Recent Advances in Citrus maxima and Its By-Products: Chemical Composition, Bioactivities, Safety, and Industrial Applications

Citrus maxima, the largest-fruited Citrus species, yields pulp and industrial by-products rich in bioactive phytochemicals with notable food and pharmaceutical potential. Yet its literature remains fragmented, lacking an integrated view of metabolite profiles, pharmacological spectrum, safety liabilities, and translational roadmaps. This Review consolidates nutritional composition, secondary metabolite diversity, and tissue-specific distribution across fruit and residues, critically appraises processing technologies, and maps applications spanning functional foods, edible packaging, nutraceuticals, pharmaceuticals, and agricultural inputs. Over 100 compounds, flavonoids, phenolic acids, coumarins, limonoid triterpenoids, acridone alkaloids, and volatile terpenes, underpin antioxidant, anti-inflammatory, antimicrobial, antitumor, antidiabetic, anti-obesity, hepatoprotective, gastroprotective, and neuroprotective effects. Toxicological data suggest pulp safety; however, furanocoumarin-mediated CYP3A4 inhibition is cultivar-dependent, as exemplified by higher furanocoumarin loads in pink/red-fleshed cultivars and ‘Guanximiyou’ than in white-fleshed types, warranting careful evaluation. Industrially, residues have been piloted in dietary fibre fortifiers, pectin extraction, craft brewing, edible films, bio-organic fertilizers, and botanical pesticides. By synthesizing dispersed findings and pinpointing gaps, cultivar-specific metabolomic variation, standardized extraction, and long-term safety, this Review bridges fundamental phytochemistry with bioprocess engineering and regulatory science, guiding high-value, sustainable utilization of this underutilized citrus resource.