| Summary: | Tese de Doutoramento em Engenharia Química e Biológica Biosurfactants are compounds with surface activity constituting the major class of natural surfactants that present interesting features (e.g. emulsifying capacity) for the food industry. These compounds have several advantages over synthetic surfactants such as degradability, can be synthesized from renewable substrates as carbohydrates and fatty acids, and low toxicity. In this sense, the purpose of this thesis is to synthesize new biosurfactants, in particular fructose, sucrose and lactose esters, for potential use in the food industry. Several synthesis experiments were performed under different experimental conditions to maximize the esterification reaction yield, and consequently the production of biosurfactant. The sugar ester biosurfactants purity was the determinant factor for these studies. The synthesis assays were performed in shake flasks under controlled temperature, time and agitation, according to the optimal criteria for the lipases used, namely Candida antarctica type B (CALB) lipase and porcine pancreas lipase (PPL). An experimental design was conducted in order to optimize the yield of fructose esters production from fructose, oleic acid and ethanol using CALB. Temperature and reaction time were found to be the most significant parameters. The optimum conditions were 57.1 ºC, 100 rpm and 37.8 h and a maximum esterification yield of 88.4% was obtained. Afterwards, the lipases from CALB and PPL were used with different carbohydrates (fructose, sucrose and lactose), fatty acids (oleic and linoleic) and solvents (ethanol and ethyl acetate), in order to explore the synthesis of novel sugar esters with improved characteristics. The optimal conditions have been established for all set of experiments and the sugar ester biosurfactants have been characterized according to their surface activity and emulsification index (EI). In the experiments for which CALB was used, lactose ester synthesized using linoleic acid and ethanol presented the ...
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