Sophorolipid production from delignined corncob residue by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 and Cryptococcus curvatus ATCC 96219

Common operational issues and possible solutions for sustainable biosurfactant production from lignocellulosic feedstock

Surfactants are compounds with high surface activity and emulsifying property. These compounds find application in food, medical, pharmaceutical, and petroleum industries, as well as in agriculture, bioremediation, cleaning, cosmetics, and personal care product formulations. Due to their widespread use and environmental persistence, ensuring biodegradability and sustainability is necessary so as not to harm the environment. Biosurfactants, i.e., surfactants of plant or microbial origin produced from lignocellulosic feedstock, perform better than their petrochemically derived counterparts on the scale of net-carbon-negativity. Although many biosurfactants are commercially available, their high cost of production justifies their application only in expensive pharmaceuticals and cosmetics. Besides, the annual number of new biosurfactant compounds reported is less, compared to that of chemical surfactants. Multiple operational issues persist in the biosurfactant value chain. In this review, we have categorized some of these issues based on their relative position in the value chain - hurdles occurring during planning, upstream processes, production stage, and downstream processes - alongside plausible solutions. Moreover, we have presented the available paths forward for this industry in terms of process development and integrated pretreatment, combining conventional tried-and-tested strategies, such as reactor designing and statistical optimization with cutting-edge technologies including metabolic modeling and artificial intelligence. The development of techno-economically feasible biosurfactant production processes would be instrumental in the complete substitution of petrochemical surfactants, rather than mere supplementation.

Screening of alternative nitrogen sources for sophorolipid production through submerged fermentation using Starmerella bombicola

To explore a sustainable sophorolipid production, several hydrolysates from agricultural byproducts, such as wheat feed, rapeseed meal, coconut waste and palm waste were used as nitrogen sources. The four hydrolysates overperformed the controls after 168 h of fermentation using Starmerella bombicola ATCC 22214. Wheat feed and coconut waste hydrolysates were the most promising feedstocks presenting a linear relationship between yeast growth and diacetylated lactonic C18:1 production at total nitrogen concentrations below 1.5 g/L (R2 = 0.90 and 0.83, respectively). At 0.31 g/L total nitrogen, wheat feed hydrolysate achieved the highest production, yielding 72.20 ± 1.53 g/L of sophorolipid crude extract and 60.05 ± 0.56 g/L of diacetylated lactonic C18:1 at shake flask scale with productivities of 0.43 and 0.36 g/L/h, respectively. Results were confirmed in a 2-L bioreactor increasing 15 % diacetylated lactonic C18:1 production. Moreover, wheat feed hydrolysate supplemented only with a hydrophobic carbon source was able to produce mainly diacetylated lactonic C18:1 congener (88.5 % wt.), suggesting that the composition of the hydrolysate significantly influences the congeners profile. Overall, this study provides valuable insights into agricultural byproduct hydrolysates as potential nitrogen feedstocks for sophorolipid production and their further application on industrial biotechnology.

Precise fermentation coupling with simultaneous separation strategy enables highly efficient and economical sophorolipids production

Sophorolipids (SLs) represent highly promising biosurfactants. However, its widespread production and application encounter obstacles due to the significant costs involved. Here, an intelligent and precise regulation strategy was elucidated for the fermentation process coupled with in-situ separation production mode, to achieve cost-effective SLs production. Firstly, a mechanism-assisted data-driven model was constructed for "on-demand feeding of cells". Moreover, a strategy of step-wise oxygen supply regulation based on the demand for cell metabolic capacity was developed, which accomplished "on-demand oxygen supply of cells", to optimize the control of energy consumption. Finally, a systematic approach was implemented by integrating a semi-continuous fermentation mode with in-situ separation technology for SLs production. This strategy enhanced SLs productivity and yield, reaching 2.30 g/L/h and 0.57 g/g, respectively. These values represented a 40.2% and 18.7% increase compared to fed-batch fermentation. Moreover, the concentration of crude SLs after separation reached 793.12 g/L, facilitating downstream separation and purification processes.

