Effect of chemical composition and sonication procedure on properties of food-grade soy lecithin liposomes with added glycerol

The effect of two-step and five-step acetone washing of soybean lecithin (SL) on compositional properties of partially purified phosphatidylcholines (PW2 and PW5) was studied. Trace amounts of protein were detected in SL, PW2 and PW5, with a predominance of glutamic acid and aspartic acid. Increasing the number of acetone washing steps significantly reduced the total content of gamma-, delta- and alpha-tocopherol. Similar reductions (approximate to 90%) of neutral lipids were found in both PW2 and PW5, but the removal of free fatty acids was higher in PW5 than in PW2 (78% vs. 71%). Linoleic acid was the main constituent in both the neutral lipids and the phospholipid fractions of SL, PW2 and PW5, accounting for around 53-59% of total fatty acids; however, a considerable amount of it was removed by increasing the number of washing steps. All phospholipid classes were mostly concentrated in the first two-step washing of lecithin. Further washing increased the concentration of phosphatidylcholine (PC) in PW5, as compared to PW2. Glycerol-containing liposomes from PW2 and PW5 were produced using two different-intensity sonication procedures (method A: 120 W, 5 min; method B: 30 W, 2 min) using a probe-type sonicator (100 mL volume suspension). Liposomes of soy lecithin and liposomes of PW5 without glycerol were also obtained by using strong sonication (method A). The liposomal dispersion with the highest purification and the stronger sonication was clearly distinguished from the others, both in particle size and in zeta potential. DSC results showed noticeable interference of glycerol in the membrane structure, but minimal changes in particle size and surface charge.