Abstract: In this experiment, a mixture of grape pomace and molasses wastes from the brewing of fruit wine and fruit vinegar was fermented sequentially with yeast and acetic acid bacteria followed by lactic acid bacteria to produce a functional beverage with higher nutritional value through the transformation and utilization of substances during the fermentation process. Under the ultrasonic conditions of frequency 40 kHz, power 50 W and temperature 30 ℃, the influence of inoculum amount, initial pH value, sugar addition, and ultrasonic time on the activity of superoxide dismutase (SOD) and the number of viable bacteria were examined. The interaction among these variables was also investigated. Using response surface methodology based on a four-variable three-level experimental design, the optimum fermentation conditions were obtained as follows: initial pH value 5.0, sugar concentration 8%, inoculum amount 12%, and ultrasonic time 60 min. The optimized process was scaled up to a 5 L fermentor with improved feeding mode. At the end of the fermentation, the pH was 3.5, the titratable acidity was 2.89%, and the total phenolic content was 5.5 mg/mL. Functional components such as procyanidins (3.78 mg/mL) and SOD activity (988 U/mL) were detected in the fermented grape pomace. The 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical cation scavenging capacity (Trolox equivalent antioxidant capacity, TEAC) was determined as (44.5 ± 2.5) μg/g using a commercial total antioxidant capacity assay kit. The fermented grape pomace was rich in tartaric acid, malic acid, succinic acid, and citric acid. During the fermentation process, the unique aroma compounds alcohol, phenol, and quinones were emitted. The fermented grape pomace had a unique and dense aroma. The fermented supernatant was transparent and bright in color, with soft aroma and high sensory scores for taste and mouthfeeling.

Key words: probiotic fermented grape pomace, process optimization, physical and chemical indicators, functional composition analysis, antioxidant capacity