Physicochemical and sensory characteristics of Roselle fortified yoghurts stored in refrigerator

Abstract

Background: Cow’s milk yoghurt is nutritionally rich in protein and micronutrients but has poor keeping quality and is devoid of most bioactive constituents present in plants. Phenolic bioactive constituents could enhance shelf life of yoghurt and promote health of consumers.

Objective: The study evaluated the effects of roselle calyx on the physicochemical and sensory properties of yoghurts stored in a refrigerator at 40C.

Methods: Ten (10), 20 and 40 grams of ground roselle calyx, were separately boiled in 100ml distilled water for 20mins, cooled and juice extracted overnight (14hours) before filtering through muslin cloth. Each filtrate was boiled (10 mins), cooled and made up to 1litre with distilled water; mixed with 125g full cream powdered cow’s milk and used to produce yoghurts coded B, C and D. A control full cream powdered milk with no roselle was also produced and coded A. The yoghurts were pasteurized (85^OC for 15 mins), fermented (44^OC for 7hours), cooled to set and analysed for quality characteristics during10 days refrigerated storage.

Results: Moisture content of yoghurts increased from 96.11% in yoghurt D to 98.83% in A and was significantly (p < 0.05) higher in A than in the roselle-treated samples. Roselle addition above 1% significantly (p < 0.05) improved the phenol content and viscosity (cp) but decreased syneresis of the yoghurt samples proportionally. Flavour and texture of the yoghurts were also improved. However, the control was most acceptable.

Conclusion: Roselle addition improved quality of plain cow’s milk yoghurt and is recommended for its bioactive polyphenols.

Key words: Quality characteristics, roselle-fortified, yoghurt, storage