The wine industry traditionally benefits from the use of tannins, extracted from grapes (proanthocyanidins) during maceration or added as exogenous coadjutants (Resolution OIV-OENO 613-2019). Monitoring the tannins content in musts/wines is crucial along the oenological production chain, but their quantification is complex and currently not feasible with rapid instruments. A recent Patent by authors (IT 102019000002585; PCT/IB2020/051304) describes an innovative method for rapid quantification of tannins in red wines (no sample preparation needed), which exploits turbidity developed by the selective reaction between tannins and animal gelatin; an innovative and portable optical prototype is used for measurements. As from the previous literature, this study confirmed that the characteristics of the colloidal suspension vary depending on the tannin/protein ratio. Studies on reaction kinetics were carried out by mixing wine-like solutions containing a titrated grape tannins extract (concentration range 93 - 1485 mg/L) with a standardized gelatin solution (protein content 300 mg/L) at a 1:1 v/v ratio; under these conditions, the development of turbidity is generally described by exponential functions, indicating faster kinetics in the very first phases of the reaction (0-30 s) slowing to stabilization within 60 s - with logarithmic curves suggesting a saturation effect for higher tannin concentrations - and then producing aggregation/ precipitation of colloids. The optical response against tannins content is linear (R2 up to 0.989) by adjusting the mixture to obtain protein excess (0.25:3.75 v/v ratio), with turbidity measures constant up to 5 min due to the formation of small complexes that are stabilized in suspension. Further studies aimed to explore the correlation between the kinetic/stability of the colloidal suspension and the reactivity of tannins; this could provide additional parameters of enological interest, i.e., the antioxidant activity and the astringency index of red wines, by statistical treatment of the optical waveforms.
Exploring tannins content and reactivity in red wines by means of an innovative and rapid optical method
Arianna Ricci
;Giuseppina P. Parpinello;Eleonora Iaccheri;Luigi Ragni;Andrea Versari
2023
Abstract
The wine industry traditionally benefits from the use of tannins, extracted from grapes (proanthocyanidins) during maceration or added as exogenous coadjutants (Resolution OIV-OENO 613-2019). Monitoring the tannins content in musts/wines is crucial along the oenological production chain, but their quantification is complex and currently not feasible with rapid instruments. A recent Patent by authors (IT 102019000002585; PCT/IB2020/051304) describes an innovative method for rapid quantification of tannins in red wines (no sample preparation needed), which exploits turbidity developed by the selective reaction between tannins and animal gelatin; an innovative and portable optical prototype is used for measurements. As from the previous literature, this study confirmed that the characteristics of the colloidal suspension vary depending on the tannin/protein ratio. Studies on reaction kinetics were carried out by mixing wine-like solutions containing a titrated grape tannins extract (concentration range 93 - 1485 mg/L) with a standardized gelatin solution (protein content 300 mg/L) at a 1:1 v/v ratio; under these conditions, the development of turbidity is generally described by exponential functions, indicating faster kinetics in the very first phases of the reaction (0-30 s) slowing to stabilization within 60 s - with logarithmic curves suggesting a saturation effect for higher tannin concentrations - and then producing aggregation/ precipitation of colloids. The optical response against tannins content is linear (R2 up to 0.989) by adjusting the mixture to obtain protein excess (0.25:3.75 v/v ratio), with turbidity measures constant up to 5 min due to the formation of small complexes that are stabilized in suspension. Further studies aimed to explore the correlation between the kinetic/stability of the colloidal suspension and the reactivity of tannins; this could provide additional parameters of enological interest, i.e., the antioxidant activity and the astringency index of red wines, by statistical treatment of the optical waveforms.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
