Citrus peels waste as a source of value-added compounds: Extraction and quantification of bioactive polyphenols

Antioxidant Activity and Healthy Benefits of Natural Pigments in Fruits: A Review

Natural pigments, including carotenoids, flavonoids and anthocyanidins, determine the attractive color of fruits. These natural pigments are essential secondary metabolites, which play multiple roles in the whole life cycle of plants and are characterized by powerful antioxidant activity. After decades of research and development, multiple benefits of these natural pigments to human health have been explored and recognized and have shown bright application prospects in food, medicine, cosmetics and other industries. In this paper, the research progress of natural fruit pigments in recent years was reviewed, including the structural characteristics and classification, distribution in fruits and analysis methods, biosynthetic process, antioxidant capacity and mechanism, bioaccessibility and bioavailability, and health benefits. Overall, this paper summarizes the recent advances in antioxidant activity and other biological functions of natural fruit pigments, which aims to provide guidance for future research.

Application of accelerating energies to the maceration of sherry vinegar with citrus fruits

BACKGROUND

In the present work we propose the use of accelerating energies (microwaves and ultrasounds) to the maceration process of sherry vinegar with citrus fruit peels (orange and lemon). For the application of microwaves, an experimental design has been developed in order to optimize the maceration conditions. To evaluate the effect of these energies on the maceration, the volatile and polyphenolic content of the samples has been analyzed, as well as their sensory characteristics.

RESULTS

Orange peel provided a higher number of volatile and polyphenolic compounds to the vinegar, while lemon's yielded a greater amount of some of them. The multivariate analysis showed that the samples macerated using microwaves were the most similar to the samples macerated in the traditional way. This aspect was corroborated by the sensory analysis, which was more noticeable when orange peel was used in the macerations.

CONCLUSION

Therefore, it seems that the use of microwaves to accelerate maceration is a good alternative to the traditional method of making sherry vinegars macerated with citrus peel, since it cuts down the maceration time from 3 days to just a few minutes. © 2020 Society of Chemical Industry.

A combined approach based on matrix solid-phase dispersion extraction assisted by titanium dioxide nanoparticles and liquid chromatography to determine polyphenols from grape residues

A simple and efficient low-cost matrix solid phase dispersion (MSPD) extraction assisted by TiO₂ nanoparticles and diatomaceous earth has been developed for the extraction of phenolic compounds from grape and grape pomace wastes. Experimental conditions for MSPD extraction were optimized by a factorial design and a surface response methodology. The simultaneous identification and quantification of eight main natural polyphenols (caffeic, p-coumaric, dihydroxybenzoic and gallic acid, rutin, resveratrol, quercetin and catechin) was possible by combining MSPD and capillary liquid chromatography coupled to a diode array detection and a mass simple quadrupole analyzer (cLC-DAD-MS). Good linearity and acceptable LOD (0.05-62 µg·g^-1) and LOQ (0.2-207 µg·g^-1) were obtained. The quantities of extracted polyphenols were within 2.4 and 333 µg·g^-1, with catechin and rutin the most abundant compounds in grape pomace and grape wastes, respectively. Furthermore, considering the prospective uses of the winery bioresidues, the extracts have been characterised in terms of bioactive properties (several antioxidant activities and bacterial inhibition against Staphylococcus aureus, Escherichia coli and Pseudomona aeruginosa) and parameters such as total polyphenol and total flavonoid content. The high antioxidant activity (IC₅₀ 5.0 ± 0.4 µg ·g^-1 against DPPH radical) and antibacterial activity (2.2 ± 0.3 mg·mL^-1) suggests that the methodology developed is efficient, rapid and promising for the extraction of phenolic compounds with potential application as bioactive ingredients in food and cosmetic industries.

