3501 - Casein, caseinates and other casein derivatives; casein glues:

This HTS category, 3501, encompasses casein and its derivatives, as well as casein glues. Casein is the principal protein found in milk, and this heading covers the pure protein itself, along with various modified forms such as caseinates (salts of casein) and other casein derivatives produced through chemical or physical processes. Casein glues, which are adhesive preparations primarily composed of casein, are also classified here.

Unlike sibling categories in entirely different chapters, such as live animals (Chapter 01) or mineral products, Chapter 35 is dedicated to a specific group of organic substances. Within Chapter 35, HTS 3501 is distinct from other albuminoidal substances, modified starches, and enzymes, which are found in other headings within the same chapter. The focus here is specifically on milk proteins and their derived adhesives.

The subcategories under 3501 provide further specificity. HTS 3501.10 covers "Casein" itself, referring to the raw or purified protein. HTS 3501.90, "Other," is a residual category for all other caseinates and casein derivatives not specifically classified as pure casein, as well as casein glues. This structure allows for precise classification based on whether the product is the basic protein or a processed derivative or adhesive.