International Numbering System (INS) for Food Additives: 904
Food additives Europe numbers: E904
Functional Category
Coating agent; encapsulating agent; film-forming agent; matrixforming agent; modified-release agent.
Applications in Pharmaceutical Formulation
Shellac is widely used as a moisture barrier coating for tablets and pellets due to its low water vapor and oxygen permeability. It has usually been applied in the form of alcoholic or aqueous solutions (pharmaceutical glazes). However, due to stability problems with alcoholic shellac solutions, it has had limited use in the pharmaceutical industry for modified-release or enteric coatings; see also Section 18. Shellac, particularly novel aqueous shellac solutions, is mainly used in food products and nutritional supplements. Recent research results indicate good application properties and chemical stability of shellac films from aqueous shellac solutions.(1,2) Aqueous ammonium shellac solutions, based on dewaxed orange shellac, do not show the problems exhibited by alcoholic shellac solutions and are used as an enteric coating for pellets, tablets, soft and hard gelatine capsules, primarily in nutritional supplements.(3) Shellac is a primary ingredient of pharmaceutical printing inks for capsules and tablets, and can be applied as a 40% w/v alcoholic solution. It has also been used to apply one or two sealing coats to tablet cores to protect them from moisture before being film- or sugar-coated. Other applications of shellac are the coating or encapsulation of powders or granules, e.g. in probiotics. Prior to the introduction of film coating, a combination of shellac, cetostearyl alcohol and stearic acid was used as an enteric coating. In cosmetics, shellac is used in hairsprays, mascara and lipstick formulations.(4) Aqueous shellac solutions are also used for colonic drug delivery.(5)
Description
Shellac is a natural resin that may be obtained in a variety of colors ranging from light yellow to dark red in the form of hard, brittle flakes with or without wax, depending on the refining process; see Sections 4 and 13. The different types of shellac include bleached shellac, bleached dewaxed shellac, dewaxed and decolorized shellac, dewaxed flake shellac, dewaxed orange shellac, dewaxed shellac, orange shellac, purified shellac, refined bleached shellac, regular bleached shellac, regular waxy shellac, wax-containing shellac, and white shellac. The flakes may be crushed or milled to a coarse or fine powder. Bleached shellac is supplied as a coarse offwhite powder. Shellac is tasteless and may have a faint odor. The typical odor of shellac is the result of a complex fragrance system.(6)
Stability and Storage Conditions
After long periods of storage, shellac becomes less readily soluble in alcohol, less fluid on heating, and darker in color; see also Section 18. Shellac should be stored in a well-closed container at temperatures below 158C. Wax-containing grades should be mixed before use to ensure uniform distribution of the wax. Orange and dewaxed orange shellac have a shelf-life of 1 to 2 years. The shelf-life of bleached shellac is approximately 6 months.
Incompatibilities
Shellac is chemically reactive with aqueous alkalis, organic bases, alcohols, and agents that esterify carboxyl groups. Therefore, shellac should be used with caution in the presence of such compounds.
Safety
Shellac is used in oral pharmaceutical formulations, food products, and cosmetics. It is generally regarded as an essentially nonirritant and nontoxic material at the levels employed as an excipient.