Techniques and modeling of polyphenol extraction from food: a review

There is a growing demand for vegetal food having health benefits such as improving the immune system. This is due in particular to the presence of polyphenols present in small amounts in many fruits, vegetables and functional foods. Extracting polyphenols is challenging because extraction techniques should not alter food quality. Here, we review technologies for extracting polyphenolic compounds from foods. Conventional techniques include percolation, decoction, heat reflux extraction, Soxhlet extraction and maceration, whereas advanced techniques are ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, high-voltage electric discharge, pulse electric field extraction and enzyme-assisted extraction. Advanced techniques are 32-36% more efficient with approximately 15 times less energy consumption and producing higher-quality extracts. Membrane separation and encapsulation appear promising to improve the sustainability of separating polyphenolic compounds. We present kinetic models and their influence on process parameters such as solvent type, solid and solvent ratio, temperature and particle size.

Electrosynthesis of three-dimensional nanoporous nickel on screen-printed electrode used for the determination of narirutin in citrus wastewater

In this study, an electrochemical sensor was designed for the detection of narirutin using three-dimensional nanostructured porous nickel on screen-printed electrode (3DnpNi/SPE). The modified electrode was successfully synthesized by the dynamic hydrogen bubble template method. The 3DnpNi/SPE was characterized by spectroscopic, microscopic, and electrochemical methods. The results showed that the 3DnpNi/SPE presents good electrocatalytic activity for the oxidation of narirutin. The quantification of narirutin was conducted by differential pulse voltammetry, which showed a wide concentration range (1.0 × 10^-7 - 1.0 × 10^-5 mol L^-1), with low detection limit (3.9 × 10^-8 mol L^-1), and excellent sensitivity (0.31 A L mol^-1). The proposed electrode was applied toward the determination of narirutin in yellow water sample from the citrus industry, where it presented a good degree of accuracy. The 3DnpNi/SPE showed repeatability, long-term stability, and selectivity. The results obtained showed agreement with those obtained by HPLC/DAD method. Chemical compounds studied in this article.

Citrus decoction by-product represents a rich source of carotenoid, phytosterol, extractable and non-extractable polyphenols

This study aimed to carry out an exhaustive chemical characterization of citrus (orange, mandarin, and grapefruit) decoctions as well as the residues obtained during the decoction process (by-products). The citrus decoctions were rich in hesperidin, naringin, and narirutin, but carotenoids and phytosterols were not detected. Interestingly, these flavanones were found in a higher concentration in the extractable polyphenol fraction of the citrus decoction by-products. Moreover, the greatest content of hesperidin and naringin was found bound to the food matrix by ether/ester bonds. Violaxanthin and β-cryptoxanthin were found as major carotenoids in the orange and mandarin decoction by-products, respectively, whereas the grapefruit decoction by-product showed a low content of carotenoids. All citrus by-products showed β-sitosterol as the major phytosterol, followed by β-campesterol. Therefore, the by-products obtained during the elaboration of citrus decoctions are rich sources of bioactive compounds that can be used for the development of functional foods or dietary supplements.

Anti-inflammatory activity of ethyl acetate and n-butanol extracts from Ranunculus macrophyllus Desf. and their phenolic profile

ETHNOPHARMACOLOGICAL RELEVANCE

The members of the genus Ranunculus have counter-irritating properties and thus, they are traditionally used for treating anti-inflammatory disorders and other skin conditions. Ranunculus macrophyllus Desf. is a wild medicinal plant growing in Algeria and traditionally used to treat some cutaneous skin disorders.

AIM

The aim of this study was to characterize the composition of the ethyl acetate and n-butanol extracts from Ranunculus macrophyllus Desf. as well as to elucidate and to compare their effect against acute skin inflammation. Moreover, both the antioxidant activity and the acute toxicity of the plant extracts were also studied.

