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 γ-, δ- and α-tocopherol. Similar reductions (≈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: 120W, 5min; method B: 30W, 2min) using a probe-type sonicator (100mL 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.
Three antioxidant extracts (collagen hydrolysate, pomegranate peel extract, shrimp lipid extract) were encapsulated in soy phosphatidylcholine liposomes with the addition of glycerol. The particle size of the fresh liposomes ranged from 75.7 to 81.0 nm and zeta potential from -64.6 to -88.2 mV. Freeze-drying increased particle size (199-283 nm), and slightly decreased zeta potential. The lyophilized liposomes were incorporated in squid surimi gels at 10.5% concentration. An alternative functional formulation was also prepared by adding 2% of non-encapsulated bioactive extract. The gels were characterized in terms of colour, texture and oxidative stability (TBARS) after processing and also after frozen storage. The incorporation of the freeze-dried liposomes caused a slight decrease in gel strength and contributed to maintaining the stability of the gels during long-term frozen storage. The antioxidant properties of the bioactive extracts, liposomes and in vitro digested surimi gels were determined.
Liposomes made from soy phosphatidylcholine entrapping food waste compounds (collagen hydrolysate, L-HC; pomegranate peel extract, L-PG; and shrimp lipid extract, L-SL) were freezedried and stored for seven months. The freeze-drying process increased the particle size and decreased water solubility. The freeze-dried L-HC and L-PG preparations presented large multivesicular vesicles with spherical and unilamellar morphology. Large multilamellar vesicles were observed in L-SL, coinciding with greater structural changes in the membrane bilayer and increased thermal stability, as observed by ATR-FTIR and DSC. Dynamic oscillatory rheology revealed a slight hardening in the dried liposomes, induced by storage time. A sharp rigidifying effect in the temperature range from 40 to 90°C was observed in L-SL. The loading with antioxidant compounds prevented freeze-drying-induced lipid oxidation. The storage stability of freeze-dried liposomes and their technological aptitude as a food ingredient varied depending on the chemical nature of the entrapped compounds.
Soy phosphatidylcholine liposomes encapsulating increasing concentrations of two sea fennel extracts (aqueous and ethanolic) prepared by ultrasonication were freeze-dried, using glycerol as lyoprotectant. Particle properties, water dispersibility, colour, thermal properties and antioxidant capacity (radical scavenging capacity, ferric ion reducing power, Folin-reactive substances) of the liposomal preparations were determined. The freeze-drying process caused an overall increase in particle size and polydispersity index, while the zeta-potential became more electronegative. Both sea fennel extracts were rich in chlorogenic acid (42.61 and 58.48 mg/g for the aqueous and ethanolic extracts, respectively) and showed great antioxidant activity. Vitamin C was identified in the aqueous extract, whereas rutin and rosmarinic acid in the ethanolic one. The entrapment efficiency, determined in the liposomes prepared at the highest extract concentration, was 65.6% and 49.1% for the aqueous extract and the ethanolic extract, respectively. The liposomal antioxidant activity and total phenolic content followed a linear increasing tendency as a result of increasing the extract concentration, irrespective of the type of extract. Higher antioxidant activity was found in the liposomes loaded with the ethanolic extract, in a clear relationship to the greater amount of highly antioxidant phenolic compounds extracted, and also to their lower entrapment efficiency, which caused a greater amount of extract to remain outside the liposome. Both extracts were suitable for producing liposomes with antioxidant properties which could be dried and used to design functional foods.
A collagen hydrolysate (HC) obtained from giant squid (Dosidicus gigas) tunics was encapsulated in soy phosphatidylcholine liposomes in the presence and absence of glycerol. The z-average and ζ-potential of empty and loaded liposomes ranged from 92.4 to 96.0 nm and from-30.4 to-34.5 mV, respectively. The HC was encapsulated with an entrapment efficiency of 80-83%, and the resulting liposomal dispersions showed ≈50% of angiotensin-converting enzyme (ACE) inhibitory capacity. An in vitro process of gastrointestinal digestion of the liposomes increased the antihypertensive potential, regardless of the presence or absence of glycerol. The liposomal dispersions were incorporated into carboxymethyl cellulose films, in which two ways of adding glycerol were compared: adding it directly to the film-forming dispersion or incorporating it previously into the liposomes. The presence of intact liposomes in the films, which was corroborated by transmission electronic microscopy at cryogenic temperature, decreased the water solubility and increased adhesiveness. The results demonstrated that glycerol-containing liposomes were less affected by the film drying step and also the subsequent simulated gastrointestinal digestion, with greater preservation of vesicle size and morphology, than if glycerol was added directly to the film-forming solution.
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