Description
A lake is a water-insoluble pigment composed of a water-soluble straight color strongly adsorbed onto an insoluble substratum through use of a precipitant. The regulations in part 82 (21 CFR part 82), where lakes are provisionally listed, use the term "basic radical" to denote a precipitant. The FDA is proposing to replace the term "basic radical" with the more scientifically accurate term "precipitant".
The first step in manufacturing a lake is the preparation of an aqueous slurry of the substratum (e.g., alumina). This aqueous slurry is mixed with an aqueous solution of a straight color to produce a partially precipitated (or laked) product. The laking process is completed by the addition of a precipitant (e.g., aluminum chloride), which results in the production of the salt (e.g., aluminum salt) of the straight color and the adsorption of the salt onto the substratum. The resulting lake is washed, dried, and finely ground before marketing.
The literature reports several variations of the basic laking process. Some substrata are synthesized in situ; i.e., the components used to prepare the substratum, rather than the preformed substratum, are added during the laking procedure. For example, alumina slurries may be prepared by precipitation of hydrated alumina from an aluminum sulfate solution with a sodium carbonate or sodium hydroxide solution. These slurries are used directly in the synthesis of lakes, without isolation of the precipitated substratum.
Some lakes are themselves prepared in situ. In this process, the chemical precursors for the straight color are mixed directly with the substratum and the precipitant during the laking procedure. The lake is produced as the straight color is synthesized, without isolation of the straight color as a discrete batch.
The chemical association between the components of a lake may involve various types of interactions, including ionic bonds, hydrogen bonds, and van der Waals forces. Lakes generally contain 10 to 40 percent by weight of the straight color. They also contain approximately 1 to 4 percent of the weight of the lake as the cationic precipitant. The remaining 56 to 89 percent, by weight, of lakes consists primarily of substrata. The color content of a lake depends on the desired color intensity and shade of the lake. Lakes offer many technical advantages over water-soluble straight colors. The chemical bonding of the color with substrata generally promotes light and heat stability. Furthermore, because lakes are not water-soluble, the use of lakes in aqueous foods reduces color migration.
The agency’s current regulations for lakes in part 82 were issued under section 203 of the Color Additive Amendments of 1960 (Pub. L. 86-618), which provided for the temporary, provisional listing of commercially established colors. The regulations provide that before a lake may be used in a food, drug, or cosmetic product, each batch of the lake must be certified by FDA. When requesting certification of a batch of a lake, the requester submits a sample from the batch to the agency for analysis. If the agency finds that the concentrations of impurities in the sample are within the levels specified, and the batch otherwise appears to comply with the applicable regulations, the agency certifies the batch by issuing the requester a certificate showing the certification lot number assigned to that batch of lake.
Lakes represent approximately 25 percent of the total poundage of color additives certified by FDA. Approximately 80 percent of the lakes certified are FD & C (food, drugs, and cosmetics) lakes and the remaining 20 percent are D&C (drugs and cosmetics) lakes.
Properties and Applications
colourful green light blue. Blue fine powder, odourless. Hardly soluble in water, oil and most solvent, but can be scattered, mixed with water, oil liquid and solid powder. Light resistance, heat resistance, the sex of good resistance to oxidation, have certain resistance to acid, alkali resistance. This product is suitable for oil products, powder of solid and colloid water-soluble colorants are difficult to use items shading. The product is made of a certain amount of strong HCL, added with a certain volume of two potassium hydrogen sulfate solution diluted, the maximum absorption wavelength for 630 + 2 nm.
