Citric acid bioproduction and downstream processing: Status, opportunities, and challenges

Optimizing broiler growth, health, and meat quality with citric acid- assessing the optimal dose and environmental impact: Citric acid in Broiler Health and Production

The need for sustainable and safe alternatives to antibiotic growth promoters has driven researchers to explore organic acids (OAs) inclusion in broiler diets. Citric acid (CA), a notable OA, has emerged as a promising alternative due to its various physiological benefits, including improved nutrient digestibility, antioxidant properties, and enhanced weight gain. Despite the improved growth performance, the feed conversion ratio (FCR) does not seem to be consistently affected by CA inclusion. A considerable number of research papers suggest that CA can replace antibiotic growth promoters and has proved to be more effective when combined with other additives like probiotics and microbial phytase. However, despite numerous trials, the near-accurate dose remains in doubt. Dietary addition between 1.65 % and 2.65 % seems to positively affect broiler performance. Being an organic acid, CA brings no risk to the environment and does not economically burden producers. It has the capability to enhance certain meat qualities and extend shelf life. However, there is a risk of acidic stress and liver damage with excessive inclusion. This review study seeks to offer a thorough and all-encompassing summary of the present level of understanding regarding the use of CA supplementation in broiler diets by describing its impacts on growth efficiency, nutrient utilization, intestinal condition, immune response, meat quality, optimal dose, and environmental sustainability. Further research focused on determining precise dosage levels and understanding the synergistic or antagonistic effects of citric acid when combined with other feed additives is essential for optimizing broiler performance.

Bioleaching of rare earth elements from ores and waste materials: Current status, economic viability and future prospects

Rare earth elements (REEs) are critical components of numerous products widely used in many areas, and the demand for REEs is increasing dramatically in recent years. Physical-chemical leaching is commonly adopted for the recovery of REEs from ores and solid wastes, but concerns over the generation of hazards, operation safety, and environmental pollution have urged the transition to greener and more sustainable leaching methods. Bioleaching is considered an excellent alternative for the recovery of REEs. This review provided an overview on the REEs recovery from primary and secondary resources via different bioleaching strategies. The techno-economics of bioleaching for REEs recovery were highlighted, and key factors affecting the economic viability of bioleaching were identified. Finally, strategies including the utilization of low-cost substrates as feedstocks, non-sterile bioleaching, recycling and reutilization of biolixiviants, and development of robust bioleaching strains were proposed to improve the economic competitiveness of bioleaching. It is expected that this review could serve as a useful guideline on the design of more economically competitive bioleaching processes for the recovery REEs from different resources.

Effect of Citric Acid Hard Anodizing on the Mechanical Properties and Corrosion Resistance of Different Aluminum Alloys

Hard anodizing is used to improve the anodic films' mechanical qualities and aluminum alloys' corrosion resistance. Applications for anodic oxide coatings on aluminum alloys include the space environment. In this work, the aluminum alloys 2024-T3 (Al-Cu), 6061-T6 (Al-Mg-Si), and 7075-T6 (Al-Zn) were prepared by hard anodizing electrochemical treatment using citric and sulfur acid baths at different concentrations. The aim of the work is to observe the effect of citric acid on the microstructure of the substrate, the mechanical properties, the corrosion resistance, and the morphology of the hard anodic layers. Hard anodizing was performed on three different aluminum alloys using three citric-sulfuric acid mixtures for 60 min and using current densities of 3.0 and 4.5 A/dm2. Vickers microhardness (HV) measurements and scanning electron microscopy (SEM) were utilized to determine the mechanical characteristics and microstructure of the hard anodizing material, and electrochemical techniques to understand the corrosion kinetics. The result indicates that the aluminum alloy 6061-T6 (Al-Mg-Si) has the maximum hard-coat thickness and hardness. The oxidation of Zn and Mg during the anodizing process found in the 7075-T6 (Al-Zn) alloy promotes oxide formation. Because of the high copper concentration, the oxide layer that forms on the 2024-T6 (Al-Cu) Al alloy has the lowest thickness, hardness, and corrosion resistance. Citric and sulfuric acid solutions can be used to provide hard anodizing in a variety of aluminum alloys that have corrosion resistance and mechanical qualities on par with or better than traditional sulfuric acid anodizing.

