Fermentative polyhydroxybutyrate production from a novel feedstock derived from bakery waste

Large-scale cultivation of Synechocystis sp. PCC6803 for the production of Poly(3-hydroxybutyrate) and its potential applications in the manufacturing of bulk and medical prototypes

Polyhydroxyalkanoates (PHAs) are biopolymers produced by microorganisms under nutrient limiting conditions and in the presence of excess carbon source. PHAs have gained popularity as a sustainable alternative to traditional plastics. However, large scale production of PHAs is economically challenging due to the relatively high costs of organic carbon. Alternative options include using organisms capable of phototrophic or mixotrophic growth. This study aimed at the production of poly(3-hydroxybutyrate) P(3HB), a type of PHA, at pilot scale using the freshwater cyanobacterium Synechocystis sp. PCC6803. First, to identify optimal conditions for P(3HB) production from Synechocystis sp. PCC6803, different supplemental carbon source concentrations and salinity levels were tested at laboratory scale. The addition of 4 g/L acetate with no added NaCl led to P(3HB) accumulation of 10.7 % dry cell weight on the 28th day of cultivation. Although acetate additions were replicated in an outdoor 400 L serpentine photobioreactor, P(3HB) content was lower, implying uncontrolled conditions impact on biopolymer production efficiency. An optimized P(3HB) extraction methodology was developed to remove pigments, and the biopolymer was characterized and subjected to 3D printing (fused deposition modelling) to confirm its processability. This study thus successfully led to the large-scale production of P(3HB) using sustainable and environmentally friendly cyanobacterial fermentation.

Sustainable media feedstocks for cellular agriculture

The global food system is shifting towards cellular agriculture, a second domestication marked by cultivating microorganisms and tissues for sustainable food production. This involves tissue engineering, precision fermentation, and microbial biomass fermentation to establish food value chains independent of traditional agriculture. However, these techniques rely on growth media sourced from agricultural, chemical (fossil fuels), and mining supply chains, raising concerns about land use competition, emissions, and resource depletion. Fermentable sugars, nitrogen, and phosphates are key ingredients derived from starch crops, energy-intensive fossil fuel based processes, and finite phosphorus resources, respectively. This review explores sustainable alternatives to reduce land use and emissions associated with cellular agriculture media ingredients. Sustainable alternatives to first generation sugars (lignocellulosic substrates, sidestreams, and gaseous feedstocks), sustainable nitrogen sources (sidestreams, green ammonia, biological nitrogen fixation), and efficient use of phosphates are reviewed. Especially cellulosic sugars, gaseous chemoautotrophic feedstocks, green ammonia, and phosphate recycling are the most promising technologies but economic constraints hinder large-scale adoption, necessitating more efficient processes and cost reduction. Collaborative efforts are vital for a biotechnological future grounded in sustainable feedstocks, mitigating competition with agricultural land and emissions.

Lipid Production of Schizochytrium sp. HBW10 Isolated from Coastal Waters of Northern China Cultivated in Food Waste Hydrolysate

Marine oleaginous thraustochytrids have attracted increasing attention for their great potential in producing high-value active metabolites using various industrial and agricultural waste. Food waste containing abundant nutrients is considered as an excellent feedstock for microbial fermentation. In this study, a thraustochytrid strain Schizochytrium sp. HBW10 was isolated from a water column in Bohai Bay in Northern China for the first time. Further lipid production characteristics of S. sp. HBW10 were investigated utilizing sulfuric acid hydrolysate of food waste (FWH) from two different restaurants (FWH1 and FWH2) with the initial pH value adjusted by NaOH or NaHCO3. Results showed that the highest concentration of total fatty acids (TFAs) was observed in FWH2 medium with the 50% content level on the fifth day, reaching up to 0.34 g/L. A higher initial pH promoted the growth and saturated fatty acid (SFA) accumulation of S. sp. HBW10, achieving nearly 100% of the sum of saturated and monounsaturated fatty acids (SMUFAs) in TFAs with initial pH7 and pH8 in FWH1 medium. This work demonstrates a possible way for lipid production by thraustochytrids using food waste hydrolysate with a higher initial pH (pH7~pH8) adjusted by NaHCO3.