Microbial surfactants: characteristics, production and broader application prospects in environment and industry

Microbial surfactants are green molecules with high surface activities having the most promising advantages over chemical surfactants including their ability to efficiently reducing surface and interfacial tension, nontoxic emulsion-based formulations, biocompatibility, biodegradability, simplicity of preparation from low cost materials such as residual by-products and renewable resources at large scales, effectiveness and stabilization under extreme conditions and broad spectrum antagonism of pathogens to be part of the biocontrol strategy. Thus, biosurfactants are universal tools of great current interest. The present work describes the major types and microbial origin of surfactants and their production optimization from agro-industrial wastes in the batch shake-flasks and bioreactor systems through solid-state and submerged fermentation industries. Various downstream strategies that had been developed to extract and purify biosurfactants are discussed. Further, the physicochemical properties and functional characteristics of biosurfactants open new future prospects for the development of efficient and eco-friendly commercially successful biotechnological product compounds with diverse potential applications in environment, industry, biomedicine, nanotechnology and energy-saving technology as well.

Reduced-Cost Production of Sophorolipids by Starmerella bombicola CGMCC1576 Grown on Cottonseed Molasses and Cottonseed Oil-Based Medium

A large-scale application of sophorolipids (SLs) was blocked by their high production cost. One feasible way to reduce the cost of SL production is to develop cheap feedstocks as the substrates for SL fermentation. In the present work, cottonseed molasses (CM), a waste from raffinose production, was used as the hydrophilic substrate;, and cottonseed oil (CO) was used as a hydrophobic substrate for SL production by Starmerella bombicola CGMCC 1576. The primary optimization of carbon sources, nitrogen source and inorganic salts, produced 57.6 ± 2.3 g/L of total SLs and 24.0 ± 1.2 g/L of lactonic SLs on CM and CO, almost equal to the titer of SLs produced from glucose and oleic. A response surface method was applied to optimize the fermentation medium for growth and SL production of S. bombicola. The production of total SLs reached 58.4 ± 3.4 g/L, and lactonic SLs were elevated to more than 25.0 ± 1.9 g/L. HPLC–MS analysis showed that the compositions of SLs produced by S. bombicola on CM and CO were very similar to those on glucose and oleic acid. These results suggested that cottonseed molasses and cottonseed oil can be used as renewable cheap substrates for the reduced-cost production of SLs.

Sustainable production of biosurfactants via valorisation of industrial wastes as alternate feedstocks

Globally, the rapid increase in the human population has given rise to a variety of industries, which have produced a variety of wastes. Due to their detrimental effects on both human and environmental health, pollutants from industry have taken centre stage among the various types of waste produced. The amount of waste produced has therefore increased the demand for effective waste management. In order to create valuable chemicals for sustainable waste management, trash must be viewed as valuable addition. One of the most environmentally beneficial and sustainable choices is to use garbage to make biosurfactants. The utilization of waste in the production of biosurfactant provides lower processing costs, higher availability of feedstock and environmental friendly product along with its characteristics. The current review focuses on the use of industrial wastes in the creation of sustainable biosurfactants and discusses how biosurfactants are categorized. Waste generation in the fruit industry, agro-based industries, as well as sugar-industry and dairy-based industries is documented. Each waste and wastewater are listed along with its benefits and drawbacks. This review places a strong emphasis on waste management, which has important implications for the bioeconomy. It also offers the most recent scientific literature on industrial waste, including information on the role of renewable feedstock for the production of biosurfactants, as well as the difficulties and unmet research needs in this area.

