Search Results (82)

Citrus peel is examined here as a naturally evolved protective surface, with the goal of developing a transferable quantitative framework for extracting engineering-relevant descriptors from biological protective surfaces and using them as design templates for biomimetic counterparts. A single-specimen-per-species design is adopted to map intra-fruit geometric variation across regions and magnifications; absolute descriptor values are therefore reported as ordinal indicators of inter-species ranking rather than as population means. Five citrus species (lemon, orange, mandarin, grapefruit, and bitter orange) were characterised by mechanical testing (cutting, puncture, and compression; five replicates per fruit), gravimetric peel density and thickness, and scanning electron microscopy (SEM) at 100×–10,000×. The 135-image SEM dataset was processed with an automatic-calibration pipeline performing per-image scale-bar detection, multilevel-Otsu segmentation of albedo air space, cell-bounded surface segment (CBSS) and oil-gland segmentation on flavedo, and grey-level co-occurrence matrix (GLCM) texture analysis with a directional anisotropy index $A_F$. Calibration was consistent across all images (FoV × magnification $=\mathrm{403,273}\pm 410$ $\mathsf{\mu }$m$·\times$, $\pm 0.10\%$). Principal component analysis separated flavedo and albedo at every magnification (PC1 + PC2 = 84–92%). Within this dataset, grapefruit showed the densest CBSS cover (1072 ${\mathrm{mm}}^{-2}$) together with the highest oil-gland density (2.77 ${\mathrm{mm}}^{-2}$); bitter orange showed the largest CBSS area (23.7 $\mathsf{\mu }{\mathrm{m}}^2$) and the thickest peel (13.1 mm); mandarin showed the most directionally oriented flavedo film ($A_F=0.0885$); and lemon showed the most open albedo (${\phi }_{2D}=36.2\%$). Oil-gland equivalent diameter was essentially invariant (∼45 $\mathsf{\mu }$m) across the five fruits, while gland density varied 4.4-fold. The structural metrics define a layered descriptor space—a dense isotropic surface relief versus a thick cellular bulk—that supplies two distinct bioinspired-design priors: dense surface films as a structural prior for selective-permeability membranes and layered cellular cores as a prior for impact-absorbing panels. A modified-atmosphere packaging (MAP)-compatible biomimetic film is identified as one downstream design hypothesis requiring direct gas-permeability verification on synthetic membranes. Full article

The high consumption of citrus fruits generates large amounts of peel bioresidues, whose valorization represents an important strategy for sustainable agri-food systems. This study aimed to characterize the nutritional, chemical, and bioactive properties of flours obtained from orange (FL), tangerine (FT), lime (FLA), and lemon (FLO) peels, and to evaluate their potential as functional food ingredients. The flours were evaluated for proximate composition, organic acids, phenolic compounds, fatty acids, free sugars, and bioactive properties. Lime flour showed the highest protein, ash, dietary fiber, and total phenolic contents, with hesperidin identified as the predominant compound. The corresponding extracts exhibited relevant antioxidant, antimicrobial, antiproliferative, and nitric oxide (NO) production inhibitory activities, with lime flour presenting the strongest overall bioactive potential. Based on these results, lime flour was selected for application in a food model by partially replacing wheat flour (10% and 20%) in “Madalenas”, a traditional Portuguese muffin cake. The incorporation of lime flour improved product preservation compared with the control formulation and samples containing a synthetic preservative (potassium sorbate). These findings highlight the potential of citrus peel flours, particularly lime flour, as natural functional ingredients and sustainable alternatives for food formulations, contributing to waste valorization and circular economy approaches in the agri-food sector. Full article

