Ace the eatrightPREP RD Exam 2026 – Fuel Your Dietitian Dreams!

Hydrolytic rancidity happens when lipase enzymes break triglycerides into free fatty acids, and that reaction needs water and active lipase. Butter fits this scenario well because it’s an emulsion with water and milk solids that bring lipases into contact with fat. At room temperature, these enzymes can act on butter fat, releasing free fatty acids (notably butyric acid), which produce a rancid aroma and flavor. In contrast, the oils listed—fish, soybean, and olive oil—have very low water activity and are more prone to oxidative rancidity, where fats react with oxygen to form off-flavors and smells, especially in unsaturated fats. Thus butter is most likely to deteriorate from hydrolytic rancidity when stored at room temperature.