Industrial Side Streams Research Articles

Wood hemicelluloses as protective materials for preserving the viability of probiotic Lacticaseibacillus rhamnosus GG during spray drying

Wood hemicelluloses from forest industry side-streams are promising economic and sustainable alternatives for encapsulating bioactive compounds. This study explores their suitability for probiotic encapsulation, specifically for maintaining cell viability and structure. The ability of galactoglucomannans (GGM) and glucuronoxylans (GX) to support the survival of Lacticaseibacillus rhamnosus GG (LGG) during spray drying at solid feed concentrations of 15 and 20 % and inlet air temperatures of 105 and 140 °C (outlet air temperature of 50 °C) was investigated and compared to the results obtained using maltodextrin (MD). Across all investigated conditions, LGG survival rates exceeded 85 % (>107 cfu/g) in GX and GGM microcapsule powders, which similar to that in MD microcapsules despite the differences in pH, particle size, and viscosity of their feed dispersions. The GX microcapsules demonstrated the highest process yield (50–58 %), followed by MD (39–51 %). All the microcapsule powders exhibited an amorphous structure consisting of spherical particles with an average diameter of 10 μm, sufficient for LGG accommodation. Atomic force microscopy analysis confirmed the encapsulation of LGG cells within microcapsules with intact rod-shaped chains post-spray drying. Overall, the spray-dried microencapsulation of probiotics using wood hemicelluloses maintains high probiotic viability and offers an eco-friendly, cost-effective alternative to traditional materials.

Turning trash into treasure: Hermetia illucens microbiome and biodegradation of industrial side streams.

Organic side streams from various industries pose a challenge to the environment. They are often present in huge amounts and are mostly discarded, incinerated, used for biogas production, or as feed for ruminant animals. Many plant-based side streams contain difficult-to-digest fiber as well as anti-nutritional or even insecticidal compounds that could harm the animals. These challenges can be addressed using black soldier fly larvae, which are known to degrade various organic substrates and convert them into valuable biomass. This will help mitigate agro-industrial side streams via efficient waste management and will contribute to the more economical and sustainable farming of insects.

Potato and dairy industry side streams as feedstock for fungal and plant cell cultures

Utilization of industrial side streams as nutrient source for cellular agriculture is a promising option to improve the sustainability of the production processes. The aim of the study was to evaluate usability of two liquid food industry side streams, potato cell fluid and acid whey, as nutrient source for production of food ingredients with plant cell cultures (arctic bramble (Rubus arcticus L.) and tobacco BY-2 (Nicotiana tabacum L.)) and filamentous fungi (Paecilomyces variotii, Rhizopus oligosporus and Trichoderma reesei). The side streams were found to contain various sugars and other potential nutrients suitable for the studied organisms. The side streams were used as a sole nutrient source (fungi) or as a replacement of selected nutrients in the growth media (fungi and plant cells) in flask scale cultivations. Acid whey was successfully used as a growth medium for filamentous fungi, but it inhibited plant cell growth presumably due to high organic acid content (14 g/l). Potato side stream was found suitable as a fungal and plant cell growth media supplement, and it was used together with glucose for filamentous fungi, or as a partial replacer of macronutrients for plant cells, in bioreactor cultivations yielding high fungal (up to 36 g/l dry weight) and good plant cell (9.5 g/l dry weight) biomass production. Analyses of the produced biomasses revealed good nutritional value in terms of amino acid (17–27 % of dry matter) and dietary fiber (23–30 % of dry matter) contents, giving good premises for utilization in human nutrition.

Variability in n-caprylate and n-caproate producing microbiomes in reactors with in-line product extraction.