Study on the mechanism of sodium ion inhibiting citric acid fermentation in Aspergillus niger

Excessive sodium significantly inhibits citric acid fermentation by Aspergillus niger during the recycling of citric acid wastewater. This study aimed to elucidate the inhibition mechanism at the interface of physiology and transcriptomics. The results showed that excessive sodium caused a 22.3 % increase in oxalic acid secretion and a 147.6 % increase in H+-ATPase activity at the 4 h fermentation compared to the control. Meanwhile, a 13.1 % reduction in energy charge level and a 15.2 % decline in NADH content were found, which implied the effects on carbon metabolism and redox balance. In addition, transcriptomic analysis revealed that excessive sodium altered the gene expression profiles related to ATPase, hydrolase, and oxidoreductase, as well as pathways like glyoxylate metabolism, and transmembrane transport. These findings gained insights into the metabolic regulation of A. niger response to environmental stress and provided theoretical guidance for the construction of sodium-tolerant A. niger for industrial application.

Citric Acid: Properties, Microbial Production, and Applications in Industries

Citric acid finds broad applications in various industrial sectors, such as the pharmaceutical, food, chemical, and cosmetic industries. The bioproduction of citric acid uses various microorganisms, but the most commonly employed ones are filamentous fungi such as Aspergillus niger and yeast Yarrowia lipolytica. This article presents a literature review on the properties of citric acid, the microorganisms and substrates used, different fermentation techniques, its industrial utilization, and the global citric acid market. This review emphasizes that there is still much to explore, both in terms of production process techniques and emerging new applications of citric acid.

Simultaneous reuse and treatment of sugar-sweetened beverage wastes for citric acid production

This study aimed to evaluate the feasibility of using sugar-sweetened beverages (SSB) for citric acid (CA) production and its impact on chemical oxygen demand (COD) of SSB. Five types of SSB were used as a carbon source for CA production by A. niger, and the COD of each SSB was measured before and after the bioprocess. Results showed that all tested SSB were suitable for CA production, with maximum yields ranging from 13.01 to 56.62 g L- 1. The COD was reduced from 53 to 75.64%, indicating that the bioprocess effectively treated SSB wastes. The use of SSB as a substrate for CA production provides an alternative to traditional feedstocks, such as sugarcane and beet molasses. The low-cost and high availability of SSB makes it an attractive option for CA production. Moreover, the study demonstrated the potential of the bioprocess to simultaneously treat and reuse SSB wastes, reducing the environmental impact of the beverage industry.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05761-9.

Metabolic engineering and fermentation optimization strategies for producing organic acids of the tricarboxylic acid cycle by microbial cell factories

The organic acids of the tricarboxylic acid (TCA) pathway are important platform compounds and are widely used in many areas. The high-productivity strains and high-efficient and low-cost fermentation are required to satisfy a huge market size. The high metabolic flux of the TCA pathway endows microorganisms potential to produce high titers of these organic acids. Coupled with metabolic engineering and fermentation optimization, the titer of the organic acids has been significantly improved in recent years. Herein, we discuss and compare the recent advances in synthetic pathway engineering, cofactor engineering, transporter engineering, and fermentation optimization strategies to maximize the biosynthesis of organic acids. Such engineering strategies were mainly based on the TCA pathway and glyoxylate pathway. Furthermore, organic-acid-secretion enhancement and renewable-substrate-based fermentation are often performed to assist the biosynthesis of organic acids. Further strategies are also discussed to construct high-productivity and acid-resistant strains for industrial large-scale production.

