Читать книгу Biosurfactants for a Sustainable Future - Группа авторов - Страница 54

High volumes of effluents, extremely rich in starch and cellulose, are generated during the commercial extraction of starch using various staple crops like maize, rice, cassava, wheat, and potato, which could be utilized as a growth medium to produce different products like surfactins [76, 117, 118]. Potato waste, for example, comprises 16–20% of starchy material, 2–2.5% of proteins, 1–1.8% of fibers, and 0.15% of fatty acids. It was earlier reported [119] that potato with surface skin contains elevated potassium, B complex vitamins and vitamin C, and minerals like P, Mg, and Fe.

Thompson et al. [120] examined potato waste as a possible source of carbon in shake flask culture to produce biosurfactants using B. subtilis ATCC‐21332. They evaluated different potato‐based fermentation media for biosurfactant production, which includes defined potato media, liquefied and solid potato waste media, synthetically made starchy medium by the addition of pure starch in mineral media. In a solid medium, the surface tension decreased from 71.3 to 28.3 mN/m, and CMC 100 mg/l was reported when only 60 g/l of potato substrate was used for microbial cultivation, without adding any other nutrient in the fermentation medium. They also examined the surfactin synthesis by using B. subtilis 21332 strain in a medium containing potato industrial effluent with 16.2 and 6.5 g/l of potato solid components. The potato effluent was diluted at 1 : 10 by adding minerals and corn steep liquor to the modified and unmodified media. Surfactin produced using small potato solids showed a better production of biosurfactants with a production concentration of 0.44 g/l than that of large potato solids. Thompson et al. [120] and Noah et al. [76] demonstrated the usage of corn steep liquor for surfactin production. Noah et al. [76] subsequently produced surfactin with a low‐solid potato effluent with the same microbial strain in batch‐mode operated chemostat and recorded ~0.8–0.9 g/l production after 52 h of fermentation. Another study conducted by Das and Mukherjee [121] documented the production of lipopeptides using B. subtilis DM03 and DM04 strain with 5 g potato peel waste under solid‐state fermentation and 2% w/v substratum in submerged fermentation. During fermentation, the production of lipopeptide by B. subtilis DM‐03 was reported with 80 and 67 mg/g in submerged and solid‐state fermentation, respectively.

Wang et al. [122] used B. subtilis B6–1 for fengycin and poly‐β‐glutamic acid(α‐PGA) production by incorporating 5 g/l of soy curd and 5 g/l of sweet potato residue in solid‐state fermentation. The quantity of lipopeptide was reached at the maximum level after 54 hours of incubation; however, the highest amount of γ‐PGA (3.63%) was achieved after 42 hours of incubation. The researchers also emphasized the potential use of these lipopeptides as a biocontrol agent and fertilizer synergists.

Cassava wastewater is another extremely rich carbohydrate waste used for biosurfactant production [123, 124]. The Bacillus sp. strain LB5a produced biosurfactants from cassava wastewater [125]. The results of a Nitschke and Pastore [126] study showed that bacteria were able to grow and yield biosurfactants in both solid and liquid medium, but the best results were reported in broth medium with the surface tension of 26.6 mN/m. They also examined the efficiency of B. subtilis ATCC 21332 and B. subtilis LB5a for biosurfactant production using cassava wastewater in another study. B. subtilis LB5a lowered the medium surface tension up to 26 mN/m with 3.0 g/l of biosurfactant, while the strain ATCC‐21332 produced crude biosurfactant (2.2 g/l) and changed medium surface tension up to 25.9 mN/m [127, 128]. The above studies emphasized the potential use of starchy byproducts and associated carbon sources for synthesis of biosurfactants. The potential of starch‐rich waste as a carbon source for the production of biosurfactants and some other useful products is promising; however, multidisciplinary collaborative research is needed to meet the industrial needs in terms of product quantity and quality.