The Role of Whey in Functional Microorganism Growth and Metabolite Generation: A Biotechnological Perspective

The valorization of cheese whey, a rich by-product of the dairy industry that is rich in lactose (approx. 70%), proteins (14%), and minerals (9%), represents a promising approach for microbial fermentation. With global whey production exceeding 200 million tons annually, the high biochemical oxygen demand underlines the important need for sustainable processing alternatives. This review explores the biotechnological potential of whey as a fermentation medium by examining its chemical composition, microbial interactions, and ability to support the synthesis of valuable metabolites. Functional microorganisms such as lactic acid bacteria (Lactobacillus helveticus, L. acidophilus), yeasts (Kluyveromyces marxianus), actinobacteria, and filamentous fungi (Aspergillus oryzae) have demonstrated the ability to efficiently convert whey into a wide range of bioactive compounds, including organic acids, exopolysaccharides (EPSs), bacteriocins, enzymes, and peptides. To enhance microbial growth and metabolite production, whey fermentation can be carried out using various techniques, including batch, fed-batch, continuous and immobilized cell fermentation, and membrane bioreactors. These bioprocessing methods improve substrate utilization and metabolite yields, contributing to the efficient utilization of whey. These bioactive compounds have diverse applications in food, pharmaceuticals, agriculture, and biofuels and strengthen the role of whey as a sustainable biotechnological resource. Patents and clinical studies confirm the diverse bioactivities of whey-derived metabolites and their industrial potential. Whey peptides provide antihypertensive, antioxidant, immunomodulatory, and antimicrobial benefits, while bacteriocins and EPSs act as natural preservatives in foods and pharmaceuticals. Also, organic acids such as lactic acid and propionic acid act as biopreservatives that improve food safety and provide health-promoting formulations. These results emphasize whey's significant industrial relevance as a sustainable, cost-efficient substrate for the production of high-quality bioactive compounds in the food, pharmaceutical, agricultural, and bioenergy sectors.

Boosting volatile fatty acids (VFAs) production during anaerobic digestion of rich lignocellulose pulp mill excess sludge by inoculating rumen fluid and the study on the microbial community structures and functions

Hydrolysis is the rate-limiting step in the anaerobic digestion of lignocellulose. In the present study, pulp and paper mill sludge (PPMS), a lignocellulose-rich, high-volume waste, which is difficult to be treated by traditional anaerobic digestion, was inoculated with rumen microorganisms for VFAs production. The maximum extent of VFA accumulation was 3839 mg/L after 84 h in the rumen fluid-inoculated digester, versus 2338 mg/L after 96 h in the digester without rumen fluid addition. The amount was 1.64 times higher than that of digester leachate inoculum. During VFAs production, the hydrolysable of lignocellulose and extracellular polymers were promoted by inoculating rumen liquid. High-throughput sequencing results (16S rRNA genes) showed that there was a significant succession of dominant microbial community during in vitro fermentation of PPMS by rumen fluid. Fermentation by rumen fluid is a potentially effective technology to boost VFAs production from a lignocellulose-rich biomass.

Boosting Food Packaging Sustainability Through the Valorization of Agri-Food Waste and By-Products

The environmental concerns associated with synthetic polymers have intensified the search for sustainable and biodegradable alternatives, particularly for food packaging applications. Natural biopolymers offer promising solutions due to their biodegradability, reduced environmental impact, and reliance on renewable resources. Among these, agri-food waste and by-products have gained significant attention as valuable feedstocks for polymer production, supporting a circular economy approach. This review critically examines the current status of biopolymers derived from plant, animal, and microbial sources, focusing on their physical and chemical properties and their application in food packaging. The findings underscore that the properties of plant- and animal-based biopolymers are heavily influenced by the source material and extraction techniques, with successful examples in biodegradable films, coatings, and composite materials. However, a critical gap remains in the characterization of microbial biopolymers, as research in this area predominantly focuses on optimizing production processes rather than evaluating their material properties. Despite this limitation, microbial biopolymers have demonstrated considerable potential in composite films and fillers. By addressing these gaps and evaluating the key factors that influence the success of biopolymer-based packaging, we contribute to the ongoing efforts to develop sustainable food packaging solutions and reduce the environmental impact of plastic waste.

