Modelling the Extraction of Pectin towards the Valorisation of Watermelon Rind Waste

Enhancing pectin extraction from orange peel through citric acid-assisted optimization based on a dual response

Pectin is widely used in several products in the industry. Conventionally, strong and harmful acids are used for its extraction. This study optimized the extraction of orange peel's pectin using citric acid, considering yield and degree of esterification (DE) as response variables. Proximal analyses were performed, and the samples were subjected to a Box-Behnken design on three central points, considering as variables the temperature, time, and pH. The results of proximate analyses of the orange peels revealed 11.76 % moisture content, 87.26 % volatiles, 0.09 % ash, 50.45 % soluble carbohydrates, 70.60 % total carbohydrates, 0.89 % fixed carbon, 5.35 % lipids, and 36.75 mg GAE/g of phenolic compounds. The resulting second-order polynomial model described the relation of the input and output variables related to each other. The best performance to obtain a higher yield (18.18 %) of high methoxyl pectin (DE 50 %) was set at 100 °C/30 min/pH 2.48. Pectin showed antioxidant properties by ABTS and DPPH assays and similar thermal properties to the commercial polymer. Its equivalent weight was 1219.51 mol/g, and the methoxyl and anhydrouronic acid were 2.23 and 67.10 %, respectively. Hence, pectin extraction with citric acid results in a high-quality polymer and could be used as a gelling agent, stabilizer, or texturizer in food products.

Unraveling the role of polysaccharide-goethite associations on glyphosate' adsorption-desorption dynamics and binding mechanisms

HYPOTHESIS

Glyphosate retention at environmental interfaces is strongly governed by adsorption and desorption processes. In particular, glyphosate can react with organo-mineral associations (OMAs) in soils, sediments, and aquatic environments. We hypothesize mineral-adsorbed biomacromolecules modulate the extent and rate of glyphosate adsorption and desorption where electrostatic and noncovalent interactions with organo-mineral surfaces are favored.

EXPERIMENTS

Here we use in-situ attenuated total reflectance Fourier-transform infrared, X-ray photoelectron spectroscopy, and batch experiments to characterize glyphosate' adsorption and desorption mechanisms and kinetics at an organo-mineral interface. Model polysaccharide-goethite OMAs are prepared with a range of organic (polysaccharide, PS) surface loadings. Sequential adsorption-desorption studies are conducted by introducing glyphosate and background electrolyte solutions, respectively, to PS-goethite OMAs.

FINDINGS

We find the extent of glyphosate adsorption at PS-goethite interfaces was reduced compared to that at the goethite interface. However, increased polysaccharide surface loading resulted in lower relative glyphosate desorption. At the same time, increased PS surface loading yielded slower glyphosate adsorption and desorption kinetics compared to corresponding processes at the goethite interface. We highlight that adsorbed PS promotes the formation of weak noncovalent interactions between glyphosate and PS-goethite OMAs, including the evolution of hydrogen bonds between (i) the amino group of glyphosate and PS and (ii) the phosphonate group of glyphosate and goethite. It is also observed that glyphosate' phosphonate group preferentially forms inner-sphere monodentate complexes with goethite in PS-goethite whereas bidentate configurations are favored on goethite.

Extraction of pectin from watermelon and pomegranate peels with different methods and its application in ice cream as an emulsifier

Pectin extraction from watermelon peel (WP) and pomegranate peel (PP) was carried out using three different extraction methods: classical solvent extraction (CSE), ultrasound-assisted extraction (UAE), and microwave-assisted extraction (MAE). Extraction parameters (pH, temperature, time, and speed/amplitude/power) were optimized to target maximum crude pectin yield (CPY), while the sample-to-solvent ratio (SS) was determined to be fixed at 1:10 w/v at all experiments. CPY was increased by low pH, high temperature, and long time. The pectins obtained at optimum conditions were characterized regarding the physicochemical and rheological properties, and the pectin solutions were found to be typical pseudoplastic fluids. WP pectin extracted with MAE and PP pectin extracted with UAE were determined to have the best emulsifying properties and added to the ice cream formulations. MAE had the maximum CPY of 9.40% for WP (pH = 1.3, 6 min, 596 W) and the best emulsifying properties. UAE had the best emulsifying properties for PP and the CPY was 11.56% in conditions of pH = 1.5, a temperature of 69°C, an extraction time of 29 min, and a 32% amplitude. The use of PP pectin resulted in a significant increase in the apparent viscosity of ice cream mix and also the first dripping time and the hardness of ice cream over commercial emulsifier. Melting properties and hardness values of ice cream with WP pectin were comparatively closer to those of ice cream with commercial emulsifier. On the other hand, the first dripping time and hardness value of ice cream with PP pectin having 60.25 min and 3.84 N, respectively, were higher than those of commercial ice cream having 53.75 min and 2.14 N, respectively. Practical Application: The utilization of WP and PP, which are good sources for pectin production, benefits both a sustainable environment and a sustainable food industry. Pectin extracted from WP and PP as an emulsifier in ice cream can ensure the production of ice creams with good melting properties. Pectin can be used as a healthy, sustainable, and economical alternative emulsifier in the ice cream industry.