The valorization of citrus peel residues represents an important strategy for promoting circular bioeconomy approaches in the agri-food sector. This study evaluated the biorefinery potential of ten citrus varieties cultivated in Bolívar Province, Ecuador, including mandarin (Citrus reticulata criolla, Citrus nobilis Loureiro, Citrus tangerina, Citrus unshiu), lemon (Citrus aurantifolia Swingle, Citrus limonia, Citrus limonum, Citrus latifolia), and grapefruit (Citrus paradisi, Citrus paradisi Macfad.), focusing on the extraction and characterization of essential oils from peel biomass. The residual biomass was characterized through proximate and elemental analyses to determine its physicochemical properties, and essential oils were extracted under two maceration times (8 and 12 h) to evaluate the influence of extraction conditions on yield. Chemical composition was determined by gas chromatography–mass spectrometry (GC-MS). The results revealed significant variability among varieties in moisture, ash, and volatile solids content. Citrus nobilis Loureiro showed the highest extraction yield, while grapefruit varieties exhibited the greatest increase in yield with extended maceration time. Limonene was identified as the predominant compound in all essential oils, reaching concentrations above 90% in grapefruit samples, and significant intervarietal differences in monoterpene profiles were observed. Extraction kinetics were evaluated using seven mathematical models, among which the Monod model showed the best fit to the experimental data (R² > 0.99), demonstrating strong predictive capability. These findings highlight the potential of citrus peel residues as sustainable sources of high-value essential oils and provide a quantitative framework for optimizing extraction processes within citrus biorefinery systems. Full article

This review examines the implementation dimensions of integrated lemon biorefinery systems, including cascade valorisation design, circular-economy integration, life-cycle assessment, techno-economic feasibility, and regulatory frameworks. Bibliometric analysis of Web of Science data (2015–2025) reveals exponential growth in citrus-biorefinery research, with lemon representing a burgeoning subset. Techno-economic assessments indicate that cascade biorefineries recovering essential oils, pectin, polyphenols, nanocellulose, and bioenergy can achieve cumulative revenues of USD 400–650 per tonne of dry peel. Whilst small-scale units (<500 tonnes per year) struggle to achieve viability, industrial simulations demonstrate Internal Rates of Return exceeding 18% at processing scales above 100,000 tonnes annually (2025 basis). Life-cycle assessments confirm environmental benefits, with greenhouse gas reductions of 60–85% relative to conventional disposal. Critical success factors include adopting green extraction technologies to preserve bioactive integrity and mitigating D-limonene inhibition in downstream anaerobic digestion. These findings establish essential oil extraction and pectin recovery as commercially mature technologies, whilst integrated multi-product lemon biorefineries remain economically promising based on techno-economic modelling and pilot-scale demonstrations, provided regulatory hurdles are effectively navigated. Full article

The global citrus-processing industry generates 15–32 million tonnes of waste annually. Lemon-processing residues—peels, seeds, and pomace—constitute 45–55% of fruit mass and harbour high-value bioactive compounds amenable to cascade valorisation. This review (Part I of a two-part series) examines green extraction technologies for recovering bioactive compounds from lemon waste streams. Following bibliometric analysis of 847 publications (2003–2025), this work delineates the compositional heterogeneity of lemon fractions and establishes a hierarchical framework for value-added products encompassing essential oils, pectin, polyphenols, seed oils, citric acid, industrial enzymes, α-cellulose, and nanocrystalline cellulose. Four sustainable extraction methodologies are systematically evaluated: ultrasound-assisted extraction, microwave-assisted extraction, supercritical CO₂ extraction, and enzyme-assisted extraction. Comparative assessment demonstrates yield improvements of 16–112% over conventional approaches, processing-time reductions of 89–98%, and energy savings up to 95%. Critical research gaps include fragmented single-product valorisation, insufficient techno-economic assessment, and limited industrial-scale validation. Integrated cascade biorefineries employing sequential green extraction protocols offer economically viable pathways for transforming lemon waste into diversified revenue streams. Industrial implementation, circular-economy integration, and techno-economic feasibility are addressed in Part II. Full article

Flavonoids are a diverse group of natural polyphenolic compounds, recognized for their ability to modulate cellular pathways and mitigate the pathological processes of many neurodegenerative diseases. This study investigates the neurotrophic potential of a polyphenolic-rich lemon peel extract (Lpe) in a Zebrafish larvae spinal cord injury (SCI) model. To evaluate its potential effects, embryos were divided into six experimental groups: a baseline control group in which larvae were neither subjected to spinal cord injury nor treated (Ctrl Group); a group with larvae subjected to spinal cord injury at 3 dpf without treatment (SCI Group); a group treated continuously with Lpe (25 µg/mL) from 0 to 5 dpf without injury (Continuous Group); a group treated continuously with Lpe and injured at 3 dpf (Continuous SCI Group); a group treated with Lpe starting at 3 dpf without injury (Curative Group); and finally, a group injured at 3 dpf and treated simultaneously with Lpe (Curative SCI Group). Lpe treatment significantly downregulated proinflammatory cytokines (tnfa, il1b, and xcl8), and modulated the neuroregenerative pathways Wnt/β catenin, and neurotrophic factor Bdnf. Immunohistochemical analysis further revealed Sox2-positive cells localized around the central canal, consistent with activation of ependymal progenitor populations involved in injury-induced repair processes. These findings support the exploration of Lpe for mitigating SCI-induced damage. Full article

