Q: Are there any nutritional advantages or disadvantages to cooking an egg so the yolk remains soft?
Answer : “None that I am aware of, except the concern about runny yolks and bacterial contamination,” says Alice H. Lichtenstein, DSc, Stanley N. Gershoff Professor of Nutrition Science and Policy at the Friedman School. That concern is potentially quite serious for lovers of runny egg yolks, however. The US Food and Drug Administration (FDA) warns: “Even eggs with clean, uncracked shells may occasionally contain bacteria called salmonella that can cause an intestinal infection.” So the agency advises, “Cook eggs until both the yolk and the white are firm. Scrambled eggs should not be runny. Casseroles and other dishes containing eggs should be cooked to 160 degrees F. Use a food thermometer to be sure.”
If you must have runny yolks or are making dishes that call for raw or undercooked eggs, such as Caesar salad dressing and homemade ice cream, use either shell eggs that have been treated to destroy salmonella, by pasteurization or another approved method, or pasteurized egg products.