Variations of peel essential oils during fruit ripening in four lemon (Citrus limon (L.) Burm. F.) cultivars

Coumarins in the Flavedo of Citrus limon Varieties-Ethanol and Natural Deep Eutectic Solvent Extractions With HPLC-DAD Quantification

INTRODUCTION

Peels are an abundant but still underutilized waste product in the Citrus fruit industry. They contain coumarins with antiadipogenic potential that could be promising targets in new valorization strategies for Citrus peels.

OBJECTIVES

In this study, these coumarins, that is, citropten, bergamottin, and 5-geranyloxy-7-methoxycoumarin (5G7MC), were investigated in Citrus limon peels of different commercial varieties by HPLC-DAD after extraction with ethanol and choline chloride-based natural deep eutectic solvents (NADES) as alternative extraction agents in green natural product extraction.

RESULTS

Target coumarins were almost exclusively found in the flavedo (exocarp) peel layer and in whole peel samples, but not in the albedo (mesocarp) layer. Flavedo samples from varieties "Verdelli" (ES) and "Lisbon" (ZA) showed particularly high concentrations in ethanolic extracts. When applying NADES extraction, best results for citropten were achieved with malonic acid, 1,2-propanediol, and citric acid as hydrogen bond donors (HBDs), with higher yields than the reference solvent ethanol. For bergamottin and 5G7MC, promising results were obtained for 1,2-propanediol as HBD, though lower yields than with ethanol. The possible chlorination of coumarin epoxides byakangelicol and oxypeucedanin was recognized for acidic NADES in LC-MS analysis.

CONCLUSION

Overall, C. limon peels proved to be a relevant starting material for valorization through coumarin extraction with ethanol and NADES.

Postharvest Quality of Citrus medica L. (cv Liscia-Diamante) Fruit Stored at Different Temperatures: Volatile Profile and Antimicrobial Activity of Essential Oils

Citron (Citrus medica L. cv. Liscia-diamante), cultivated in the "Riviera dei Cedri" (southern Italy), is mainly utilized in the production of candied fruit and essential oils (EOs). Up to now, no information regarding the effect of storage temperatures on citron has been reported. Here, citron samples, after harvesting, were stored at different temperatures (5, 10 and 20 °C at 70% relative humidity) for two weeks, and the main postharvest quality parameters were evaluated. Moreover, EOs extracted from the stored samples were chemically characterized to reveal changes in the volatiles profile and antimicrobial activity. The EOs presented monoterpene hydrocarbons (87.1 to 96.3% of the total oil profile) as the most abundant compounds, followed by oxygenated metabolites ranging from 9.7 to 3.1% of the total pattern. Postharvest quality traits showed a good retention of green peel color during storage at 5 °C, while EOs from samples stored for 7 and 14 days at 10 and 20 °C, respectively, showed the highest antimicrobial activity against most assayed strains. The results indicated storage at 10 °C for 7 days as the most suitable for the preservation of the postharvest quality of the fruit and the antimicrobial activity of the extracted EOs.

Comparative Evaluation of Secondary Metabolite Chemodiversity of Citrus Genebank Collection in Greece: Can the Peel be More than Waste?

Citrus fruits are among the most economically important crops in the world. In the global market, the Citrus peel is often considered a byproduct but substitutes an important phenotypic characteristic of the fruit and a valuable source of essential oils, flavonoids, carotenoids, and phenolic acids with variable concentrations. The Mediterranean basin is a particularly dense area of autochthonous genotypes of Citrus that are known for being a source of healthy foods, which can be repertoires of valuable genes for molecular breeding with the focus on plant resistance and quality improvement. The scope of this study was to characterize and compare the main phenotypic parameters (i.e., peel thickness, fruit volume, and area) and levels of bioactive compounds in the peel of fruits from the local germplasm of Citrus in Greece, to assess their chemodiversity regarding their polyphenolic, volatile, and carotenoid profiles. A targeted liquid chromatographic approach revealed hesperidin, tangeretin, narirutin, eriocitrin, and quercetin glycosides as the major polyphenolic compounds identified in orange, lemon, and mandarin peels. The content of tangeretin and narirutin followed the tendency mandarin > orange > lemon. Eriocitrin was a predominant metabolite of lemon peel, following its identification in lower amounts in mandarin and at least in the orange peel. For these citrus-specific metabolites, high intra- but also interspecies chemodiversity was monitored. Significant diversity was found in the essential oil content, which varied between 1.2 and 3% in orange, 0.2 and 1.4% in mandarin, and 0.9 and 1.9% in lemon peel. Limonene was the predominant compound in all Citrus species peel essential oils, ranging between 88 and 93% among the orange, 64 and 93% in mandarin, and 55 and 63% in lemon cultivars. Carotenoid analysis revealed different compositions among the Citrus species and accessions studied, with β-cryptoxanthin being the most predominant metabolite. This large-scale metabolic investigation will enhance the knowledge of Citrus peel secondary metabolite chemodiversity supported by the ample availability of Citrus genetic resources to further expand their exploitation in future breeding programs and potential applications in the global functional food and pharmaceutical industries.

