Liposomes as food ingredients and nutraceutical delivery systems
Over the last 20 years, there has been rapid development of liposomes, i.e. enclosed phospholipid vesicles with bilayered membrane structures, as carriers of bioactive ingredients in food and nutrition. Because they are able to enhance the performance of encapsulated components by increasing physicochemical stability and improving bioavailability in vitro and in vivo, liposomes have received much attention with respect to the encapsulation of antioxidants, enzymes, vitamins, flavours etc. However, for the further successful development of encapsulation systems and to explore new generations of products, some limitations of liposomes must be overcome.
Microencapsulation is a rapidly developing technology that packages functional ingredients within a specific matrix. In the past decade, this technology has been widely applied in the food, pharmaceutical and cosmetics industries. The materials used for encapsulation are usually based on lipid, carbohydrate and protein, and various microencapsulation systems, such as liposomes, emulsions, quantum dots and polymeric nanoparticles, have been explored recently (1-4).
After liposomes were first reported by Bangham and his co-workers in 1965, they were quickly developed as delivery systems (5, 6). A liposome is a self-assembled lipid bilayer that encapsulates a fraction of the surrounding aqueous medium. It is prepared from a complex mixture of phospholipids isolated from natural sources or a synthetic phospholipid. The general chemical structures of natural and synthetic phospholipids are shown in Figure 1. The isolated phospholipids, which are usually derived from soybean, milk and egg (7-9), are hard to characterise because of their complex compositions (Figure 1(a)). Recently, new generations pure phospholipids have been synthesised ...