Citrus Residues Research Articles

Evaluation of Different Pectic Materials Coming from Citrus Residues in the Production of Films.

This article explores the use of citrus residues as a source of different pectic materials for packaging film production: a water-soluble orange residue extract (WSE) (~5% pectin), semi-pure pectins extracted in citric acid (SP) (~50% pectin), and commercial pure citrus pectins (CP). First, these materials were characterized in terms of chemical composition. Then, films were produced using them pure or mixed with chitosan or glycerol through solvent-casting. Finally, antioxidant activity, functional properties (e.g., mechanical and gas barrier properties), and visual appearance of the films were assessed. WSE films showed the highest antioxidant activity but the lowest mechanical strength with the highest elongation at break (EB) (54%); incorporating chitosan increased the films' strength (Young's modulus 35.5 times higher). SP films showed intermediate mechanical properties, reinforced by chitosan addition (Young's modulus 4.7 times higher); they showed an outstanding dry O2 barrier. CP films showed a similar O2 barrier to SP films and had the highest Young's modulus (~29 MPa), but their brittleness required glycerol for improved pliability, and chitosan addition compromised their surface regularity. Overall, the type of pectic material determined the film's properties, with less-refined pectins offering just as many benefits as pure commercial ones.

The Advantage of Citrus Residues as Feedstock for Biogas Production: A Two-Stage Anaerobic Digestion System

Anaerobic digestion (AD) is an important step in waste recovery. In Colombia, the production of citrus food significantly contributes to environmental impact via waste generation. In 2021, the waste produced, specifically citrus rind, amounted to 725,035 tons/year. During degradation, wastes generate leachate and greenhouse gases (GHGs), which negatively impact water sources (leachate), soil, and human and animal health. This article describes the design of a two-phase biodigestion system for the degradation of organic matter and biogas production. The system uses citrus waste to produce biogas with neutral emissions. The biodigestion process begins with the stabilization of the methanogenesis reactor (UASB), which takes approximately 19 days. During this period, the biogas produced contains approximately 60% methane by volume. Subsequently, the packed bed reactor operates for 7 days, where hydrolytic and acetogenic bacteria decompose the citrus waste, leading to the production and accumulation of volatile fatty acids. The final step involves combining the two phases for 5 days, resulting in a daily biogas production ranging from 700 to 1100 mL. Of this biogas, 54.90% is methane (CH4) with a yield of 0.51 LCH4gSV−1. This study assesses the methane production capacity of citrus waste, with the process benefiting from the pH value of the leachate, enhancing its degradability. Consequently, this approach leads to a notable 27.30% reduction in solids within the digestion system. The two-phase anaerobic biodigestion system described in this article demonstrates a promising method to mitigate the environmental impact of citrus waste while concurrently producing a renewable source of energy.

Extraction of citrus pectin using pressurized carbon dioxide and production of its oligosaccharides

In this study, we utilized pressurized carbon dioxide (pCO2) for pectin extraction from citrus residues because of its potential to produce acid without chemicals, that is non-toxic, green technology for humans and the environment. The pCO2 was performed at 2.5 MPa and 90 °C for 90 min, while the conventional method (CM) for pectin extraction using HCl was performed under atmospheric pressure at 90 °C for 90 min. Pectin extraction yields with pCO2 depended on the type of citrus fruit and were lower than those obtained with the CM. However, pCO2-extracted pectin (pCO2-pectin) provided a higher degree of esterification (DE), neutral sugar side-chain substitution on the pectate backbone, and greater molecular size than those of pectin extracted using the conventional method (CM-pectin). Pectin oligosaccharide (POS) was prepared from CM-pectin and pCO2-pectin using viscozyme L hydrolysis under optimum conditions. These POSs were then designated as CM-POS and pCO2-POS, respectively. Both pCO2-POS and CM-POS stimulated the growth of Lactobacillus and Bifidobacterium species, and induced them to produce short-chain fatty acids, and slightly suppressed immunoglobulin E production in U266 cells. Furthermore, pCO2-POS had higher angiotensin-converting enzyme inhibitory activity compared to CM-POS. This study suggests that pCO2 is a novel method for extracting pectin with unique molecular properties affecting POS functionality in vitro.