Development and Evaluation of an Eco-Friendly Hand Sanitizer Formulation Valorized from Fruit Peels

Hand sanitizer usage has proven to be a common and practical method for reducing the spread of infectious diseases which can be caused by many harmful pathogens. There is a need for alcohol-free hand sanitizers because most hand sanitizers on the market are alcohol-based, and regular use of them can damage the skin and can be hazardous. India is the world's largest producer of fruits and one of the major problems after fruit consumption is their peels, causing waste management problems and contributing to the formation of greenhouse gases leading to air pollution and adding to the problem of climate change. Valorization of such wastes into other value-added products and their incorporation into formulations of eco-friendly alcohol-free hand sanitizers would solve these issues, save the environment, benefit the society, and help in achieving the sustainable development goals. Thus, this research focuses on formulating an effective natural alcohol-free hand sanitizer that harnesses the antimicrobial properties of the various types of bioactive components found in fruit peels of pomegranate, sweet lime, and lemon. The peel extracts and the formulated sanitizer proved considerable antimicrobial activity against the pathogenic Escherichia coli and hand microflora. Molecular docking was also applied to examine ligand-protein interaction patterns and predict binding conformers and affinity of the sanitizer phytocompounds towards target proteins in COVID-19, influenza, and pneumonia viruses. The binding affinities and the protein-ligand interactions virtual studies revealed that the sanitizer phytocompounds bind with the amino acids in the target proteins' active sites via hydrogen bonding interactions. As a result, it is possible to formulate a natural, alcohol-free hand sanitizer from fruit peels that is effective against pathogenic germs and viruses using the basic structure of these potential findings.

Fruit quality assessment based on mineral elements and juice properties in nine citrus cultivars

Introduction

Citrus fruit is considered a superfood due to its multiple nutritional functions and health benefits. Quantitative analysis of the numerous quality characteristics of citrus fruit is required to promote its sustainable production and industrial utilization. However, little information is available on the comprehensive quality assessment of various fruit quality indicators in different citrus cultivars.

Methods

A total of nine different fresh citrus fruits containing seeds were collected as the experimental materials. The objectives of this study were: (i) to determine the morphological and juice properties of citrus fruits, (ii) to measure the mineral elements in the peel, pulp, and seeds, and (iii) to evaluate the fruit quality index (FQI) using the integrated quality index (IQI) and the Nemoro quality index (NQI) methods.

Results

There were significant differences in fruit quality characteristics, including morphological, mineral, and juice quality, among the investigated citrus cultivars. The proportion of pulp biomass was the highest, followed by that of peel and seeds. N and Cu had the highest and lowest concentrations, respectively, among the measured elements across all citrus fruits, and the amounts of N, P, Mg, Cu, and Zn in seeds, K and Al in pulp, and Ca, Fe, and Mn in peel were the highest, dramatically affecting the accumulation of minerals in the whole fruit and their distribution in various fruit parts. Additionally, Ningmeng fruits had the highest vitamin C and titratable acidity (TA) but the lowest total soluble solids (TSS) and total phenolic (TP) contents, resulting in the lowest TSS/TA and pH values. In contrast, Jinju fruits had the highest TSS and TP contents. Based on the mineral element and juice quality parameters, principal component analysis showed that the citrus fruits were well separated into four groups, and the dendrogram also showed four clusters with different distances. The FQI range based on the IQI method (FQIIQI) and NQI method (FQINQI) was 0.382-0.590 and 0.106-0.245, respectively, and a positive relationship between FQIIQI and FQINQI was observed.

