Biodiesel has a higher affinity toward moisture content than petroleum diesel, and the water retaining capacity of biodiesel is higher than diesel. The water content in fuels can be classified in free, emulsionated, and soluble water. High water content in biodiesel and diesel can cause problems such as water accumulation and microbial growth in fuel tanks and transportation equipment. Currently, there is a lack of information on water absorbance in biodiesel and biodiesel/diesel blends. Experiments were conducted to determine the water absorbance of biodiesel and biodiesel− diesel fuel blends evaluating the temperature and blend ratio parameters. Soluble water in biodiesel ranged from (1500 to 1980) mg•kg −1 in the temperature range of (283.15 to 323.15) K, which was 10 to 15 times higher than diesel. Results also showed that, at constant relative humidities, biodiesel absorbed 6.5 times more moisture than diesel. The presence of free and/or emulsionated water in biodiesel and blends was determined through turbidity experiments.

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Três lipases microbianas nativas (Aspergillus niger, Rhizopus javanicus e Penicillium solitum) foram utilizadas na hidrólise do óleo de salmão (teor de AGPI n-3 de 30,1%) com o objetivo de concentrar o conteúdo de ácidos graxos poliinsaturados n-3 (AGPI n-3) nos acilgliceróis residuais. A metodologia de planejamento experimental e análise de superfície de resposta foi usada para se chegar às condições otimizadas de cada reação enzimática, utilizando as seguintes variáveis; temperatura (X 1), quantidade de lipase (X 2) e taxa de água/óleo (X 3). Com base nos resultados do planejamento, a lipase de Aspergillus niger foi a mais eficiente na concentração dos AGPI n-3, sendo que as condições ótimas de reação foram: concentração de enzima de 500 U g-1 óleo, temperatura 45 °C e taxa de água/óleo de 2:1 m/m após 24 h de reação. O grau de hidrólise (60%) conduziu a um aumento do conteúdo de ácido docosahexaenóico (DHA) de 14,4% para 34,0% (enriquecimento de 2,4 vezes) nos acilgliceróis residuais após a hidrólise do óleo de salmão. In an attempt to concentrate the content of n-3 polyunsaturated fatty acids (n-3 PUFA) in the residual acylglycerol, salmon oil (n-3 PUFA content of 30.1%) was hydrolyzed with three kinds of native microbial lipases (Aspergillus niger, Rhizopus javanicus and Penicillium solitum). For each lipase, a response surface methodology was used to obtain maximum PUFA content and to optimize the parameters of enzymatic reactions with respect to important reaction variables; temperature (X 1), amount of lipases (X 2) and water/oil ratio (X 3). Based on these results, optimal reaction conditions were established. Aspergillus niger lipase was the most effective in concentrating n-3 PUFA. The degree of hydrolysis (60%) led to an increase in the docosahexaenoic acid (DHA) content from 14.4% in the original oil to 34.0% (2.4-fold enrichment) in the residual acylglycerol under optimum conditions: enzyme concentration of 500 U g-1 oil, reaction temperature of 45 °C and water/oil mass rate of 2:1 (m/m) after 24 h reaction.

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