Sophorolipids bioproduction in the yeast Starmerella bombicola: Current trends and perspectives

Sophorolipids are highly active green surfactants (glycolipid biosurfactants) getting tremendous appreciation worldwide due to their low toxicity, biodegradability, broad spectrum of applications, and significant biotechnological potential. Sophorolipids are mainly produced by an oleaginous budding yeast Starmerella bombicola using low-cost substrates. Therefore, the recent state-of-art literature information about S. bombicola yeast is hereby provided, especially the underlying production pathways, biosynthetic gene cluster, and regulatory enzymes. Moreover, the S. bombicola offers flexibility for regulating the structural diversity of sophorolipids, either genetically or by varying fermentative conditions. The emergence of advanced technologies like 'Omics and CRISPR/Cas have certainly boosted rational engineering research for designing high-performing platform strains. Therefore, currently available genetic engineering tools in S. bombicola were reviewed, thereby opening up exciting new possibilities for improving the overall bioproduction titers, structural variability, and stability of sophorolipids. Finally, some technical perspectives to address the current challenges were discussed.

Biosurfactants produced from corncob: a bibliometric perspective of a renewable and promising substrate

The reuse of agro-industrial waste has been a recurring issue since the 20th century. With a composition rich in carbohydrates and because of the massive amount of residue produced daily all over the world, corncob became a low-cost and suitable substrate to produce high added-value compounds. Biosurfactants are bioproducts of versatile applications due to their chemical structure with hydrophilic and hydrophobic regions. The current work performed a bibliometric analysis to identify research related to the synthesis of biosurfactants using corncob as substrate. Despite the high availability of corncobs, only nine articles were found in Scopus and Web of Science using different pretreatment processes and microorganisms. After an initial screening, data regarding research organizations, scientific journals, citations, countries, institutions, and keywords were analyzed. Results indicated that corncobs were also used to produce enzymes, adsorbents, activated carbon, and furfural. The presented evaluation updated the status of art, identifying a serious need for more research, especially because of corncob's high potential to provide fermentable sugars and the wide range of variables influencing fermentation processes that still need to be studied. A future association of this low-cost substrate with other methods can result in a promising scenario for technology transference.

Sweet sorghum bagasse and corn stover serving as substrates for producing sophorolipids

To make the process of producing sophorolipids by Candida bombicola truly sustainable, we investigated production of these biosurfactants on biomass hydrolysates. This study revealed: (1) yield of sophorolipds on bagasse hydrolysate decreased from 0.56 to 0.54 and to 0.37 g/g carbon source when yellow grease was dosed at 10, 40 and 60 g/L, respectively. In the same order, concentration of sophorolipids was 35.9, 41.9, and 39.3 g/L; (2) under similar conditions, sophorolipid yield was 0.12, 0.05 and 0.04 g/g carbon source when corn stover hydrolysate was mixed with soybean oil at 10, 20 and 40 g/L. Sophorolipid concentration was 11.6, 4.9, and 3.9 g/L for the three oil doses from low to high; and (3) when corn stover hydrolysate and yellow grease served as the substrates for cultivating the yeast in a fermentor, sophorolipid concentration reached 52.1 g/L. Upon further optimization, sophorolipids production from ligocellulose will be indeed sustainable.

Sophorolipids production from rice straw via SO3 micro-thermal explosion by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576

A novel lignocellulose material, holocellulose from rice straw via the pretreatment of SO3 micro-thermal explosion, was developed to produce sophorolipids (SLs) with Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The influence factors of inoculum dose, yeast extract concentration and pH regulators (chemical regents used for adjusting/influencing pH) was investigated and discussed. Results showed that W. domercqiae can grow in the rice straw holocellulose hydrolysate, and acquire relative high SL yield of 53.70 ± 2.61 g/L in shake flask culture. Inoculum dose, yeast extract concentration and pH regulator made obvious influence on fermentation parameters, especially on final broth pH and SLs production. Furthermore, there is a strong negative linear correlation existing between final broth pH and lactonic SL or ratio of lac SL/tot SL. Additionally, comparison between SL production and non-glucose carbon sources, culture methods, microbes in previous reports was carried out. These results will be benefit for acquiring SL mixture with suitable lac SL/tot SL ratio for specific purpose and scope economically.