MATERIALS AND METHODS

Spectrophotometric and chromatographic methods were employed to identify and quantify phenolic compounds and triterpenoids from R. macrophyllus Desf. fractions. The antioxidant activity was estimated using the phosphomolebdenum, DPPH, reducing power and β-carotene bleaching assays. The ethyl acetate and n-butanol extracts were screened for their anti-inflammatory activities using ex-vivo membrane stabilizing assays and in-vivo acute skin inflammation model.

RESULTS

Ethyl acetate fraction showed the highest amounts of total phenolic compounds (413 ± 4 μg GAE/mg extract) and triterpenoids (70.4 ± 1.8 μg UAE/mg extract). Rutin, hesperidin, myricetin and kaempferol were the major compounds identified in the different fractions. Ethyl acetate fraction exhibited strong DPPH^• radical scavenging ability (IC₅₀ 1.6 ± 0.2 μg/mL), high total antioxidant capacity (447 ± 7 μg AAE/mg extract) and reducing power (514 ± 8 μg AAE/mg extract). Ethyl acetate fraction inhibited (73.4 ± 0.3) % of linoleic acid peroxidation. Ethyl acetate and n-butanol fractions did not have any visible toxicity at 2000 mg/kg and presented excellent membrane stabilizing ability. The inhibition of xylene induced ear inflammation was (38 ± 4) % and (46 ± 1) % for RM-B and RM-EA, respectively.

CONCLUSIONS

The high content of both phenolic compounds and triterpenoids combined with the remarkable anti-inflammatory effect and antioxidant activity of ethyl acetate and n-butanol extracts from R. macrophyllus Desf. support the wide spread use of this traditional plant on some skin disorders (inflammatory skin disorders).

Industrial Fruits By-Products and Their Antioxidant Profile: Can They Be Exploited for Industrial Food Applications?

Fruit by-products have a low economic value and have proven biological activities, such as antioxidant capacity due to the presence of active compounds. The main objective of this study was to obtain and determine the antioxidant capacity, through DPPH radical assay and β-carotene bleaching assay, of three food grade extracts from apple, lemon, and orange industrial by-products. Furthermore, the extracts were characterized by ultra-high performance liquid chromatography coupled to mass spectrometry (UHPLC-MS/MS). LC with diode array detector (LC-DAD) was used for the quantification of the main polyphenols. Lemon extract presented the highest inhibition percentage of DPPH radical (51.7%) and the highest total phenolics content (43.4 mg GAE/g) from the by-products studied. Orange by-product was that with the higher number of polyphenols while lemon extract was that with the highest content of individual phenolics. The by-product obtained from the lemon was that with higher amounts of hydroxycinnamic acids (407 µg/g of by-product), mainly chlorogenic acid (386.7 µg/g), followed by the apple by-product (128.0 µg/g of by-product), which showed higher amounts of rosmarinic and chlorogenic acids. These industrial by-products have great potential as a source of natural antioxidants to be used directly as food additives or to be incorporated in packaging to produce active food packaging.

Selective extraction of bioactive compounds from plants using recent extraction techniques: A review

Plant extraction has existed for a long time and is still of interest. Due to technological improvements, it is now possible to obtain extracts with higher yields. While global yield is a major parameter because it assesses the extraction performance, it can be of interest to focus on the extraction of particular compounds (specific metabolites) to enrich the sample and to avoid the extraction of unwanted ones, for instance the primary metabolites (carbohydrates, triacylglycerols). The objective then is to improve extraction selectivity is then considered. In solid-liquid extraction, which is often called maceration, the solvent has a major impact on selectivity. Its polarity has a direct influence on the solutes extracted, related to the chemical structure of the compounds, and modelling compound/solvent interactions by using various polarity or interaction scales is a great challenge to favor the choice of the appropriate extracting liquid. Technical advances have allowed the development of recent, and sometimes green, extraction techniques, such as Microwave-Assisted Extraction (MAE), Ultrasound-Assisted Extraction (UAE), Pressurized Liquid Extraction (PLE) and Supercritical Fluid Extraction (SFE). This review focuses on the specificity of these recent techniques and the influence of their physical parameters (i.e. pressure, intensity, etc.). In addition to the solvent selection, which is of prime interest, the physical parameters applied by the different techniques influence the extraction results in different ways. Besides, SFE is a versatile and green technique suitable to achieve selectivity for some compounds. Due to its properties, SC-CO₂ allows tailoring conditions to improve the selectivity.