Gustatory stimulus interventions for older adults with dysphagia: a scoping review

BACKGROUND

Gustatory stimulus interventions have been shown to improve swallowing function in older adults with dysphagia. However, the optimal intervention strategies as well as their effects and safety remain unclear.

AIMS

To explore current evidence regarding gustatory stimulus interventions for dysphagia in older adults.

METHODS

Nine electronic databases (PubMed, Web of Science, Embase, CINAHL, Cochrane Library, China National Knowledge Infrastructure, Wanfang Database, China Science and Technology Journal Database, and Sinomed) were searched from their inception to August 2022.

RESULTS

This review identified 263 articles, and 15 met the inclusion criteria. The types of gustatory stimulus interventions included spicy (n = 10), sour (n = 3), and mixed (sour-sweet) stimuli (n = 2), with most studies focusing on spicy stimuli. The most frequently reported spicy stimulus was capsaicin. Further, the most commonly reported intervention frequency was thrice a day before meals for 1-4 weeks. The stimuli concentrations and dosages could not be standardized due to the among-study heterogeneity. These studies reported 16 assessment tools and 42 outcomes, which mainly included videofluoroscopy and swallowing response time respectively. More than half of the included studies reported no adverse effects of gustatory stimulus interventions.

CONCLUSION AND DISCUSSIONS

Gustatory stimulus interventions improved swallowing function in older adults with dysphagia. However, assessment tools and outcomes for dysphagia should be standardized in the future, and explore personalized interventions based on different diseases and their stages, to determine the most cost-effective interventions, and to prevent its complications.

An innovative and efficient hydrogen peroxide-citric acid pretreatment of bamboo residues to enhance enzymatic hydrolysis and ethanol production

Organic peracids has attracted widespread attention from researchers in biomass pretreatment. As a weak acid with high production, low price and toxicity, citric acid (CA) was mixed with hydrogen peroxide at the room temperature to generate peroxy-citric acid with strong oxidative functions. An innovative and efficient pretreatment method using peroxy-citric acid (HPCA) was proposed to enhance enzymatic hydrolysis and bioethanol production of bamboo residues. After D. giganteus (DG) was pretreated with HPCA at 80 °C for 3 h, lignin of 95.36% and xylan of 55.41% was effectively removed, and the enzymatic saccharification yield of HPCA-treated DG enhanced by about 8-9 times compared with CA pretreated DG. The ethanol recovery of 17.18 g/L was achieved. This work provided a reference for the mild biomass pretreatment, which will promote the large-scale application of organic peracids system in biorefinery processes.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Formulation improvement of a concentrated enzyme detergent for high-speed rail trains through life cycle assessment methodology

High-speed rail has been operating in more than 25 countries (mainly in Asia, Europe and North America), and has become an important part of global economic development. However, the cleaning and maintenance of high-speed rail is a comprehensive task, which may easily cause environmental pollution. This study aims to analyze and improve the sustainability of the formulation and production process of a concentrated complex enzyme detergent used as the maintenance agent for high-speed trains via the life cycle assessment (LCA) method. The eFootprint software system with built-in China, European and Swiss Ecoinvent databases was used to establish the LCA model with the system boundary being from cradle to gate. The LCA model showed that the production of 1 kg of concentrated detergent generates the global warming potential of 2.53 kg CO2 eq, and other environmental emissions including acidification potential of 0.01 kg SO2 eq, eutrophication potential of 3.76E-03 kg PO43-eq, inhalable inorganic matter of 3.17E-03 kg PM2.5 eq, ozone depletion potential of 5.3E-06 kg CFC-11 eq, photochemical ozone formation potential of 3.44E-03 kg NMVOC eq, primary energy demand of 3.17 MJ, abiotic depletion potential of 4.97E-6 kg antimony eq, and water use of 0.84 kg. LCA results are not strongly dependent to the assumptions of the research, and the uncertainties of LCA results are between 8 and 16%, which is mainly due to the regional differences in technology sources, the year of technical data collection, and the representativeness of technology collection companies. Carbon footprint analysis showed that the production processes of enzyme stabilizer (glycerol) and surfactants contributed the most, while changes in power consumption during production and transportation distance of raw materials had limited effect on total carbon emissions. Therefore, the formulation of the concentrated complex enzymatic detergent was improved based on the LCA results. The new formulations with less enzyme stabilizer showed similar detergency to the original formulation. The new formulations could reduce carbon emissions by 5,500-9,200 tons per year and save between $4.4 and $7.4 million in annual production of 10,000 tons.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-023-03122-2.

