Hydrogen, ethanol, lactic acid, succinic acid, lipids, and PHA are examples of high-value products generated by the microbial fermentation of BW (Montemurro et al, 2022). Therefore, BW can potentially be utilized as a valuable and sustainable carbon/nitrogen source that would contribute to a sustainable coproduction of archaea SCP/PHBV while simultaneously addressing waste reduction and resource optimization challenges.…”

“…Numerous investigations on the production of PHA using H. mediterranei have focused on harnessing industrial and agricultural byproducts, such as extruded rice bran (Huang, Duan, Huang, & Chen, 2006), vinasse (Bhattacharyya et al, 2012), rice-based ethanol stillage (Bhattacharyya et al, 2015), cheese whey (Pais, Serafim, Freitas, & Reis, 2016), olive mill wastewater (Alsafadi & Al-Mashaqbeh, 2017), molasses wastewater (Cui, Gong, Shi & Wang, 2017), macroalgal biomass (Ghosh et al, 2019), ricotta cheese (Raho et al, 2020), date palm fruit waste (Alsafadi, Ibrahim, Alamry, Hussein, & Mansour, 2020), and bread waste (Montemurro et al, 2022). However, the industrial production of PHA is still hindered by the costly feed materials (Koller et al, 2005).…”

Production of Polyhydroxyalkanoates for Biodegradable Food Packaging Applications Using Haloferax mediterranei and Agrifood Wastes

“…With this approach, using seawater seems a viable strategy for PHA production. Montemurro et al [ 77 ] used wasted bread as a carbon substrate for microbial growth, to which microfiltered seawater was added instead of the expensive minerals supplement frequently used for this microorganism.…”