The quest for healthier beverage options has led to the development of low-calorie alternatives to conventional sugary drinks. This study focused on the use of ultrasonication-enzymatic extraction to produce a low-calorie ready-to-drink Kangra orthodox black tea with the natural sweetener Stevia rebaudiana. By employing sonication time (9 to 45 min) and temperature (35 to 55 °C) as independent variables, statistical analysis revealed significant effects of these parameters on key quality indicators. In the ultrasonicated-assisted enzymatic extraction, the optimal conditions were 27.58 min at 45.06 °C with 0.0095% Tannase, to maximize the water extract content, total phenolic content, antioxidant capacity, caffeine, tannins content, colour, theaflavins, thearubigins, total colour, brightness, a*, b* colour value and overall acceptability and to minimize the pH, tea cream, and colour value L* of the ultrasonicated-assisted enzymatic extraction of Kangra orthodox black tea. The predicted water extract was 47.69%, the total phenolic content was 233.77 µg GAE/100 mL, the antioxidant capacity was 78.50 mM TE/mL, caffeine was 35.30 µg CAE/100 mL, tannins were 167.14 µg TAE/100 mL, theaflavins were 0.88%, thearubigins were 8.49%, the total colour percentage was 9.22%, the brightness was 14.98%, a* was 5.02, b* was 8.88, the overall acceptability was 8.14, the pH was 5.61, tea cream was 0.36 g/100 mL, and the L* colour value was 23.66 under optimum ultrasonication-assisted enzymatic extraction conditions. To improve the overall palatability of the Kangra Orthodox ready-to-drink tea, sugar (7–11° Brix) was utilized to balance the taste. The optimal sugar concentration for ready-to-drink Kangra orthodox tea based on a sensory score of 10° Brix was the highest. The substitution of sucrose with stevia up to 60% led to an equi-sweet taste eliminating any characteristic bitter aftertaste, in addition to a substantial decline in energy value from 31.44 to 15.72 kcal/100 g. A low-calorie Kangra Orthodox ready-to-drink tea beverage was developed that contained a high level of functional compounds at a reduced energy level. This tea offers a healthy alternative to traditional sweetened beverages and is potentially appealing to a broad market of health-conscious consumers.
