Ascorbyl Palmitate

What is ascorbyl palmitate?

Because ascorbic acid is inherently unstable (R), it is commonly chemically modified by esterification of the hydroxyl group with long-chain acids to produce more stable molecules (R). Ascorbyl palmitate is one such ester formed from ascorbic acid and palmitic acid in a chemical- or enzyme-catalyzed reaction (R, R, R, R, R, R, R, R).

Is ascorbyl palmitate stable?

Ascorbyl palmitate is less stable than other derivatives of ascorbic acid including magnesium ascorbyl phosphate and sodium ascorbyl phospate, as esterification at the 6 position does not prevent hydrolysis of the molecule (R, R). In an accelerated aging test, a 1% ascorbyl palmitate solution had a 23% concentration loss after 60 days of storage at room temperature. This was better than the 72% loss for ascorbic acid, but worse than the 5% loss of magnesium ascorbyl phosphate. In addition, magnesium ascorbyl phosphate in a cosmetic emulsion kept its stability by up to 95% even after 60 days of storage in the dark at 42°C, but only 27% of ascorbyl palmitate could be recovered after storage under the same conditions (R).

Several methods can be employed to improve the stability of ascorbyl palmitate. The structural properties of the formulation matters; a cream-gel vehicle seems to be a more suitable vehicle than oil-in-water emulsions (R). Incorporating ascorbyl palmitate into colloidal carrier systems such as microemulsions, liposomes and solid lipid nanoparticles also helps, especially in systems where the hydrophilic part of ascorbyl palmitate is exposed to a less polar environment. In an analysis of chemical stability, ascorbyl palmitate was found to be most resistant to oxidation in non-hydrogenated soybean lecithin liposomes, followed by solid lipid nanoparticles, microemulsions, and hydrogenated soybean lecithin liposomes (R). Adding the co-antioxidant 4-(tridecyloxy)benzaldehyde oxime (TDBO) to oil-in-water microemulsions of ascorbyl palmitate increases its stability as well (R).

Storage temperature is also important; ascorbyl palmitate kept at 4°C is more stable than at room temperature or at 40°C (R). Exposure to light also accelerates the degradation of ascorbyl palmitate, whereas a high concentration of ascorbyl palmitate reduces the extent of its degradation (R).

Does ascorbyl palmitate get absorbed?

Ascorbyl palmitate has lipophilic properties due to its hydrophobic palmitate side chain that may allow it to penetrate the stratum corneum (R). When applied topically to the skin of guinea pigs, ascorbyl palmitate penetrated the skin barrier, increasing the ascorbic acid content of the skin, liver and blood by 8-fold, 7-fold and 4-fold respectively (R). It has also been shown to penetrate to the epidermis and dermis of human skin (R, R), and has even been used as a skin permeation enhancer (R).

The combined use of a negative lipogel with electrical assistance can enhance the skin delivery of ascorbyl palmitate (R). Ascorbyl palmitate can also be encapsulated into lamellar liquid crystalline systems (R), nanoparticles (R, R, R), nanostructured lipid carriers (R, R), nanosuspensions (R) and nanoemulsions (R) for dermal delivery. Nanocarriers fabricated from a curcumin-grated polyvinyl polymer have been shown to be trapped in the shunts of hair follicles and to delay the degradation of ascorbyl palmitate, indicating that they can create a reservoir, slowly supplying the skin with undegraded ascorbyl palmitate (R).

It is important to note that the formulation appears to play an important role in the absorption of ascorbyl palmitate, as a commercial product containing 10% ascorbyl palmitate failed to increase skin levels of ascorbic acid in an experiment on white Yorkshire pigs (R).