Waste to wealth: Polyhydroxyalkanoates (PHA) production from food waste for a sustainable packaging paradigm

The growing demand for sustainable food packaging and the increasing concerns regarding environmental pollution have driven interest in biodegradable materials. This paper presents an in-depth review of the production of Polyhydroxyalkanoates (PHA), a biodegradable polymer, from food waste. PHA-based bioplastics, particularly when derived from low-cost carbon sources such as volatile fatty acids (VFAs) and waste oils, offer a promising solution for reducing plastic waste and enhancing food packaging sustainability. Through optimization of microbial fermentation processes, PHA production can achieve significant efficiency improvements, with yields reaching up to 87 % PHA content under ideal conditions. This review highlights the technical advancements in using PHA for food packaging, emphasizing its biodegradability, biocompatibility, and potential to serve as a biodegradable alternative to petroleum-based plastics. However, challenges such as high production costs, mechanical limitations, and the need for scalability remain barriers to industrial adoption. The future of PHA in food packaging hinges on overcoming these challenges through further research and innovation in production techniques, material properties, and cost reduction strategies, along with necessary legislative support to promote widespread use.

Recent advances in dark fermentative hydrogen production from vegetable waste: role of inoculum, consolidated bioprocessing, and machine learning

Waste-centred-bioenergy generation have been garnering interest over the years due to environmental impact presented by fossil fuels. Waste generation is an unavoidable consequence of urbanization and population growth. Sustainable waste management techniques that are long term and environmentally benign are required to achieve sustainable development. Energy recovery from waste biomass via dark fermentative hydrogen production is a sustainable approach to waste management. Vegetable waste is generated in plenty over the food supply chain and being a rich source of carbon and other nutrients it has been studied for production of biohydrogen. This review aims to offer a comprehensive overview on the potential of vegetable waste as a feedstock for dark fermentative biohydrogen production. The hydrogen output from dark fermentative process is lower and additional strategies are required to improve the production. This review addresses the challenges generally encountered during dark fermentative hydrogen production using vegetable waste and the importance of methods such as bioaugmentation and application of extremophiles for process enhancement. The role of machine learning in the field of biohydrogen production is briefly discussed. The application of dark fermentative effluents for secondary valuable product generation and its contribution to the biohydrogen biorefinery is discussed as well.

A review on microbes mediated resource recovery and bioplastic (polyhydroxyalkanoates) production from wastewater

BACKGROUND

Plastic is widely utilized in packaging, frameworks, and as coverings material. Its overconsumption and slow degradation, pose threats to ecosystems due to its toxic effects. While polyhydroxyalkanoates (PHA) offer a sustainable alternative to petroleum-based plastics, their production costs present significant obstacles to global adoption. On the other side, a multitude of household and industrial activities generate substantial volumes of wastewater containing both organic and inorganic contaminants. This not only poses a threat to ecosystems but also presents opportunities to get benefits from the circular economy. Production of bioplastics may be improved by using the nutrients and minerals in wastewater as a feedstock for microbial fermentation. Strategies like feast-famine culture, mixed-consortia culture, and integrated processes have been developed for PHA production from highly polluted wastewater with high organic loads. Various process parameters like organic loading rate, organic content (volatile fatty acids), dissolved oxygen, operating pH, and temperature also have critical roles in PHA accumulation in microbial biomass. Research advances are also going on in downstream and recovery of PHA utilizing a combination of physical and chemical (halogenated solvents, surfactants, green solvents) methods. This review highlights recent developments in upcycling wastewater resources into PHA, encompassing various production strategies, downstream processing methodologies, and techno-economic analyses.

SHORT CONCLUSION

Organic carbon and nitrogen present in wastewater offer a promising, cost-effective source for producing bioplastic. Previous attempts have focused on enhancing productivity through optimizing culture systems and growth conditions. However, despite technological progress, significant challenges persist, such as low productivity, intricate downstream processing, scalability issues, and the properties of resulting PHA.

Efficient polyhydroxybutyrate production using acetate by engineered Halomonas sp. JJY01 harboring acetyl-CoA acetyltransferase

Polyhydroxybutyrate (PHB) is a well-known biodegradable bioplastic synthesized by microorganisms and can be produced from volatile fatty acids (VFAs). Among VFAs acetate can be utilized by Halomonas sp. YLGW01 for growth and PHB production. In this study, Halomonas sp. JJY01 was developed through introducing acetyl-CoA acetyltransferase (atoAD) with LacIq-Ptrc promoter into Halomonas sp. YLGW01. The effect of expression of atoAD on acetate was investigated by comparison with acetate consumption and PHB production. Shake-flask study showed that Halomonas sp. JJY01 increased acetate consumption rate, PHB yield and PHB production (0.27 g/L/h, 0.075 g/g, 0.72 g/L) compared to the wild type strain (0.17 g/L/h, 0.016 g/g, 0.11 g/L). In 10 L fermenter scale fed-batch fermentation, the growth of Halomonas sp. JJY01 resulted in higher acetate consumption rate, PHB yield and PHB titer (0.55 g/L/h, 0.091 g/g, 4.6 g/L) than wild type strain (0.35 g/L/h, 0.067 h/h, 2.9 g/L). These findings demonstrate enhanced acetate utilization and PHB production through the introduction of atoAD in Halomonas strains.