Medium-chain carboxylates (MCCs) are used in various industrial applications. These chemicals are typically extracted from palm oil, which is deemed not sustainable. Recent research has focused on microbial chain elongation using reactors to produce MCCs, such as n-caproate (C6) and n-caprylate (C8), from organic substrates such as wastes. Even though the production of n-caproate is relatively well-characterized, bacteria and metabolic pathways that are responsible for n-caprylate production are not. Here, three 5 L reactors with continuous membrane-based liquid-liquid extraction (i.e., pertraction) were fed ethanol and acetate and operated for an operating period of 234 days with different operating conditions. Metagenomic and metaproteomic analyses were employed. n-Caprylate production rates and reactor microbiomes differed between reactors even when operated similarly due to differences in H2 and O2 between the reactors. The complete reverse β-oxidation (RBOX) pathway was present and expressed by several bacterial species in the Clostridia class. Several Oscillibacter spp., including Oscillibacter valericigenes, were positively correlated with n-caprylate production rates, while Clostridium kluyveri was positively correlated with n-caproate production. Pseudoclavibacter caeni, which is a strictly aerobic bacterium, was abundant across all the operating periods, regardless of n-caprylate production rates. This study provides insight into microbiota that are associated with n-caprylate production in open-culture reactors and provides ideas for further work.IMPORTANCEMicrobial chain elongation pathways in open-culture biotechnology systems can be utilized to convert organic waste and industrial side streams into valuable industrial chemicals. Here, we investigated the microbiota and metabolic pathways that produce medium-chain carboxylates (MCCs), including n-caproate (C6) and n-caprylate (C8), in reactors with in-line product extraction. Although the reactors in this study were operated similarly, different microbial communities dominated and were responsible for chain elongation. We found that different microbiota were responsible for n-caproate or n-caprylate production, and this can inform engineers on how to operate the systems better. We also observed which changes in operating conditions steered the production toward and away from n-caprylate, but more work is necessary to ascertain a mechanistic understanding that could be predictive. This study provides pertinent research questions for future work.

Antioxidant Marine Hydrolysates Isolated from Tuna Mixed Byproducts: An Example of Fishery Side Streams Upcycling.

The aim of this research is to propose simple and scalable processes to obtain bioactive peptides extensively hydrolyzed starting from a tuna mixed biomass. The upcycling of this powdered biomass is challenging since it comes from the unsorted industrial side streams of the tuna canning process (cooked residues from fillet trimming) after a patented mild dehydration useful for preventing its degradation until its exploitation. Two different protocols were proposed, with and without the inclusion of an exogenous enzyme (Enzymatic-Assisted Extraction, EAE), with no relevant differences in yields (24% vs. 22%) and a comparable amino acid composition. Nevertheless, the former protocol (with EAE) provided peptides with an average molecular weight of 1.3 kDa, and the second one (without EAE) provided peptides with an average molecular weight of 2.2 kDa. The two corresponding types of tuna protein hydrolysates (Enzymatic Hydrolysates (EH) and Non-Enzymatic Hydrolysates (NEH)) were characterized by proximate compositions, pH, color profile, amino acid analysis, FTIR spectra, and molecular weight distribution. In addition, several biological analyses were performed to assess their potential use as nutraceutical supplements: special attention has been paid to antioxidant activity using three different methods to quantify it. EH showed the most promising antioxidant activity which could be exploited also in other fields (e.g., biomaterials, cosmetics).

Retention of prions in the polychaete Hediste diversicolor and black soldier fly, Hermetia illucens, larvae after short-term experimental immersion and feeding with brain homogenate from scrapie infected sheep

Finding alternative protein and lipid sources for aquafeeds is crucial for the sustainable growth of fed aquaculture. Upcycling industrial side streams and byproducts using extractive species can reduce waste and help reduce the sector's dependence on fish meal and fish oils. Polychaete worms (Hediste diversicolor) and black soldier fly (Hermetia illucens) larvae (BSFL) are promising candidates for converting waste materials into valuable protein and lipid sources. However, further research and evaluations are needed to ensure the safety and regulatory compliance of these alternative feed sources, especially regarding prions spreading potential in the unlikely case that prions would be introduced in the value chain via feedstocks. In the present investigation, BSFL and juvenile polychaetes that had received a massive dose of scrapie prions through immersion and oral inoculation were found to harbour detectable prions using an ultrasensitive amplification method known as PMCA. This observation suggests that both H. diversicolor and BSFL have the potential to serve as mechanical vectors for prions diseases. However, it is important to note that insects, lacking the prion protein gene, are incapable of propagating prions. Therefore, the quantity of prions present in the larvae will inevitably be lower than the amount of prions they encountered. This is the first study to report on the fate of prions through ingestion by these marine and terrestrial invertebrate species.

