Which of the following is NOT a factor in the extent to which fat is incorporated into a stable emulsion?

• A. pH
• B. fat particle size
• C. amount and type of soluble protein
• D. amount of emulsion

Answer: (D)

The main idea here is what governs how much fat actually becomes part of a stable oil‑in‑water emulsion. That depends on how well the interfacial film around fat droplets is formed and maintained, which is controlled by pH, the surface area of the fat droplets, and the ability of soluble proteins to act as emulsifiers.

pH changes the charge on proteins and droplets. When the pH is far from the protein’s isoelectric point, proteins carry more charge and spread more readily to the oil–water interface, forming a stronger stabilizing film and allowing more fat to be incorporated into a stable emulsion. Near the isoelectric point, proteins are less effective at stabilizing interfaces, so fat incorporation into a stable emulsion can drop.

Fat particle size matters because smaller droplets present a larger total surface area that must be covered by emulsifier. If there’s enough protein to cover that surface, the fat can be well stabilized and incorporated into the emulsion; if not, droplets coalesce and the emulsion becomes unstable.

The amount and type of soluble protein directly affect how readily the interface is stabilized. More or better-suited emulsifying protein improves adsorption to the droplet surface, thickening the interfacial film and supporting greater, more stable fat incorporation.

The total amount of emulsion, by itself, does not determine the fraction of fat that can be incorporated into a stable emulsion. It’s about the interfacial chemistry and the emulsifier’s ability to cover and stabilize the oil droplets, which are governed by pH, droplet surface area, and protein characteristics.