Study Reveals Food Waste’s Hidden Potential in Biopolymer Production

By Dr. Noopur JainReviewed by Laura ThomsonJul 24 2025

In a recent article published in the journal Bioresource Technology, researchers explored an integrated approach to utilizing food waste (FW) as a raw material for the sustainable production of biodegradable polymers, particularly polyhydroxybutyrate (PHB), through microbial fermentation processes.

Background

The accumulation of food waste poses significant environmental challenges worldwide, prompting the need for innovative waste management and resource recovery solutions. Food waste contains substantial amounts of organic compounds such as carbohydrates, proteins, and lipids, which can serve as substrates for microbial fermentation.

Previous research has highlighted the potential of native microbiota in FW to produce organic acids, which can subsequently be utilized as precursors for biopolymer synthesis. Among these, polyhydroxyalkanoates (PHAs), particularly PHB, have garnered interest because of their biodegradability and biocompatibility, making them suitable substitutes for petroleum-based plastics. However, the transformation pathways, microbial community dynamics, and metabolic regulation associated with FW fermentation remain incompletely understood. There is a need to elucidate the microbial gene expression profiles and metabolic fluxes under different fermentation conditions to optimize biopolymer yields and make the process commercially viable.

The Current Study

The research employed a comprehensive experimental setup combining microbiological, biochemical, and molecular biology techniques.

Food waste samples were characterized based on their microbiota communities using 16S rRNA sequencing to gauge microbial diversity changes during storage and fermentation. The FW was subjected to autochthonous fermentation under controlled pH conditions, with particular attention to pH stabilization at 7 to maximize lactic acid (LA) production, a key precursor for PHB synthesis. The fermentation parameters, including water ratios, duration, and types of meat waste, were systematically varied to evaluate their influence on organic acid yields.

Microbial biomass growth was monitored through optical density measurements at 600 nm, converted into dry cell weight (DCW). Organic acids, specifically LA and acetic acid, were quantified at regular intervals to track fermentation progress. Cells were harvested at different time points for biochemical analyses, including nitrogenous pigment staining with Nile red to visualize PHB accumulation. PHA content was quantitatively assessed using Nile red fluorescence microscopy and confirmed via extraction and chromatographic techniques.

On the molecular level, RNA was isolated from bacterial cultures at specified time points to perform transcriptomic analysis via RNA sequencing (RNA-seq). The sequencing data were processed with bioinformatics tools to quantify gene expression levels, identify differentially expressed genes, and infer metabolic pathway activity.

Results and Discussion

The study found that the native microbiotas in FW could effectively produce organic acids, especially LA, without external inoculants, emphasizing the self-sustaining nature of the process.

Optimal lactic acid production was achieved at pH 7, with specific FW-water ratios balancing productivity and broth volume. Notably, the presence of meat waste did not significantly diminish LA yields, although it influenced the production of other organic acids such as acetic acid. These organic acids served as substrates for bacterial growth and biopolymer synthesis, with the maximum observed LA concentrations reaching around 29 g/L.

The bacterial cultures, primarily Cupriavidus necator, demonstrated considerable biomass accumulation and PHB production. Nile red staining confirmed the intracellular accumulation of PHB granules, which increased over fermentation duration, aligning with molecular findings. The transcriptomic data revealed that key genes involved in energy metabolism, including those associated with electron transport chain complexes, exhibited significant changes in expression in response to different carbon and nitrogen sources. Specifically, genes implicated in glycolysis, the TCA cycle, and CO₂ fixation pathways were upregulated, suggesting enhanced metabolic flux toward PHB biosynthesis. Some genes involved in central metabolic pathways, like gap, eno, and pyk, were particularly elevated at earlier fermentation stages, indicative of increased glycolytic activity supplying precursors like pyruvate and acetyl-CoA.

The metabolic and gene expression analyses collectively suggest that organic acid accumulation, energy metabolism, and microbial gene regulation are tightly interconnected. The upregulation of genes associated with energy production pathways supports the hypothesis that C. necator channels metabolic energy and carbon flux toward PHB synthesis under optimized conditions. The findings underscore the importance of understanding microbial energy pathways to maximize biopolymer yields efficiency.

Conclusion

This research demonstrates the feasibility of employing native food waste microbiota for the bioconversion of organic waste into biodegradable polymers, specifically PHB.

The comprehensive analysis, integrating microbial community profiling, biochemical measurements, and gene expression data, provides a detailed understanding of the metabolic mechanisms at play.

The findings reveal that optimal fermentation conditions, particularly pH stabilization and appropriate food waste formulations, can significantly enhance organic acid production, which directly correlates with biomass growth and PHB accumulation.

The transcriptomic insights into energy metabolism pathways offer valuable targets for future genetic modifications aimed at further improving biopolymer yields. Overall, the study presents a sustainable and eco-friendly strategy for valorizing food waste, contributing to waste reduction and bioplastic manufacturing, aligning with circular economy principles and advancing biotechnological applications in waste management and materials science.