Cross‐sectoral citrus sugarcane biorefinery: polyhydroxyalkanoates production in Brazil

AbstractPolyhydroxyalkanoates (PHA) are naturally occurring polyesters accumulated by bacteria under conditions of inorganic nutrient limitations and excess carbon. They offer renewable and biodegradable alternatives to petroleum‐based polymers, especially those used in transient single‐use applications. However, PHA still faces high production costs, primarily linked to the carbon source, lower productivity in processes and an early stage of technical development in comparison with well‐established fossil‐based polymers, which challenge its transition to a true commodity market. Recent research has highlighted the potential of renewable, inexpensive, abundant and non‐edible carbon‐rich residues from agriculture, municipal solid waste and industrial byproducts as alternative carbon sources in developing the production process. Recognizing Brazil's position as the leading producer of both citrus and sugarcane, this review introduces a novel citrus–sugarcane biorefinery model for PHA production, capitalizing on the geographical and operational synergies of both sectors. The proposed model integrates wet citrus pulp as a second‐generation carbon source, sugarcane industry fermenters, waste management, solvents and renewable energy from both sectors. Primary challenges involve the need for efficient, low‐cost biomass pre‐treatment to remove limonene and partially extract citric pectin, coupled with the partial hydrolysis of pectin to enhance solubility and reduce viscosity. Additional considerations include determining citrus biomass composition and sugar consumption, screening bacterial diversity for optimal PHA production, and deepening our understanding of the metabolic pathways underpinning the catabolism of citrus residues. Future research should focus on enhancing PHA concentrations and diversity and finally conducting life cycle assessment studies to evaluate the sustainability and feasibility of this proposed model.

Overview of the Biotransformation of Limonene and α-Pinene from Wood and Citrus Residues by Microorganisms

This review provides an overview of the biotransformation of limonene and α-pinene, which are commonly found in wood residues and citrus fruit by-products, to produce high-value-added products. Essential oils derived from various plant parts contain monoterpene hydrocarbons, such as limonene and pinenes which are often considered waste due to their low sensory activity, poor water solubility, and tendency to autoxidize and polymerise. However, these terpene hydrocarbons serve as ideal starting materials for microbial transformations. Moreover, agro-industrial byproducts can be employed as nutrient and substrate sources, reducing fermentation costs, and enhancing industrial viability. Terpenes, being secondary metabolites of plants, are abundant in byproducts generated during fruit and plant processing. Microbial cells offer advantages over enzymes due to their higher stability, rapid growth rates, and genetic engineering potential. Fermentation parameters can be easily manipulated to enhance strain performance in large-scale processes. The economic advantages of biotransformation are highlighted by comparing the prices of substrates and products. For instance, R-limonene, priced at US$ 34/L, can be transformed into carveol, valued at around US$ 530/L. This review emphasises the potential of biotransformation to produce high-value products from limonene and α-pinene molecules, particularly present in wood residues and citrus fruit by-products. The utilisation of microbial transformations, along with agro-industrial byproducts, presents a promising approach to extract value from waste materials and enhance the sustainability of the antimicrobial, the fragrance and flavour industry.

Citrus derived Pickering emulsion stabilized by insoluble citrus dietary fiber modified by ultra-high pressure

To make the most of citrus residues, Pickering emulsions containing bergamot oil and medium chain triglyceride were formulated using insoluble citrus dietary fiber (ICDF) particles from citrus residues after pectin and essential oil were extracted. The ICDF particles were treated using ultra-high pressure (UHP, 100, 200, 300, 400, 500 and 600 MPa) to improve their emulsifying properties. UHP did not affect the composition of ICDFs. The treatments at 100 and 200 MPa decreased the ICDF particle size and promoted interfacial adsorption and network formation in the continuous phase, improving the emulsifying property and stability of the Pickering emulsion. This study would lay a foundation for the preparation of stable Pickering emulsions using citrus fibers and the comprehensive utilization of citrus residues.

