AbstractBiosurfactants play an important role in many sectors such as agriculture, cosmetics, petrol industry, food, pharmaceuticals, plastic and machinery fields. One of the main challenge to use biosurfactants compared to chemical surfactants is the production cost. SSF plays an important role as an alternative to produce these biosurfactants as it have a few advantages compared to submerged fermentation such as low production cost, less waste effluent problem, saving of water and energy, and stability of the product because of the less dilution in the medium. By using microorganisms from Bacillus strain, biosurfactants are successfully produced using different cheap substrates such as potato peels, molasses and rice straw via SSF. The data from this review paper would serve as a platform for higher production of biosurfactants using cheap substrates via solid state fermentation.
Introduction Solid state fermentation(SSF) has received a plenty of attention from researchers regarding the several advantages that it has over the submerged fermentation(SmF). SSF is a process which involves the growth of microorganisms on moist solid substrates in the absence of free flowing water(Pandey, Soccol et al. 2000, Ghribi, Abdelkefi-Mesrati et al. 2012). The practice of SSF has been done for centuries, especially in the food production.
In recent years, the interest in SSF and its application to the production of enzymes, metabolites and organic compounds have been a resurgence. Even though SSF has many economic advantages, but it has limited devices for industrial use and is lacking in efficient and practical designs(Suryanarayan and Mazumdar 2001). SSF also have a few problems in the production such as low productivity, expensive raw materials and high costs for downstream processing. Hence, optimization of the substrate is done including selection of cheap carbon sources together with overall media optimization to produce maximum production as well as minimum costs(El-Housseiny, Aboulwafa et al. 2016). Selection of waste substrates involves the problem of finding a waste with the right balance of carbohydrates and lipids to support optimal growth and production(Makkar and Cameotra 1999). SSF uses moist substrates in the absence of free water.
This condition of substrates provide the microorganisms with carbon, nitrogen, minerals and other nutrients, as well as anchorage for the microorganisms. Agricultural residues such as wood chips, corn cob and wheat straw are used as substrates for SSF as they are widely available in most agricultural countries(Nigam, Armour et al. 2000). Biosurfactants are amphiphilic biological compounds produced by microorganisms which have the ability to reduce the interfacial tension between different fluid phases(Nalini and Parthasarathi 2014). The increase in environmental awareness including the emphasis on a sustainable society in harmony with the global environment, surfactants that come from microbial origin, also referred to as biosurfactants are getting much more attention as compared to the chemical surfactants due to mild production condition, lower toxicity, higher biodegradability and environmental compatibility. Biosurfactants have a major obstacle in the wide-scale industrial application which is the high production cost alongside the less production rate as compared to the synthetic surfactants which are available commercially(Das and Mukherjee 2007). In addition, there is a strong interest in replacing chemical surfactants with biosurfactants produced in microbial fermentation process.
Since biosurfactants typically have a lower toxicity and higher biodegradability than the chemical surfactants, the replacing of chemical surfactants involve the application of surfactants in the environment, such as in bioremediation and in microbially enhanced oil recovery(Camilios-Neto, Bugay et al. 2011). Rhamnolipid constitute one of the most important classes of biosurfactants due to their advantageous characteristics. Rhamnolipid harbours a broad range of industrial applications due to its unique properties such as foaming, detergency, sequestering, solubilizing and emulsifying(El-Housseiny, Aboulwafa et al. 2016).
In this review paper, we will cover the experiments that has been done using SSF, identify the types of microorganisms (specified for Bacillus strains) that are able to produce biosurfactants using SSF and also the effects of types of substrates on the production of biosurfactants. Literature Review1) Solid state fermentation Solid substrate fermentation is defined as processes in which the substrate itself acts as carbon/energy source, occurring in the absence or near-absence of free water whereas solid state fermentation is defined as any fermentation process occurring in the absence or near-absence of free water which employs a natural substrate, or an inert substrate used as solid support. However, substrate must possess enough moisture to support growth and metabolism of microorganism(Pandey 2003).
There are several important factors, which affect SSF processes. Among these, selection of a suitable strain and substrate, and selection of process parameters (physical, chemical and biochemical) are crucial. Many practical advantages have been attributed to the production of biologically active secondary metabolites through the SSF route. Mycotoxins, bacterial endotoxins, plant growth factors, antibiotics, immuno-suppressive drugs, alkaloids, etc.
are among the important group of bioactive compounds, which have been produced through SSF. Several studies have been carried out on the production of various antibiotics in SSF including penicillin, cephalosprin, tetracyclines, chlorotetracyclines, oxytetracyclines, iturin, surfcatin, actinorhodin, methylenomycin and monorden. Most of the studies involved the application of agro-industrial residues as substrate, although some used inert substrates such as sugarcane bagasse or agar. SSF holds tremendous potential for the production of enzymes. It can be of special interest in those processes where the crude fermented product may be used directly as enzyme source. Microbial enzymes have attained a significant role in biotransformations involving organic solvent media, mainly for bioactive compounds along with the applications in the fermentation and food industries which is now well-established.(Pandey, Soccol et al.