Valorization of food waste derived anaerobic digestate into polyhydroxyalkanoate (PHA) using Thauera mechernichensis TL1

Polyhydroxyalkanoate (PHA) is a biopolymer that can be used as a bioplastic, offering a green alternative to petroleum-based plastics. In this study, we investigated PHA production using Thauera mechernichensis TL1. The optimal molar C/N ratio was determined to be 20 from among the ratios of 4, 20, 40, 80, and 200 and in the absence of nitrogen. Food waste anaerobic digestate, mainly comprised of acetate and propionate, was used as the carbon source for PHA production by T. mechernichensis TL1, resulting in a maximum PHA content of 23.98 ± 0.52 wt% (0.52 ± 0.02 g/L PHA) with a PHA productivity of 0.043 g/L-h PHA. In addition, when using acetate and propionate, T. mechernichensis TL1 produced PHA with a maximum PHA content of 57.43 ± 2.84 wt% (2.04 ± 0.11 g/L PHA) and 50.94 ± 1.61 wt% (2.62 ± 0.16 g/L PHA), with a PHA productivity of 0.092 g/L-h PHA and 0.070 g/L-h PHA, respectively. Proton nuclear magnetic resonance spectroscopy (1H NMR) confirmed polyhydroxybutyrate (PHB) production using acetate as a carbon source, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production using propionate or food waste anaerobic digestate as the carbon source. The whole-genome analysis of T. mechernichensis TL1 confirmed the existence of a PHA biosynthesis pathway, with the presence of phaA, phaB, phaC (Class I and Class II), and phaJ genes. This study was the first to demonstrate Thauera sp.'s ability to produce PHA from food waste anaerobic digestate, rendering it as a promising candidate for PHA-producing bacteria for the valorization of food waste.

Thauera sp. Sel9, a new bacterial strain for polyhydroxyalkanoates production from volatile fatty acids

Thauera is one of the main genera involved in polyhydroxyalkanoate (PHA) production in microbial mixed cultures (MMCs) from volatile fatty acids (VFAs). However, no Thauera strains involved in PHA accumulation have been obtained in pure culture so far. This study is the first report of the isolation and characterization of a Thauera sp. strain, namely Sel9, obtained from a sequencing batch reactor (S-SBR) set up for the selection of PHA storing biomass. The 16S rRNA gene evidenced a high sequence similarity with T. butanivorans species. Genome sequencing identified all genes involved in PHA synthesis, regulation and degradation. The strain Sel9 was able to grow with an optimum of chemical oxygen demand-to-nitrogen (COD:N) ratio ranging from 4.7 to 18.9. Acetate, propionate, butyrate and valerate were used as sole carbon and energy sources: a lag phase of 72 h was observed in presence of propionate. Final production of PHAs, achieved with a COD:N ratio of 75.5, was 60.12 ± 2.60 %, 49.31 ± 0.7 %, 37.31 ± 0.43 % and 18.06 ± 3.81 % (w/w) by using butyrate, acetate, valerate and propionate as substrates, respectively. Also, the 3-hydroxybutyrate/3-hydroxyvalerate ratio reflected the type of carbon sources used: 12.30 ± 0.82 for butyrate, 3.56 ± 0.02 for acetate, 0.93 ± 0.03 for valerate and 0.76 ± 0.02 for propionate. The results allow a better elucidation of the role of Thauera in MMCs and strongly suggest a possible exploitation of Thauera sp. Sel9 for a cost-effective and environmentally friendly synthesis of PHAs using VFAs as substrate.