Citrus fruit residues as alternative precursors to developing H2O and CO2 activated carbons and its application for Cu(II) adsorption.

Due to its toxicity, the presence of Cu(II) ions released in aquatic environments presents a serious threat to the environment and human health. In search of sustainable and low-cost alternatives, there are citrus fruit residues, which are generated in large quantities by the juice industries and can be used to produce activated carbons. Therefore, the physical route was investigated for producing activated carbons to reuse citrus wastes. In this work, eight activated carbons were developed, varying the precursor (orange peel-OP, mandarine peel-MP, rangpur lime peel-RLP, and sweet lime peel-SLP) and the activating agent (CO2 and H2O) to remove Cu(II) ions of the aqueous medium. Results revealed promising activated carbons with a micro-mesoporous structure, a specific surface area of around 400 m2g-1, and a pore volume of around 0.25 cm3g-1. In addition, Cu (II) adsorption was favored at pH 5.5. The kinetic study showed that the equilibrium was reached within 60min removing about 80% of Cu(II) ions. The Sips model was the most suitable for the equilibrium data, providing maximum adsorption capacities (qmS) values of 69.69, 70.27, 88.04, 67.83mgg-1 for activated carbons (AC-CO2) from OP, MP, RLP, and SLP, respectively. The thermodynamic behavior showed that the adsorption process of Cu(II) ions was spontaneous, favorable, and endothermic. It was suggested that the mechanism was controlled by surface complexation and Cu2+-π interaction. Desorption was possible with an HCl solution (0.5mol L-1). From the results obtained in this work, it is possible to infer that citrus residues could be successfully converted into efficient adsorbents to remove Cu(II) ions from aqueous solutions.

Ultra-Small Silver Nanoparticles: A Sustainable Green Synthesis Approach for Antibacterial Activity

The present study centers on the synthesis of ultra-small silver nanoparticles (AgNPs) with antibacterial properties using citrus peel residues (orange, lemon, and grapefruit) as reducing and stabilizing agents, and on assessing their antibacterial activity against multidrug-resistant clinical Staphylococcus aureus. The synthesized AgNPs were analyzed by various techniques, including UV-Vis spectroscopy, SAED, TEM, XRD, FTIR, and Raman. The results demonstrate the formation of ultra-small, monodisperse, quasi-spherical AgNPs with an average particle size of 2.42 nm for AgNPs produced with mixed extracts. XRD analysis indicated that the AgNPs have a crystal size of 9.71 to 16.23 nm. The AgNPs exhibited potent inhibitory activity against resistant S. aureus, with a minimum inhibitory concentration (MIC) of 15.625 to 62.50 ppm. The findings suggest that the ultra-small nanometer size of the AgNPs could be attributed to the synthesis method that employs ambient conditions and the presence of polyphenolic compounds from citrus peel. Consequently, AgNPs obtained through sustainable green synthesis hold significant potential in combating clinical multi-resistant bacterial strains that are challenging to treat and eradicate. This approach also contributes to the revaluation of citrus residues in the region, which is an ongoing environmental issue today.

Environmental performance of orange citrus waste as raw material for pectin and essential oil production

