Stability of marine lipid based-liposomes under acid conditions. Influenceof xanthan gum

Liposomes are potential candidates in Human nutrition to supplement diets i n essential lipo- and hydro-soluble nutriments. In this context, marine lip id based-vesicles, rich in polyunsaturated fatty acids, and containing vita min B1 (thiamine) were prepared. Two methods were envisaged for vitamin tra pping, passive encapsulation and active loading through the use of a transm embrane PH gradient. These methods were compared in terms of thiamine trapp ing efficiency. Influence of xanthan addition was also studied. Although, t he active loading yielded to higher encapsulation ratios than the passive m ethod, encapsulation efficiency was markedly increased, in both cases, as s oon as the hydrocolloid was added after the lipid hydration phase, Liposome stability was assayed by microscopy observation and membrane permeability to thiamine in a medium that mimic that faced by the structures administrat ed by the oral route, i,e.. an acid PH medium, as in the Human stomach. Low PH value led to an instantaneous vesicle aggregation. Thiamine was totally released from liposomes prepared without xanthan after 24 h storage in a n eutral medium. This time was shortened to 1 h at PH 1.5. However, thiamine retention was significantly improved when liposomes were prepared in presen ce of the hydrocolloid, whatever the encapsulation method used. On the whol e, these results were interpreted in terms of xanthan coating around the li posome surface that would result from lipid-hydrocolloid interactions occur ring during the centrifugation steps of liposome preparation.