Place the sugar and water in a saucepan and heat slowly, stirring until the suger has dissolved. Bring to the boil and boil for 3 minutes. Set aside to cool.
Puree the tangerines, then strain through a sieve to give 280ml/ 1/2 pint (420ml/ 15fl oz) of juice. Mix in the sugar syrup and lemon juice. Chill. Break up the egg white with a fork and stir into the tangerine mix.
Fit the frozen bowl into the dessert maker and switch on. Pour in the tangerine syrup and churn until thickend and frozen. Transfer to a plastic container and freeze until required.