This study evaluated the potential environmental impact of the integrated extraction process of byproducts from orange processing, i.e., essential oil and pectin. A cradle-to-gate attributional Life Cycle Assessment was performed, considering 1 kg of pectin as the functional unit, following the ISO 14040/44 standards. The product system includes from the raw material (orange) to the stages to obtain the essential oil and pectin. The impact assessment considered eight categories from the ReCiPe Midpoint (H) v.1.02 method, using SimaPro® software as a supporting tool for modeling the product system. In addition, mathematical modeling was developed using Scilab 6.0.1 software seeking to discuss performance trade-offs versus environmental impact and process improvements. The impact assessment found that pectin production is the main hotspot, most attributed to the hydrolysis operating unit. Electricity, hydrochloric acid, and water consumption contributed most to negative environmental impacts. From the perspective of process modeling, the conventional temperature (373 K), the reduction of pH (pH=1.5), and the greater volume of water in the tank corresponded to the best effects in terms of yield, which is not necessarily related to the best environmental performance. The sensitivity analysis showed the best scenarios regarding environmental impacts correlating temperature with the energy source (SA1) and the pH with the acid used for the extraction (SA2). The analysis revealed that natural gas is the best alternative as an energy source, reducing emissions in six of the eight impact categories compared to the standard scenario. Citric acid increases emissions in all impact categories assessed due to the greater amount needed to achieve the simulated optimal extraction pH (1.5). The conventional scenario (hydrochloric acid) becomes the best alternative in this condition. These results bring a combined approach to life cycle sustainability with process modeling, identifying opportunities to improve the environmental performance of products based on citrus residues, contributing to the achievement of the 12th and 13th Sustainable Development Goals, and providing strategies to implement the Circular Economy in the citrus chain.

Insecticidal and antifungal effects of lemon, orange, and grapefruit peel essential oils from Argentina

The aim of the present work was to study the bioactivity of lemon, orange, and grapefruit peel essential oils (EOs) obtained from Argentinian plantations on different agronomically important insect and fungal species. The chemical profile of EOs was determined by Gas Chromatography-Mass Spectrometry (GC/MS); the insecticidal activity was studied through contact and fumigant assays; the antifungal activity was evaluated with fumigant tests. Orange EO was the most effective against Rhyzopertha dominica, Oryzaephilus spp. and Sitophilus granarius in fumigation tests (LC50= 89.39, 94.50, and 163.64 µL/L air, respectively); while the insecticidal effect of EOs was species-dependent in contact toxicity assays. Regarding antifungal activity, Rhizoctonia solanii was more susceptible than Sclerotium rolfsii to the tested EOs, with lemon from Industry 1 and orange being the most toxic EOs (MIC=10.77 µL/plate and 11.02 µL/plate, respectively). Conversely, S. rolfsii was strongly inhibited by lemon EO from Industry 2 (MIC= 52.40 µL/plate). Besides limonene, other compounds that could be responsible for these bioactivities were: linalool, carvone, α-pinene, β-pinene, β-myrcene, α-terpineol, terpinen-4-ol, limonene oxide, β-phellandrene, γ-terpinene, sabinene, neral, neryl acetate, β-caryophyllene and p-cymene. Citrus peel EOs can be used against different pests, contributing to the valorization of citrus residues.

Utilization of industrial citrus pectin side streams for enzymatic production of human milk oligosaccharides

This study reports the enzymatic upgrading of fucosylated xyloglucan from depectinized citrus residues into 2′-fucosyllactose, a fucosylated human milk oligosaccharide. Alkaline and enzymatic xyloglucan extractions were compared. Of the original fucose present in the depectinized residues of lemon and orange, 35–36% and 48–51% were extracted as fucosylated xyloglucan by enzyme- or alkaline treatment, respectively. Furthermore, the enzymatically extracted xyloglucan structures had a narrower molecular weight distribution around 1 kDa, contrary to a more polydisperse distribution of the alkaline extracted xyloglucans, ranging from 1 to 500 kDa. The applicability of the fucosylated-xyloglucan extracts in transfucosylation reactions, was determined by use of a selected fungal fucosidase, resulting in yields of 10.2–11.4% enzymatic extracts, and 6.5–7.4% for alkaline extracts (orange and lemon respectively). The results demonstrate that depectinized citrus side streams are a useful source of fucosylated xyloglucan, preferably extracted by an enzyme catalyzed approach.