Fungal secondary metabolites are valuable sources of natural antioxidants and antimicrobials. This study evaluated the submerged fermentation of Penicillium crustosum OR889307 supplemented with lemon peel as a co-substrate to enhance the production of bioactive compounds. Lemon peel was selected for its phenolic precursors and sustainable availability as an agro-industrial byproduct. Crude extracts, aqueous and organic fractions, and molecular-weight partitions were assessed for antioxidant activity using the DPPH assay and for antimicrobial activity against Escherichia coli, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, and Candida albicans. Semi-purified extracts from co-substrate fermentations exhibited enhanced bioactivity, showing MIC values of 185 µg/mL against P. aeruginosa and 225 µg/mL against MRSA, along with strong ABTS radical-scavenging capacity (238.95 ± 2.17 µmol TE). RP-HPLC-ESI-MS profiling revealed phenolic acids, flavanones, flavonols, and lignans, including ferulic acid 4-O-glucoside, bisdemethoxycurcumin, secoisolariciresinol, and quercetin 3-O-xylosyl-glucuronide. These findings demonstrate that lemon peel supplementation promotes the biosynthesis of antimicrobial and antioxidant metabolites by P. crustosum. This approach supports sustainable agro-waste valorization and offers a promising strategy for obtaining natural bioactive compounds with potential applications in food preservation and health-related formulations. Full article

Lemon peel, which contains a wide variety of antioxidant compounds and biopolymers, is an interesting byproduct for valorization. In this study, pectin and cellulose were obtained from lemon peel with 36% and 23% extraction yields. Meanwhile, when evaluating the extraction of secondary metabolites using various enzymes, it was found that their concentrations increased the most in the case of pectin methylesterase, by up to 21.7% for eriocitrin, although the solid residue was not affected spectroscopically by the enzymatic activity. In contrast, enzyme mixes with β-glucosidase activity showed no presence of the O-glycosylated flavonoids, suggesting their hydrolysis into the aglycones. Full article

Gastric cancer remains a leading cause of cancer-related mortality worldwide. Citrus fruits are rich in polyphenols, exerting antioxidant and chemo-preventive activities, and lemon peel represents a valuable source of such bioactive compounds. Previous studies showed that Citrus limon peel extracts (LPE) inhibited the activity of some enzymes of the antioxidant system and reduced the interleukin-6-dependent invasiveness of gastric and colon cancer cells. In the present study, we have investigated the effects of LPE on the human gastric adenocarcinoma AGS and MKN-28 cells and on the activity of a crucial redox enzyme, catalase (CAT). Indeed, LPE significantly reduced the cell viability and clonogenic potential of the gastric cancer cells and induced morphological changes indicative of cytotoxicity. Moreover, LPE modulated the intracellular redox homeostasis by decreasing levels of the hydrogen peroxide-related reactive oxygen species (ROS) while increasing those of superoxide anions and decreasing levels of superoxide dismutases (SODs). Western blotting analysis revealed that LPE downregulated CAT, SOD-1, SOD-2, and monoamine oxidase A (MAO-A) protein expression level in both cell lines. Finally, the extract inhibited CAT activity in a dose-dependent manner (IC₅₀ = 0.008 ± 0.003 mg/mL; K_i = 0.012 ± 0.002 mg/mL). These findings indicate that LPE exerts cytotoxic and redox-modulating effects through the inhibition of antioxidant enzymes and the alteration of ROS balance. Therefore, the agro-industrial by-product LPE could be considered as a promising natural source of polyphenolic compounds with potential applications in the prevention and therapy of gastric cancer. Full article