Antioxidant Molecules from Plant Waste: Extraction Techniques and Biological Properties

The fruit, vegetable, legume, and cereal industries generate many wastes, representing an environmental pollution problem. However, these wastes are a rich source of antioxidant molecules such as terpenes, phenolic compounds, phytosterols, and bioactive peptides with potential applications mainly in the food and pharmaceutical industries, and they exhibit multiple biological properties including antidiabetic, anti-obesity, antihypertensive, anticancer, and antibacterial properties. The aforementioned has increased studies on the recovery of antioxidant compounds using green technologies to value plant waste, since they represent more efficient and sustainable processes. In this review, the main antioxidant molecules from plants are briefly described and the advantages and disadvantages of the use of conventional and green extraction technologies used for the recovery and optimization of the yield of antioxidant naturals are detailed; finally, recent studies on biological properties of antioxidant molecules extracted from plant waste are presented here.

A new breakfast brioche containing bergamot fiber prevents insulin and glucose increase in healthy volunteers: a pilot study

BACKGROUND

Despite the abundance of studies on the beneficial effects of a fiber rich diet as well as polyphenols deriving from Citrus fruits on postprandial serum glucose and insulin, clinical evidence on their synergic effects on healthy subjects have never been published. We aimed to investigate the feasibility of a new dietary approach in controlling glucose and insulin response at breakfast time by testing a brioche enriched with wheat bran and bergamot fiber.

METHODS

We enrolled 11 healthy volunteers in a cross-over study. Participants consumed a classic brioche at breakfast and our functional brioche, containing wheat bran and bergamot fiber, on another day. Vital functions, biochemical parameters (including glucose and insulin), anthropometric measurements as well as resting energy expenditure and fat oxidation were evaluated before and after the intake of both meals.

RESULTS

The mean age was ~25 years. The mean BMI was 23.5 kg/m². The consumption of the functional brioche reduced the glucose C<inf>max(0-120 min)</inf> by ~6% and prevented the insulin increase over time by 30%, finally demonstrating insulin C<inf>max(0-120 min)</inf> and iAUC<inf>(0-120 min)</inf> values significantly lower compared to classic brioche (respectively P value =0.04 and 0.03). The stepwise multivariable analysis confirmed the association between the consumption of the functional brioche containing bran and bergamot fiber and glucose C<inf>max(0-120 min)</inf> (B=-0.45; P=0.034), and insulin iAUC<inf>(0-120 min)</inf> (B=-764 P=0.036).

CONCLUSIONS

The association of wheat bran and bergamot fiber significantly influences glucose metabolism and may exert insulin-like effects on healthy volunteers. If confirmed, berga-brioche would be a useful tool in preventing diabetes and controlling the glycometabolic status of type 2 diabetic patients.

A Glimpse into the Extraction Methods of Active Compounds from Plants

Naturally active compounds are usually contained inside plants and materials thereof. Thus, the extraction of the active compounds from plants needs appropriate extraction methods. The commonly employed extraction methods are mostly based on solid-liquid extraction. Frequently used conventional extraction methods such as maceration, heat-assisted extraction, Soxhlet extraction, and hydrodistillation are often criticized for large solvent consumption and long extraction times. Therefore, many advanced extraction methods incorporating various technologies such as ultrasound, microwaves, high pressure, high voltage, enzyme hydrolysis, innovative solvent systems, adsorption, and mechanical forces have been studied. These advanced extraction methods are often better than conventional methods in terms of higher yields, higher selectivity, lower solvent consumption, shorter processing time, better energy efficiency, and potential to avoid organic solvents. They are usually designed to be greener, more sustainable, and environment friendly. In this review, we have critically described recently developed extraction methods pertaining to obtaining active compounds from plants and materials thereof. Main factors that affect the extraction performances are tuned, and extraction methods are chosen in line with the properties of targeted active compounds or the objectives of extraction. The review also highlights the advancements in extraction procedures by using combinations of extraction methods to obtain high overall yields or high purity extracts.