Functionalization of pectin-depleted residue from different citrus by-products by high pressure homogenization

In the valorisation of fruit and vegetable by-products by high pressure homogenization (HPH) into texturizing ingredients, the source of the by-product is an important determining factor. This study aims to demonstrate the valorisation potential of citrus residues after acidic pectin extraction (AR) and to investigate differences between citrus species (lemon, orange, grapefruit) and fruit parts (peel and pulp) as the source of the residues. Based on the results, pectin extraction is favourable in improving the storage modulus (G′) of the residue. However, residual pectin content in the different ARs, as indicated by pectic monosaccharides (e.g., GalA, Rha, Fuc), did not correlate to G′ after HPH. The G′ of all ARs suspensions, regardless of the source, improved significantly after HPH at 20 MPa. After HPH, fragmentation and subsequently aggregation of particles were observed from the particle size reduction and microscopy visualization. Particle morphology and size did not correlate with the G′ of the suspensions. Residual pectin's Rhamnogalacturonan-I contribution and degree of methyl-esterification, protein content, and glucose content related to hemicellulose were correlated to the G′ of the suspensions before HPH. However, after HPH, no correlation was found between G′ and these characteristics, likely due to changes on the structure of the particles. The results highlight the high potential of all the citrus ARs from the different sources to be functionalized as texturizing ingredients. However, the peel AR from grapefruit and lemon exhibited better rheological properties and may be considered as better sources compared to the other citrus by-products.

Citrus flavonoids against Fusarium verticillioides in post-harvest maize: Minimization of fumonisins and alteration of fungal ultrastructure.

To minimize fumonisins (FBs) accumulation by Fusarium verticillioides in post-harvest maize, using flavonoids obtained from citrus residues: naringin (NAR), neohesperidin (NEO), quercetin (QUER), and its mixtures. Response surface methodology with Box-Behnken design was applied in maize at 0.98 and 0.95 aw . The optimal mixture found, composed of 0.40mmolkg-1 NAR, 0.16mmolkg-1 NEO and 0.37mmolkg-1 QUER, reduced the accumulation of FBs B1, B2, and B3 by 88±6%, 90±6% and 85±5%, respectively, when applied to maize at 0.98 aw . The mentioned mixture led to a 54±9% reduction of fumonisin B1 accumulation in maize adjusted to 0.95 aw . These flavonoids applied individually and as a mixture, affected the structure of both the cell wall and the cytoplasm of F. verticillioides. The cell wall lost rigidity and the cells appeared highly deformed, with ruptured plasmalemma and disrupted endomembranes. It was possible to diminish the accumulation of FBs in maize by a highly toxigenic Fusarium strain, producing severe damage to its ultrastructure. The results indicate the possible use of flavonoids from citrus industry residues as natural and environmentally friendly antifungal agents to restrain the accumulation of FBs in stored maize.

Anti-inflammatory and anti-aggregating effects of rangpur in the first trimester of growth: ultra-performance liquid chromatography-electrospray mass spectrometry profile and quantification of hesperidin.

Citrus fruits are a rich source of valuable molecules, and their industrial processing produces bagasses, little explored to generate important by-products. These Citrus residues, including seeds and peels, also contain numerous pharmacologically important substances. To reduce the impact of these Citrus by-products, young, harvested fruits could be used as a functional supplemental food while another part is grown until maturity for industrial production. This study therefore aims to valorize rangpur (Citrus limonia) in the first 3 months of its growth by investigating and comparing its monthly chemical profiles using ultra-performance liquid chromatography-electrospray mass spectrometry (UPLC-ESI-MS) and its anti-inflammatory and antiplatelet activity. Extracts obtained from the fruits harvested in November, December, and January, 2017 and 2018 (L221117, L161217, and L160118) showed different UPLC-ESI-MS profiles. Twenty-five of the 26 detected metabolites were identified as cyclitol, pyrrolidine betaine, aryl propanoyl esters, chlorogenic acids, flavonoids, coumarins, and limonoids. Quantification studies indicated an increased concentration of hesperidin from the younger fruits to the older fruits of the series. L160118 reduced nitrogen oxide (NOx), tumor necrosis factor alpha (TNF-α), and interleukin 6 (IL-6) levels more than other extracts. Their activity followed the same trends as the hesperidin concentration in each fruit. In contrast, the most promising antiplatelet activity was observed with the extracts from the two youngest fruits. This suggests combined effects of the chemical components found in these fruits' extracts. The extracts obtained from these young fruits showed considerable anti-inflammatory and antiplatelet activity. Overall, young rangpur could be used as raw material to produce functional foods without producing any waste. © 2022 Society of Chemical Industry.

