Isothermal Titration Calorimetry to Describe Polyphenol-Macromolecule Interactions
Yiliang Cheng and Aude Watrelot*
*Iowa State University, 2567 Food Science Building,
536 Farm House Lane, Ames, IA, 50011 (watrelot@iastate.edu)
This study builds on our previous findings that grape
flesh-derived macromolecules, mainly polysaccharides and
proteins, significantly affect retention of tannins and
anthocyanins during winemaking. We specifically examined how
anthocyanins in mono- and diglucoside forms influence these
interactions. Employing isothermal titration calorimetry (ITC),
we evaluated the binding affinity and thermodynamic properties
between poly(L-proline) (PLP, at 0.7 mM) and pectins (at 30 mM
galacturonic acid eq.) with commercial grape tannin
(BioTan) and procyanidin C1 (both at 3 mM epicatechin eq.). To
assess whether anthocyanins alter the binding interaction of
tannins with these macromolecules, we conducted a pre-incubation
of the macromolecules with malvidin-3-glucoside (M3G) and
malvidin-3,5-diglucoside (M35DG), each at a concentration of 3 mM
prior to titrating with tannins.
Tannins showed a strong affinity for PLP, while no interaction
was observed with pectin, even at greater concentrations. Tannins
did not interact with pure anthocyanin solutions under the
experimental conditions. Interestingly, pre-incubation of PLP
with M35DG reduced the binding affinity of BioTan to
PLP, while M3G did not significantly alter this affinity. The
nature of the tannin-PLP interaction, whether enthalpy- or
entropy-driven, varied based on the type of tannin.
The different effects of malvidin mono- and diglucoside on the strength of interaction between tannins and proteins help clarify the effects of different grape varieties on the sensory attributes and color stability of red wine. This could be used to manage the texture and mouthfeel of wine and to adjust winemaking processes such as fining, filtration, or blending. Because we observed haze formation during the ITC experiments, future research will focus on investigating the aggregation patterns between polyphenols and macromolecules using dynamic light scattering.
Funding Support: No funding source.
