Effect of guar gum and fortification by haritaki (Terminalia chebula) extract and its encapsulates on physicochemical, textural, and rheological properties of yogurt

In the present study functional yogurt was prepared by addition of guar gum (0.5% and 1.5%) and fortification by phytochemical extract of haritaki (Terminalia chebula) extracted using supercritical CO₂ and freeze dried encapsulates of the extracts. The results indicated that the addition of guar gum led to a concentration-dependent reduction in pH, with yogurt containing 1.5% guar gum exhibiting the highest acidity. During a 24-day storage period at 4°C, all samples displayed a decrease in pH and an increase in acidity. Notably, all variations exhibited sporadic syneresis patterns, with higher syneresis observed on the 1st day, followed by a decline on the 12th day and a subsequent rise on the 24th day of storage. The color of haritaki encapsulated yogurt appeared greener and more yellowish compared to the control samples on the 1st day, with noticeable changes in L*, a*, and b* values during storage. Texture analysis revealed that encapsulation significantly affected textural characteristics, with reduced firmness but comparable adhesiveness in some cases. The firmness of plain yogurt ranged from 0.69 to 0.72 N, while its adhesiveness was between 6.14 × 10⁻² and 8.51 × 10⁻²N.s. The stiffness of the samples made with encapsulates (E1–E6) ranged from 0.38 to 0.70 N, while their adhesiveness was 5.74 × 10⁻² to 8.78 × 10⁻²N.s. The findings demonstrate that encapsulation significantly affected the textural characteristics. However, the samples' firmness (F1–F3) was less than the control, ranging from 0.36 to 0.54 N. Encapsulated haritaki extract outperformed nonencapsulated haritaki extract in terms of phenolic and antioxidant activities, making it a preferred option for yogurt fortification. Furthermore, yogurt enriched with up to 0.5% guar gum exhibited sensory qualities similar to or even better than the control sample.