Use of Pressurized and Airlift Bioreactors for Citric Acid Production by Yarrowia lipolytica from Crude Glycerol

Citric acid production is generally carried out in an aqueous medium in stirred tank reactors (STR), where the solubility of oxygen is low and the oxygen demand of microbial cultures is high. Thus, for this bioprocess, providing adequate oxygen mass transfer rate (OTR) from the gas phase into the aqueous culture medium is the main challenge of bioreactor selection and operation. In this study, citric acid production by Yarrowia lipolytica W29 from crude glycerol, in batch cultures, was performed in two non-conventional bioreactors normally associated with high mass transfer efficiency: a pressurized STR and an airlift bioreactor. Increased OTR was obtained by raising the total air pressure in the pressurized STR and by increasing the aeration rate in the airlift bioreactor. An improvement of 40% in maximum citric acid titer was obtained by raising the air pressure from 1 bar to 2 bar, whereas, in the airlift bioreactor, a 30% improvement was attained by increasing the aeration rate from 1 vvm to 1.5 vvm. Both bioreactor types can be successfully applied for the citric acid production process using alternative ways of improving OTR than increasing mechanical stirring power input, thus leading to important operating saving costs.

Valorisation Potential of Invasive Acacia dealbata, A. longifolia and A. melanoxylon from Land Clearings

Acacia spp. are invasive in Southern Europe, and their high propagation rates produce excessive biomass, exacerbating wildfire risk. However, lignocellulosic biomass from Acacia spp. may be utilised for diverse biorefinery applications. In this study, attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR), high-performance anion-exchange chromatography pulsed amperometric detection (HPAEC-PAD) and lignin content determinations were used for a comparative compositional characterisation of A. dealbata, A. longifolia and A. melanoxylon. Additionally, biomass was treated with three white-rot fungi species (Ganoderma lucidum, Pleurotus ostreatus and Trametes versicolor), which preferentially degrade lignin. Our results showed that the pre-treatments do not significantly alter neutral sugar composition while reducing lignin content. Sugar release from enzymatic saccharification was enhanced, in some cases possibly due to a synergy between white-rot fungi and mild alkali pretreatments. For example, in A. dealbata stems treated with alkali and P. ostreatus, saccharification yield was 702.3 nmol mg^-1, which is higher than the samples treated only with alkali (608.1 nmol mg^-1), and 2.9-fold higher than the non-pretreated controls (243.9 nmol mg^-1). By characterising biomass and pretreatments, generated data creates value for unused biomass resources, contributing to the implementation of sustainable biorefining systems. In due course, the generated value will lead to economic incentives for landowners to cut back invasive Acacia spp. more frequently, thus reducing excess biomass, which exacerbates wildfire risk.

