Extensive research has focused on the production of microbial-originated green surfactants, known as biosurfactants, over the past fifteen years. These biomolecules not only offer a green alternative for agriculture but also exhibit reduced toxicity and excellent stability under specific environmental conditions. Biosurfactants can lower surface tension more effectively than synthetic surfactants. With properties such as detergency and foam formation, biosurfactants are suitable for various agricultural applications, particularly in pesticide and agrochemical formulations. They can function as biopesticides to manage pests, pathogens, phytopathogenic fungi, and weeds due to their antimicrobial activity. Moreover, plants can benefit from biosurfactant molecules and microorganisms as nutrients. They can also aid efficiently in the distribution of micronutrients and metals in the soil. They also stimulate plant immunity and are utilized for soil hydrophilization to ensure proper moisture levels and uniform fertilizer distribution. This review aims to provide valuable insights into the role and properties of biosurfactants as agricultural adjuvants, fostering the development of sustainable formulations to replace the chemical surfactants used in pesticides.
General Aspects of Global Agricultural Activity
With the exponential growth of the world population starting from the 1900s (Figure 1), there was a need to increase food production due to the rising demand for food, as illustrated in Figure 2. As a result, it was necessary to boost production and/or minimize crop losses caused by fungi, pests, and weeds, for which pesticides, chemical substances designed for the biological control of microorganisms, macroorganisms, and competing plants, began to be used. At the same time, the development of genetically modified organisms (GMOs) and genetically modified foods, which aimed to enhance resistance against pathogens and/or increase productivity, was also intensified to reduce pesticide usage.
However, with the use of GMOs, the use of pesticides increased up to approximately 250 tons. This occurred because GMOs exhibited increased resistance against certain pathogens but became more susceptible to others, thereby not reducing this practice. The adoption of herbicide-resistant crop technology in the United States resulted in a significant rise in herbicide usage, totaling 239 million kilograms (527 million pounds). Conversely, the implementation of Bacillus thuringiensis crops resulted in a 56-million-kilogram (123 million pounds) reduction in insecticide use. Consequently, the overall pesticide consumption in the country increased by approximately 183 million kilograms (404 million pounds), equivalent to a 7% increment.
Pesticides
Agricultural Defensives
Pesticides are chemical compounds used to control pests in a generalized way, most of which have a long degradation time and are highly toxic to humans and other animals. Many of the problems caused by pesticides occur due to incorrect use and exceeding the allowed concentration, and some studies have already shown that this indirectly affects pollinating animals. The low biodegradability of pesticides leads to their accumulation in riverbeds and an increase in their presence in a single food item. These factors contribute to the contamination of fishery resources, and humans can be indirectly affected by consuming these contaminated foods. Pesticides include herbicides, fungicides, and insecticide products.
Herbicides are pesticides used to control competing or undesirable vegetation (weeds). Since it is not possible to target only one type of vegetation in crops, it is recommended to use herbicides with different actions against various types of vegetation. However, this strategy is environmentally harmful because the herbicide mixture can be carried into riverbeds, especially when applied near the roots. Furthermore, they are the type of pesticide that affects mammals the most.
Fungicides are pesticides used to combat fungi that attack plant species, thus being among the major pathogens of crops. They represent 30% of all pesticides in the current global market. The most common fungicide is Cu, a heavy metal that can contaminate water and is highly toxic to living beings [6]. Fungicides are the main cause of poisoning in pollinating insects.
Insecticides, the last category of pesticides, are used to control pests, mainly insects, which use crops as a food source, breeding ground, and development site. Due to their accumulation on the surface of foods, they have a large impact on humans, who can absorb them.