Protective Effects of Polysaccharides on Antifungal Activity of Bread Waste-derived Bioactive Peptides During Freeze Drying

Bioactive peptides (BPs) derived from agri-food side-streams display great potential as functional ingredients and nutraceuticals. However, BPs can be susceptible to environmental stressors and food processing conditions and typically exist as an aqueous mixture of various peptides, making their storage and use in foods very challenging. Microencapsulation offers a solution, utilizing suitable wall materials to create a protective matrix and transform them into powders for improved stability and application versatility. Here, we investigated the possibility of creating freeze-dried microencapsulated BP powders from bread waste using maltodextrin as the wall material to maintain their antifungal properties against Penicillum albocoremium, Eurotium herbariorum and Penicillium roqueforti fungi. The results were compared to those obtained from galactoglucomannans (GGM) and glucuronoxylans (GX) sourced from forest industry side-streams, aiming to explore their potential suitability as innovative materials for microencapsulating BPs. Maltodextrin microcapsules exhibited the highest inhibition rate on the tested fungi (10 − 44%), followed by GX (26 − 39%) and then GGM (9 − 14%) counterparts. Interactions between wall materials and BPs, as illustrated by FTIR analyses, were found to be the cause of variations in antifungal activities among BP microcapsules. The use of wall materials, especially wood hemicelluloses, facilitated freeze drying of BPs. However, their application in food products is restricted by the decline in the BP bioactivity resulting from the freeze drying process. For this reason, additional research on alternative drying methods is needed. The results of this study are expected to open new ways of production of stable functional ingredients from side-streams of the forest and food industries.

Recovery of Omega-3-Rich Lipids: Toward the Sustainable Valorization of Sea-Bass Industry Side Streams

This study pertains to the selection of the appropriate process parameters of lipid extraction aimed at the valorization of sea-bass gutting and filleting side stream biomass. A comparative kinetic study between an environmentally friendly polar (ethanol) and a conventional non-polar solvent (hexane) was implemented to determine the effect of temperature, solvent to solid ratio and time, providing insights in terms of the yield recovery and quality of omega-3 fatty acids. Maximum recovery yield (43.8 and 34.0 g/100 g of dried gutting and filleting by-products, respectively) was achieved within 10 min. In gutting by-products, ethanol achieved full lipid recovery at 35 °C and a 50:1 ratio, while for hexane, the maximum yield was 83%. In the case of filleting side-streams, hexane achieved exhaustive recovery at a 50:1 ratio and 20 °C compared with ethanol, where a higher temperature (50 °C) was needed for exhaustive recovery to be achieved. Differences were attributed to the diverse fatty acid profiles among the two by-products, with 27.3% and 40.8% polyunsaturated fatty acids in viscera and fish frames, respectively. All extracts at 20 °C and 35 °C remained below the oxidation limit set by the Codex Alimentarius Commission (peroxide value < 5 meqO2/kgoil; p-anisidine value < 20). Therefore, green solvents could assist conventional extraction, combining high efficiency and an improved environmental impact.

Sustainable application of industrial side streams as alternative fine aggregates for cement mortar

Increase in industrialization has led to the production of huge volume of side-stream materials that need safe disposal solutions. The present study proposes the use of local industrial side streams such as ferrochrome slag, phyllite dust and mine tailings as secondary raw materials for construction, mainly as fine aggregates. Four different cement mortar mixtures, with a combination of selected side streams as a sole, binary, and ternary blends were investigated. Workability, strength, and durability properties of the derived mortar mixtures were compared with mortar produced using standard sand as reference. Mortar mixtures with a ternary blend of side-stream fine aggregates resulted in a compressive strength of 68–72 MPa at 28 days, which is 30–40% higher than that of control mix. The addition of industrial side streams resulted in a denser microstructure and enhanced the mechanical properties. The durability performance of the mortar with alternative fine aggregates is comparable with those of standard sand.

Applying industrial side streams in the neutralization of acid generating sulfide-rich sediments – The impact on pH and leaching of harmful elements

Acid sulfate soils can cause severe environmental harm due to a low pH and mobilization of harmful elements. Acid sulfate soil material is formed when oxidation of sulfide minerals causes a drop in pH to <4.0 for mineral oil materials and <3.0 for organic soil materials or when the soil materials contain enough sulfide to potentially do so.Two dredged, acid sulfate soil materials from Finland were used in this laboratory study. Chemical analyses were performed to determine the pre-incubation characteristics of both fresh dredged sediment samples and oxidized samples after 23 weeks of incubation. Total element concentrations were determined after digestion in aqua regia by ICP-MS or ICP-OES. The leachable concentration of elements was determined by using the two-stage shaking test (method SFS-EN 12457-3). The leaching of harmful elements (Cd, Co, Ni, Mn, and Zn) was high in the acidified dredged spoil samples. Also, the leaching of S was high. The soluble concentration was dependent on total concentration, pH, and the mobility of the elements.During a 23-week oxidation period, the impact of various amounts of industrial side streams (alkaline ashes, industrial lime residues) as neutralizing agents on the acid-generating dredged sediments was investigated in the laboratory. Calcite was used as a reference material. pH measurements were carried out during the incubation period. The leaching of elements was determined with a modified method based on the SFS-EN 12457-2 standard before and after oxidation.The untreated dredged spoils and the samples treated with too low amounts of neutralizing agents, acidified to pH < 4 during the oxidation period. Thus, harmful elements were leached out. However, the 100 % theoretical calculated neutralization need was suitable to prevent acidification and thus the leaching of harmful substances from the neutralized acid-generating dredged spoils. However, the leaching of Mo increased at neutral pH values. The results showed that industrial side streams can be applicable for the neutralization of acid sulfate soil materials. However, the legislation must also be considered.

