ISSUE FOCUS Alternative Proteins Magazine April 2025 25 enzymes, gut microbiota, and a physiological system adapted to fragment polymer chains (Yang et al., 2024). While the process varies by species and plastic type, recent studies have proposed a generalized biodegradation model, primarily observed in T. molitor, T. obscurus, Z. atratus, and G. mellonella: 1. Initial contact: The larva bites into the plastic and its saliva begins to partially oxidize the material using enzymes. 2. Ingestion and fragmentation: The plastic enters the digestive system, where it is physically shredded by the mouthparts and intestinal movement, reducing its size and increasing surface area. 3. Enzymatic and microbial action: Inside the gut, the plastic is exposed to a mix of digestive enzymes, bioemulsifying compounds, and intestinal microbes that work together to break down the polymer chains (depolymerization). 4. Oxidation and mineralization: Some plastic fragments are oxidized and converted into simpler molecules, such as water (H₂O) and carbon dioxide (CO₂); others are assimilated by the larva or its microbiota. 5. Excretion: The non-degraded material and byproducts of the process are expelled as frass. Among the bacteria identified as capable of breaking down complex polymers are Enterobacter, Bacillus, Pseudomonas, and Staphylococcus, while enzymes involved include lipases, esterases, cutinases, and proteases. However, in some cases, certain species appear able to degrade plastics even without microbial assistance, according to studies referenced in Yang et al. (2024). Still, other researchers argue the opposite: One study showed that when gut microbiota was suppressed using antibiotics, T. molitor larvae lost their ability to degrade plastic (Siddiqui et al., 2024). Studies show that T. molitor can convert up to 48% of EPS carbon into CO₂ in just 16 days, while another 49% is excreted as frass (Zielińska et al., 2021). Additionally, this same species fed with EPS maintained high protein levels (48.6%) without signs of toxicity, suggesting potential use in animal feed, if safety is ensured. It seems that efficiency improves when plastic is combined with a nutrient-rich diet like wheat bran, and pre-treatment methods such as UV light or plasma may further enhance degradation (Yang et al., 2024; Siddiqui et al., 2024). Taken together, these advances demonstrate that the process is functional, measurable and has the potential to be scaled up as a dual solution for plastic reduction and alternative protein production, but only if the safe use of these larvae as feed can be guaranteed. How larvae break down plastic Adapted from: Yang, S.-S et al. (2024). Radical innovation breakthroughs of biodegradation of plastics by insects. Frontiers of Environmental Science & Engineering, 18 (6), Article 78. https://doi.org/10.1007/s11783-024-1838-x Initial contact 1 Excretion 5 Enzymatic and microbial action 3 Oxidation and mineralization 4 Ingestion and fragmentation 2 A generalized model of insect biodegradation, represented in this image by a T. molitor larva, combines digestive enzymes, gut microbiota, and a physiological system adapted to break down polymer chains
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