Biological Control
In contrast to pesticides, biological control utilizes nature itself to achieve control. As a result, it does not impact the environment, although it may not have the same efficiency as a pesticide and requires certain special conditions for its application. Biological control can be carried out with parasitoids, predators, and entomopathogens. Parasitoids are introduced by inoculating insect larvae into the eggs of a pest, where they feed, develop, and then emerge as adults. An example is Trichogramma pretiosum, which parasitizes moth eggs. One of the oldest methods for pest control involves introducing a predator into the same environment as the pest so that it can use it as food. Harmonia axyridis (ladybug) is a good example, as it feeds on Myzus persicae (aphid). Entomopathogens, on the other hand, are fungi or bacteria that attack pests (insects or microorganisms). This method is not common but, in some cases, it proves to be the most efficient.
Agricultural Biodefensives
Agricultural biodefensives include bioherbicides, biofungicides, and biopesticides. Bioherbicides use organic products, such as fungus extracts, oil extracts, fruit enzymes, and other biological materials. Biofungicides are a group of agricultural biodefensives based on competing fungi that do not affect the development of the agricultural product. The use of seeds as biofungicides has also been described. Finally, biopesticides are the most used agricultural biodefensives to replace pesticides. Similar to other agricultural biodefensives, they are derived from plant or microorganism extracts, fruits, crustaceans, seeds and tree saps, and cellular mass, among other natural substances. Their use has significantly increased in North America in recent years.
Formulation of Agricultural Biodefensives
Formulations of agricultural biodefensives can either be diluted in water or other solvents or can be applied as such. Formulations for dilution in water can be sold as an Emulsifiable Concentrate (EC), in the form of emulsions with small amounts of water, giving them a milky appearance; as Suspension Concentrates (SCs), which are inert and stable and need to be shaken before application; as Soluble Powder (SP) or as Wettable Powder (WP), which is very similar to SP but does not dissolve in water when applied, requiring agitation during application; or as Microencapsulated, which is a specific characteristic of WP as it is not in direct contact with water but encapsulated for continuous and controlled release over time during application. Formulations for dilution in other solvents are marketed in high concentrations and need to be diluted in oils or organic solvents. Formulations for direct application are provided in the form of Dry Powder (DP), which is essentially applied in a mixture with inert powders such as talc and clay when water spraying can damage the area or agricultural products, in the form of Granules (GRs), which are similar to Dry Powder but consist of larger granular solids (ranging from 0.3 to 0.6 mm) for slower and continuous release of the biodefensive, or in the form of Baits, which are composed of even larger granular solids than the GR formulations and are intended to be consumed by pests.
Agricultural Adjuvants as Activators or Enhancers of Agricultural Defensives
The market offers many solutions and products to ensure application quality, reduce losses, and increase the efficiency of phytosanitary management. Adjuvants encompass a wide range of chemical substances that are commonly included in spray tanks to enhance the efficacy and application efficiency of pesticides. Their primary function is to improve the pesticide’s performance and mode of application.
Agricultural adjuvants have a long history dating back to the 18th and 19th centuries. During this time, various additives such as resins, molasses, flour, pitch, and sugar were combined with sulfur, arsenates, lime, and copper to enhance “adhesion” and improve biological performance by altering the chemical and physical features of the applied mixture. Research indicates that adjuvants can influence various factors in pesticide applications. The main points are related to altering solution properties, increasing biological efficacy, and improving operational performance. Benefits such as increased wetting, better spreading on leaves, greater efficiency, and speed of active ingredient absorption on the target (crop, weeds, and insects) can be achieved using adjuvants.
It should be noted that there are many barriers involved in agricultural pesticide applications. Regarding plants, leaf surfaces have waxes that are difficult to wet and prevent liquid entry into the plant. These waxes are primary obstacles to the deposition, retention, spread, and penetration of agrochemical droplets. Adjuvants can overcome these impediments and increase the deposition, spread, absorption, and penetration of products into the plant.
As for climatic barriers, several factors can negatively affect applications. Deviation from the trajectory, preventing the droplets from reaching the target, is mainly related to droplet size and wind speed. Environmental conditions greatly influence the outcome of the operation, so it is necessary to understand the spectrum of sprayed droplets, adjusting not only their diameter but also seeking other tools. Adjuvants such as oils can be an alternative to achieve greater leaf penetration, while surfactants reduce evaporation, and nozzle selection helps produce more suitable droplets.