A High-Yield Process for Production of Biosugars and Hesperidin from Mandarin Peel Wastes

In this research, novel biorefinery processes for obtaining value-added chemicals such as biosugar and hesperidin from mandarin peel waste (MPW) are described. Herein, three different treatment methods were comparatively evaluated to obtain high yields of biosugar and hesperidin from MPW. Each method was determined by changes in the order of three processing steps, i.e., oil removal, hesperidin extraction, and enzymatic hydrolysis. The order of the three steps was found to have a significant influence on the production yields. Biosugar and hesperidin production yields were highest with method II, where the processing steps were performed in the following order: oil removal, enzymatic hydrolysis, and hesperidin extraction. The maximum yields obtained with method II were 34.46 g of biosugar and 6.48 g of hesperidin per initial 100 g of dry MPW. Therefore, the methods shown herein are useful for the production of hesperidin and biosugar from MPW. Furthermore, the utilization of MPWs as sources of valuable materials may be of considerable economic benefits and has become increasingly attractive.

Comprehensive Comparison on the Chemical Profile of Guang Chen Pi at Different Ripeness Stages Using Untargeted and Pseudotargeted Metabolomics

The peel of Citrus reticulata 'Chachi' (GCP), which is highly valued in China for its health-promoting effects, is usually collected at different development stages to be processed into various functional foods. In the present work, a rapid method based on ultra-high-performance liquid chromatography Q Exactive Orbitrap mass spectrometry-incorporated untargeted and pseudotargeted metabolomics analysis was developed to investigate the chemical variations in GCP at different ripeness stages. Samples that originated from an individual tree were collected at immature, near mature, and mature stages. A total of 112 compounds were identified or tentatively identified, and flavonoids malonyl glycosides and polymethoxyfolavones glycosides were reported for the first time. Untargeted metabolomics analysis indicated the distinct chemical profiles and significant changes during ripeness stages. Then, a validated pseudotargeted metabolomics method based on parallel reaction monitoring was further applied with a wide coverage of targeted compounds. The GCP samples were found differing in the content variations of flavonoid aglycones, flavonoid O-/C-glycosides, polymethoxyfolavones, limonoids, alkaloids, and phenolic acid, which are important for phenotypic variations at different development stages. The present study is expected to provide new insight on comprehensive utilization of citrus peels at different ripeness stages.

Non-Extractable Polyphenols from Food By-Products: Current Knowledge on Recovery, Characterisation, and Potential Applications

Non-extractable polyphenols (NEPs), or bound polyphenols, are a significant fraction of polyphenols that are retained in the extraction residues after conventional aqueous organic solvent extraction. They include both high molecular weight polymeric polyphenols and low molecular weight phenolics attached to macromolecules. Current knowledge proved that these bioactive compounds possess high antioxidant, antidiabetic, and other biological activities. Plant-based food by-products, such as peels, pomace, and seeds, possess high amount of NEPs. The recovery of these valuable compounds is considered an effective way to recycle food by-products and mitigate pollution, bad manufacturing practice, and economic loss caused by the residues management. The current challenge to valorise NEPs from plant-based by-products is to increase the extraction efficiency with proper techniques, choose appropriate characterising methods, and explore potential functions to use in some products. Based on this scenario, the present review aims to summarise the extraction procedure and technologies applied to recover NEPs from plant-based by-products. Furthermore, it also describes the main techniques used for the characterisation of NEPs and outlines their potential food, pharmaceutical, nutraceutical, and cosmetic applications.

