Addition of Red Dragon Fruit (Hylocereus Polyrhizus) on Yogurt: Impact on Nutrition, Physicochemical Properties, Microbial Cell Count and Sensory Evaluation.

Tong, Yun Xi (2024) Addition of Red Dragon Fruit (Hylocereus Polyrhizus) on Yogurt: Impact on Nutrition, Physicochemical Properties, Microbial Cell Count and Sensory Evaluation. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Yogurt is a semisolid fermented milk product obtained by the action of specific lactic acid bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) when added to heat-treated milk. The development of yogurt incorporates red dragon fruit puree, considering its growing popularity due to its nutritive value and antioxidant quality. Red dragon fruit puree was added to two experimental yoghurt samples at varied amounts (10% and 20%) while plain yoghurt served as the control. This study encompassed comprehensive assessments of nutritional composition, physicochemical properties, and sensory acceptability. The moisture content varied between 80.40% and 81.81%. Notably, yoghurt with 10% and red dragon fruit puree had higher protein contents (3.97% and 3.98%, respectively) than plain yoghurt (3.49%). The plain yoghurt has the greatest percentage of crude fat (6.55%). All of the yoghurt had an ash percentage ranging from 4.10% to 4.30%. The pH values varied from 4.29 to 4.43, with titratable acidity levels all exceeding 0.6%. Total soluble solids (Brix°) ranged from 15.4 to 16.2 after fermentation. The occurrence of syneresis was seen in all yoghurt samples, with a growing pattern with the storage time. The antioxidant activity of plain yoghurt (4.94%) was increased by the inclusion of red dragon fruit (6.10% to 7.26%). Furthermore, as compared to plain yoghurt, the dragon fruit enhanced yoghurts had a higher total phenolic content. On MRS agar, all of the yoghurt samples had a minimum lactic acid bacteria count of 106. Sensory evaluation using a 9-point hedonic scale found that the mean overall acceptability scores of all yoghurt samples ranged between 5.93 and 6.10. In the ranking test, the yoghurt with 10% red dragon fruit puree received the highest rating, followed by plain yoghurt and yoghurt with 20% red dragon fruit puree.