In order to explore the effect of electric charge on detergent solubilization of phospholipid bilayers, the interaction of nine electrically charged surfactants with neutral or electrically charged liposomes has been examined. The detergents belonged to the alkyl pyridinium, alkyl trimethylammonium or alkyl sulphate families. Large unilamellar liposomes formed by egg phosphatidylcholine plus or minus stearylamine or dicetyl phosphate were used. Solubilization was assessed as a decrease in light-scattering of the liposome suspensions. The results suggest that electrostatic forces do not play a significant role in the formation of mixed micelles and that hydrophobic interactions are by far the main forces involved in solubilization. In addition, from the study of thirty different liposome-surfactant systems, we have derived a series of empirical rules that may be useful in predicting the behaviour of untested surfactants: (i) the detergent concentration producing the onset of solubilization (Don) decreases as the alkyl chain length increases; the decrease follows a semi-logarithmic pattern in the case of alkyl pyridinium compounds; (ii) for surfactants with critical micellar concentrations (cmc) less than 6 x 10(-3) M, Don. is independent of the nature of the detergent and the bilayer composition; for detergents having cmc greater than 6 x 10(-3) M, Don. increases linearly with the cmc; and (iii) Don. varies linearly with the surfactant concentration that produces maximum solubilization.
Polycyclic aromatic hydrocarbons (PAH) belong to a large chemical family comprising many different compounds with important biological activity in mutagenic and carcinogenic processes. PAH have been detected in both raw and processed foods. The presence of PAH in non-processed foods is associated with environmental pollution from both human and industrial activities, whereas contamination of processed foods can be caused by certain preservation and processing procedures. Both toxicological and epidemiological studies have shown a relation between such compounds and tumor development. The data indicate that PAH must undergo a biotransformation process that causes the formation of biologically active metabolites. In this process, the presence of an enzyme complex that is induced by different xenobiotics is implied, making the toxicity of such compounds hard to predict. As setting a threshold limit below which toxicity could be considered negligible is difficult, the presence of PAH in foodstuffs should be reduced to as low as possible by controlling environmental contamination and all procedures that could cause PAH contamination during food processing, preserving, and packaging.
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