Identification and genetic characterization of mitochondrial citrate transporters in Aspergillus niger

Aspergillus niger is a major cell factory for citric acid production, and the process of citrate export from mitochondria to cytoplasm is predicted to be one of rate-limiting steps in citric acid accumulation. Currently, the mitochondrial citrate transporters (Ctps) in A. niger are not fully characterized. Here, six putative Ctp encoding genes (ctpA to ctpF) were identified based on their homology with a mitochondrial citrate transporter ScCtp1 from Saccharomyces cerevisiae. Disruption of individual ctpA to ctpF caused varying degrees of decline in citric acid accumulation at different fermentation stages, whereas a mutant strain S1696 with disruption of all six ctps showed complete loss of citiric acid production. S1696 also exhibited delayed growth, reduced conidia formation, and decreased pigmentogenesis. Exogenous addition of citrate partially restored the conidia formation and pigmentogenesis in S1696 mutant. Reintroduction of individual ctps (ctpA to ctpF) into S1696 at the amyA locus showed that ctpA, ctpB, and ctpD restored the citric acid titers to 88.5, 93.8, and 94.6% of the parent strain, respectively. Additionally, the formation of conidia and pigment production was partially restored after reintroduction of ctpA, ctpB, or ctpD. Overexpression of respective ctpA, ctpB, and ctpD in the parent strain resulted in increases in citric acid accumulation by 32.8, 19.3, and 24.2%, respectively. These results demonstrate that CtpA, CtpB, and CtpD play important roles in citric acid transport across the mitochondrial membrane and function in a redundant manner. Enhancement of citric acid transport process can serve as a target for boosting citric acid accumulation in A. niger.

Bioreactor as the root cause of the “manganese effect” during Aspergillus niger citric acid fermentations

High-yield citric acid production by the filamentous Ascomycete fungus Aspergillus niger requires a combination of extreme nutritional conditions, of which maintaining a low manganese (II) ion concentration (<5 μg L⁻¹) is a key feature. Technical-scale production of citric acid predominantly uses stainless-steel tank fermenters, but glass bioreactors used for strain improvement and manufacturing process development also contain stainless steel components, in which manganese is an essential alloying element. We show here that during citric acid fermentations manganese (II) ions were leaching from the bioreactor into the growth media, resulting in altered fungal physiology and morphology, and significant reduction of citric acid yields. The leaching of manganese (II) ions was dependent on the fermentation time, the acidity of the culture broth and the sterilization protocol applied. Manganese (II) ion leaching was partially mitigated by electrochemical polishing of stainless steel components of the bioreactor. High concentrations of manganese (II) ions during early cultivation led to a reduction in citric acid yield. However, the effect of manganese (II) ions on the reduction of citric acid yield diminished towards the second half of the fermentation. Since maintaining low concentrations of manganese (II) ions is costly, the results of this study can potentially be used to modify protocols to reduce the cost of citric acid production.

Impact of the Cooking Process on Metabolite Profiling of Acanthocereus tetragonus, a Plant Traditionally Consumed in Mexico

Acanthocereus tetragonus (L.) Hummelinck is used as an alternative food source in some Mexican communities. It has been shown that the young stems of A. tetragonus provide crude protein, fiber, and essential minerals for humans. In this work, we analyzed the phytochemical profile, the total phenolic content (TPC), and the antioxidant activity of cooked and crude samples of A. tetragonus to assess its functional metabolite contribution to humans. The phytochemical profile was analyzed using Ultra-High-Performance Liquid Chromatography coupled to High-Resolution Mass Spectrometry (UHPLC-PDA-HESI-Orbitrap-MS/MS). Under the proposed conditions, 35 metabolites were separated and tentatively identified. Of the separated metabolites, 16 occurred exclusively in cooked samples, 6 in crude samples, and 9 in both crude and cooked samples. Among the detected compounds, carboxylic acids, such as threonic, citric, and malic acids, phenolic acids, and glycosylated flavonoids (luteolin-O-rutinoside) were detected. The TPC and antioxidant activity were analyzed using the Folin–Ciocalteu method and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical inhibition method, respectively. The TPC and antioxidant activity were significantly reduced in the cooked samples. We found that some metabolites remained intact after the cooking process, suggesting that A. tetragonus represents a source of functional metabolites for people who consume this plant species.