Conclusion

Our results highlight the great differences in mineral and juice characteristics among fruit parts, which mediated fruit quality. The strategy of fruit quality assessment using the FQI can be expanded for targeted utilization in the citrus industry.

Functional Ingredients and Additives from Lemon by-Products and Their Applications in Food Preservation: A Review

Citrus trees are among the most abundant fruit trees in the world, with an annual production of around 124 million tonnes. Lemons and limes are among the most significant contributors, producing nearly 16 million tonnes per year. The processing and consumption of citrus fruits generates a significant amount of waste, including peels, pulp, seeds, and pomace, which represents about 50% of the fresh fruit. Citrus limon (C. limon) by-products are composed of significant amounts of bioactive compounds, such as phenolic compounds, carotenoids, vitamins, essential oils, and fibres, which give them nutritional value and health benefits such as antimicrobial and antioxidant properties. These by-products, which are typically discarded as waste in the environment, can be explored to produce new functional ingredients, a desirable approach from a circular economy perspective. The present review systematically summarizes the potential high-biological-value components extracted from by-products to achieve a zero-waste goal, focusing on the recovery of three main fractions: essential oils, phenolic compounds, and dietary fibres, present in C. limon by-products, and their applications in food preservation.

Qualitative and Quantitative Analyses of the Chemical Components of Peels from Different Pomelo Cultivars (Citrus grandis [L.] Osbeck) Based on Gas Chromatography-Mass Spectrometry, Ultraperformance Liquid Chromatography-Q-Exactive Orbitrap-MS, and High-Performance Liquid Chromatography-Photodiode Array Detection

The volatile and nonvolatile phytochemicals in peels of 5 major pomelo cultivars (including Citrus grandis cv. Yuhuanyou, C. grandis cv. Liangpingyou, C. grandis cv. Guanximiyou, C. grandis cv. Duweiwendanyou, and C. grandis cv. Shatianyou) from 11 places in China were characterized. First, 194 volatile compounds in pomelo peels were identified by gas chromatography-mass spectrometry (GC-MS). Of these, 20 major volatile compounds were subjected to cluster analysis. The heatmap indicated that the volatile compounds in peels of C. grandis cv. Shatianyou and C. grandis cv. Liangpingyou were different from those in other varieties, while there was no difference among C. grandis cv. Guanximiyou, C. grandis cv. Yuhuanyou, and C. grandis cv. Duweiwendanyou from different origins. Second, 53 nonvolatile compounds were identified in pomelo peels by ultraperformance liquid chromatography-Q-exactive orbitrap tandem MS (UPLC-Q-exactive orbitrap-MS), of which 11 components were detected for the first time. Third, six major nonvolatile compounds were quantitatively analyzed with high-performance LC-photodiode array detection (HPLC-PDA). Combining the results of HPLC-PDA and the heatmap, 6 nonvolatile compounds in 12 batches of pomelo peel were well separated among varieties. Comprehensive analysis and identification of chemical components in pomelo peels are of great significance for their further development and utilization.

Evaluation of the antimicrobial effects of Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta: A review

The extensive use of antibiotics and vaccines against microbial infections can result in long-term negative effects on humans and the environment. However, there are a number of plants that have antimicrobial effects against various disease-causing microbes such as bacteria, viruses, and fungi without negative side effects or harm to the environment. In this regard, four particular plants- Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta have been widely considered due to their excellent antimicrobial effect and ample availability. In this review, we discuss their antimicrobial effects due to the presence of thymoquinone, p-cymene, pinene, alkaloids, limonene, camphene, and melanin. These antimicrobial compounds disrupt the cell membrane of microbes, inhibit cellular division, and form biofilm in bacterial species, eventually reducing the number of microbes. Extraction of these compounds from the respective plants is carried out by different methods such as soxhlet, hydro-distillation, liquid-liquid extraction (LLE), pressurized liquid extraction (PLE), solid-phase extraction (SPE), supercritical fluid extraction (SFE), pulsed electric field (PEF), microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE), and high-voltage electrical discharge. Suitable selection of the extraction technique highly depends upon the associated advantages and disadvantages. In order to aid future study in this field, this review paper summarizes the advantages and disadvantages of each of these approaches. Additionally, the discussion covers how antimicrobial agents destroy harmful bacteria. Thus, this review offers in-depth knowledge to researchers on the antibacterial properties of Capsicum, Nigella sativa, Musa paradisiaca L. peels, and Citrus limetta.