Bread Surplus: A Cumulative Waste or a Staple Material for High-Value Products?

Food waste has been widely valorized in the past years in order to develop eco-friendly materials. Among others, bread waste is currently of increasing interest, as it is considered a huge global issue with serious environmental impacts and significant economic losses that have become even greater in the post-pandemic years due to an increase in cereal prices, which has led to higher production costs and bread prices. Owing to its richness in polysaccharides, bread waste has been previously studied for its physico-chemical characteristics and its numerous biotechnological applications. The present review highlights the re-use of bread waste and its valorization as a valuable resource by making value-added products through numerous technological processes to increase efficiency at all stages. Many research studies reporting several transformation methods of surplus bread into ethanol, lactic acid, succinic acid, biohydrogen, hydroxymethylfurfural, proteins and pigments, glucose-fructose syrup, aroma compounds, and enzymes are widely discussed. The wide variety of suggested applications for recycling bread waste provides significant insights into the role of technology development in potentially maximizing resource recovery and consequently contributing to environmental performance by reducing the amount of bread waste in landfills.

Cultivation of microalgae on food waste: Recent advances and way forward

Microalgae are photosynthetic microbes that can synthesize compounds of therapeutic potential with wide applications in the food, bioprocessing and pharmaceutical sector. Recent research advances have therefore, focused on finding suitable economic substrates for the sustainable cultivation of microalgae. Among such substrates, food derived waste specifically from the starch, meat, dairy, brewery, oil and fruit and vegetable processing industries has gained popularity but poses numerous challenges. Pretreatment, dilution of waste water supernatants, mixing of different food waste streams, utilizing two-stage cultivation and other biorefinery approaches have been intensively explored for multifold improvement in microalgal biomass recovery from food waste. This review discusses the advances and challenges associated with cultivation of microalgae on food waste. The review suggests that there is a need to standardize different waste substrates in terms of general composition, genetically engineered microalgal strains, tackling process scalability issues, controlling wastewater toxicity and establishing a waste transportation chain.

Biotechnological impacts of Halomonas: a promising cell factory for industrially relevant biomolecules

Extremophiles are the most fascinating life forms for their special adaptations and ability to offer unique extremozymes or bioactive molecules. Halophiles, the natural inhabitants of hypersaline environments, are one among them. Halomonas are the common genus of halophilic bacteria. To support growth in unusual environments, Halomonas produces various hydrolytic enzymes, compatible solutes, biopolymers like extracellular polysaccharides (EPS) and polyhydroxy alkaloates (PHA), antibiotics, biosurfactants, pigments, etc. Many of such molecules are being produced in large-scale bioreactors for commercial use. However, the prospect of the remaining bioactive molecules with industrial relevance is far from their application. Furthermore, the genetic engineering of the respective gene clusters could open up a new path to bio-prospect these molecules by overproducing their products through heterologous expression. The present survey on Halomonas highlights their ecological diversity, application potential of the their various industrially relevant biomolecules and impact of these biomolecules on respective fields.

A Review on Enhancing Cupriavidus necator Fermentation for Poly(3-hydroxybutyrate) (PHB) Production From Low-Cost Carbon Sources

In the context of a circular economy, bioplastic production using biodegradable materials such as poly(3-hydroxybutyrate) (PHB) has been proposed as a promising solution to fundamentally solve the disposal issue of plastic waste. PHB production techniques through fermentation of PHB-accumulating microbes such as Cupriavidus necator have been revolutionized over the past several years with the development of new strategies such as metabolic engineering. This review comprehensively summarizes the latest PHB production technologies via Cupriavidus necator fermentation. The mechanism of the biosynthesis pathway for PHB production was first assessed. PHB production efficiencies of common carbon sources, including food waste, lignocellulosic materials, glycerol, and carbon dioxide, were then summarized and critically analyzed. The key findings in enhancing strategies for PHB production in recent years, including pre-treatment methods, nutrient limitations, feeding optimization strategies, and metabolism engineering strategies, were summarized. Furthermore, technical challenges and future prospects of strategies for enhanced production efficiencies of PHB were also highlighted. Based on the overview of the current enhancing technologies, more pilot-scale and larger-scale tests are essential for future implementation of enhancing strategies in full-scale biogas plants. Critical analyses of various enhancing strategies would facilitate the establishment of more sustainable microbial fermentation systems for better waste management and greater efficiency of PHB production.