Comparative study of various processes used for removal of bitterness from kinnow pomace and kinnow pulp residue

The current study was focused on new approaches for debittering of by-products like kinnow pomace and kinnow pulp residue by using various food grade mild chemical methods, such as alkali treatment, acid treatment, and solventogenesis. Whereas in the studied various chemical treatments, the solventogenesis method with acetone resulted in maximum extraction of naringin and limonene from kinnow pomace and pulp residue and showed high acceptability for food product development. The acetone treatment was further optimized by RSM for the maximum extraction of naringin and limonene. Under optimized conditions, the maximum amount of naringin and limonene extracted were found to be 8.955, 2.122 mg/g from kinnow pomace and 9.971, 3.838 mg/g from pulp residue, respectively. This process can not only result in the effective utilization of agro-industrial by-product but also provide a sustainable solution to the environmental pollution caused by kinnow juice industry.

Simultaneous determination of phenolic metabolites in Chinese citrus and grape cultivars

Background

As the major bioactive compounds in citrus and grape, it is significant to use the contents of flavonoids and phenolic acids as quality evaluation criteria to provide a better view of classifying the quality and understanding the potential health benefits of each fruit variety.

Methods

A total of 15 varieties of citrus and 12 varieties of grapes were collected from Fujian, China. High-performance liquid chromatography method was used for the simultaneous determination of 17 phenolic compounds, including gallic acid, chlorogenic acid, caffeic acid, syringic acid, ρ-coumaric acid, ferulic acid, benzoic acid, salicylic acid, catechin, epicatechin, resveratrol, rutin, naringin, hesperidin, quercetin, nobiletin and tangeritin in the peels of citrus and grape cultivars. Further, the cultivars of citrus and grape were classified using principal component analysis (PCA) and hierarchical cluster analysis (HCA).

Results

A thorough separation of the 17 compounds was achieved within 100 min. The tested method exhibited good linearity (the limits of detection and limits of quantification were in the range of 0.03–1.83 µg/mL and 0.09–5.55 µg/mL, respectively), precision (the relative standard deviations of repeatability were 1.02–1.97%), and recovery (92.2–102.82%) for all the compounds, which could be used for the simultaneous determination of phenolic compounds in citrus and grape. Hesperidin (12.93–26,160.98 µg/g DW) and salicylic acid (5.35–751.02 µg/g DW) were the main flavonoids and phenolic acids in 15 citrus varieties, respectively. Besides, the hesperidin (ND to 605.48 µg/g DW) and salicylic acid (ND to 1,461.79 µg/g DW) were found as the highest flavonoid and the most abundant phenolic acid in grapes, respectively. A total of 15 citrus and 12 grape samples were classified into two main groups by PCA and HCA with strong consistency.

Advances and Prospects of Phenolic Acids Production, Biorefinery and Analysis

Biotechnological production of phenolic acids is attracting increased interest due to their superior antioxidant activity, as well as other antimicrobial, dietary, and health benefits. As secondary metabolites, primarily found in plants and fungi, they are effective free radical scavengers due to the phenolic group available in their structure. Therefore, phenolic acids are widely utilised by pharmaceutical, food, cosmetic, and chemical industries. A demand for phenolic acids is mostly satisfied by utilising chemically synthesised compounds, with only a low quantity obtained from natural sources. As an alternative to chemical synthesis, environmentally friendly bio-based technologies are necessary for development in large-scale production. One of the most promising sustainable technologies is the utilisation of microbial cell factories for biosynthesis of phenolic acids. In this paper, we perform a systematic comparison of the best known natural sources of phenolic acids. The advances and prospects in the development of microbial cell factories for biosynthesis of these bioactive compounds are discussed in more detail. A special consideration is given to the modern production methods and analytics of phenolic acids.