Elucidation of the impact of four different drying methods on the phenolics, volatiles, and color properties of the peels of four types of citrus fruits

BACKGROUND

Citrus fruit peels are considered to be process waste in the fruit juice industry but they are a valuable raw material due to their volatile and bioactive components. Drying is one of the most common methods to preserve this material. In this study, four drying processes were applied to the peels of four kinds of citrus fruits. The drying processes were convective drying (CD), microwave drying (MD), conductive hydro drying (CHD), and freeze drying (FD). The citrus fruits used were orange, bitter orange, grapefruit, and lemon.

RESULTS

The influence of dehydration on the aroma and phenolic composition, microstructure, and color properties were studied in detail. It was determined that drying increased the amount of both phenolics and volatiles in the dried samples. The MD and FD methods better preserved the color and phenolics of the samples, and the MD and CD processes increased the amount of aroma substances.

CONCLUSION

The MD method would be more suitable for drying citrus peels due to its shorter duration and its positive effects on the phenolic and aroma components. © 2022 Society of Chemical Industry.

In-Depth Study of Thymus vulgaris Essential Oil: Towards Understanding the Antibacterial Target Mechanism and Toxicological and Pharmacological Aspects

Questions have been raised apropos the emerging problem of microbial resistance, which may pose a great hazard to the human health. Among biosafe compounds are essential oils which captured consumer draw due to their multifunctional properties compared to chemical medication drugs. Here, we examined the chemical profile and the mechanism(s) of action of the Thymus vulgaris essential oil (TVEO) against a Gram-negative bacterium Salmonella enterica Typhimurium ATTCC 10028 (S. enterica Typhimurium ATTCC 10028) and two Gram-positive bacteria Staphyloccocus aureus ATCC 6538 (S. aureus ATCC 6538) and Listeria monocytogenes ATCC 19117 (L. monocytogenes ATCC 19117). Findings showed that TVEO was principally composed of thymol, o-cymene, and γ-terpinene with 47.44, 16.55, and 7.80%, respectively. Molecular docking simulations stipulated that thymol and β-sesquiphellandrene (a minor compound at 1.37%) could target multiple bacterial pathways including topoisomerase II and DNA and RNA polymerases of the three tested bacteria. This result pointed plausible impairments of the pathogenic bacteria cell replication and transcription processes. Through computational approach, the VEGA quantitative structure–activity relationship (QSAR) model, we revealed that among twenty-six TVEO compounds, sixteen had no toxic effects and could be safe for human consumption as compared to the Food and Drug Administration (FDA) approved drugs (ciprofloxacin and rifamycin SV). Assessed by the SwissADME server, the pharmacokinetic profile of all identified TVEO compounds define their absorption, distribution, metabolism, and excretion (ADME) properties and were assessed. In order to predict their biological activity spectrum based on their chemical structure, all TVEO compounds were subjected to PASS (Prediction of Activity Spectra for Substances) online tool. Results indicated that the tested compounds could have multiple biological activities and various enzymatic targets. Findings of our study support that identified compounds of TVEO can be a safe and effective alternative to synthetic drugs and can easily combats hazardous multidrug-resistant bacteria.

Volatile composition changes in lemon during fruit maturation by HS-SPME-GC-MS

BACKGROUND

Volatiles are determinants of fruit aroma and flavor characteristics and also provide valuable information for lemon as ingredient for the food and drinks industry. Volatiles in 'Eureka' lemon and 'Xiangshui' lemon pulps from 130 to 186 days after flowering were enriched by headspace-solid-phase microextraction (HS-SPME), and analyzed by gas chromatography-mass spectrometry (GC-MS).

RESULTS

Seventy-seven volatiles of two lemon cultivars at the different ripening stages were identified and divided into six categories. Varieties and ripening stages had significant effects on individual volatiles in each category. The proportion of monoterpenes was found to be higher in 'Eureka' lemon, while 'Xiangshui' lemon had a higher proportion of sesquiterpenes, aldehydes and alcohols. The proportion of monoterpene fluctuation decreased during fruit ripening, while fluctuation of sesquiterpenes, alcohols, aldehydes and esters increased. Among the hydrocarbons, monoterpenes decreased their relative abundance from 91.67% to 81.04% in 'Eureka' lemon, and from 83.01% to 60.04% in 'Xiangshui' lemon; conversely, sesquiterpenes increased from 0.73% to 2.89% in 'Eureka' lemon, and from 3.21% to 8.48% in 'Xiangshui' lemon. Among the oxygenated volatiles, the proportions of alcohols, aldehydes and esters were higher at 186 days after flowering in both two cultivars.

