Is caffeic acid, as the major metabolite present in Moscatel wine protein haze hydrolysate, involved in protein haze formation?

- Isolation of metabolites present in wine protein precipitate alkaline hydrolysate.
- Caffeic acid identified as the major metabolite.
- No correlation found between caffeic or caftaric acid concentration and haze formation.

This work was conducted to identify the major low molecular weight compounds present in the wine precipitate and to assess their potential contribution to wine protein haze formation. The heat-induced protein precipitate from a white Moscatel of Alexandria wine was subjected to alkaline hydrolysis. The major compound present was found to be caffeic acid among other minor, unidentified compounds. Caffeic acid was identified by both UV-vis and 1H NMR spectra. The concentration of caffeic acid in the original wine sample was 1.1 mg/L, as quantified by HPLC following SPE. Heat stability tests were performed using two different concentrations of caffeic acid and its ester caftaric acid in model wine solution added of isolated wine protein. No correlation was found between caffeic or caftaric acid concentration and haze forming potential in wine model solution. This work shows that caffeic acid is present in considerable amounts in Moscatel wine protein haze, but does not seem to trigger or participate in the protein aggregation mechanism upon heating.

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