The portfolio of adjuvants available on the market is extensive and mainly includes mineral and/or vegetable oils, silicones, surfactants, emulsifiers, nitrogen, phosphorus, organic resins, EDTA, and essential oils, among others. Therefore, it is essential to classify them according to their benefits. Several authors define adjuvants as utility or activator-based.
Surfactants
Agrochemical formulations require surfactants for physical stability and biological efficiency.
Research suggests that less than 0.1% of pesticides utilized for weed and pest control hit their intended targets. Most of these chemicals are lost due to factors such as spray drift, off-target deposition, runoff, and photodegradation.
Agrochemical products use around 230,000 tons of surfactants annually, typically in formulations containing 1-10% of one or more surfactants. As a plasticizer, the surfactant softens the crystalline waxes on the cuticle, thereby increasing the mobility of agrochemicals through the cuticular membrane.
Surfactants of various types are being used in the pesticide production industry . In particular, they are commonly used in pesticide formulations, which, however, leads to their accumulation in the soil, thus affecting texture, color, and plant growth. These hazardous chemicals are also leached from the soil into groundwater, persist in the soil for years, can spread through the air and water, and can even be found on the outer surfaces of fruits and vegetables. Synthetic surfactants are also considered powerful organic contaminants in the soil.
Given the negative effects of pesticides and surfactants used in pesticides, environmentally friendly biosurfactants should be used to replace the hazardous synthetic ones in the multibillion-dollar pesticide industry, thus reducing contamination.
Depending on the characteristics of their molecule, surfactants can reduce surface tension and solubilize water in oil or oil in water since these molecules have a hydrophilic part and a hydrophobic part, allowing water encapsulation within an oily substance or, vice versa, forming a structure known as amphiphilic.
The best method for characterizing a surfactant is to measure the attractive forces among liquid molecules, thereby assessing the surfactant’s ability to influence surface and interfacial tensions. Effective surfactants reduce surface tensions, facilitating interactions between molecules with different polar features. The critical micelle concentration (CMC) is defined as the minimum surfactant concentration required to reach the lowest surface tension. Upon reaching the CMC, the amphiphilic molecules aggregate with the hydrophilic portions positioned outward and the hydrophobic portions inward. After reaching CMC, no further addition of surfactant will result in an additional reduction in surface tension. Thus, surfactants with a lower CMC are preferably used compared with those with higher CMC values.
Surfactants can be divided into two categories: chemical surfactants and green surfactants. Green surfactants are further divided into two subclasses: biosurfactants and biobased surfactants.
Chemical Surfactants
Chemical surfactants originate from petrochemicals and dominate the global surfactant market, accounting for 90% of it. Due to their large-scale production, chemical surfactants are more competitively priced compared with natural surfactants. However, despite their high surface activity and lower cost, they pose various problems due to their high toxicity and long degradation time. There are four types of surfactants categorized by the nature of their hydrophilic group: anionic, cationic, nonionic, and amphoteric.
According to Xu et al., surfactants reduce the surface tension of droplets on leaf surfaces, ensuring greater coverage and foliar absorption. Their concentration greatly influences the efficacy of agrochemical applications. For instance, increasing surfactant concentration from 0.01% to 1% promoted better foliar absorption of products; however, for some surfactants, higher concentrations can have a negative effect on chemical absorption.
Anionic surfactants often include sulfonate, sulfate, or carboxylate groups, with counterions such as sodium or calcium. Among them, linear alkylbenzene sulfonates (LASs) are extensively produced worldwide as household cleaning detergents, and calcium LAS is used as an adjuvant in many agrochemical formulations.