CONCLUSION

The volatile organic compounds during fruit ripening of lemon varieties with different resistance were elucidated. The proportion of oxygenated volatiles increased during fruit ripening, and disease-resistant varieties had a higher proportion. These results provided important theoretical support for the utilization of lemon fruits and the innovation of disease-resistant germplasm resources. © 2021 Society of Chemical Industry.

Chemical constituents, biological activities and anti-rheumatoid arthritic properties of four citrus essential oils

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease with predominant synovitis that has no complete cure or preventive treatment. Citrus essential oils, used in natural fragrances, contain a variety of functional ingredients that are worthy of investigation for their potential as natural anti-inflammatory drug sources. In this study, essential oils were hydro distilled from the peels of four citrus species: Citrus sinensis (L.) Osbeck (CSEOs), Citrus paradisi Macfad. (CPEOs), Citrus limon (L.) Osbeck (CLEOs) and Citri Reticulatae Pericarpium (CREOs). Altogether, 81 compounds were identified using gas chromatography-mass spectrometry (GC-MS), of which d-limonene (17.96%-94.66%) was an abundant component of all four oils. The stable 1,1-diphenyl-2-pyrrole hydrazine (DPPH) free radical test showed that all four essential oils had excellent antioxidant properties (IC₅₀ , 0.76-13.86 μg/mL). Furthermore, the oils remarkably increased the first G1 phase of the cell cycle, which inhibited the pro-inflammatory factor expression. An immunohistochemical analysis indicated that the four essential oils inhibited the expression of tumor necrosis factor-α and cyclooxygenase-2 and they exhibited anti-inflammatory activity in a rat model that was similar to that of the common drug, Ibuprofen. These results show that the CSEOs, CPEOs, CLEOs, and CREOs have significant antirheumatic activities and thus have great potential in developing functional food or drugs for treating RA.

Essential Oils in Citrus Fruit Ripening and Postharvest Quality

Citrus essential oils (EOs) are widely used as flavoring agents in food, pharmaceutical, cosmetical and chemical industries. For this reason, their demand is constantly increasing all over the world. Besides industrial applications, the abundance of EOs in the epicarp is particularly relevant for the quality of citrus fruit. In fact, these compounds represent a natural protection against postharvest deteriorations due to their remarkable antimicrobial, insecticidal and antioxidant activities. Several factors, including genotype, climatic conditions and cultural practices, can influence the assortment and accumulation of EOs in citrus peels. This review is focused on factors influencing variation of the EOs’ composition during ripening and on the implications on postharvest quality of the fruit.

Evaluation of Morphological, Qualitative, and Metabolomic Traits during Fruit Ripening in Pomegranate (Punica granatum L.)

Pomegranate is characterized by several local accessions and cultivars widespread across different countries, each with different bio-agronomic features. Physiological and biochemical processes occur during fruit ripening, leading to changes in size, color, and flavor, improving the fruit’s acceptability for the consumer. The aim of this study was to evaluate the changes in physico-chemical and nutritional traits of three Italian germplasm genotypes (‘Santa Lucia’, ‘Di Benedetto’, and ‘Arborea’) to determine the differences for these parameters both within the same cultivar during four ripening stages, and between individual cultivars in the same ripening stage. Morphological traits and fruit pigmentation showed variation during the ripening process, with higher values at the final stage. The highest fruit weight was detected in ‘Di Benedetto’ (392.19 g), while ‘Arborea’ displayed high juice content. Qualitative traits, such as soluble solids, increased until stage III, while titratable acidity values decreased during the ripening stage in ‘Di Benedetto’ and ‘Arborea’. In all three accessions, a reduction in the total polyphenols up to the III ripening stage was observed. Metabolomic analyses using 1H-NMR (proton nuclear magnetic resonance) showed a variation in citric acid and sugar content according to the ripening stage and accession considered. This study found high variability in nutraceutical traits among the analyzed pomegranates. The three pomegranate genotypes showed significant differences in qualitative and metabolomic characteristics. Principal component analysis revealed the main traits that contribute to the positive and negative correlations with PC1 and PC2, highlighting the great variability in the investigated pomegranate genotypes.

