**Background:** Citrus fruits, particularly lemons (Citrus limon L.), are among the most abundant fruit crops globally, with annual production of approximately 124 million tonnes for citrus and nearly 16 million tonnes for lemons and limes. Processing generates about 50% waste (peels, pulp, seeds, pomace), which is rich in bioactive compounds including phenolic compounds, carotenoids, vitamins, essential oils, and dietary fibers. These by-products, often discarded in landfills, represent both an environmental problem and a lost economic opportunity. This review systematically examines the potential of recovering three main fractions—essential oils, phenolic compounds, and dietary fibers—from lemon by-products for food preservation applications.
**Methods:** The authors conducted a systematic search of the Web of Science database using keywords "lemon peels" and "lemon by-products" covering publications from 2002 to 2022. Abstracts were classified into five categories: essential oils extraction/characterization, phenolic compounds extraction/characterization, pectin extraction/characterization, bioactive properties, and food applications. Meeting abstracts, patents, and non-English papers were excluded.
**Key Results:** The search identified 147 papers published since 2002, with a clear increasing trend: 13 papers (2002–2008), 22 (2009–2013), 47 (2014–2017), and 65 (2018–2022). Regarding essential oils, limonene is the major volatile compound, ranging from 57.7% to 76.9% of total essential oil composition depending on cultivar and ripening stage. Eureka variety showed the highest limonene concentration (22.7 g/kg). Microwave-assisted distillation achieved comparable yields (0.2%) to hydrodistillation (0.2%) and cold pressing (0.1%) but in only 30 minutes versus 3 hours and 1 hour, respectively. Lemon peel essential oil showed 55.1% DPPH inhibition, with MIC and MBC against Staphylococcus aureus of 1.3% and 5%, respectively. For phenolic compounds, hesperidin was the predominant flavanone (range 10.3–3315 µg/g fresh weight), and caffeic acid (9.31–741.6 µg/g FW) and chlorogenic acid (2.70–527.5 µg/g FW) were dominant phenolic acids. Peels contained higher polyphenol concentrations than pulp, with antioxidant capacity ranking: peels > whole fruit > pulp > seed > juice. Ultrasound-assisted extraction improved antioxidant activity (39.73% DPPH inhibition) compared to maceration (22.46%). Pulsed electric field (7 kV/cm) increased polyphenol extraction efficiency by 300%. For dietary fibers, peels contain approximately 65% total dietary fiber, with insoluble fiber representing 67% and soluble fiber 33%. Pectin content in peels was 13% dry weight, with cellulose at 23.06% and hemicellulose at 8.09%. The degree of esterification of lemon peel pectin ranged from 87.19% to 92.6%, classifying it as high-methoxyl pectin. Lemon pectin showed antioxidant activity of 71.46 ± 1.39 mg TE/g sample (ABTS method) and ORAC value of 122,200 μmol TE/100 g. Food applications included direct incorporation (e.g., lemon peel powder in synbiotic yogurt increased antioxidant activity to 71.10%; lemon essential oil at 0.06–0.312 mg/g inhibited Listeria monocytogenes in beef), edible coatings (chitosan with lemon essential oil delayed strawberry ripening and reduced respiration rate; pectin coating with lemon extract reduced bacterial counts to 2.58 log CFU/g in carrots), and antioxidant dietary fibers (lemon albedo in bologna sausages decreased fat and residual nitrite; lemon fiber at 2–6% reduced cholesterol and saturated fatty acids in low-fat beef burgers).
**Clinical Implications:** Lemon by-products represent a rich, underutilized source of natural antimicrobial and antioxidant compounds that can replace synthetic preservatives such as BHA, BHT, sodium nitrites, and benzoates. The incorporation of these fractions into food products and edible coatings can improve food safety, extend shelf life, and enhance nutritional value. From a public health perspective, the dietary fiber content (particularly pectin) offers potential benefits for gastrointestinal health, including prebiotic effects, reduced glucose and cholesterol absorption, and anti-inflammatory properties. The circular economy approach to valorizing lemon by-products addresses both environmental sustainability and the growing consumer demand for clean-label, natural food ingredients. However, the authors note that more research is needed on pectin bioactivities and that challenges remain regarding essential oil off-flavors, toxicity at high concentrations, and the need for cost-effective extraction technologies.