Current status in biotechnological production and applications of glycolipid biosurfactants

Biosurfactants are natural compounds with surface activity and emulsifying properties produced by several types of microorganisms and have been considered an interesting alternative to synthetic surfactants. Glycolipids are promising biosurfactants, due to low toxicity, biodegradability, and chemical stability in different conditions and also because they have many biological activities, allowing wide applications in different fields. In this review, we addressed general information about families of glycolipids, rhamnolipids, sophorolipids, mannosylerythritol lipids, and trehalose lipids, describing their chemical and surface characteristics, recent studies using alternative substrates, and new strategies to improve of production, beyond their specificities. We focus in providing recent developments and trends in biotechnological process and medical and industrial applications.

Glycolipid biosurfactants: main properties and potential applications in agriculture and food industry

Glycolipids, consisting of a carbohydrate moiety linked to fatty acids, are microbial surface active compounds produced by various microorganisms. They are characterized by high structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface, respectively. Rhamnolipids, trehalolipids, mannosylerythritol lipids and cellobiose lipids are among the most popular glycolipids. They have received much practical attention as biopesticides for controlling plant diseases and protecting stored products. As a result of their antifungal activity towards phytopathogenic fungi and larvicidal and mosquitocidal potencies, glycolipid biosurfactants permit the preservation of plants and plant crops from pest invasion. Also, as a result of their emulsifying and antibacterial activities, glycolipids have great potential as food additives and food preservatives. Furthermore, the valorization of food byproducts via the production of glycolipid biosurfactant has received much attention because it permits the bioconversion of byproducts on valuable compounds and decreases the cost of production. Generally, the use of glycolipids in many fields requires their retention from fermentation media. Accordingly, different strategies have been developed to extract and purify glycolipids. © 2016 Society of Chemical Industry.

Culture strategies for lipid production using acetic acid as sole carbon source by Rhodosporidium toruloides

Rhodosporidium toruloides AS 2.1389 was tested using different concentrations of acetic acid as a low-cost carbon source for the production of microbial lipids, which are good raw materials for biodiesel production. It grew and had higher lipid contents in media containing 4-20 g/L acetic acid as the sole carbon source, compared with that in glucose-containing media under the same culture conditions. At acetic acid concentrations as high as 20 g/L and the optimal carbon-to-nitrogen ratio (C/N) of 200 in a batch culture, the highest biomass production was 4.35 g/L, with a lipid content of 48.2%. At acetic acid concentrations as low as 4 g/L, a sequencing batch culture (SBC) with a C/N of 100 increased biomass production to 4.21 g/L, with a lipid content of 38.6%. These results provide usable culture strategies for lipid production by R. toruloides AS 2.1389 when using diverse waste-derived volatile fatty acids.

Hydrolysis of olive mill waste to enhance rhamnolipids and surfactin production

The aim of this work was to demonstrate the effectiveness of hydrolysis pretreatment of olive mill (OMW) waste before use as a carbon source in biosurfactant production by fermentation. Three hydrolysis methods were assessed: enzymatic hydrolysis, acid pretreatment plus enzymatic hydrolysis, and acid hydrolysis. Fermentation was carried out using two bacterial species: Pseudomonas aeruginosa and Bacillus subtilis. Our results showed that the enzymatic hydrolysis was the best pretreatment, yielding up to 29.5 and 13.7mg/L of rhamnolipids and surfactins respectively. Glucose did not show significant differences in comparison to enzymatically hydrolysed OMW. At the best conditions found rhamnolipids and surfactins reached concentrations of 299 and 26.5mg/L; values considerably higher than those obtained with non-hydrolysed OMW. In addition, enzymatic pretreatment seemed to partially reduce the inhibitory effects of OMW on surfactin production. Therefore, enzymatic hydrolysis proved to effectively increase the productivity of these biosurfactants using OMW as the sole carbon source.