Freeze-drying pretreatment of watermelon peel to improve the efficiency of pectin extraction: RSM optimization, extraction mechanism, and characterization

This study assessed the processing parameters and mechanism of pectin extraction and pectin qualities from freeze-dried (FD) pretreatment watermelon peel. The optimal extraction conditions for the highest pectin yield (21.83 %) were a liquid/solid ratio (w/w) of 29, pH of 1.8, ultrasonic power of 573 W, and ultrasonic time of 43 min. Compared to hot-air dried (HD) method, the extraction of pectin from FD watermelon peel was facilitated by the increased cross-sectional areas of cells, transfer rate of extracting solution, mass transfer rate, and reduced rehydration time during the extraction. HD pectin (HDP) exhibited browning, whereas FD pectin (FDP) displayed bright brownish-yellow coloration. Furthermore, the L* value of pectin from FDP was significantly higher and a* and b* values were significantly lower than pectin from HDP (P < 0.05). Additionally, the moisture, ash and protein contents of FDP were significantly higher than those in HDP (P < 0.05). Structural characterization demonstrated FDP as a low-methoxy acetylated pectin, with significantly lower degree of methoxylation and molecular weight compared to that of HDP (P < 0.05). Besides, FDP demonstrated significantly superior emulsification performance compared to HDP (P < 0.05). These findings suggest FD as a potent, efficient, and time-saving technology for drying fresh watermelon peel for pectin preparation.

Watermelon Rind Mediated Biosynthesis of Bimetallic Selenium-Silver Nanoparticles: Characterization, Antimicrobial and Anticancer Activities

One of the most hazardous diseases that influences human health globally is microbial infection. Therefore, bimetallic nanoparticles have received much attention for controlling microbial infections in the current decade. In the present study, bimetallic selenium-silver nanoparticles (Se-Ag NPs) were effectively biosynthesized using watermelon rind WR extract through the green technique for the first time. UV-visible spectroscopy, transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX) methods were used to characterize the produced NPs. The results indicated that the bimetallic Se-Ag NPs had synergistic antimicrobial activity at low concentrations, which helped to reduce the toxicity of Ag NPs after the bimetallic Se-Ag NPs preparation and increase their great potential. Se-Ag NPs with sizes ranging from 18.3 nm to 49.6 nm were detected by TEM. Se-Ag NP surfaces were uniformly visible in the SEM picture. The cytotoxicity of bimetallic Se-Ag NPs was assessed against the Wi38 normal cell line to check their safety, where the IC50 was 168.42 µg/mL. The results showed that bimetallic Se-Ag NPs had antibacterial action against Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca, Bacillus subtilis, and Staphylococcus aureus with a minimum inhibitory concentration (MIC) of 12.5 to 50 µg/mL. Additionally, bimetallic Se-Ag NPs had promising anticancer activity toward the MCF7 cancerous cell line, where the IC50 was 21.6 µg/mL. In conclusion, bimetallic Se-Ag NPs were biosynthesized for the first time using WR extract, which had strong antibacterial, antifungal and anticancer properties.