Variations of Flavonoid Composition and Antioxidant Properties among Different Cultivars, Fruit Tissues and Developmental Stages of Citrus Fruits

A large number of biologically active compounds are present in ripe citrus fruits. However, few studies have been focused on the changes in flavonoids and the evolution of antioxidant activity during citrus fruit growth. In this study, fruits of five citrus cultivars cultivated in China were sampled at 60-210 days post-anthesis (DPA) at intervals of 30 days. The amounts of main flavonoids in the peel and pulp were analyzed by HPLC and their activities were studied by DPPH, ABTS and FRAP. The results showed that the contents of hesperidin, diosmin, eriodictyol, rutin and nobiletin increased before 90 DPA and then decreased with the growth and development of fruits, but an opposite tendency was observed for naringin and narirutin. The antioxidant activities in citrus peel and pulp were found to be significantly correlated with some flavonoids. The results may be of guiding values in citrus production and utilization of citrus fruit by-products.

Citrus Peel Flavonoids as Potential Cancer Prevention Agents

Citrus fruit and in particular flavonoid compounds from citrus peel have been identified as agents with utility in the treatment of cancer. This review provides a background and overview regarding the compounds found within citrus peel with putative anticancer potential as well as the associated in vitro and in vivo studies. Historical studies have identified a number of cellular processes that can be modulated by citrus peel flavonoids including cell proliferation, cell cycle regulation, apoptosis, metastasis, and angiogenesis. More recently, molecular studies have started to elucidate the underlying cell signaling pathways that are responsible for the flavonoids' mechanism of action. These growing data support further research into the chemopreventative potential of citrus peel extracts, and purified flavonoids in particular. This critical review highlights new research in the field and synthesizes the pathways modulated by flavonoids and other polyphenolic compounds into a generalized schema.

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.

Bioactives From Agri-Food Wastes: Present Insights and Future Challenges

Sustainable utilization of agri-food wastes and by-products for producing value-added products (for cosmetic, pharmaceutical or food industrial applications) provides an opportunity for earning additional income for the dependent industrial sector. Besides, effective valorisation of wastes/by-products can efficiently help in reducing environmental stress by decreasing unwarranted pollution. The major focus of this review is to provide comprehensive information on valorisation of agri-food wastes and by-products with focus laid on bioactive compounds and bioactivity. The review covers the bioactives identified from wastes and by-products of plants (fruits, exotic fruits, vegetables and seeds), animals (dairy and meat) and marine (fish, shellfish seaweeds) resources. Further, insights on the present status and future challenges of sustainably utilizing agri-food wastes/by-products for value addition will be highlighted.

Extraction of polyphenols and synthesis of new activated carbon from spent coffee grounds

A valorization process of spent coffee grounds (SCG) was studied. Thus, a two-stage process, the first stage of polyphenols extraction and synthesis of a carbonaceous precursor and a subsequent stage of obtaining activated carbon (AC) by means of a carbonization process from the precursor of the previous stage, was performed. The extraction was carried out with a hydro-alcoholic solution in a pressure reactor, modifying time, temperature and different mixtures EtOH:H2O. To optimize the polyphenols extraction, a two-level factorial experimental design with three replicates at the central point was used. The best results were obtained by using a temperature of 80 °C during 30 min with a mixture of EtOH:H2O 50:50 (v/v). Caffeine and chlorogenic acid were the most abundant compounds in the analysed extracts, ranging from 0.09 to 4.8 mg∙g-1 and 0.06 to 9.7 mg∙g-1, respectively. Similarly, an experimental design was realized in order to analyze the influence of different variables in the AC obtained process (reaction time, temperature and KOH:precursor ratio). The best results were 1 h, 850 °C, and a mixture of 2.5:1. The obtained activated carbons exhibit a great specific surface (between 1600 m2∙g-1 and 2330 m2∙g-1) with a microporous surface. Finally, the adsorption capacity of the activated carbons was evaluated by methylene blue adsorption.