Isolation of arabinose and galactose from industrial sidestreams in high yield and purity

Monosaccharides such as L-arabinose (Ara) and D-tagatose (derived from D-galactose, Gal) are low-calorie sweeteners associated with improved glycaemic and insulin control compared to disaccharides such as sucrose. However, alternative sources and better sugar-sugar separation methods are needed to improve the sustainability and economics of their production. Here, these sugars were obtained from purified and ultrafiltered compression screw pressate (CSP) of thermo-mechanical pulping of softwood (Pinus radiata) and orange peels (OPs). Ba-substituted zeolite X (BaX) molecular sieves showed superior separation performance of Ara from other sugars compared to conventional Ca-form ion exchange resin. To facilitate subsequent separation of sugars, OP hydrolysates were fermented to leave just Ara and Gal, while OP pectin was hydrolysed to generate a Gal-rich mixture. Overall, BaX has good potential for separating Ara from Ara-rich hydrolysates containing several different sugars. It is also suited for separating Ara and another monosaccharide such as Gal or Xyl in the absence of other sugars.

Open (non-sterile) cultivations of Debaryomyces hansenii for recombinant protein production combining industrial side-streams with high salt content

The halotolerant non-conventional yeast Debaryomyces hansenii can grow in media containing high concentrations of salt (up to 4 M), metabolize alternative carbon sources than glucose, such as lactose or glycerol, and withstand a wide range of temperatures and pH. These inherent capabilities allow this yeast to grow in harsh environments and use alternative feedstock than traditional commercial media. For example, D. hansenii could be a potential cell factory for revalorizing industrial salty by-products, using them as a substrate for producing new valuable bioproducts, boosting a circular economy. In this work, three different salty by-products derived from the dairy and biopharmaceutical industry have been tested as a possible feedstock for D. hansenii’s growth. The yeast was not only able to grow efficiently in all of them but also to produce a recombinant protein (Yellow Fluorescent Protein, used as a model) without altering its performance. Moreover, open cultivations at different laboratory scales (1.5 mL and 1 L) were performed under non-sterile conditions and without adding fresh water or any nutritional supplement to the cultivation, making the process cheaper and more sustainable.

Trophic interactions shape the spatial organization of medium-chain carboxylic acid producing granular biofilm communities.

Granular biofilms producing medium-chain carboxylic acids (MCCA) from carbohydrate-rich industrial feedstocks harbor highly streamlined communities converting sugars to MCCA either directly or via lactic acid as intermediate. We investigated the spatial organization and growth activity patterns of MCCA producing granular biofilms grown on an industrial side stream to test (i) whether key functional guilds (lactic acid producing Olsenella and MCCA producing Oscillospiraceae) stratified in the biofilm based on substrate usage, and (ii) whether spatial patterns of growth activity shaped the unique, lenticular morphology of these biofilms. First, three novel isolates (one Olsenella and two Oscillospiraceae species) representing over half of the granular biofilm community were obtained and used to develop FISH probes, revealing that key functional guilds were not stratified. Instead, the outer 150-500 µm of the granular biofilm consisted of a well-mixed community of Olsenella and Oscillospiraceae, while deeper layers were made up of other bacteria with lower activities. Second, nanoSIMS analysis of 15N incorporation in biofilms grown in normal and lactic acid amended conditions suggested Oscillospiraceae switched from sugars to lactic acid as substrate. This suggests competitive-cooperative interactions may govern the spatial organization of these biofilms, and suggests that optimizing biofilm size may be a suitable process engineering strategy. Third, growth activities were similar in the polar and equatorial biofilm peripheries, leaving the mechanism behind the lenticular biofilm morphology unexplained. Physical processes (e.g., shear hydrodynamics, biofilm life cycles) may have contributed to lenticular biofilm development. Together, this study develops an ecological framework of MCCA-producing granular biofilms that informs bioprocess development.