What Is New in the Field of Industrial Wastes Conversion into Polyhydroxyalkanoates by Bacteria?

The rising global consumption and industrialization has resulted in increased food processing demand. Food industry generates a tremendous amount of waste which causes serious environmental issues. These problems have forced us to create strategies that will help to reduce the volume of waste and the contamination to the environment. Waste from food industries has great potential as substrates for value-added bioproducts. Among them, polyhydroxyalkanaotes (PHAs) have received considerable attention in recent years due to their comparable characteristics to common plastics. These biodegradable polyesters are produced by microorganisms during fermentation processes utilizing various carbon sources. Scale-up of PHA production is limited due to the cost of the carbon source metabolized by the microorganisms. Therefore, there is a growing need for the development of novel microbial processes using inexpensive carbon sources. Such substrates could be waste generated by the food industry and food service. The use of industrial waste streams for PHAs biosynthesis could transform PHA production into cheaper and more environmentally friendly bioprocess. This review collates in detail recent developments in the biosynthesis of various types of PHAs produced using waste derived from agrofood industries. Challenges associated with this production bioprocess were described, and new ways to overcome them were proposed.

Co-Fermentation of Food Waste and Municipal Sludge from the Saudi Arabian Environment to Improve Lactic Acid Production by Lactobacillus rhamnosus AW3 Isolated from Date Processing Waste

Food waste and municipal sludge were used as the substrates for the biosynthesis of lactic acid in a batch fermentor. The probiotic bacterial strain Lactobacillus rhamnosus AW3 isolated from date processing waste was used to produce lactic acid in a batch fermentor. Co-fermentation enhanced the biosynthesis of lactic acid and decreased substrate inhibition more than mono-substrate fermentation. A maximum yield of 28.4 ± 0.87 g/L of lactic acid was obtained through co-fermentation of food waste and municipal sludge at an optimized ratio of 2:0.5. Lactic acid production was improved by the supplementation of fructose, peptone, and sodium dihydrogen phosphate at pH 5.5 after 48 h fermentation. This production was approximately three-fold higher than that during mono-fermentation of food waste. The tested bacterial strains were obtained from the Microbial Type Culture Collection (MTCC). Lactic acid showed potent antimicrobial activity against pathogenic organisms, such as Bacillus subtilis MTCC 5981 (14 mm), Staphylococcus aureus MTCC 737 (20 mm), Pseudomonas aeruginosa MTCC 424 (24 mm), Enterobacter aerogenes MTCC111 (19 mm), Escherichia coli MTCC 443 (18 mm), Penicillium chrysogenum MTCC 5108 (19 mm), and Aspergillus niger MTCC 282 (19 mm). The antimicrobial properties of lactic acid have significant potential to inhibit the growth of pathogenic bacteria and fungi and improve probiotic properties. The lactic acid extracted from L. rhamnosus AW3 decreased the pH value of soil (p < 0.01) and increased the availability of soil phosphorus (p < 0.01). These findings demonstrate the bioconversion of food waste and municipal sludge into lactic acid, and the recycling of food wastes in urban areas to enhance soil nutrients.

Estimation of the economy of heterotrophic microalgae- and insect-based food waste utilization processes

An estimation of the economy of Hermetia illucens and Chlorella pyrenoidosa cultivations as food waste treatment with benefits was carried out. For both organisms, a process scale was assumed to treat 56.3 t of wet food waste per day, which is equivalent to the amount of food waste appearing in a catchment area of 141,000 inhabitants. Using hypothetical insect and heterotrophic microalgae cultivation processes, a daily production of 3.64 t and 7.14 t dried biomass, respectively, can be achieved. For the cultivation of H. illucens, equipment and daily operational costs were estimated at 79,358.15 € and 5,281.56 €, respectively. Equipment and operational costs for the C. pyrenoidosa cultivation was 50 and 6 times higher, respectively. The higher costs reflect the more complex and advanced process compared to H. illucens cultivation. The internal return rate for a plant lifetime of 20 times revealed an economic benefit when C. pyrenoidosa biomass is produced. Nevertheless, both processes were found economically feasible when dried biomass is directly commercialized as food without any further downstream processing. However, extraction and purification of special chemicals, such as unsaturated fatty acids and pigments, can significantly increase the revenue.