Use of near-infrared spectroscopy combined with chemometrics for authentication and traceability of intact lemon fruits

The reflectance NIR spectroscopy and chemometric data treatment on mature intact lemons, Limone di Sorrento PGI (cv Ovale di Sorrento) and Limone Costa D'Amalfi PGI (cv Sfusato Amalfitano) from Campania region, collected in 2018 and 2019, were used to predict properties, and discriminate cultivar and geographical provenance. By PCA, lemon NIR spectra grouped for production years due to the year variation of lemon properties attributable to annual climatic differences, homogeneous in all sites. This agrees with lemon chemical and physical differences by production year. Consequently, the relationship of NIR spectra with lemon quality properties by MLR and the cultivar and provenances discrimination by LDA were affected by year climatic difference; therefore, better model reliability was for single production year. NIR detectability of lemon properties did not appear beyond lemon thick peels, therefore the measured properties of lemon juices could derive from measurable properties of peel correlating with pulp properties.

Amphiphilic triblock copolymer as the gas chromatographic stationary phase with high-resolution performance towards a wide range of isomers and the components of lemon essential oil

This work presents the investigation of using the amphiphilic triblock copolymer composed of poly(ethylene oxide)(PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) (denoted as EPE) as the stationary phase for gas chromatographic (GC) analyses. The EPE capillary column exhibited moderate polarity and column efficiency of 4348 plates/m determined by naphthalene at 120 °C (k = 11.52). Different from the PEG and polysiloxane homopolymers, it showed high-resolution performance towards a wide range of aliphatic and aromatic isomers in terms of polarity and acid-base properties. Particularly, the EPE column displayed distinct advantages for separating the critical isomers of alkanes, anilines and phenols and the components of the lemon essential oil over the commercial PEG and polysiloxane columns. In addition, the EPE column exhibited excellent separation repeatability and reproducibility with the relative standard deviation (RSD) values in the range of 0.03% - 0.08% for run-to-run, 0.14% - 0.61% for day-to-day and 3.1% - 4.0% for column-to-column, respectively. Moreover, the EPE column was investigated in terms of thermal stability, the minimum allowable operating temperature (MiAOT) and sample loadability. Its application to GC-MS analysis of the essential oil demonstrated its feasibility for practical analyses. This work demonstrates the promising future of triblock copolymers as a new class of selective stationary phases for GC analyses, which is barely reported up to date. The findings of this work is of important value for fundamental researches and practical applications.

Untargeted Metabolomics of Rind Essential Oils Allowed to Differentiate Two Closely Related Clementine Varieties

Chemical characterization of clementine varieties (Citrus clementina Hort. ex Tan.) essential oils (EO) can lead to variety identification and valorization of their potential use in food and aroma industries. The goal of this study was the chemometric discrimination between two very closely related and morphologically identical clementine varieties, Clemenules (NL) and Clemenpons (PO), based on their rind EO, to identify the differential volatile organic compounds (VOCs) and to determine their antioxidant capacity. EO rind volatile profile was determined by gas chromatography coupled to mass spectrometry in Citrus fruit at different ripening stages grown two independent years in two different locations. Untargeted metabolomics and multivariate data analysis showed an evolution of EO volatile profiles markedly parallel in both varieties. Although EO qualitative composition was identical in both varieties, PLS-DA allowed the identification of characteristic VOCs, quantitatively discriminating them along all the ripening process. PO showed higher accumulation of several mono- and sesquiterpene compounds such as trans-carveol, while NL showed higher levels of aldehyde and alcohol non-terpenoids like dodecanal. Both varieties evinced identical EO antioxidant activities, indicating a similar value for food preservation. Hence, untargeted metabolomics approach based on rind EO volatiles was revealed as a powerful technique able to differentiate between morphologically undistinguishable Citrus varieties.

A review of chemical constituents and health-promoting effects of citrus peels

Citrus is one of the main fruits processed worldwide, producing a lot of industrial by-products. As the main part of citrus "residue", citrus peels have a wide application prospect. They could not only be directly used to produce various food products, but also be used as promising biofuels to produce ethanol and methane. Additionally, functional components (flavonoids, limonoids, alkaloids, essential oils and pectin) extracted from citrus peels have been related to the improvement of human health against active oxygen, inflammatory, cancer and metabolic disorders. Therefore, it is clear that the citrus peels have great potential to be developed into useful functional foods, medicines and biofuels. This review systematically summarizes the recent advances in current uses, processing, bioactive components and biological properties of citrus peels. A better understanding of citrus peels may provide reference for making full use of it.

