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Vegetable oil processing units produce significant quantities of garbage and byproducts (like soap products, oilseed cakes, lipid residues, semi‐solid effluents, and water‐soluble effluents) that are rich in fats, oils, and other compounds [91]. Such waste products have become a major source of pollution in the hydrosphere and lithosphere because of their low biodegradable lipid content. This being so, it is crucial to deploy waste material as a substrate for product formation since it puts such waste to more constructive use.

Mercade et al. [95] presented the application of olive‐oil mill effluent as a substrate for rhamnolipid biosynthesis using Pseudomonas sp. JAMM with 0.058 g/g biosurfactant production by using 100 g/l of olive oil mill effluents and NaNO₃ (2.5 g/l). The glycolipids produced in this process reduced the media surface tension from almost 40 to around 30 mN/m. In another study conducted by Abalos et al. [96], the application of Pseudomonas aeruginosa AT10 was reported for rhamnolipid production using soybean‐oil refinery waste in the fermentation medium. They reported that P. aeruginosa AT10 produced 9.5 g/l of glycolipids with 26.8 mN/m surface tension and 122 mg/l critical micelle concentration (CMC) value. Benincasa et al. [97] documented that water‐immiscible waste (soapstock) from refining vegetable oil processing unit can be used as a substrate for rhamnolipid production of 15.8 g/l using P. aeruginosa LBI. Meanwhile De Faria et al. [98] supplemented raw glycerol as substrate produced from a biodiesel fermentation unit for surfactin (C14/Leu7) synthesis as sole carbon sources with 1.36 g/l final product. In another study, George and Jayachandran [99] communicated the use of waste coconut oil for rhamnolipid production (1.97 g/l) using P. aeruginosa. Similarly, Moya Ramírez et al. [100] evaluated the role of olive mill waste (OMW) as a substrate for rhamnolipid production using P. aeruginosa and reported production of 29.5 mg/l rhamnolipids. They found the rhamnolipids and surfactins production reached up to 299 and 26.5 mg/l under optimum fermentation conditions. Most of the above research findings used various types of lipid‐rich waste as a carbon source and Pseudomonas as a primary organism for rhamnolipid synthesis. They concluded that water‐immiscible substrate produced a better amount of biosurfactant than water‐miscible substrate, like fructose and glucose. The byproducts of food and vegetable oil used as raw materials for the production of biosurfactants are shown in Table 3.2.

Table 3.2 The byproduct of foodstuffs and vegetable oil used in the production of biosurfactants.

Source: Modified based on Kaur et al. [21].

Raw material/byproduct	Type of biosurfactant	Microbial strain
Molasses	Rhamnolipids	Pseudomonas putida strain B17
Canola oil	Rhamnolipids	Pseudomonas sp. strain DSM 2874
Cusi oil	Sophorolipids	Candida lipolytica strain IA 1055
Turkish maize oil	Sophorolipids	Candida bombicola strain ATCC 22214
Sunflower and Soybean oil	Rhamnolipids	Pseudomonas aeruginosa strain DS10–129
Sunflower oil	Lipopeptide	Serratia marcescens
Soybean oil	Mannosylerythritol lipid	Candida sp. strain SY16
Whey and Liquor industry waste	Rhamnolipids	Pseudomonas aeruginosa strain BS2

In 2004, Bednarski et al. [101] described the use of two Candida yeast strains (C. antarctica strain ATCC 20509 and C. apicola strain ATTC 96134) for the biosynthesis of glycolipids from waste residues isolated from two oil refineries. They supplemented the fermentation media with 5–12% v/v soap stock and found that yeast strains produced ~7–13 g/l glycolipid content, respectively, whereas 6.6 and 10.5 g/l glycolipid were produced from the use of post‐refinery trans‐fatty acids at 2–5% v/v, respectively. The researchers [101] concluded that adding soap stock seemed to have a beneficial impact on glycolipid biosynthesis.

Nitschke et al. [102] experimented with soybean, cottonseed, babassu, and maize seed oil waste from oil refineries for rhamnolipid synthesis by applying P. aeruginosa LBI strain. Their findings revealed that out of four kinds of oil refinery waste, 2% w/v soybean soap stock could be utilized as the most preferred raw material for 11.7 g/l rhamnolipid production with 26.9 mN/m surface tension and 51.5 mg/l CMC. A sequential factorial method was introduced by Rufino et al. [103] to maximize the development of C. lipolytica in a fermentation medium supplemented with soybean oil as a substrate supplemented with refinery waste, glutamic acid, and yeast extract for biosurfactant production. They reported biosurfactant production with 25.29 mN/m surface tension when a combination of oil residue (6%) and glutamic acid (1%) was used in the fermentation medium. The biosurfactants produced had stability over a more comprehensive pH (2–12), temperature (0–120 °C) and salinity (2–10% sodium chloride) levels. Rufino et al. [103] investigated the cell surface characteristics, including its relation to the development of biosurfactants for diverse uses. This research group [103] cultivated six strains of Candida in fermentation medium supplemented with glucose, corn‐steep liquor, soybean refinery oil residues, peanut oil refinery residues, and n‐hexadecane. Their studies indicated that the biosurfactants produced with yeast could be used to extract hydrophobic substances with 90% capability to eliminate hydrophobic pollutants from soil.