Optimization of Protease and Amylase Production by Rhizopus oryzae Cultivated on Bread Waste Using Solid-State Fermentation

This research was carried for the coproduction of two industrial enzymes: α-amylase and protease via SSF by Rhizopus oryzae on humidified bread waste. Fermentation time, inoculum size, initial moisture content, salt solutions, and the thickness of the substrate were investigated one by one. Fungus culture was carried out in sterile aluminum trays, and pH was adjusted to 5.5. The main results showed that the highest levels of enzyme production were obtained at 120 h, 65% relative humidity, height media of 1 cm, 105 spore/g, and M-9 solution (g/L): NaH2PO4, 12.8; KH2PO4, 3; NaCl, 0.5; NH4Cl, 1; MgSO4 7H2O, 0.5; CaCl2 2H2O, 0.01. α-Amylase (100 U/g) and protease (2400 U/g) produced by SSF from Rhizopus oryzae (CH4) on BW as substrate are of great interest in industries and could be valorized as enhancers of the bread making process.

Combining submerged and solid state fermentation to convert waste bread into protein and pigment using the edible filamentous fungus N. intermedia

Waste streams from ethanol and bread production present inexpensive, abundant and underutilized renewable substrates that are highly available for valorisation into high-value products. A combined submerged to solid state fermentation strategy was studied using the edible filamentous fungus Neurospora intermedia to biotransform ethanol plant residues 'thin stillage' and waste bread as substrates for the production of additional ethanol, biomass and a feed product rich in pigment. The fungus was able to degrade the stillage during submerged fermentation, producing 81 kg ethanol and 65 kg fungal biomass per ton dry weight of thin stillage. Concurrently, the second solid state fermentation step increased the protein content in waste bread by 161%. Additionally, 1.2 kg pigment per ton waste bread was obtained at the best conditions (6 days solid state fermentation under light at 95% relative humidity at 35 °C with an initial substrate moisture content of 40% using washed fungal biomass to initiate fermentation). This study presents a means of increasing the value of waste bread while reducing the treatment load on thin stillage in ethanol plants.

Food waste biorefinery: Sustainable strategy for circular bioeconomy

Enormous quantity of food waste (FW) is becoming a global concern. To address this persistent problem, sustainable interventions with green technologies are essential. FW can be used as potential feedstock in biological processes for the generation of various biobased products along with its remediation. Enabling bioprocesses like acidogenesis, fermentation, methanogenesis, solventogenesis, photosynthesis, oleaginous process, bio-electrogenesis, etc., that yields various products like biofuels, platform chemicals, bioelectricity, biomaterial, biofertilizers, animal feed, etc can be utilized for FW valorisation. Integrating these bioprocesses further enhances the process efficiency and resource recovery sustainably. Adapting biorefinery strategy with integrated approach can lead to the development of circular bioeconomy. The present review highlights the various enabling bioprocesses that can be employed for the generation of energy and various commodity chemicals in an integrated approach addressing sustainability. The waste biorefinery approach for FW needs optimization of the cascade of the individual bioprocesses for the transformation of linear economy to circular bioeconomy.

Valorisation of food waste via fungal hydrolysis and lactic acid fermentation with Lactobacillus casei Shirota

Food waste recycling via fungal hydrolysis and lactic acid (LA) fermentation has been investigated. Hydrolysates derived from mixed food waste and bakery waste were rich in glucose (80.0-100.2gL(-1)), fructose (7.6gL(-1)) and free amino nitrogen (947-1081mgL(-1)). In the fermentation with Lactobacillus casei Shirota, 94.0gL(-1) and 82.6gL(-1) of LA were produced with productivity of 2.61gL(-1)h(-1) and 2.50gL(-1)h(-1) for mixed food waste and bakery waste hydrolysate, respectively. The yield was 0.94gg(-1) for both hydrolysates. Similar results were obtained using food waste powder hydrolysate, in which 90.1gL(-1) of LA was produced with a yield and productivity of 0.92gg(-1) and 2.50gL(-1)h(-1). The results demonstrate the feasibility of an efficient bioconversion of food waste to LA and a decentralized approach of food waste recycling in urban area.

