Water-Based Kefir Flavored with Solid Grape Waste from Wine Production: Physicochemical, Microbiological, and Sensory Evaluation

The utilization of solid waste from winemaking, a product rich in antioxidants, has the potential for use in flavoring kefir. Kefir is obtained by fermenting tibico grains in water and brown sugar. The beverage is classified as functional, containing probiotics and micronutrients. Thus, this work aimed to produce and evaluate the physicochemical characteristics, microbiological viability, and sensory acceptance of water-based kefir flavored with waste from the wine production agroindustry in the municipality of Chapada dos Guimarães, MT. The water kefir was flavored with pasteurized grape residue (Vitis vinifera L), in four treatments (addition of 25% - K25, 37.5% - K37.5, and 50% - K50, and a control - KC) along with 5% (m/v) kefir grains and 10% brown sugar. The mixture was fermented in an aerobic environment (25°C, 24h), followed by a secondary anaerobic fermentation (25°C, 24h). The beverage was evaluated for pH, acidity, reducing sugar content, anthocyanins, total phenolic compounds (TPC), and the viability of lactic acid bacteria (LAB) and yeasts during refrigerated storage (1–4°C) on days 0, 7, 14, and 21. The beverages with added grape residue showed the lowest pH (K50: 3.7), and during storage, there was a reduction in pH (KC: 4.3 to 3.5). The addition of grape residue increased the acidity (2.07 to 6.60% of total acid), and the acidity continued to rise during the storage period. Regarding reducing sugars, a reduction was observed during storage, which indicates that the microorganisms continued to consume them, producing CO2 and organic acids. This process justifies the observed decrease in pH and the increase in acidity. Regarding anthocyanins, treatments K37.5 and K50 showed the highest values, at 29.89 and 33.56 mg cyanidin-3-glucoside equivalent/L, respectively. Samples with a higher percentage of grape residue had the highest TPC content (K50: 4.31±0.06 mg/g), while the control (KC: 0.74±0.06 mg/g) had the lowest. Lactic acid bacteria (LAB) showed an increase throughout storage (from 5.0x10⁴ to 1.2x10⁵ CFU/ml), and the yeast count remained constant (around 1.2x10⁷ CFU/ml). In the sensory analysis (n=120), 58.33% of participants reported they do not habitually consume water-based kefir; however, the acceptance index for the K25 beverage was 76.11%, and about 65% of the tasters stated they would buy the beverage. The results demonstrate that water-based kefir flavored with grape residue is viable for production, has a high concentration of bioactive compounds, and shows good sensory acceptance.