Valorization of Hesperidin from Citrus Residues: Evaluation of Microwave-As

The aim of the current study was the valorization of hesperidin, the dominant flavonoid in citrus processing waste, by microwave-assisted synthesis of hesperidin-Mg complex, improving its antioxidant activity and insecticidal potential. Here we show, for the first time, that microwaveassisted synthesis of [Mg(hesp)2(phen)]OAc (1) (hesp: hesperidin, phen: phenanthroline) improve the reaction rate and yield. The nuclear magnetic resonance (NMR) experiments proved to be powerful tools for the identification of three isomers in metal complexes. Moreover, we explore the insecticidal potential of 1 and [Mg(phen)2(Isov)]OAc (2) (Isov : isovanillic acid) complexes against three insects. Complex 1 killed 80% of adults whitefly at 0.14 μmol L-1, and 2 76% at 0.36 μmol L-1. There was a total mortality of Spodoptera frugiperda with 2 at 0.39 μmol L-1, and 83% with 1 at 0.14 μmol L-1. Both have similar activity, and represent a novel group of insecticide for Bemisia tabaci and S. frugiperda; nevertheless, the benefits of both as Myzus persicae repellent require further evaluation.

The mealworm Tenebrio molitor (Coleoptera: Tenebrionidae) as a potential candidate to valorize crop residues

Agricultural activities generate important amount of crop residues that need to be managed in appropriate way usingecofriendly and cost effective tools. The mealworm Tenebrio molitor (Coleoptera: Tenebrionidae) is a potential candidate to valorize crop residues thatcan produce atthe same time an alternative feed based on insect larvae. Four crop residues (citrus, tomato, pepper and potato) mixedwith wheat bran (ratio 50:50) were evaluated as diets for mass rearing of T. molitor under controlled environmental conditions (T= 28 ± 1°C; RH=70 ± 5 % and total darkness). Five zootechnical parameters (weight gain, growth rate, mortality rate, weight of consumed feed and conversion rate) were adopted to evaluate thegrowth and life developmental traits of larvae during 45 days. The effect of crop residues used as diet had a significant impact on bothweight gain and growth rate. Importantly, crop residues used alone has a negative effect on all zootechnical parameters evaluated. Indeed, the amendment of wheat bran has a significant positive impact on these parameters. Citrus and tomato were the most toxic diets showing a mortality rate of 92 and 98 %, respectively. The most efficient diets werethe mixture of citrus residues andwheat branfollowed by the mixture of potato residues and wheat bran and the mixture ofpepper residues and wheat bran. Fed substrate had no impact on conversion rate.

On the basic chemical composition of selected biomass types from four regions of Mexico, for bioenergetic purposes

The chemical composition of hardwoods sawdust and citrus residues from four states of the Mexican Republic (Quintana Roo, Durango, Veracruz, and Sonora) were determined. The results ranged as follows: total extractives from 8.2% (Quercus spp.) to 35.0% (lime leaves), holocellulose from 45.4% (lime leaves) to 70.6% (Lysiloma latisiliquum), lignin from 3.9% (lemon peels) at 25.4% (Caesalpinia platyloba), ash from 0.4% (orange branches) to 6.3% (lemon peels), pH from 5.1 (Swartzia cubensis) to 7.3 (orange branches), and calorific value of 19.8 MJ/kg (Lysiloma latisiliquum and Quercus spp.) to 21.7 MJ/kg (Olneya tesota). With the exception of the oak samples, in all the biomass samples the extractives content is relatively high (10.1% for Lysiloma latisiliquum to 35% for Persian lime leaves), and could represent a potential for future study and applications in the field of antioxidants. Due to the chemical properties and calorific value, the biomass samples studied present potential for local use as densified biofuels (pellets or briquettes).

