The Dextro brand, which includes energy drinks and bars based on dextrose, is the market leader for dextrose products in Germany.
Zertus will gain control of the business on 5 March, taking on its 160 staff and factory in Krefeld.
Dextro Energy became part of Unilever in 2000 with the Bestfoods acquisition. The company is selling the unit to focus on core brands.
Zertus said the range fits well with its portfolio as well as the marketing and distribution competence of its subsidiary companies Importhaus Wilms/Impuls-Vermarktung, Germany's leading food distributor.