In nonionic surfactants, the hydrophilic behavior is achieved through polymerized glycol ether or glucose units. They are predominantly synthesized by adding ethylene oxide or propylene oxide to fatty alcohols, alkylphenols, amines, acids, or fatty acid amides. Nonionic surfactants find significant applications as emulsifiers, detergents, dispersants, and wetting agents, and a substantial portion of them are used as adjuvants in agrochemical formulations.
Cationic surfactants, which have hydrophilic portions formed by quaternary ammonium ions, have gained importance due to their bacteriostatic properties and are applied as disinfectants and antiseptics in personal care products. They are also used as textile softeners, flotation agents, and corrosion inhibitors due to their high adsorptive capacity.
Amphoteric surfactants are water-soluble and compatible with other surfactants, as they possess both cationic and anionic groups in their structure, which make them zwitterionic compounds. Their charge changes with pH, influencing detergency and foam formation, among other properties. They have properties that closely resemble those of nonionic surfactants and are commonly used in shampoos, but they are also starting to be used in agrochemical formulations.
Biobased Surfactants
The term biobased surfactant refers to green surfactants synthesized through chemical or enzymatic processes using renewable raw materials. The main resources used for their synthesis are vegetable oil triacylglycerides, methyl esters of fatty acids, fatty alcohols, fatty acids, glycerol, carbohydrates, and amino acids. Triglycerides form the hydrophobic moiety, while sugars or amino acids and peptides act as the hydrophilic ones. Although biobased surfactants are still relatively new, they have already shown excellent results in various applications.
Biosurfactants
Biosurfactants constitute a subclass of green surfactants of biological origin, which can be obtained from plant extracts, roots, and fruits or through the metabolic transformation of microorganisms, especially bacteria, and yeasts. Microbial biosurfactants are the most efficient and widely studied and possess the same specifications as chemical surfactants, but they exhibit biodegradability, reduced toxicity, and biocompatibility.
Biosurfactants have diverse industrial applications, ranging from petroleum and cleaning products to cosmetics, textiles, food, and agriculture. In the agricultural sector, biosurfactants can be used in the formulation of biopesticides, biofertilizers, and biostimulants.
At present, biosurfactants make up only 10% of the world’s total surfactant production, which is around ten million tons annually. However, if synthetic surfactants were replaced with biosurfactants, it could reduce CO2 emissions by 8% over the long term. This would prevent the release of roughly 1.5 million tons of CO2 into the atmosphere. The first studies in the field of microbial biosurfactant research occurred in the 1960s, and since then, research has led to the commercialization of numerous products containing them. In the last decade, studies focused on biosurfactant production have intensified due to their efficiency and biocompatibility.
Currently marketed biosurfactants have a higher production cost compared with their synthetic counterparts, despite their high efficiency. On the other hand, this cost can be reduced through the selection of more suitable substrates during fermentation, that is, with lower cost, and the selection of microbial strains with greater capacity for biosurfactant production. In most cases, strains produce a mixture of different biosurfactants. However, for certain applications in the food, medical, and pharmaceutical industries, a high level of purity is necessary, which can be a limiting factor for their use. Therefore, it is crucial to develop strategies that facilitate the production and large-scale application of biosurfactants. The microbial source and molecular structure are the most important criteria for classifying biosurfactants, the main classes of which are glycolipids, lipopeptides, phospholipids, polymeric biosurfactants, particulate biosurfactants, and fatty acids. Biosurfactants are categorized into low and high molecular weights based on their average molecular weight, which ranges from 500 to 1500 Da. Low molecular weight biosurfactants have the ability to reduce surface tension efficiently, while higher molecular weight biosurfactants are commonly used for stabilizing oil-water emulsions. Biosurfactants such as proteins, lipoproteins, polysaccharides, and lipopolysaccharides, which are of high molecular weight, are commonly referred to as emulsifiers, while the low-molecular-weight ones, which include glycolipids, lipopeptides, and phospholipids, are considered classic biosurfactants.
