Nutritional, Functional, and Safety Aspects of Single‐Cell Protein Produced via Microbial Fermentation From Fruit‐Processing Waste: A Comprehensive Review

The projected global protein deficit, expected to exceed 250 million tons by 2050, coincides with fruit-processing residues that represent nearly 30%-40% of processed biomass, highlighting the need for integrated solutions that simultaneously address nutritional security and food-waste valorization. This review critically synthesizes current evidence on single-cell protein (SCP) production from fruit-processing waste, examining how substrate composition, microbial metabolism, and downstream processing determine nutritional quality, techno-functional performance, safety, and industrial feasibility. Reported systems consistently produce 45%-65% crude protein, with essential amino-acid profiles comparable to soybean meal and fishmeal. Comparative analysis indicates that carbon-to-nitrogen ratio, pretreatment severity, oxygen transfer, and nucleic-acid reduction strategies, rather than microorganism type alone, are the dominant factors controlling yield and composition. Techno-functional properties, including water-holding capacity (2.1-4.8 g/g), emulsifying activity (35%-62%), and foaming capacity (28%-55%), are strongly influenced by cell-wall structure and protein recovery approaches, while bioactive potential is increasingly enhanced through omics-guided strain optimization. Economic assessments identify downstream processing and biomass drying as the major cost drivers, accounting for more than 40% of total production costs, and reveal that feedstock compositional variability is the principal source of inconsistent productivity across studies. Safety evaluations highlight persistent knowledge gaps related to mycotoxin contamination, allergenicity, and acceptable nucleic-acid levels, which currently limit regulatory acceptance despite favorable environmental outcomes demonstrated by life-cycle analyses. Unlike earlier reviews that primarily catalog substrates and microorganisms, this work integrates nutritional, functional, safety, techno-economic, and technological-readiness perspectives, emphasizing the need for process integration, predictive consortium control, and standardized safety frameworks to enable the large-scale adoption of fruit-waste-derived SCP in sustainable food and feed systems.