Towards Valorization of Food-Waste-Derived Pectin: Recent Advances on Their Characterization and Application

Pectin, a natural biopolymer, can be extracted from food waste biomass, adding value to raw materials. Currently, commercial pectin is mostly extracted from citrus peels (85.5%) and apple pomace (14.0%), with a small segment from sugar beet pulp (0.5%). However, driven by high market demand (expected to reach 2.12 billion by 2030), alternative agro-industrial waste is gaining attention as potential pectin sources. This review summarizes the recent advances in characterizing pectin from both conventional and emerging food waste sources. The focus is the chemical properties that affect their applications, such as the degree of esterification, the neutral sugars' composition, the molecular weight, the galacturonic acid content, and technological-functional properties. The review also highlights recent updates in nutraceutical and food applications, considering the potential use of pectin as an encapsulating agent for intestinal targeting, a sustainable biopolymer for food packaging, and a functional and emulsifying agent in low-calorie products. It is clear from the considered literature that further studies are needed concerning the complexity of the pectin structure extracted from emerging food waste raw materials, in order to elucidate their most suitable commercial application.

Pectin-based aerogel particles for drug delivery: Effect of pectin composition on aerogel structure and release properties

In this work, nanostructured pectin aerogels were prepared via a sol-gel process and subsequent drying under supercritical conditions. To this end, three commercially available citrus pectins and an in-house produced and enzymatically modified watermelon rind pectin (WRP) were compared. Then, the effect of pectin's structure and composition on the aerogel properties were analysed and its potential application as a delivery system was explored by impregnating them with vanillin. Results showed that the molecular weight, degree of esterification and branching degree of the pectin samples played a main role in the production of hydrogels and subsequent aerogels. The developed aerogel particles showed high specific surface areas (468-584 m²/g) and low bulk density (0.025-0.10 g/cm³). The shrinkage effect during aerogel formation was significantly affected by the pectin concentration and structure, while vanillin loading in aerogels and its release profile was also seen to be influenced by the affinity between pectin and vanillin. Furthermore, the results highlight the interest of WRP as a carrier of active compounds which might have potential application in food and biomedical areas, among others.

Extraction and characterization of pectin from watermelon rind using acetic acid

In this work, watermelon rind was used for extraction of pectin with acetic acid solution. The effects of pH, temperature and extraction time on the pectin yield were investigated. Response surface based on Box-Behnken model was employed to optimize the extraction parameters. The model shows an optimum pectin yield of 18.21%, which is in agreement with the value confirmed through experiment (18.20%). The moisture content, ash content, degree of esterification, degree of methylation, equivalent weight, methoxy content, and anhydrouronic acid of the extracted pectin were determined. The values of the moisture content, ash content, degree of esterification, degree of methylation, equivalent weight, methoxy content, anhydrouronic acid are 8.42%, 5.1%, 57.30%, 23.5%, 983.9 mg/mol, 7.3% and 72.36%, respectively. The results show watermelon peel can be an alternative source for pectin production with reasonable pectin yield and pectin quality.

Pectin in Metabolic Liver Disease

Alterations in the composition of the gut microbiota (dysbiosis) are observed in nutritional liver diseases, including non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) and have been shown to be associated with the severity of both. Editing the composition of the microbiota by fecal microbiota transfer or by application of probiotics or prebiotics/fiber in rodent models and human proof-of-concept trials of NAFLD and ALD have demonstrated its possible contribution to reducing the progression of liver damage. In this review, we address the role of a soluble fiber, pectin, in reducing the development of liver injury in NAFLD and ALD through its impact on gut bacteria.

Structure and bioactivity of apple pectin isolated with arabinanase and mannanase

It was assumed that, high purity endo-arabinanase and endo-mannanase could be useful in the isolation of pectin of enhanced health-promoting potential. Extraction was carried out with 50 U of enzymes per gram of apple pomace at 40 °C, obtaining up to 22% increase in effectiveness, as compared to the acid extraction. The pectins, despite their high M_w, were homogeneous and contained more galacturonic acid, rhamnose, galactose, fucose, and ferulic acid than the conventional product, thanks to which they quenched free radicals up to five times more efficiently. Compared with pectin with recognised anticancer and prebiotic activity, they had a significantly greater ability to inhibit proliferation and migration of HT-29 and B16F10 cells. They were also more effective in preventing the adhesion of E. coli and S. typhimurium to enterocytes. Endo-arabinanase- and endo-mannanase-assisted extraction is an effective method of obtaining pectins with enhanced antiradical, anticancer and prebiotic potential.