Preparation and characterisation of alkali-activated blast furnace slag and Na-jarosite catalysts for catalytic wet peroxide oxidation of bisphenol A

ABSTRACT In this study, cost-effective alkali-activated materials made from industrial side streams (blast furnace slag and Na-jarosite) were developed for catalytic applications. The catalytic activity of the prepared materials was examined in catalytic wet peroxide oxidation reactions of a bisphenol A in an aqueous solution. All materials prepared revealed porous structure and characterisation expressed the incorporation of iron to the material via ion exchange in the preparation step. Furthermore, the materials prepared exhibited high specific surface areas (over 200 m2/g) and were mainly mesoporous. Moderate bisphenol A removal percentages (35%–37%) were achieved with the prepared materials during 3 h of oxidation at pH 7–8 and 50°C. Moreover, the activity of catalysts remained after four consecutive cycles (between the cycles the catalysts were regenerated) and the specific surface areas decreased only slightly and no changes in the phase structures were observed. Thus, the prepared blast furnace slag and Na-jarosite-based catalysts exhibited high mechanical stability and showed good potential in the removal of bisphenol A from wastewater through catalytic wet peroxide oxidation.

A preliminary appraisal for utilizing abandoned industrial side streams as alternatives to cement within radiation protection applications

Recently, there has been arising a severe alert regarding climate crisis all over the world. As industrial production capacities have been soaring every passing day, the primary sources of the earth's crust have been depleting like there is no tomorrow. Sustainable and greener suggestions should be followed to overcome the upcoming catastrophic climate change. With this motivation, cement material, whose influence on global warming is excessive, has been studied to be replaced by alternative material systems in different application areas, and radiation shielding applications may be regarded as one of these emerging fields. In this study, the authors were motivated to replace ordinary Portland cement (OPC) with alternative side streams (SS) that have accumulated in nature without any benefits. First, the high-quantity SS were determined and presented as follows: fly ash (FA), blast furnace slag (BFS), red mud (RM), electric arc furnace slag (EAFS), fayalite slag (FS), rice husk ash (RHA), silica fume (SF), ferrochrome slag (FS), and copper mining tailings (CMT). Each side stream's average chemical compositions were obtained, and their theoretical density values were calculated. After that, the theoretical radiation shielding properties were assessed using Phy-X/PSD software within the 0.15–15 MeV photon energy range. Some essential parameters such as linear attenuation coefficient (LAC), half-value layer (HVL), effective atomic number (Zeff), radiation protection efficiency (RPE), and build-up factors (EBF and EABF) paved the way for comparing SS with OPC material. The results for radiation protection demonstrated that high-density-oxide-containing SS like RM, FS, and EAFS could replace OPC material with a good performance. Owing to this replacement, the authors strongly believe that the future can be sustained in a more secure environment without OPC material, but with SS in radiation shielding applications.

Gel characteristics of low-acetyl spruce galactoglucomannans

Galactoglucomannans (GGM) recovered from abundant forest industry side-streams has been widely recognized as a renewable hydrocolloid. The low molar mass and presence of O-acetyl side-groups results in low viscous dispersions and weak intermolecular interactions that make GGM unsuitable for hydrogel formation, unless forcefully chemically derivatized and/or crosslinked with other polymers. Here we present the characterization of hydrogels prepared from GGM after tailoring the degree of acetylation by alkaline treatment during its recovery. Specifically, we investigated gel characteristics of low-acetyl GGM dispersions prepared at varied solid concentrations (5, 10 and 15 %) and pH (4, 7 and 10), and then subjected to ultrasonication. The results indicated that low-acetyl GGM dispersions formed gels (G′ > G″) at all other studied solid concentration and pH level combinations except 5 % and pH 4. High pH levels, leading to further removal of acetyl groups, and high solid concentration facilitated the gel formation. GGM hydrogels were weak gels with strong shear-thinning behavior and thixotropic properties, and high hardness and water holding capacity; which were enhanced with increased pH and solid concentration, and prolonged storage time. Our study showed the possibility to utilize low-acetyl GGM as mildly processed gelling or thickening agents, and renewable materials for bio-based hydrogels.

Ligneous amendments increase soil organic carbon content in fine-textured boreal soils and modulate N2O emissions.

