fruit syrup as a fortifying agent: effect on physicochemical, microbiological, rheological, sensory and antioxidant properties of yoghurt.

Unlabelled: This study aims to assess the antioxidant and the antibacterial activities of fruits and to valorize its syrup by the incorporation in bi-layer yoghurt. The antioxidant activity of the ethanol 80% fruits and syrup extracts was evaluated by three methods namely DPPH, ABTS and FRAP. The antibacterial activity was tested against seven pathogenic bacteria using agar well diffusion method. The yoghurt was prepared using 10 and 20% layers of syrup, physicochemical, rheological, microbiological and sensorial characteristics and the antioxidant activity were investigated during cold storage. The results revealed that the heat treatment decreased the phenolic compounds contents and the antioxidant activity in the syrup extract. Both fruits and syrup extracts demonstrated an antibacterial activity against the tested bacteria. The highest inhibition diameter (40 mm) was recorded for at 100 mg/mL of fruit echtanolic extract. The prepared bi-layer yoghurts showed stability for the physicochemical and microbiological properties during storage. The rheological properties revealed that the syrup increases the yoghurt consistency (k). The antioxidant activity of the yoghurt indicated that fermentation improved the radical scavenging power of the syrup at the beginning and the activity decreased slowly during storage.

Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-023-05801-4.