Utilization of protein-rich residues in biotechnological processes

A drawback of biotechnological processes, where microorganisms convert biomass constituents, such as starch, cellulose, hemicelluloses, lipids, and proteins, into wanted products, is the economic feasibility. Particularly the cost of nitrogen sources in biotechnological processes can make up a large fraction of total process expenses. To further develop the bioeconomy, it is of considerable interest to substitute cost-intensive by inexpensive nitrogen sources. The aim of this mini-review was to provide a comprehensive insight of utilization methods of protein-rich residues, such as fish waste, green biomass, hairs, and food waste. The methods described include (i) production of enzymes, (ii) recovery of bioactive compounds, and/or (iii) usage as nitrogen source for microorganisms in biotechnological processes. In this aspect, the utilization of protein-rich residues, which are conventionally considered as waste, allows the development of value-adding processes for the production of bioactive compounds, biomolecules, chemicals, and materials.

Techno-economic analysis of a food waste valorization process via microalgae cultivation and co-production of plasticizer, lactic acid and animal feed from algal biomass and food waste

A techno-economic study of food waste valorization via fungal hydrolysis, microalgae cultivation and production of plasticizer, lactic acid and animal feed was simulated and evaluated by Super-Pro Designer®. A pilot-scale plant was designed with a capacity of 1 metric ton day(-1) of food waste with 20 years lifetime. Two scenarios were proposed with different products: Scenario (I) plasticizer & lactic acid, Scenario (II) plasticizer & animal feed. It was found that only Scenario I was economically feasible. The annual net profits, net present value, payback period and internal rate of return were US$ 422,699, US$ 3,028,000, 7.56 years and 18.98%, respectively. Scenario II was not economic viable due to a deficit of US$ 42,632 per year. Sensitivity analysis showed that the price of lactic acid was the largest determinant of the profitability in Scenario I, while the impact of the variables was very close in Scenario II.

Batch dark fermentation from enzymatic hydrolyzed food waste for hydrogen production

A combination bioprocess of solid-state fermentation (SSF) and dark fermentative hydrogen production from food waste was developed. Aspergillus awamori and Aspergillus oryzae were utilized in SSF from food waste to generate glucoamylase and protease which were used to hydrolyze the food waste suspension to get the nutrients-rich (glucose and free amino nitrogen (FAN)) hydrolysate. Both glucose and FAN increased with increasing of food waste mass ratio from 4% to 10% (w/v) and the highest glucose (36.9 g/L) and FAN (361.3mg/L) were observed at food waste mass ratio of 10%. The food waste hydrolysates were then used as the feedstock for dark fermentative hydrogen production by heat pretreated sludge. The best hydrogen yield of 39.14 ml H2/g food waste (219.91 ml H2/VSadded) was achieved at food waste mass ratio of 4%. The proposed combination bioprocess could effectively accelerate the hydrolysis rate, improve raw material utilization and enhance hydrogen yield.

Metabolic Engineering of Escherichia coli for Poly(3-hydroxybutyrate) Production under Microaerobic Condition

The alcohol dehydrogenase promoter P_adhE and mixed acid fermentation pathway deficient mutants of Escherichia coli were employed to produce poly(3-hydroxybutyrate) (P3HB) under microaerobic condition. The E. coli mutant with ackA-pta, poxB, ldhA, and adhE deletions accumulated 0.67 g/L P3HB, up to 78.84% of cell dry weight in tube cultivation. The deletion of pyruvate formate-lyase gene pflB drastically decreased P3HB production and P3HB content to 0.09 g/L and 24.44%, respectively. Overexpressing pflB via the plasmid in its knocked out mutant restored cell growth and P3HB accumulation, indicating the importance of the pyruvate formate-lyase in microaerobic carbon metabolism. The engineered E. coli BWapld (pWYC09) produced 5.00 g/L P3HB from 16.50 g/L glucose in 24 h batch fermentation, and P3HB production yield from glucose was 0.30 g/g, which reached up to 63% of maximal theoretical yield.