E904 (Shellac) is a purified chemical compound of a natural material and is produced, after appropriate purification, from the resin produced by the insect Laccifer lacca, a cochineal, which is found in India, Thailand and in other countries of South East Asia. It is composed of long chain fatty acids, aliphatic polyhydric acids, wax esters, fatty alcohols and alkanes (1).

Shellac. The term originates from the word "shell-lac", with "lac" being a type of resinous substance secreted by certain insects. The word "shell" was added because the substance was sold in the form of "shells" or flakes.

Shellac is processed and sold as dry flakes, which are dissolved in alcohol to make liquid shellac. The liquid shellac is used as a brush-on colorant, food glaze, and wood finish. Shellac functions as a tough natural primer, sanding sealant, tannin-blocker, odour-blocker, stain, and high-gloss varnish.

The synthesis process takes place in different steps:

• Harvesting. The raw shellac, which contains lac bug secretions, bark from the host trees, and other impurities, is scraped off the trees and collected.
• Heat Treatment. The harvested raw shellac is heated to a high temperature to kill any insects and to remove most of the impurities.
• Sieving and Crushing. The shellac is then sieved to remove the remaining impurities and crushed into small flakes.
• Dissolving in Alcohol. The shellac flakes are dissolved in ethyl alcohol to make liquid shellac, which can be applied as a finish or colorant.
• Purification. The shellac can be further purified through a process called dewaxing, which removes the natural waxes to produce a product that dries more quickly and produces a harder finish.

It appears in the form of of reddish scales.

What it is used for and where

Food

Ingredient listed in the European food additives list as E904 as a coating agent  and, as a wax, to give a shiny appearance to fruit and vegetables.

E904 (Shellac) is used in the food as a coating agent (2) and, as a wax, to impart a glossy appearance to fruit and vegetables.

In lipid-based food products, fat crystals are used as components to create a 3D gel-like crystalline network that produces palatability and texture effects in food products. The recent ban on the use of trans fats in the US, together with concerns about the negative effects of saturated fat consumption, has led to a growing interest in alternative edible oils. Hence, the introduction of shellac (3).

Medical

It is used in the food and pharmaceutical industry as a coating agent (2).

Cosmetics

Binder agent. Ingredient that is used in cosmetic, food and pharmaceutical products as an anti-caking agent with the function of making the product in which it is incorporated silky, compact and homogenous. The binder, either natural such as mucilage, gums and starches or chemical, may be in the form of a powder or liquid.

Film-forming agent. It produces a continuous ultra-thin film with an optimal balance of cohesion, adhesion and stickiness on the skin or hair to counteract or limit damage from external phenomena such as chemicals, UV rays and pollution.

Hair fixative. This ingredient has the ability to create, with its protective film, stiffness and hold in the hair, and also has the ability to form, with its hydrophilic and elastic properties, bonds between the hair fibres, to keep the hair in a particular shape for a certain time.

Skin conditioning agent - Emollient. Emollients have the characteristic of enhancing the skin barrier through a source of exogenous lipids that adhere to the skin, improving barrier properties by filling gaps in intercorneocyte clusters to improve hydration while protecting against inflammation. In practice, they have the ability to create a barrier that prevents transepidermal water loss.  Emollients are described as degreasing or refreshing additives that improve the lipid content of the upper layers of the skin by preventing degreasing and drying of the skin. The problem with emollients is that many have a strong lipophilic character and are identified as occlusive ingredients; they are oily and fatty materials that remain on the skin surface and reduce transepidermal water loss. In cosmetics, emollients and moisturisers are often considered synonymous with humectants and occlusives.

Viscosity control agent. It controls and adapts viscosity to the required level for optimal chemical and physical stability of the product and dosage in gels, suspensions, emulsions, solutions. 

Also used as a nail dye.

Pharmaceuticals

In the pharmaceutical industry, shellac is used as a safe film for drug delivery, as its nanofibres are gradually converted into nano-particles and completely dissolved in the body (4).

It was evaluated as a dielectric layer in organic field-effect transistors (5).

Commercial applications

Paints and Finishes. Shellac has traditionally been used as a protective varnish for furniture and other wooden items.

Food Industry. Serves as a coating or glazing agent for some foods, like candies and fruit, to give a shiny finish.

Pharmaceuticals. Used as a coating agent in some medications to control the release of the active ingredient.

Electronics. Used as an insulator in some electronic components.

• Molecular Formula: C₃₀H₅₀O₁₁
• Molecular Weight: 586.719 g/mol
• CAS: 9000-59-3
• EC number:  232-549-9

Synonyms : 

• Gum lac
• Lac resin
• Candy glaze
• Lacca

References_____________________________________________________________________

(1) Weinberger H, Gardner WMH. Chemical composition of shellac. Ind. Eng. Chem. 1938;30:454–458.

(2) Debeaufort F, Quezada-Gallo J-A, Voilley A. Edible films and coatings: Tomorrow's packagings: A review. Crit. Rev. Food Sci. Nutr. 1998;38:299–313

(3) Patel AR, Dewettinck K. Comparative evaluation of structured oil systems: Shellac oleogel, HPMC oleogel, and HIPE gel.   Eur J Lipid Sci Technol. 2015 Nov;117(11):1772-1781. Epub 2015 May 5.

(4) Wang X, Yu DG, Li XY, Bligh SW, Williams GR. Electrospun medicated shellac nanofibers for colon-targeted drug delivery.  Int J Pharm. 2015 Jul 25;490(1-2):384-90. doi: 10.1016/j.ijpharm.2015.05.077. Epub 2015 Jun 1.

(5) Baek SW, Ha JW, Yoon M, Hwang DH, Lee J. Shellac Films as a Natural Dielectric Layer for Enhanced Electron Transport in Polymer Field-Effect Transistors. ACS Appl Mater Interfaces. 2018 Jun 6;10(22):18948-18955. doi: 10.1021/acsami.8b03288.