This paper presents the study information related to the processing of fruit by combined methods. Is presented on the concept of water activity and its role in product quality; mathematical modeling methods (GAB, BET et al.) in estimate the activity coeffi cients of non-electrolyte and electrolyte mixture. Have been carried experimental research to study the evolution of the biologically active substances in frozen strawberries with and without sugar addition. It proved that frozen strawberries with sugar, during storage are more stable regarding antioxidants content that strawberry frozen without sugar.