You can substitute one 10-ounce package of frozen strawberries (thawed); with frozen berries, decrease sugar to 2/3 cup.
This recipe contains raw egg. We recommend that pregnant women, young children, the elderly, and the infirm do not consume raw egg. Learn more about egg safety from our article, How to Make Your Eggs Safe.
Substitute 1/4 cup pasteurized liquid egg whites for the raw egg whites, if you prefer. Pasteurized whites take longer to whip, but will work just fine.