Glycolipids have been extensively studied among the different types of biosurfactants. The structure of glycolipids consists of a hydrophilic carbohydrate moiety connected to hydrophobic fatty acid chains of different lengths via an ester group. These glycolipids are commonly characterized based on the structure of their carbohydrate fraction, with sophorolipids, rhamnolipids, mannosylerythritol lipids, and trehalose lipids being the most investigated subclasses.
Rhamnolipids consist of one or two fatty acids attached to one or two rhamnose sugar molecules. The primary source of rhamnolipids is the Gram-negative bacterium known as Pseudomonas aeruginosa, although subsequent research has shown that other bacterial species are actively producing rhamnolipid-type biosurfactants. Rhamnolipids are a class of biosurfactants with unique characteristics that depend on the strain, carbon source, and cultivation conditions. Various renewable materials such as exhausted oils or waste from the food industry can be used as carbon sources for their production. Rhamnolipids can lower the air-water surface tension from 72 mN/m to around 30 mN/m, as well as the water-oil interfacial tension from 43 mN/m to around 1 mN/m. The CMC of pure rhamnolipids and their mixtures largely depends on the chemical composition of the constituents and ranges from 50 to 200 mg/L.
Sophorolipids consist of a sophorose head, in which two glucose units are connected by a β-1,2 bond, and a long-chain fatty acid (hydroxyl) tail connected by a glycosidic bond. These biosurfactants, which are generally synthesized by yeasts such as Starmerella bombicola, have a surface tension of around 33 mN/m and an interfacial tension of about 5 mN/m in n-hexadecane and water. S. bombicola is considered one of the most productive strains, being capable of producing about 300 g/L of sophorolipids.
Trehalose lipids, which contain the disaccharide trehalose linked to a fatty acid (mycolic acid), are mainly produced by species of the genera Nocardia, Rhodococcus, Mycobacterium, and Corynebacterium and have high structural diversity. Trehalose lipids produced by Rhodococcus erythropolis and Arthrobacter spp. can decrease surface and interfacial tensions to 25-40 and 1-5 mN/m, respectively.
Pseudozyma antarctica yeast produces mannosylerythritol lipids (MELs) in large quantities from vegetable oils. MELs are made up of mannose and fatty acid and can be further classified based on the hydrophobic chain length, degree of saturation, and acetylation at positions C4 and C6 of the monosaccharide.
There are different types of low-molecular-weight biosurfactants, such as lipopeptides, phospholipids, and polymeric surfactants. One of these is surfactin, which is produced by the Gram-positive bacterium Bacillus subtilis. Surfactin is a cyclic lipopeptide that contains seven hydrophobic amino acids with a length of 13 to 15 carbon atoms. It also has a mixture of seven amino acids, which are L-asparagine (Asn), L-leucine (Leu), glutamic acid (Glu), L-leucine (Leu), L-valine (Val), and two D-leucines, connected through a lactone bond. It is widely recognized that surfactin is among the most powerful biosurfactants on record, and due to its antibacterial, antiviral, and antifungal activities, it is widely used in various applications; it is also utilized as an efficient stabilizer, emulsifier, and surface modifier in the food industry. Due to its ability to reduce surface tension to 27 mN/m at a concentration of less than 5% and its low CMC, it is explored in different applications.
Phospholipidic biosurfactants are produced during the growth of yeasts and bacteria on n-alkanes, including Acinetobacter spp. and Thiobacillus trioxidans. Liposan and emulsan are examples of polymeric biosurfactants. These compounds are good emulsifiers and can be also synthesized by bacteria and yeasts of the Candida genus. The literature describes the use of liposan as an emulsifier in the food and cosmetic industries.
Figure 3 shows examples of microbial surfactants.