Lemon Oils Attenuate the Pathogenicity of Pseudomonas aeruginosa by Quorum Sensing Inhibition

The chemical composition of three Citrus limon oils: lemon essential oil (LEO), lemon terpenes (LT) and lemon essence (LE), and their influence in the virulence factors production and motility (swarming and swimming) of two Pseudomonas aeruginosa strains (ATCC 27853 and a multidrug-resistant HT5) were investigated. The main compound, limonene, was also tested in biological assays. Eighty-four compounds, accounting for a relative peak area of 99.23%, 98.58% and 99.64%, were identified by GC/MS. Limonene (59-60%), γ-terpinene (10-11%) and β-pinene (7-15%) were the main compounds. All lemon oils inhibited specific biofilm production and bacterial metabolic activities into biofilm in a dose-dependent manner (20-65%, in the range of 0.1-4 mg mL^-1) of both strains. Besides, all samples inhibited about 50% of the elastase activity at 0.1 mg mL^-1. Pyocyanin biosynthesis decreases until 64% (0.1-4 mg mL^-1) for both strains. Swarming motility of P. aeruginosa ATCC 27853 was completely inhibited by 2 mg mL^-1 of lemon oils. Furthermore, a decrease (29-55%, 0.1-4 mg mL^-1) in the synthesis of Quorum sensing (QS) signals was observed. The oils showed higher biological activities than limonene. Hence, their ability to control the biofilm of P. aeruginosa and reduce the production of virulence factors regulated by QS makes lemon oils good candidates to be applied as preservatives in the food processing industry.

Utilization of Plantago major seed mucilage containing Citrus limon essential oil as an edible coating to improve shelf-life of buffalo meat under refrigeration conditions

This study is aimed to develop a novel edible coating based on Plantago major seed mucilage (PMSM) and Citrus limon essential oil (CLEO) to increase the shelf-life of buffalo meat during cold storage. The CLEO was firstly isolated by the hydrodistillation method, and it contained mainly limonene (40.5%) and carene (15.4%) with remarkable antioxidant activity (55.7%, 63.8%, and 51.85% based on the DPPH-radical scavenging, ABTS-radical scavenging, and carotene-linoleic acid bleaching tests, respectively) and antibacterial effect against some pathogenic and spoilage microorganisms. The CLEO (0%, 0.5%, 1%, 1.5%, and 2%) was then incorporated into PMSM solution to develop a novel CLEO-loaded PMSM edible coating for improving the shelf-life of buffalo meat. The edible coating was able to significantly reduce the progression of lipid oxidation (peroxide value) and microbial growth (total viable count, psychrotrophic bacteria, Escherichia coli, Staphylococcus aureus, and fungi) in buffalo meat during storage period of 10 days at 4°C in comparison with the control (noncoated sample). The meat hardness and sensory properties (i.e., odor, color, appearance, texture, and overall acceptability) were also maintained better upon edible coating applications. Based on the results, the CLEO-rich PMSM edible coating could be applied as a new and effective preservative to improve the stability of meat products to lipid oxidation and microbial spoilage.

Phenolic composition, antioxidant potential and health benefits of citrus peel

Citrus peel (CP) forms around 40-50% of the total fruit mass but is generally thought to be a waste. However, it is a substantial source of naturally occurring health enhancing compounds, particularly phenolic compounds and carotenoids. Phenolic compounds in CP mainly comprise phenolic acids (primarily caffeic, p-coumaric, ferulic and sinapic acid), flavanones (generally naringin and hesperidin) and polymethoxylated flavones (notably nobiletin and tangeretin). It has also been noted that CP's contain more amounts of these compounds than corresponding edible parts of the fruits. Phenolic compounds present in CP act as antioxidants (by either donation of protons or electrons) and protect cells against free radical damage as well as help in reducing the risk of many chronic diseases. Owing to the more abundance of polyphenols in CP's, their antioxidant activity is also higher than other edible fruit parts. Therefore, peels from citrus fruits can be used as sources of functional compounds and preservatives for the development of newer food products, that are not only safe but also have health-promoting activities. The present review provides in-depth knowledge about the phenolic composition, antioxidant potential and health benefits of CP.