Torulaspora delbrueckii Phenotypic and Metabolic Profiling towards Its Biotechnological Exploitation

Wine is a particularly complex beverage resulting from the combination of several factors, with yeasts being highlighted due to their fundamental role in its development. For many years, non-Saccharomyces yeasts were believed to be sources of spoilage and contamination, but this idea was challenged, and many of these yeasts are starting to be explored for their beneficial input to wine character. Among this group, Torulaspora delbrueckii is gaining relevance within the wine industry, owing to its low volatile acidity production, increased release of aromatic compounds and enhanced color intensity. In addition, this yeast was also attracting interest in other biotechnological areas, such as bread and beer fermentation. In this work, a set of 40 T. delbrueckii strains, of varied geographical and technological origins, was gathered in order to characterize the phenotypic behavior of this species, focusing on different parameters of biotechnological interest. The fermentative performance of the strains was also evaluated through individual fermentations in synthetic grape must with the isolates’ metabolic profile being assessed by HPLC. Data analysis revealed that T. delbrueckii growth is significantly affected by high temperature (37 °C) and ethanol concentrations (up to 18%), alongside 1.5 mM SO₂, showing variable fermentative power and yields. Our computation models suggest that the technological origin of the strains seems to prevail over the geographical origin as regards the influence on yeast properties. The inter-strain variability and profile of the products through the fermentative processes reinforce the potential of T. delbrueckii from a biotechnological point of view.

State of the Art on the Microbial Production of Industrially Relevant Organic Acids

The industrial relevance of organic acids is high; because of their chemical properties, they can be used as building blocks as well as single-molecule agents with a huge annual market. Organic acid chemical platforms can derive from fossil sources by petrochemical refining processes, but most of them also represent natural metabolites produced by many cells. They are the products, by-products or co-products of many primary metabolic processes of microbial cells. Thanks to the potential of microbial cell factories and to the development of industrial biotechnology, from the last decades of the previous century, the microbial-based production of these molecules has started to approach the market. This was possible because of a joint effort of microbial biotechnologists and biochemical and process engineers that boosted natural production up to the titer, yield and productivity needed to be industrially competitive. More recently, the possibility to utilize renewable residual biomasses as feedstock not only for biofuels, but also for organic acids production is further augmenting the sustainability of their production, in a logic of circular bioeconomy. In this review, we briefly present the latest updates regarding the production of some industrially relevant organic acids (citric fumaric, itaconic, lactic and succinic acid), discussing the challenges and possible future developments of successful production.

Recent Advances in Environmentally Friendly and Green Degumming Processes of Silk for Textile and Non-Textile Applications

Silk has been widely used not only in the textile field but also in non-textile applications, which is composed of inner fibrous protein, named fibroin, and outer global protein, named sericin. Due to big differences, such as appearance, solubility, amino acid composition and amount of reactive groups, silk fibroin and sericin usually need to be separated before further process. The residual sericin may influence the molecular weight, structure, morphology and properties of silk fibroin, so that degumming of silk is important and necessary, not only in textile field but also in non-textile applications. Traditional textile degumming processes, including soap, alkali or both, could bring such problems as environmental damage, heavy use of water and energy, and damage to silk fibroin. Therefore, this review aims to present a systematic work on environmentally friendly and green degumming processes of raw silk, including art of green degumming process, quantitative and qualitative evaluation, influence of degumming on molecular weight, structure, morphology and properties of silk. It is anticipated that rational selection and design of environmentally friendly and green degumming process is quite important and meaningful, not only for textile application but also for non-textile application.

Advances in downstream processes and applications of biological carboxylic acids derived from organic wastes

Recovering carboxylic acids derived from organic wastes from fermentation broth is challenging. To provide a reference for future study and industrial application, this review summarized recent advances in recovery technologies of carboxylic acids including precipitation, extraction, adsorption, membrane-based processes, etc. Meanwhile, applications of recovered carboxylic acids are summarized as well to help choose suitable downstream processes according to purity requirement. Integrated processes are required to remove the impurities from the complicated fermentation broth, at the cost of loss and expense. Compared with chemical processes, biological synthesis is better options due to low requirements for the substrates. Generally, the use of toxic agents, consumption of acid/alkaline and membrane fouling hamper the sustainability and scale-up of the downstream processes. Future research on novel solvents and materials will facilitate the sustainable recovery and reduce the cost of the downstream processes.

