In recent decades, the rapid expansion of the food processing industry has led to significant losses and waste, with the fruit and vegetable sector among the most affected. According to the Food and Agriculture Organization of the United Nations (FAO), losses in this category can reach up to 60%. Vegetable waste includes edible parts discarded during processing, packaging, distribution, and consumption, often comprising by-products rich in bioactive compounds such as polyphenols, carotenoids, dietary fibers, vitamins, and enzymes. The underutilization of these resources constitutes both an economic drawback and an environmental and ethical concern. Current recovery practices, including their use in animal feed or bioenergy production, contribute to a circular economy but are often limited by high operational costs. In this context, fermentation has emerged as a promising, sustainable approach for converting vegetable by-products into value-added food ingredients. This process improves digestibility, reduces undesirable compounds, and introduces probiotics beneficial to human health. The present review examines how fermentation can improve the nutritional, sensory, and functional properties of plant-based foods. By presenting several case studies, it illustrates how fermentation can effectively valorize vegetable processing by-products, supporting the development of novel, health-promoting food products with improved technological qualities.

Background/Objectives: Hermetia illucens larvae can efficiently convert agri-food residues into high-protein biomass for animal feed and nutrient-rich frass for soil amendment. However, the potential spread of carbapenem resistance genes (CRGs), which confer resistance to last-resort carbapenem antibiotics, and Enterobacteriaceae, common carriers of these genes and opportunistic pathogens, raises important safety concerns. This study aimed to assess the influence of different agri-food-based diets on Enterobacteriaceae loads and the CRG occurrence during the bioconversion process. Methods: Four experimental diets were formulated from agri-food residues and anaerobic digestate: Diet 1 (peas and chickpea waste), Diet 2 (peas and wheat waste), Diet 3 (onion and wheat waste), and Diet 4 (wheat waste and digestate). Enterobacteriaceae were quantified by viable counts, while five CRGs (bla_KPC, bla_NDM, bla_OXA-48, bla_VIM, and bla_GES) were detected and quantified using quantitative PCRs (qPCRs). Analyses were performed on individual substrates, formulated diets, larvae (before and after bioconversion), and frass. Results: Plant-based diets sustained moderate Enterobacteriaceae loads. In contrast, the digestate-based diet led to a significant increase in Enterobacteriaceae in both the frass and mature larvae. CRGs were detected only in legume-based diets: bla_VIM and bla_GES were found in both mature larvae and frass, while bla_OXA-48 and bla_KPC were found exclusively in either larvae or frass. No CRGs were detected in onion- or digestate-based diets nor in young larvae or diet inputs. Conclusions: The findings suggest that the diet composition may influence the proliferation of Enterobacteriaceae and the persistence of CRGs. Careful substrate selection and process monitoring are essential to minimize antimicrobial resistance risks in insect-based bioconversion systems.

Background: Hermetia illucens larvae provide a sustainable bioconversion pathway that transforms agro-industrial residues into protein- and nutrient-dense biomass and frass, suitable for animal feed and soil amendment, respectively. Nevertheless, the potential spread of antibiotic resistance (AR) genes and pathogenic microorganisms poses biosafety concerns. This study examined the impact of four residue-based diet formulations; peas and chickpea (D1), peas and wheat (D2), onion and wheat (D3), and wheat with digestate (D4), on microbial safety during the bioconversion process. Methods: Enterococcus spp. (viable counts), Salmonella spp. (presence/absence), and 13 AR genes associated with resistance to tetracyclines, macrolide-lincosamide-streptogramin B, β-lactams, vancomycin, and aminoglycosides were quantified in single substrates, diets, larvae, and frass using qPCR. Results: Principal component analysis revealed diet-driven AR gene profiles. D1 lowered the levels of the greatest number of tested AR genes, particularly erm(B), tetracycline, and β-lactam genes in frass, as well as tet(O) and vanB in mature larvae. In contrast, D2 increased the AR gene levels in frass. All diets except D4 eliminated Salmonella spp. Enterococcus spp. loads varied by diet and larval stage, with D2 reducing counts in frass. Conclusions: Diet composition directly shapes microbial dynamics and AR gene dissemination, indicating that legume-based substrates may enhance biosafety in bioconversion systems.