Casein is the dominant protein group in milk, accounting for approximately 80% of bovine milk protein, and reaches confectionery formulators as acid casein, rennet casein, and a family of soluble caseinates. Because casein carries an unusually flexible, amphiphilic structure (carrying both water-attracting and fat-attracting regions on the same molecule) and exceptional heat stability, it is often the protein of choice in caramels, toffees, and chocolate systems where whey protein would denature or falter.

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What types of casein are used in confectionery?

Casein and its derivatives reach confectionery formulators in several standardized forms:

• Acid casein: precipitated from skim milk by acidification to pH 4.6, washed and dried. Insoluble in water and used primarily as a raw material for producing caseinates rather than directly in candy [1].

• Rennet casein: precipitated using rennet (chymosin) rather than acid. Retains calcium phosphate in its structure, producing a firmer curd used mostly in industrial applications and analog cheese [1,2].

• Sodium caseinate: acid casein neutralized with sodium hydroxide, then spray dried. Highly soluble across a broad pH range, excellent emulsifier — the most common form in confectionery [2,3].

• Calcium caseinate: acid casein neutralized with calcium hydroxide. Lower solubility than sodium caseinate but useful when calcium fortification or a whiter color is needed.

• Potassium caseinate: alternative to sodium caseinate for low-sodium applications, less common in candy.

• Micellar casein: recovered from skim milk by microfiltration without acidification, preserving the native micellar structure. A newer form used where native protein functionality matters.

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How is casein produced?

Casein production starts with pasteurized skim milk. In the acid casein route, mineral acid — typically hydrochloric or sulfuric — is added to lower the pH to approximately 4.6, the isoelectric point of the casein fraction. The proteins lose colloidal stability and precipitate; the curd is separated, washed extensively to remove residual acid and lactose, then dried [1,2]. In the rennet casein route, rennet enzyme is added to milk at approximately neutral pH; the enzyme cleaves κ-casein at a specific bond, destabilizing the micelles and producing a coagulum that retains its native calcium phosphate [1,4].

Caseinates are produced by re-dissolving acid casein in an alkaline solution — sodium hydroxide, potassium hydroxide, or calcium hydroxide — bringing the mixture to approximately pH 6.7 and spray drying the result [2,3]. Micellar casein is produced through microfiltration of skim milk on membranes with a pore size of approximately 0.1 μm, which separates the casein micelles from whey proteins and lactose without any acidification step.

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What does casein do in confections?

Casein contributes several distinct functions across candy categories. In caramels, toffees, and fudge, sodium caseinate serves as a highly effective emulsifier that stabilizes the fat-water interface and contributes to characteristic chewy texture through water binding and interaction with sucrose and reducing sugars [1,7]. In chocolate and compound coatings, milk protein solids — often supplied as caseinates within milk powder — influence flavor development, fat crystallization behavior, and mouthfeel. In aerated confections, caseinates can stabilize foams, though whey proteins are typically preferred where high overrun is the goal [3,5]. Caseinates also drive Maillard browning during the extended cook cycles required for caramels and toffees, contributing to color and flavor development.

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What is the molecular structure of casein?

The casein fraction consists of four principal proteins: αs1-casein (~40% of total casein), αs2-casein (~10%), β-casein (~35%), and κ-casein (~15%) [1,6]. Unlike globular proteins such as whey, caseins are rheomorphic — they lack a defined tertiary structure and exist as open, flexible chains. Their high proline content prevents α-helix and β-sheet formation, keeping the polypeptide backbone extended and accessible. Molecular weights range from approximately 19 kDa for κ-casein to 25 kDa for αs2-casein [1].

In native milk, the four caseins assemble into colloidal casein micelles approximately 50–500 nm in diameter, held together by nanoclusters of calcium phosphate bound to phosphorylated serine residues [3,4]. κ-Casein sits at the micelle surface, where its glycosylated C-terminal region — the "hairy layer" — provides steric and electrostatic stabilization. This open, amphiphilic architecture is what makes casein such an effective surfactant and heat-stable ingredient.

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What are the functional properties of casein in confections?

• Solubility: Acid casein is essentially insoluble in water. Sodium caseinate and potassium caseinate are highly soluble across a broad pH range, while calcium caseinate has more limited solubility. All forms show minimum solubility near pH 4.6 [2,3].

• Emulsification: Caseinates are exceptional emulsifiers due to the amphiphilic nature of the individual caseins, with distinct hydrophobic and hydrophilic domains along the polypeptide chain [3,5]. This is a primary reason for their use in caramels and toffees.

• Thermal Behavior: Casein has no defined denaturation temperature and remains functional at UHT temperatures (>140°C) — an unusual property among food proteins that reflects its lack of ordered secondary or tertiary structure [1,4].

• Water Binding: Caseinates bind water effectively, contributing to the chewy texture characteristic of caramels and fudge.

• Interaction with Calcium: Sodium caseinate can precipitate in the presence of high calcium concentrations, a formulation consideration in systems containing calcium salts or hard water [3].

• Maillard Reactivity: Lysine ε-amino groups react readily with reducing sugars during extended cooking, driving desirable browning in caramels and undesirable color development during storage [1,7].

• Hygroscopicity and Shelf Stability: Caseinate powders are moderately hygroscopic and prone to caking at elevated humidity. Storage is primarily limited by Maillard browning and, where residual fat is present, lipid oxidation.

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How is casein regulated?

In the United States, casein and caseinates are not GRAS-listed under 21 CFR Part 184 but have a long history of safe use as food ingredients and are permitted in food applications. Labeling is governed by 21 CFR 101.4, which requires that products containing sodium or calcium caseinate declare them by their common name.

Under the Food Allergen Labeling and Consumer Protection Act (FALCPA), casein and caseinates must be declared as milk allergens. In the European Union, casein products carry no E-number but must be labeled as containing milk under Regulation (EU) No 1169/2011. Codex Standard 290-1995 establishes international identity and compositional requirements for edible casein products [9].

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References

1. Fox, P.F., Uniacke-Lowe, T., McSweeney, P.L.H., & O'Mahony, J.A. (2015). *Dairy Chemistry and Biochemistry* (2nd ed.). Springer.

2. Walstra, P., Wouters, J.T.M., & Geurts, T.J. (2006). *Dairy Science and Technology* (2nd ed.). CRC Press.

3. Swaisgood, H.E. (2003). Chemistry of the caseins. In P.F. Fox & P.L.H. McSweeney (Eds.), *Advanced Dairy Chemistry — Volume 1: Proteins* (3rd ed., pp. 139–201). Kluwer Academic.

4. Horne, D.S. (2006). Casein micelle structure: models and muddles. *Current Opinion in Colloid & Interface Science*, 11(2–3), 148–153.

5. Dickinson, E. (1999). Caseins in emulsions: interfacial properties and interactions. *International Dairy Journal*, 9(3–6), 305–312.

6. Damodaran, S., & Parkin, K.L. (Eds.). (2017). *Fennema's Food Chemistry* (5th ed.). CRC Press.

7. Minifie, B.W. (1989). *Chocolate, Cocoa and Confectionery: Science and Technology* (3rd ed.). Van Nostrand Reinhold.

8. U.S. Food and Drug Administration. 21 CFR 101.4 — Food; designation of ingredients.

9. Codex Alimentarius Commission. Codex Standard 290-1995 — Edible Casein Products.

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