The Effect of Ethanol, SO2, and Transition Metals on Browning Kinetics in Low- and No-Alcohol Model Wine

The study delved into the rate of browning (A₄₂₀ nm) within a model wine solution, aiming to elucidate mechanisms impacting real product scenarios, including low- and no-alcohol wines. The model wine solutions were prepared by adding tartaric acid, caffeic acid, and catechin into an aqueous ethanol solution containing transition metals (iron [Fe] and copper [Cu]) along with sulfur dioxide (SO₂). The results indicated that the model wines without ethanol exhibited the highest browning rates both in the presence (k = 0.0022 day⁻¹) and absence (k = 0.0035 day⁻¹) of SO₂. Notably, ethanol concentration showed a negative correlation with kinetic rates in both scenarios: with SO₂ (r = −0.9317) and without SO₂ (r = −0.9667). The addition of Fe and Cu separately led to a slight elevation in browning, particularly evident with Fe, while adding only Cu exhibited nonsignificant impact. However, their combined addition revealed a marked synergistic effect, rendering the rate notably sensitive to Cu concentration.