This study focuses on the optimization of modern extraction techniques for selected by-product materials, including apple, lemon, and tangerine peels, and onion skins, using artificial neural network (ANN) models. The extraction methods included ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) with water as the extractant, as well as maceration (MAC) with natural deep eutectic solvents (NADES). Key parameters, such as total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities, including reducing power (EC₅₀) and free radical scavenging capacity (IC₅₀), were evaluated to compare the efficiency of each method. Among the techniques, UAE outperformed both MAE and MAC in extracting bioactive compounds, especially from onion skins and tangerine peels, as reflected in the highest TPC, TFC, and antioxidant activity. UAE of onion skins showed the best performance, yielding the highest TPC (5.735 ± 0.558 mg CAE/g) and TFC (1.973 ± 0.112 mg RE/g), along with the strongest antioxidant activity (EC₅₀ = 0.549 ± 0.076 mg/mL; IC₅₀ = 0.108 ± 0.049 mg/mL). Tangerine peel extracts obtained by UAE also exhibited high phenolic content (TPC up to 5.399 ± 0.325 mg CAE/g) and strong radical scavenging activity (IC₅₀ 0.118 ± 0.099 mg/mL). ANN models using multilayer perceptron architectures with high coefficients of determination (r² > 0.96) were developed to predict and optimize the extraction results. Sensitivity and error analyses confirmed the robustness of the models and emphasized the influence of the extraction technique and by-product type on the antioxidant parameters. Principal component and cluster analyses showed clear grouping patterns by extraction method, with UAE and MAE showing similar performance profiles. Overall, these results underline the potential of UAE- and ANN-based modeling for the optimal utilization of agricultural by-products. Full article

In the present study, the essential oils (EOs) of peels and leaves from the new limonime lime, ‘Eugene’ hybrid, were analyzed for the first time and compared with those of its parental plants, Citrus latifolia var. latifolia (Persian lime) and Citrus × limon cv. Zambetakis (lemon). This hybrid represents the first successful cross between these two species, exhibiting distinctive features such as aroma and shape. GC-MS analysis identified a total of 30 and 44 metabolites in the hybrid’s peel and leaf EOs, respectively. Limonene was the predominant volatile in both peels and leaves across all genotypes. In the peel EOs, the monoterpenes γ-terpinene, β-pinene, and geranial were among the most abundant compounds. In contrast, the leaf EOs showed differences between genotypes: the hybrid and Persian lime had similar volatile profiles dominated by geranial, neral, and neryl acetate, while β-pinene was only detected in lemon. Additionally, the total phenolic content and DPPH radical scavenging activity of the methanolic extracts of peels and leaves were evaluated, and revealed that lemon extracts were richer in phenolic compounds and with higher antioxidant activity compared to those of hybrid and Persian lime. Overall, the development of improved Greek varieties like the ‘Eugene’ hybrid holds significant potential to enrich the genetic diversity of Greek Citrus germplasm and broaden the commercial portfolio of citrus fruits with unique and desirable traits. Full article

Citrus by-products are increasingly recognized as a valuable source of bioactive compounds (BCs), particularly flavonoids. Their incorporation into food matrices as functional ingredients aligns with sustainability goals and consumer demand for health-promoting products. However, challenges such as poor stability and undesirable sensory properties limit their direct use in food systems. This study aimed to develop and evaluate functional cookies enriched with microencapsulated flavonoid-rich extracts derived from lemon and orange peels. Flavonoids were extracted with hydroethanolic solvent and characterized by HPLC-DAD. The extracts exhibited high total flavonoid contents: 1960.1 mg/L for orange and 845.7 mg/L for lemon. The extracts were encapsulated using a 1% sodium alginate and 1.36% corn starch blend, producing thermally stable microbeads with flavonoid retention higher than 85% after heating at 230 °C for 30 min. These microbeads were incorporated into gluten-free oat and buckwheat cookies, delivering 166.11 mg/100 g (orange) and 177.13 mg/100 g (lemon) of flavonoids in the product, which covers approximately one-third of the recommended daily intake. Sensory analysis using triangle tests (ISO 4120) (n = 23) showed no significant difference (p > 0.05) between control and enriched cookies, indicating successful masking of potential bitterness or astringency associated with flavonoids. These results demonstrate the effectiveness of microencapsulation in protecting citrus flavonoid-rich extracts and support the development of sustainable, health-oriented bakery products. Moreover, this approach promotes the valorization of agro-industrial by-products, contributing to a more circular food supply chain. Full article

