Carrageenan as possible stabilizer of calcium tartrate in wine

Calcium-induced instability has recently become a major issue in bottled wines, as an effect of compositional changes induced by global warming. Up to date, few tools are available for calcium stabilization purposes. The present research was aimed at evaluating the potential activity of carrageenans (mixture of ι- and κ-) as stabilizers of calcium tartrate (CaT) in white and rosé wines. Four white and two rosé wines, with differing CaT and potassium bitartrate (KHT) stability were characterized. The addition of carrageenans improved both CaT and KHT stability, determining a decrease of saturation temperatures of both CaT and KHT (TsatCaT and TsatKHT). Sodium bentonite was used to evaluate possible synergic effect. The addition of carrageenans (0.75 g L−1) followed by sodium bentonite (0.5 g L−1) allowed to stabilize CaT in all wines, with a TsatCa2+ mean value of 6.7 °C; all samples also reached protein stability, with the exception of one sample that slightly exceeded the conventional threshold of protein stability. As a plus, KHT stability was also improved. The mini-contact test with seeds of micronized CaT, DLS analysis and FTIR spectra confirmed that CaT stability was due to Ca2+ ions colloidal stabilization rather than removal; that the mechanism of stabilization could include ternary complexes involving carrageenan, calcium ions and proteins; and that the synergic effect of bentonite could be attributed to competitive adsorption of proteins, with consequent adsorption of larger amounts of Ca2+ ions by carrageenan.