Author(s): Maeiro, Maria Inês de Sousa Franklin
Date: 2009
Persistent ID: http://hdl.handle.net/10400.5/1135
Origin: Repositório da UTL
Subject(s): interesterificação; lipase imobilizada; lipidos estruturados; interesterification; immobilized lipase; structured lipids
Mestrado em Engenharia Alimentar - Tecnologia dos Produtos Vegetais - Instituto Superior de Agronomia
There has been a great interest in the production of structured lipids over the last decade due to their significant potential application in cocoa butter equivalents, conventional oils enriched with polyunsaturated fatty acids, lowcaloric structured lipids, infant formulas, and other products. Structured lipids (SLs) consist of TAG that have been (i) modified by the incorporation of new fatty acids (FA), (ii) restructured to change the positions of FA or FA profile, from the natural state, or synthesized to yield novel TAG, either chemically or enzymatically. These modified fats with novel properties present important medical, nutraceutical and food applications. Currently, chemical processes are used in the Food Industry for fat and oil modification and for SLs production. These reactions are carried out at high temperature and under extreme pressure conditions and catalyzed by non-selective inorganic catalysts. The heat sensitivity of some fatty acids and the requirement for lipids with specific structures and compositions has led to the development of lipase-catalyzed methods of production. The replacement of the inorganic catalysts by enzymes (lipases) is highly desirable in this area. Lipases are versatile catalysts. Traditionally, lipases are considered as hydrolases that catalyse the hydrolysis of water insoluble esters (e.g. TAG) in water/oil interfaces, exhibiting, most of them, an interfacial catalytic kinetics. In addition, lipases are also able to catalyse different reactions, namely esterification and interesterification reactions when in nonaqueous media at low water activity (aw). Moreover, lipases accept a wide variety of substrates while maintaining their regioselectivity and stereoselectivity, conversely to the inorganic catalysts. Enzymatic interesterification with sn-1,3 specific lipases has also been used by the industry for the production of cocoa butter-like fats and human milk fat substitutes. The demand for specific-structured triacylglycerols, produced by exploiting the sn-1,3 regiospecificity of the lipases, are currently increasing. In this study, the Aspergillus niger lipase was immobilized in different supports (AlPO4- Sepiolite, Eupergit® C and Eupergit® C 250 L) and used as catalyst for the interesterification of fats rich in Omega-3 polyunsaturated fatty acids (omega-3 PUFA), at 60ºC, in solvent-free media. Different enzyme loads and water activity (aw) values of the biocatalyst were tested on the interesterification kinetics. Reaction media consisted of blends of palm stearin, palmkernel oil and a concentrate of triacylglycerols rich in omega-3 PUFA (“EPAX 4510TG”). The interesterification reaction was evaluated by the reduction of the solid fat content at 35ºC (SFC35ºC). Also, free fatty acids (FFA), coming from hydrolysis of triacylglycerols and/or from the first interesterification step, and first and final oxidation products were quantified. Thermal oxidation showed to be negligible under the reactions conditions followed. FFA content increased with lipase load. No significant increase in interesterification activity was observed for loadings higher than 10% in AlPO4-Sepiolite. The enzyme load in Eupergit® C and Eupergit® C 250 L was 20% (w/w) in all the experiments. For all the biocatalysts tested, the catalytic activity increased with the aw. A 100%, 43% and 26% of SFC 35ºC reduction was observed after 6 hours of reaction, respectively when the lipase was immobilized in AlPO4-Sepiolite, Eupergit® C and Eupergit® C 250 L, at aw of 1. However, a low operational stability of the lipase in AlPO4-Sepiolite was observed. When this biocatalyst was reused in 8 consecutive batches of 23 hours duration each, a half-life time of only about 2,2 days, when used in consecutive batches.
RESUMO - A lipase de Aspergillus niger foi imobilizada em diferentes suportes (AlPO4-Sepiolite, Eupergit® C e Eupergit® C 250 L). Testaram-se diferentes concentrações de lipase e valores de actividade da água (aw) do biocatalisador, na cinética da interesterificação de gorduras ricas em ácidos gordos polinsaturados ómega-3 (ómega-3 PUFA), a 60ºC. O meio reaccional foi constituído por estearina de palma, óleo de palmiste e um concentrado de triacilgliceróis ricos em ómega-3 PUFA. A reacção de interesterificação foi avaliada pela redução do teor de gordura sólida a 35ºC (SFC35ºC). Quantificaram-se ainda os ácidos gordos livres (AGL) provenientes da hidrólise e/ou do primeiro passo da interesterificação, e os produtos de oxidação. A termoxidação dos lípidos foi desprezável e os AGL aumentaram com a carga de biocatalisador. Cargas lipásicas em AlPO4-Sepiolite superiores a 10% não conduziram a aumento na actividade catalítica. Para todos os biocatalisadores testados, a actividade catalítica aumentou com a aw. Observou-se uma redução de 100%, 43% e 26% de SFC35ºC após 6h de reacção catalisada, respectivamente, pela lipase em AlPO4-Sepiolite, em Eupergit® C e C 250 L, com aw de 1. Contudo, a lipase em AlPO4–Sepiolite apresentou um tempo de meia vida de apenas 2,2 dias em ensaios de reutilização sucessiva.
