Fruitculture is one of the economic sectors that generate the most revenue for Brazil. However, this activity is responsible for the generation of environmental problems due to the precarious management of the residues produced by the processing. The agro-industrial residues of guava are rich in compounds of great interest, which can be extracted and/or transformed into products with high added value. Among these compounds, we highlight the free fatty acids that are widely applied in several industrial segments and can be converted into rhamnolipids (RHLs) through the action of microorganisms. RHLs act as biosurfactants, and currently, they have aroused great interest from researchers, since they represent a highly viable alternative concerning synthetic surfactants offering a range of advantages such as better surface and interfacial activity, greater tolerance to temperature variations, pH and ionic strength, better biodegradability and less toxicity. RHLs are used especially in the pharmaceutical, cosmetic, textile, food (human and animal), agrochemical, and civil construction industries. However, in recent years, the oil industry has consolidated itself as the largest biosurfactant market due to its use in the production of fuels and incorporation in the formulation of lubricating oils. Thus, due to their great relevance, the estimate of the commercialization of these compounds until 2023 is approximately US $ 23 billion. Thus, the development of new analytical methods for determining RHLs is extremely important to contribute to a greater appreciation of guava agro-industrial waste and consequently mitigate the negative impacts on the environment. On the other hand, the RHLs produced by Pseudoma aeruginosa have as one of their main constituents the 3-hydroxydecanoic acid, whose determination constitutes a relevant topic in the research by fast and low-cost analytical methods and of great importance for the development of fruit production. In the literature, several methods of analysis are reported in general based on the use of chromatographic techniques, which demand the use of solvents, the need for derivatization of samples, and the high cost of equipment. However, the use of electrochemical sensors shows numerous advantages mainly concerning the low cost of equipment, high selectivity, low detection limit, the wide linear range of concentration, which allows the determination of a large number of compounds without the need for exhaustive sample preparation. Therefore, the objective of this work is the development of an electrochemical sensor based on molecularly printed polymers on a nanostructured surface containing reduced graphene oxide and metallic nanoparticles for the determination of 3-hydroxydecanoic acid in RHLs obtained from agro-industrial residues of guava.
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