Place raspberries in food processor, and process until smooth. Press purée through a sieve; set purée aside, and discard seeds.
Combine the sugar, sliced strawberries, and lemon juice in processor, and process until smooth. Add raspberry purée, evaporated milk, and egg substitute, and process until blended. Pour mixture into a large bowl, and stir in low-fat milk.
Pour berry mixture into the freezer can of a 2-quart ice-cream freezer, and freeze according to the manufacturer's instructions. Spoon into a freezer-safe container; cover and freeze for at least 1 hour.