Organic soil amendments are used to improve soil quality and mitigate climate change. However, their effects on soil structure, nutrient and water retention as well as greenhouse gas (GHG) emissions are still poorly understood. The purpose of this study was to determine the residual effects of a single field application of four ligneous soil amendments on soil structure and GHG emissions. We conducted a laboratory incubation experiment using soil samples collected from an ongoing soil-amendment field experiment at Qvidja Farm in south-west Finland, two years after a single application of four ligneous biomasses. Specifically, two biochars (willow and spruce) produced via slow pyrolysis, and two mixed pulp sludges from paper industry side-streams were applied at a rate of 9-22 Mg ha-1 mixed in the top 0.1 m soil layer. An unamended fertilized soil was used as a control. The laboratory incubation lasted for 33 days, during which the samples were kept at room temperature (21°C) and at 20%, 40%, 70% or 100% water holding capacity. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes were measured periodically after 1, 5, 12, 20 and 33 days of incubation. The application of ligneous soil amendments increased the pH of the sampled soils by 0.4-0.8 units, whereas the effects on soil organic carbon content and soil structure varied between treatments. The GHG exchange was dominated by CO2 emissions, which were mainly unaffected by the soil amendment treatments. The contribution of soil CH4 exchange was negligible (nearly no emissions) compared to soil CO2 and N2O emissions. The soil N2O emissions exhibited a positive exponential relationship with soil moisture. Overall, the soil amendments reduced N2O emissions on average by 13%, 64%, 28%, and 37%, at the four soil moisture levels, respectively. Furthermore, the variation in N2O emissions between the amendments correlated positively with their liming effect. More specifically, the potential for the pulp sludge treatments to modulate N2O emissions was evident only in response to high water contents. This tendency to modulate N2O emissions was attributed to their capacity to increase soil pH and influence soil processes by persisting in the soil long after their application.

Cooling and Evaporative Crystallization of α‐D‐Galactose from a Highly Viscous Industrial Side Stream

AbstractAn industrial side stream containing mainly glucose and galactose was used to crystallize α‐D‐galactose. The dynamic viscosity of samples containing galactose and glucose solutions was measured and compared with pure glucose and galactose solutions. Various crystallization conditions were investigated in terms of temperature range and batch times in cooling crystallization and their influence on the product crystal properties. The obtained results were compared with the results of evaporative crystallization. Several characterization methods were used for studying crystal size and shape, crystal structure, and purity. The overall crystallization time of α‐D‐galactose was shortened by cooling crystallization based on stepwise temperature decrease and the desired crystal properties were achieved.

Valorizing industrial side streams through microalgae cultivation: A roadmap for process scale-up

Currently, there is an increased need for more sustainable production processes and to move towards zero-waste manufacturing. In this sense, microalgae have been used as an alternative to traditional remediation techniques with the advantage of generating high value-added products. Some of the industries with the highest amount of waste streams belong to the agro-industrial, food and beverages. Based on this premise, a database compiling different studies in which microalgae were cultured with a working volume of at least 5 L and with industrial wastewater as substrate was developed (>TRL5). The aim of the present review is to provide a roadmap into microalgae use regarding biomass productivity, biomass concentration, removal of nitrogen, phosphorus and Chemical Oxygen Demand and the percentages of lipids, proteins and carbohydrates reported in the literature to better guide academics and industrial stakeholders on making decision to further optimize and valorize their side-streams.

Recent advances in the production of malic acid by native fungi and engineered microbes.

Malic acid is mainly produced by chemical methods which lead to various environmental sustainability concerns associated with CO2 emissions and resulting global warming. Since malic acid is naturally synthesized, microorganisms offer an eco-friendly and cost-effective alternative for its production. An additional advantage of microbial production is the synthesis of pure L-form of malic acid. Due to its numerous applications, biotechnologically- produced L-malic acid is a much sought-after platform chemical. Malic acid can be produced by microbial fermentation via oxidative/reductive TCA and glyoxylate pathways. This article elaborates the potential and limitations of high malic acid producing native fungi belonging to Aspergillus, Penicillium, Ustilago and Aureobasidium spp. The utilization of industrial side streams and low value renewable substrates such as crude glycerol and lignocellulosic biomass is also discussed with a view to develop a competitive bio-based production process. The major impediments present in the form of toxic compounds from lignocellulosic residues or synthesized during fermentation along with their remedial measures are also described. The article also focuses on production of polymalic acid from renewable substrates which opens up a cost-cutting dimension in production of this biodegradable polymer. Finally, the recent strategies being employed for its production in recombinant organisms have also been covered.