This study was undertaken in order to investigate the effect of adding four tannin fractions from wine pomace to replace sulfur dioxide (SO₂) before fermentation on wine flavor quality. Cabernet Sauvignon wine pomace was selected as raw material for the extraction and purification of grape skin high-polymer tannin (HRSK), grape skin low-polymer tannin (LRSK), grape seed high-polymer tannin (HRSD), and grape seed low-polymer tannin (LRSD). Before alcoholic fermentation for red wine-making, the four tannin fractions and SO₂ were separately added. Samples with nothing added served as control. The six wines were analyzed for basic physicochemical indexes, CIELab color parameters, redox potential, total tannin and total phenol contents, volatile components and sensory quality. The results showed that there was no significant difference between the four tannin and the SO₂ groups in terms of color indexes, total tannin, total phenol contents, bitterness or astringency, which indicated that substitution of tannins for SO₂ did not affect the changes in wine color, taste or flavor. In addition, it was found that compared with SO₂, the four tannins significantly reduced the content of 3-methylthiopropanol in wine while significantly reducing the perceptible reduced off-flavor. Aroma analysis by gas chromatography-mass chromatography (GC-MS) revealed that the addition of HRSD resulted in higher contents of volatile constituents such as alcohols and esters compared with the other treatments, the effect being similar to that of SO_2. In conclusion, wine pomace tannins can be used as an alternative to SO₂ in wine-making, and the effect of HRSD is the most pronounced.

To investigate the effect of electron beam irradiation (EBI) on the structure and functional properties of goat milk whey protein concentrate (WPC), WPC treated with different doses of EBI (0, 1, 3, 5, 7, 9, 11, 13, and 15 kGy) were analyzed for structural properties by determining particle size, zeta potential, surface hydrophobicity, fluorescence spectroscopy, color parameters, free sulfhydryl group, total sulfhydryl group, and carbonyl group content as well as using electrophoresis, Fourier transform infrared spectroscopy (FTIR), thermal stability, microstructure. The functional properties were evaluated by measuring the solubility, emulsifying, and foaming properties of WPC. The results showed a close correlation between structural and functional properties, with EBI exerting a dose-dependent effect on WPC. At a dose of 5 kGy, the average particle size of WPC was the smallest, measuring (309.17 ± 2.12) nm. Electrophoretic patterns revealed significant differences in the composition of WPC exposed to varying doses of EBI. FTIR results indicated the internal structure of WPC underwent unfolding and aggregation. Changes in intrinsic fluorescence intensity and surface hydrophobicity suggested that EBI induced protein unfolding and refolding, thereby affecting the exposure and masking of hydrophobic groups. Changes in free sulfhydryl group, total sulfhydryl group, and carbonyl contents indicated that EBI induced the cleavage and formation of disulfide bonds, as well as the oxidation of WPC. Scanning electron microscopy (SEM) observations showed puncture holes on the surface of WPC particles, indicating compromised surface integrity. These findings demonstrated that EBI induced the denaturation of WPC. An EBI dose of 5 kGy resulted in a significant increase in the solubility, foaming capacity, and emulsifying activity from (70.00 ± 1.93)% to (88.80 ± 1.58)%, from (113.8 ± 1.8)% to (119.5 ± 0.7)%, and (25.0 ± 0.3) to (33.3 ± 1.7) m²/g, respectively (P < 0.05). Thus, EBI treatment affects the structure and consequently the functional properties of WPC, providing technical support for the high-value utilization of WPC.