Current Advancements in Pectin: Extraction, Properties and Multifunctional Applications

Pectin is a heterogeneous hydrocolloid present in the primary cell wall and middle lamella in all dicotyledonous plants, more commonly in the outer fruit coat or peel as compared to the inner matrix. Presently, citrus fruits and apple fruits are the main sources for commercial extraction of pectin, but ongoing research on pectin extraction from alternate fruit sources and fruit wastes from processing industries will be of great help in waste product reduction and enhancing the production of pectin. Pectin shows multifunctional applications including in the food industry, the health and pharmaceutical sector, and in packaging regimes. Pectin is commonly utilized in the food industry as an additive in foods such as jams, jellies, low calorie foods, stabilizing acidified milk products, thickener and emulsifier. Pectin is widely used in the pharmaceutical industry for the preparation of medicines that reduce blood cholesterol level and cure gastrointestinal disorders, as well as in cancer treatment. Pectin also finds use in numerous other industries, such as in the preparation of edible films and coatings, paper substitutes and foams. Due to these varied uses of pectin in different applications, there is a great necessity to explore other non-conventional sources or modify existing sources to obtain pectin with desired quality attributes to some extent by rational modifications of pectin with chemical and enzymatic treatments.

Microwave-assisted extraction of pectin from grape pomace

The utilization of microwave technique for the pectin extraction from grape pomace (Fetească Neagră and Rară Neagră), its influence on yield, galacturonic acid content, degree of esterification and molecular weight of pectin were analyzed. The optimal conditions of the extraction process were microwave power of 560 W, pH of 1.8 for 120 s. The pectin samples extracted by MAE in optimal conditions were analyzed by comparing with commercial apple and citrus pectin based on FT-IR analysis, thermal behavior, rheological characteristics and microstructure. The FT-IR analysis established the presence of different functional groups which are attributed to the finger print region of extracted pectin, while the rheological behavior presented a good viscoelasticity of pectin solutions. The obtained data assumes that grape pomace has a great potential to be a valuable source of pectin which can be extracted by simple and quick techniques, while maintaining analogous quality to conventional sources of pectin.

Chain conformations and steady-shear viscosity properties of pectic polysaccharides from apple and tomato

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Apple pectin was a high-ester polysaccharide, and tomato pectin was a low-ester one.

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The weight-average molecular weight (M_w) of AP was about 243 kDa, and that of TP was about 19 kDa.

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Two pectins presented semi-rigid chain conformation in aqueous solution.

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Elucidated the mechanism about shear thickening of two pectins.

In this study, apple pectin (AP) and tomato pectin (TP) were demonstrated to be a high-ester (74.8%) polysaccharide with the weight-average molecular weight (M_w) of ∼ 243 kDa and a low-ester (45.9%) polysaccharide with the M_w of ∼ 19 kDa, respectively. The semi-rigid chain conformations of pectic polysaccharides in NaNO₃ aqueous solution were deduced according to the Smidsrød “B values” of AP (0.025) and TP (0.029), while AP and TP exhibited higher stiffness in water due to the electric repulsion of carboxyl groups, which was visually observed by AFM images. Under steady shear, the shear-thickening behaviors of AP and TP in NaNO₃ aqueous solutions were observed in the shear rate range of < 1 s⁻¹, which were attributed to the disruption of the ordered arrangement induced by semi-rigid pectin chains into randomly entangled structure by weak shear force. AP exhibited stronger shear-thickening behavior due to the formation of more entanglements resulted from the higher M_w and longer side chains highly branched at rhamngalacturonan region. This study provides the scientific basis for the construction of the relationship of steady-shear property with chain conformation and molecular weight of pectin.

Free Amino Acids and Volatile Aroma Compounds in Watermelon Rind, Flesh, and Three Rind-Flesh Juices