Conversion of Calcium Citrate to Citric Acid with Compressed CO2

Citric acid is mainly produced in the fermentation industry, which needs complex processes and produces a high amount of CaSO₄ as waste. In this study, CO₂ has been used to convert calcium citrate to citric acid and CaCO₃ by controlling the reaction parameters (reactants ratio, temperature, and pressure). The CaCO₃ produced in this conversion could further be used in the fermentation industry for citric acid production. The transformation condition has been optimized by controlling temperature, pressure, reaction time, and mass ratio of calcium citrate and water. The highest conversion could reach up to 94.7% under optimal experimental conditions of 18 MPa of pressure, 65 °C of reaction temperature, 4 h of reaction time, and 2 g/L of calcium citrate/water suspension solution. This method features simple process, easy separation of citric acid, and environmentally friendly process, which could be a potentially alternative route for downstream treatment in fermentation production of citric acid.

Added-value biomolecules' production from cocoa pod husks: A review

Cocoa beans are produced through on-farm processing where residual biomass is discarded, including cocoa pod husks (CPH), cocoa bean shells and cocoa sweatings. CPH represents about 80% of these residues that are generated during the initial cocoa bean processing steps and their disposal occupies large areas, causing social and environmental concerns. In the last decades, the lignocellulosic composition of CPH has attracted the attention of the scientific and productive sector. Recently, some studies have reported the use of CPH in the production of medium to high value-added molecules, with potential applications in food and feed, agriculture, bioenergy, and other segments. This review presents biotechnological approaches and processes for the exploitation of CPH, including pre-treatment methods for the production of different biomolecules. Great perspectives and innovations were found concerning CPH exploitation and valorisation, but still more efforts are needed to valorise this potential feedstock and give support to producers in-development countries.

Citric acid assisted hydrothermal pretreatment for the extraction of pectin and xylooligosaccharides production from cocoa pod husks

The main purpose of this work was the development of a new citric acid assisted hydrothermal pretreatment of cocoa pod husks (CPH), which has not yet been exploited for pectin recovery. CPH́s pectin recovery was improved with concomitant production of xylooligosaccharides (XOS) through efficient enzymatic hydrolysis of the solid fraction. A central composite experimental design was planned to analyze the effect of pretreatment conditions. Under optimal conditions at 120 °C, 10 min and 2% w.v^-1, the recovery of pectin accounted for 19.3% of the biomass submitted to pretreatment with 52.2% of methyl esterification degree. Additionally, 51.9 mg.g^-1 of XOS were also produced. The enzymatic conversion efficiency of the cellulosic fraction was 58.9%, leading to a production of 92.4 kg of glucose per ton of CPH. Great perspectives were observed in the implementation of CPH hydrothermal pretreatment for the production of value-added biomolecules under a biorefinery concept.

Silk Fibroin as a Green Material

Silk fibroin has been explored as a suitable biomaterial due to its biocompatibility, tunable degradability, low toxicity, and mechanical properties. To harness silk fibroin's innate properties, it is purified from native silkworm cocoons by removing proteins and debris that have the potential to cause inflammatory responses. Typically, within the purification and fabrication steps, chemical solvents, energy-intensive equipment, and large quantities of water are used to reverse engineer silk fibroin into an aqueous solution and then process into the final material format. Gentler, green methods for extraction and fabrication have been developed that reduce or remove the need for harmful chemical additives and energy-inefficient equipment while still producing mechanically robust biomaterials. This review will focus on the alternative green processing and fabrication methods that have proven useful in creating silk fibroin materials for a range of applications including consumer and medical materials.