Incorporation strategies of grape pomace in fermented milk: effects on stability, bioactivity, and consumer acceptance

Abstract

By-product of Vitis labrusca is an alternative to improve fermented milk nutritional and functional properties. Fermented milk was formulated with grape pomace (GP) at concentrations of 6.25%, 12.5%, and 25%, following two methodological approaches: (F1) GP incorporation prior to fermentation and (F2) GP incorporation post-fermentation. Technological properties were evaluated over a 21-day storage period at 5 °C. Based on the technological properties, the most promising formulation was subjected to total phenolic compounds (TPC), antioxidant activity, microbiological, and sensory analysis. The incorporation of GP into fermented milk significantly influenced its technological properties. The F1 method, in which GP was added prior to fermentation, improved water retention capacity (47.26% in 25% GP-F1 versus 49.57% in the control) and reduced syneresis, resulting in enhanced structural stability. These results indicate that the F1 approach is more appropriate for improving the technological properties of fermented milk. The total phenolic compounds (TPC) increased from 343.50±38.02 μg gallic acid equivalents (GAE)/g (control) to 3093.31±13.67 μg GAE/g (25% GP, F1). Antioxidant activity, measured by DPPH, ABTS, and FRAP assays, showed a significant increase in the 25% GP-F1 sample (DPPH: 9150.00±229.32 μmol/g; ABTS: 1916.13±61.16 μmol/g; FRAP: 24.798±2.580 μmol/g), compared to the control (DPPH: 958.27±88.00 μmol/g; ABTS: 485.96±18.69 μmol/g; FRAP: 1160.69±61.98 μmol/g). Lactic acid bacteria remained viable throughout storage, with counts exceeding 107 CFU/ml in all samples. Sensory evaluation indicated that the 12.5% GP-F1 formulation achieved the highest acceptance score (9.0), balancing technological advantages and consumer preference. These findings suggest that GP is a valuable natural ingredient for functional dairy product development, enhancing nutritional, sensory, and technological properties.