Watermelon rind is treated as agricultural waste, causing biomass loss and environmental issues. This study aimed to identify free amino acids and volatiles in watermelon rind, flesh, and rind-flesh juice blends with ratios of 10%, 20%, and 30%. Among the 16 free amino acids quantified, watermelon rind alone contained higher total amino acids (165 mg/100 g fresh weight) compared to flesh alone (146 mg/100 g). The rind had significantly higher (1.5×) and dominant amounts of citrulline and arginine (61.4 and 53.8 mg/100 g, respectively) than flesh. The rind, however, contained significantly lower amounts of essential amino acids. Volatile analysis showed that watermelon rind total volatiles (peak area) comprised only 15% of the flesh volatiles. Of the 126 volatiles identified, the rind alone contained 77 compounds; 56 of these presented in all five samples. Aldehydes and alcohols were most prevalent, accounting for >80% of the total volatiles in all samples. Nine-carbon aldehyde and alcohol compounds dominated both the flesh and rind, though the rind lacked the diversity of other aldehydes, alcohols, ketones, terpenes, terpenoids, esters and lactones that were more abundant in the watermelon flesh. Watermelon rind was characterized by the major aroma compounds above their thresholds, including 17 aldehydes and six unsaturated nine-carbon alcohols. This study demonstrated the potential for rind as a food or beverage supplement due to its key features such as concentrated citrulline and arginine, relatively low odor intensity, and valuable volatiles associated with fresh, green, cucumber-like aromas.

The Influence of Extraction Conditions on the Yield and Physico-Chemical Parameters of Pectin from Grape Pomace

Grape pomace is one of the most abundant by-products generated from the wine industry. This by-product is a complex substrate consisted of polysaccharides, proanthocyanidins, acid pectic substances, structural proteins, lignin, and polyphenols. In an effort to valorize this material, the present study focused on the influence of extraction conditions on the yield and physico-chemical parameters of pectin. The following conditions, such as grape pomace variety (Fetească Neagră and Rară Neagră), acid type (citric, sulfuric, and nitric), particle size intervals (<125 µm, ≥125−<200 µm and ≥200−<300 µm), temperature (70, 80 and 90 °C), pH (1, 2 and 3), and extraction time (1, 2, and 3 h) were established in order to optimize the extraction of pectin. The results showed that acid type, particle size intervals, temperature, time, and pH had a significant influence on the yield and physico-chemical parameters of pectin extracted from grape pomace. According to the obtained results, the highest yield, galacturonic acid content, degree of esterification, methoxyl content, molecular, and equivalent weight of pectin were acquired for the extraction with citric acid at pH 2, particle size interval of ≥125−<200 µm, and temperature of 90 °C for 3 h. FT-IR analysis confirmed the presence of functional groups in the fingerprint region of identification for polysaccharide in the extracted pectin.

Watermelon Rind and Flesh Volatile Profiles and Cultivar Difference

Watermelon rind is treated as agricultural waste and commonly discarded, causing environmental issues and biomass loss. This study aimed to identify volatile profiles of watermelon rind and flesh and their cultivar difference. Volatiles were analyzed using solid-phase microextraction–gas chromatography–mass spectrometry (SPME-GC-MS). A total of 132 volatiles were identified, including aldehydes, alcohols, ketones, terpenes/terpenoids, esters, lactones, acids, and sulfides. In both rind and flesh, the most dominant compounds in numbers and abundance (peak area) were aldehydes and alcohols, which accounted 94–96% of the total volatile abundance in the rind and 85–87% in the flesh. Total volatile in watermelon rind was only 28–58% of the corresponding flesh samples. Both rind and flesh shared nine-carbon aldehydes and alcohols, though the rind lacked additional diversity. Volatile difference between rind and flesh was greater than the difference among cultivars, although volatiles in the rind could be two times difference between Fascination and other three watermelons (Captivation, Exclamation, and Excursion). This study provides the first-hand knowledge regarding watermelon rind volatile profiles and cultivar difference and shows the potential use of rind in food or beverages due to its naturally contained nine-carbon compounds.

Bioactive extracts from persimmon waste: influence of extraction conditions and ripeness

In this work, a bioactive persimmon extract was produced from discarded fruits. A central composite design was used to evaluate the effect of different extraction parameters and ripeness stages of persimmon fruits on the total phenolic content and antioxidant activity of the resulting extracts. Significantly greater phenolic contents were obtained from immature persimmon (IP) fruits. The optimum IP extract with the conditions set by the experimental design was industrially up-scaled and its composition and functional properties were evaluated and compared with those obtained under lab-scale conditions. Both extracts contained significant protein (>20%) and phenolic contents (∼11-27 mg GA/g dry extract) and displayed significant antiviral activity against murine norovirus and hepatitis A virus. Moreover, the extract showed no toxicity and significantly reduced the fat content and the cellular ageing of Caenorhabditis elegans (C. elegans) without affecting the worm development. These effects were mediated by down-regulation of fat-7, suggesting an anti-lipogenic activity of this extract.