Biosurfactants and synthetic surfactants share several properties such as reducing surface tension, foam-forming capacity, emulsification, stabilization ability, solubility, and detergent activity. However, biosurfactants possess some properties listed below that make them more appealing than their synthetic counterparts:
- Surface activity: Surfactant efficiency is measured with the CMC, which ranges from 1 to 2000 mg/L based on molecular structure, as discussed earlier. An optimal biosurfactant can reduce the surface tension of water from 72 to 30-35 mN/m and the interfacial tension of oil and water from 40 to 1 mN/m. Compared with synthetic surfactants, most microbial surfactants have lower surface and interfacial tensions and CMC values, making them more effective.
- Foam capacity: Biosurfactants are compounds that can reduce the surface tension of liquids, making it easier to create foam, or improve their colloidal stability by preventing bubbles from merging. They are particularly effective at the gas-liquid interface, where they form bubbles that move through the liquid, creating foam. In short, biosurfactants are substances that promote the production of foam.
- Emulsification and demulsification: Biosurfactants have emulsifying and demulsifying properties. Emulsions are a colloidal system of two immiscible liquids, wherein a liquid phase is dispersed and suspended in the form of small droplets, the dimensions of which range from 1 nm to 1 μm, in a second liquid (continuous phase). The two types of emulsions are water-in-oil (W/O) and oil-in-water (O/W). Biosurfactants signify the solubilization of large particles with micellar structures by assisting the dispersion of one liquid into another and making it easier for two immiscible liquids to be mixed. Demulsification is a process that occurs in two steps. Firstly, flocculation takes place when droplets come together to form flocs. Then, coalescence occurs when water droplets combine to form larger droplets. This reduction in the quantity of water droplets leads to demulsification. During the demulsification process, the stable interface between the internal and bulk levels is disturbed, causing the emulsions to split. Biosurfactants help to make the demulsification process easier.
- Solubilization: When the concentration of biosurfactants in a liquid surpasses a certain point known as the CMC, they spontaneously group together and form small nano-sized aggregates. These aggregates have a hydrophobic core and a hydrophilic surface that is exposed to water. This unique structure enhances the bioavailability of water-insoluble substances, such as chemical agents or molecules, by enabling their transportation and confinement within the aqueous phase.
- Wetting: Wetting capability refers to a liquid’s ability to connect with another surface and spread evenly over it. When a liquid with a high wetting capacity comes in contact with a surface, it creates a thin and continuous film. Biosurfactants are effective wetting agents because they can lower liquid surface tension by reducing attractive forces, which increases their affinity toward different surfaces. Instead of being connected to surface tension, they penetrate through the pores.
- Dispersion: Dispersion occurs when the cohesive attraction between similar particles decreases. A small amount of dispersing agent (such as BS) is added to a suspension to prevent insoluble particles from aggregating. For example, BS can remove hydrophobic molecules from rock surfaces, making them more mobile and easier to recover during oil extraction. Dispersion also plays a role in reducing or completely preventing the formation of biofilms by unwanted microbes.
- Temperature, pH, and ionic strength tolerance: Several biosurfactants remain effective in adverse conditions, such as high temperatures, a pH range of 3-12, and up to a 10% saline concentration, while synthetic surfactants are inactivated by ≥2% NaCl.
- Specificity: The high diversity of molecules, each with its own complexity and specific functional groups, confers particular/specific activities to biosurfactants. Similar to synthetic surfactants, biosurfactants show the ability to self-aggregate and form micelles, which increase their specificity and allow them to have different morphological structures. In addition, their ability to create spherical, rod-shaped, and vesicle-like structures has caught the attention of various industries like food, cosmetics, and pharmaceuticals. They also have the potential to detoxify pollutants and demulsify industrial emulsions.
- Biocompatibility and digestibility: The composition of biosurfactants makes them more biodegradable and biocompatible than their chemical counterparts under variations in temperature, pH, and degradation time.