Thorough Investigation of the Effects of Cultivation Factors on Polyhydroalkanoates (PHAs) Production by Cupriavidus necator from Food Waste-Derived Volatile Fatty Acids

Volatile fatty acids (VFAs) have become promising candidates for replacing the conventional expensive carbon sources used to produce polyhydroxyalkanoates (PHAs). Considering the inhibitory effect of VFAs at high concentrations and the influence of VFA mixture composition on bacterial growth and PHA production, a thorough investigation of different cultivation parameters such as VFA concentrations and composition (synthetic and waste-derived VFAs) media, pH, aeration, C/N ratio, and type of nitrogen sources was conducted. Besides common VFAs of acetic, butyric and propionic acids, Cupriavidus necator showed good capability for assimilating longer-chained carboxylate compounds of valeric, isovaleric, isobutyric and caproic acids in feasible concentrations of 2.5–5 g/L. A combination of pH control at 7.0, C/N of 6, and aeration of 1 vvm was found to be the optimal condition for the bacterial growth, yielding a maximum PHA accumulation and PHA yield on biomass of 1.5 g/L and 56%, respectively, regardless of the nitrogen sources. The accumulated PHA was found to be poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with the percentage of hydroxybutyrate in the range 91–96%. Any limitation in the cultivation factors was found to enhance the PHA yield, the promotion of which was a consequence of the reduction in biomass production.

Potato peel waste biorefinery for the sustainable production of biofuels, bioplastics, and biosorbents

Potato is the fourth most abundant crop harvested annually worldwide. Potato peel waste (PPW) is the main waste stream of potato-processing industries which is generated in large quantities and is a threat to the environment globally. However, owing to its compositional characteristics, availability, and zero cost, PPW is a renewable resource for the production of high-value bioproducts. Hence, this study provides a state-of-the-art overview of advancements in PPW valorization through biological and thermochemical conversions. PPW has a high potential for biofuel and biochemical generation through detoxification, pretreatment, hydrolysis, and fermentation. Moreover, many other valuable chemicals, including bio-oil, biochar, and biosorbents, can be produced via thermochemical conversions. However, several challenges are associated with the biological and thermochemical processing of PPW. The insights provided in this review pave the way toward a PPW-based biorefinery development, providing sustainable alternatives to fossil-based products and mitigating environmental concerns.

Effect of short- and medium-chain fatty acid mixture on polyhydroxyalkanoate production by Pseudomonas strains grown under different culture conditions

Short- and medium-chain fatty acids (SMCFAs) derived from the acidogenic anaerobic mixed culture fermentation of acid whey obtained from a crude cheese production line and their synthetic mixture that simulates a real SMCFA-rich stream were evaluated for polyhydroxyalkanoate (PHA) production. Three individual Pseudomonas sp. strains showed different capabilities of growing and producing PHAs in the presence of a synthetic mixture of SMCFAs. Pseudomonas sp. GL06 exhibited the highest SMCFA tolerance and produced PHAs with the highest productivity (2.7 mg/L h). Based on these observations, this strain was selected for further investigations on PHA production in a fed-batch bioreactor with a SMCFA-rich stream extracted from the effluent. The results showed that PHA productivity reached up to 4.5 mg/L h at 24 h of fermentation together with the ammonium exhaustion in the growth medium. Moreover, the PHA monomeric composition varied with the bacterial strain and the type of the growth medium used. Furthermore, a differential scanning calorimetric and thermogravimetric analysis showed that a short- and medium-chain-length PHA copolymer made of 3-hydroxybutyric, -hexanoic, -octanoic, -decanoic, and -dodecanoic has promising properties. The ability of Pseudomonas sp. to produce tailored PHA copolymers together with the range of possible applications opens new perspectives in the development of PHA bioproduction as a part of an integrated valorization process of SMCFAs derived from waste streams.

Conversion of Short and Medium Chain Fatty Acids into Novel Polyhydroxyalkanoates Copolymers by Aeromonas sp. AC_01

Polyhydroxyalkanoates (PHAs) production by Aeromonas sp. AC_01 was investigated using synthetic and waste derived short and medium chain fatty acids (SMCFAs). The obtained results revealed that the analyzed bacterial strain was able to grow and synthesize PHAs using SMCFAs. The highest PHA productivity was observed in the cultivation supplemented with a mixture of acetic acid and butyric acid (3.89 mg/L·h). Furthermore, SMCFAs-rich stream, derived from acidogenic mixed culture fermentation of acid whey, was found to be less beneficial for PHA productivity than its synthetic mixture, however the PHA production was favored by the nitrogen-limited condition. Importantly, Aeromonas sp. AC_01 was capable of synthesizing novel scl-mcl copolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 3-hydroxytridecanoate (3HtriD) and/or 3-hydroxytetradecaonate (3HTD) with high 3HB and 3HV fractions. They were identified with alterable monomers composition depending on the culture conditions used. Moreover, in-depth thermal analyses proved that they are highly resistant to thermal degradation regardless of their monomeric composition. The obtained results confirm that Aeromonas sp. AC_01 is a promising candidate for the biotechnological production of PHAs from SMCFAs with thermal properties that can be tuned together with their chemical composition by the corresponding adjustment of the cultivation process.