Transformation of Bioactive Compounds in Coffee Ground Kombucha: The Effect of Sugar Sources on Chemical and Sensory Properties

Spent coffee grounds still contain valuable bioactive compounds that can be valorized through kombucha fermentation to develop functional beverages and support the sustainable utilization of coffee processing by-products. This study aimed to evaluate the effect of different sugar sources on the transformation of bioactive compounds and the chemical and sensory properties of coffee ground kombucha. Kombucha was prepared using spent coffee grounds as the fermentation substrate with three sugar sources (sucrose, glucose, and fructose) and fermented for 15 days at 28 °C using a standard SCOBY culture. Microbial growth, reducing sugar, total acidity, and pH were monitored, while total phenolic content, antioxidant activity, and sensory properties were analyzed. The results showed that the sugar source significantly influenced fermentation and product characteristics. Glucose promoted the most intensive fermentation, resulting in the highest acidity (13.94 g/L) and lowest pH (2.20). In contrast, fructose produced the highest total phenolic content (1341.81 µg/mL) and antioxidant activity (83.22%). Sensory evaluation indicated that fructose-based kombucha was the most preferred due to its balanced aroma, flavor, sweetness, and acidity. Overall, fructose was identified as the most suitable sugar source for producing coffee ground kombucha with enhanced bioactive and sensory qualities.