Modeling and cost analysis of drying of citrus residues as biomass in rotary dryer for bioenergy

The valorization of residues in any industrial processing activities aims at the reuse, recycling or composting of solid wastes, in such a way as to generate useful products or sources of energy. Citrus residues have been recognized as a promising biomass for renewable energy and liquid fuels. Drying is an interesting alternative to add value to solid waste, as long as it is economically viable, and one of the most important operations for efficient performance of the energy conversion technologies. In this work, a dynamic model of drying citrus residues in a rotating drum was developed and verified experimentally. From overall heat and mass balances, a series of perfectly stirred tanks was added together for each solid recycle and residence time in order to fully describe citrus solid wastes drying in the semi-industrial rotary drum. Process cost analysis was also performed to assess the most suitable drying level to balance process costs with the biomass quality in terms of the moisture content. Results showed that the model performed reasonably well so that simulation and measurements were in good agreement to be part of process optimization strategies.

Microbial Succession and Identification of Effective Indigenous Pectinolytic Yeasts From Orange Juice Processing Wastewater

Although the management of citrus residues is of concern, their valorization is a challenging alternative. In this work, raw orange juice processing wastewater was spontaneously fermented to determine the succession in microbial communities and identify new indigenous microbial strains of high pectinolytic activity. Pectinolytic strains were isolated using citrus pectin as growth substrate. A shift in fungal population observed during spontaneous fermentation, where the abundances of Hanseniaspora, Cystofilobasidium and Meyerozyma were significantly increased, whereas Pichia fermentans followed by Saccharomyces spp. became the predominant taxa in the fermented wastewater. A significant reduction in the relative abundance of homofermentative aerococci and an increase in the relative abundance of heterofermentative leuconostocs and lactobacilli occurred during fermentation, while enterococci were predominant throughout the fermentation process. Regarding ecological indices, opposite changes took place in the bacterial compared to fungal community structure, but in a less pronounced degree. Examination of beta-diversity revealed the key role of Pichia species in driving fungal community structure during fermentation. P. fermentans, the predominant taxon in the fermented wastewater, was found to be the most effective pectinolytic microorganism. Pectin hydrolysis, carbohydrate fermentation to ethanol, lactic acid and acetate, and citric acid fermentation were the most important factors, influencing microbial community structure.

Characterization of Mexican waste biomass relative to energy generation

In this work, physical and chemical analyses of 28 sawdust samples (tropical woods, pine woods, and oak woods) derived from the primary process of wood transformation and 4 samples of citrus residues were performed, as an option to make densified biofuels. The study included the determination of initial moisture, particle size distribution, proximate analysis, ultimate analysis, calculation of the calorific value, and ash microanalysis. The initial moisture content of the biomass samples ranged from 6.04 to 75.21%. The biomass granulometry results indicate that the highest proportion corresponds to the 1.0-mm (33.10%) (Fraction retained in mesh 0.5 mm). Other results obtained indicate the following ranges: ash content (0.27 to 6.27%), volatile matter (78.90 to 90.50%), fixed carbon (9.10 to 20.44%), carbon (49.13 to 50.78%), oxygen (42.62 to 44.49%), and hydrogen (5.24 to 6.55%). The calculated calorific value ranged from 17.65 MJ/kg to 20.72 MJ/kg. The chemical elements with the highest concentration in the biomass samples were K and Ca, followed in some cases by Al and P. The biomass with the greatest possibilities for making densified biofuels of better quality is the group of pine woods because they have low mineral content, low nitrogen content, and high calorific value.