Synthetic surfactants are used in remediation and wastewater treatment; therefore, they can be released into industrial wastewater. When this industrial effluent is intentionally or accidentally discharged into a natural body of water, its presence can pose a threat to marine and freshwater ecosystems. When the concentrations of surfactants released into the environment reach high levels, they will accumulate in animals up to toxic levels through the food chain, eventually affecting humans through food consumption. In contrast, biosurfactants are less toxic to aquatic fauna and flora, since they are products of microbial fermentation, in addition to being more easily degraded by microorganisms in soil and aquatic environments. The biocompatibility of these compounds has increasingly attracted industries seeking to replace synthetic surfactants with green surfactants.
Biosurfactants are produced by excretion or cell adhesion. The primary function of biosurfactants is to reduce surface tension between phases, making insoluble substrates more available for absorption and metabolism by microorganisms. Different mechanisms of substrate absorption are described, namely, direct absorption of hydrocarbons dissolved in the aqueous phase, interaction with emulsified droplets, and direct contact between cells and large hydrocarbon droplets. In addition to emulsifying the carbon source, biosurfactants are also involved in microbial cell adhesion to hydrocarbons, i.e., biosurfactant excretion after adsorption of microbial cells onto insoluble substrates allows them to grow on these carbon sources.
Achieving the highest possible production of biosurfactants is difficult due to various factors that affect microbial growth and metabolism during fermentation. Numerous studies have attempted to identify the ideal combination of substrates for a specific culture medium, which can enhance intracellular diffusion and the synthesis of desired compounds. To optimize biosurfactant production with the selected microorganism, defining culture conditions is crucial. Factors to be considered include carbon and nitrogen sources, the concentration of the lipophilic substrate, inoculum size, micronutrients, temperature, aeration rate, pH, and agitation. While most biosurfactant-producing microorganisms produce these compounds under restrictive conditions, e.g., after depletion of an important nutrient, the phase in which the highest yield is achieved (exponential or stationary growth phase) should also be investigated. Statistical methods can optimize the physicochemical parameters of the fermentation process. This allows for the study of how different variables interact and helps find the most cost-effective conditions for maximum biosurfactant production.
Therefore, to cheaply produce biosurfactants, production needs to be associated with downstream processing and explore alternatives to improve production using genetically modified microbial strains, innovative statistical approaches (e.g., surface methodology), and techniques based on Artificial Intelligence (AI) such as Artificial Neural Intelligence coupled with Genetic Algorithm (ANN-GA). Genetically modified microbial strains, cheap substrates, optimized media, enhanced fermentation process, and downstream processing and purification of final products using well-developed static models can be biological and engineering solutions from the commercial point of view to achieve economically sustainable large-scale industrial production of biosurfactants.
The increasing production costs associated with microbial surfactants compared with synthetic surfactants can be overcome by using raw materials obtained from other industrial processes. The implementation of biosurfactant production on an industrial scale can become economically viable with the use of agro-industrial by-products. The use of low-cost raw materials obtained from other industrial processes, however, needs to be evaluated to provide the necessary amounts and types of nutrients to microorganisms, maintaining a balance of carbohydrates and lipids so that microbial metabolism occurs appropriately for the production of the target surfactant. These raw materials also need to provide substantial amounts of micronutrients, including iron, magnesium, phosphorus, manganese, and sulfur, which can further reduce the cost associated with the production process.
In selecting components for production, considerations such as nutritional content, waste availability, transportation and storage costs, pretreatment requirements, and waste purity should be considered. Each type of raw material has unique characteristics that affect how microorganisms interact with it. This is why some microorganisms may be able to produce effective biosurfactants from a certain raw material while others cannot.
The reuse of industrial waste to produce valuable compounds is essential for both economic benefits and waste management. On the other hand, the utilization of industrial waste cannot solely rely on the low cost of these raw materials, i.e., the availability, stability, and variability in each component should be also considered. Variability is an important limit to industrial use since the structures and properties of biomolecules must remain well-defined and constant, requirements that cannot always be guaranteed when using these substrates.