Pineapple and lemon processing generates large volumes of peel waste, which is a valuable source of dietary polyphenols and flavonoids with potent antioxidant activity. This study employed a strategy of micronization and ultrasound-assisted extraction (UAE) with acidified ethanol to valorize pineapple peel (PP) and lemon peel (LP). Physicochemical characteristics, total polyphenol content, total flavonoid content, and antioxidant activities (DPPH, FRAP, and ABTS⁺) were evaluated under varying particle sizes, ethanol concentrations, extraction times, and pH conditions. Optimal extraction was achieved with 30 min of UAE using 75% ethanol acidified with citric acid at pH 5 for PP (96.6 µm) and pH 4 for LP (91.7 µm). These conditions maximized polyphenol yields, with the LP micropowder produced containing 65.7 µg/mg of hesperidin and 23.2 µg/mg of eriocitrin. Contour plots and principal component analysis confirmed that the antioxidant extraction selectivity of micropowder was dependent on pH and extraction time. Microstructural and Fourier-transform infrared spectroscopy analyzes further supported that short-dried period and a lower particle size significantly improve solute release. This study not only demonstrates the efficacy of micronization and UAE in enhancing the selective extraction of antioxidants from fruit peels but also offers a digital visualization strategy for optimizing extraction processes to support sustainable bioprocessing and functional ingredient development. Full article

Orange allergy is estimated to account for up to 3–4% of food allergies. Major allergens identified in orange (Citrus sinensis) include Cit s 1 (germin-like protein) and Cit s 2 (profilin), while Cit s 3 (non-specific lipid transfer protein, nsLTP) and Cit s 7 (gibberellin-regulated protein) have also been described. The objective of this study was to investigate the presence and IgE-binding capacity of germin-like proteins in citrus fruits other than oranges. We describe five patients with immediate allergic reactions after orange ingestion. All patients underwent skin prick tests (SPT) to aeroallergens and common food allergens, prick-by-prick testing with orange, lemon, and mandarin (pulp, peel, seeds), total IgE, specific IgE (sIgE), anaphylaxis scoring (oFASS), and the Food Allergy Quality of Life Questionnaire (FAQLQ-AF). Protein extracts from peel and pulp of orange, lemon, and mandarin were analyzed by Bradford assay, SDS-PAGE, and IgE immunoblotting using patient sera. Selected bands were identified by peptide mass fingerprinting. A 23 kDa band was recognized by all five patients in orange (pulp and peel), lemon (peel), and mandarin (peel). This band was consistent with Cit s 1, a germin-like protein already annotated in the IUIS allergen database for orange but not for lemon or mandarin. Peptide fingerprinting confirmed the germin-like identity of the 23 kDa bands in all three citrus species. Germin-like proteins of approximately 23 kDa were identified as IgE-binding components in peel extracts of orange, lemon, and mandarin, and in orange pulp. These findings suggest a potential shared allergen across citrus species that may contribute to allergic reactions independent of LTP sensitization. Full article

This research analyzes the innovative development of carnauba wax coatings enriched with essential oils (EOs: lemon, orange, grapefruit, clove, oregano, and cinnamon) or fruit by-products (FBPs: avocado, tomato, carrot, orange, lemon, and grapefruit) to improve postharvest preservation of organic oranges and lemons. Six EOs and six FBPs were evaluated for total phenolic content (TPC) and in vitro antifungal activity against Penicillium digitatum. Based on results, grapefruit, oregano, and clove EOs were selected for lemons, while avocado, orange, and grapefruit FBPs were selected for oranges. An in vivo test at 20 °C for 15 days with carnauba wax coatings assessed antifungal performance. Clove EO and avocado FBP showed strong in vitro inhibition and consistent hyphal suppression (~100 and ~82%, respectively). In vivo, coatings with grapefruit EO and avocado FBP significantly reduced fungal decay and sporulation (~75%) in lemons and oranges, respectively. Coated fruits also retained weight losses by ~25% compared to uncoated ones. These findings suggest that phenolic-rich natural extracts, especially from agro-industrial residues like avocado peels, offer a promising and sustainable strategy for postharvest citrus disease control. Further studies should test coating effectiveness in large-scale trials under refrigeration combined with other preservation strategies. Full article