Phospholipid Complexes of Phenolic Esters: Novel Structured Lipids for Controlled Dual Release of Polyphenols

Butyl gallate (BG, GA-OC₄H₉), dodecyl gallate (DG, GA-OC₁₂H₂₅), octyl gallate (OG, GA-OC₈H₁₇), and hexadecyl gallate (HG, GA-OC₁₆H₃₃) were among the alkyl gallates (A-GAs, belonging to phenolic esters) that were used to synthesize phospholipid complexes using an ethanol evaporation method. The everted rat gut sac model (ERGSM) in conjunction with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection illustrated that these complexes were capable of releasing A-GAs (sustained-release behavior 1) in ERGSM, which were later subjected to hydrolysis to produce free gallic acid (GA) (sustained-release behavior 2) that could penetrate mucous membrane of small intestine. The dual-release rate of phospholipid complexes was related to the acyl chain length of A-GAs, and complexes (OG-lecithin from soybean [SL]) with a moderate chain length of 8 exhibited the fastest hydrolysis rate. It was worth noting that unlike complexes containing longer alkyl chains, the BG released by BG-SL could also cross the intestinal mucosa and may undergo hydrolysis to yield GA (sustained-release behavior 2). The behavior of the release of polyphenols from phospholipid complexes means that the retention time of polyphenols in vivo is extended, thereby increasing the extent to which they can be absorbed and utilized by the body. More crucially, the acyl chain lengths of phenolic esters in phospholipid complexes can be readily changed to control such dual-release behavior.

Practical applications: Phospholipid complexes of phenolic esters exhibit a good dual-release effect on polyphenols, which can more effectively enhance the bioavailability of polyphenols. By controlling the acyl chain lengths, the number of phenolic hydroxyl groups, and ester bond structures (viz., phenolic acid-COO-C_nH_2n+1 or polyphenol-OOC-C_nH_2n+1), a controlled dual-release behavior of polyphenols from phospholipid complexes of phenolic esters, such as alkyl gallates, will be easily achieved. In view of this, phospholipid complexes of phenolic esters can be potentially utilized as a functional food ingredient.