Concluding Remarks and Future Perspectives
Surfactants are necessary as adjuvants for fungicides, insecticides, and herbicides, as discussed earlier. The synthetic surfactants currently used in agricultural pesticides act as emulsifiers, dispersants, and wetting agents, enhancing their efficiency. Additionally, they are also used in the formulation of insecticides in modern agriculture as they possess defensive properties. Various types of surfactants, including anionic, cationic, amphoteric, and nonionic, are currently being used in various pesticide manufacturing industries. However, it is important to note that the surfactants present in pesticide formulations accumulate in the soil and affect the texture, color, and growth of plants. These harmful pesticides are also leached from the soil into groundwater. Pesticide residues can persist in soil for years and spread through air and water. Additionally, they can remain on the surface of vegetables and fruits.
Given the harmful effects of pesticides and their associated surfactants, it is crucial to utilize environmentally safe surfactants as alternatives in pesticide industries, thereby mitigating environmental pollution. The use of soil bacteria that can utilize chemical surfactants in agricultural soil as a carbon source could be another alternative to solve such an environmental problem. Moreover, effective formulation technologies are needed in agrochemical industries to widely use green surfactant-based products in agriculture. Many corporations are now prioritizing microbial surfactants due to their sustainability initiatives and green agendas. Despite the advantages of biosurfactants, the use of these biocompatible adjuvants in the agricultural and agrochemical industries is still limited. The exact function of surfactants as facilitators of biocontrol is not yet well understood and requires further investigation. It is crucial to evaluate the environmental impact of biosurfactants to determine their overall sustainability. The production, distribution, and end-use of biosurfactants should be carefully planned before establishing their viability as sustainable products. However, the literature on these issues is currently limited, and the use of biosurfactants as sustainable products within societal, commercial, and environmental frameworks requires focused attention.
Such studies will help replace synthetic surfactants and aggressive chemicals with green surfactants. Investments to reduce the production costs of biosurfactants and enable market application of these biomolecules are essential not only in agriculture but also in other industrial sectors. The use of agricultural waste for the overproduction of biosurfactants also requires further in-depth studies. The chemical composition of biocontrol potential biosurfactants can also be altered with changes in the production process (medium, cultivation conditions, etc.). This approach can lead to the biosynthesis of highly specific surfactants for a particular application. The presence of biosurfactants and/or their producing bacteria in the rhizosphere indicates the potential of these biomolecules in sustainable agriculture. However, few genera of microorganisms have been explored in the literature as producers of biosurfactants for agricultural applications. Extending our understanding of biosurfactant-producing strains requires consideration of morphology, genetics, and biochemistry. Screening for virulent strains and improving process technology can help reduce production costs. It is crucial to conduct more genetic and bioengineering studies to identify genes that play a role in biosurfactant production. In addition, the implementation of advanced CRISPR (clustered regularly interspaced short palindromic repeats) technology can enhance the production of biosurfactants. By identifying biosurfactant genes and incorporating them into microbial species commonly found in contaminated sites using the CRISPR tool, we can improve the process of pesticide remediation.
Biosurfactants have various applications including treating polluted soils and water, heavy metals, enhancing oil restoration, treating skin conditions, preserving food, and eliminating plant diseases. Recent research indicates that utilizing biosurfactants in the aerobic composting process of municipal waste, yard waste, and crop residues can lead to improved composting efficiency and product quality. Combining BSs with nanotechnology is a promising approach for crop improvement. Therefore, research on green surfactants should be seen not only as an alternative but mainly as a priority in preventing the negative effects caused by synthetic surfactants used in many commercial sectors, including the agrochemical industries. Joint knowledge in several areas, such as microbiology, molecular biology, biochemistry, environmental science, and engineering, is essential for technological advances in including these green molecules in the global market.
In agriculture: The surfactant can be used insolubilization, wetting, emulsification, foaming. Dora presents the natural surfactants to meet the standard of organic agriculture, ensure the organic throughout.
For additional insights into agricultural surfactant options, refer to the Dora surfactant series.