Comparison of microcalorimetry and haze formation to quantify the association of B-type procyanidins to poly-l-proline and bovine serum albumin

•Two methods are compared to study interactions of proteins and B-type procyanidins.•Spectrophotometric method and ITC inform on different parameters.•Poly-l-proline binds to procyanidin oligomers with low haze formation.•Bovine serum albumin binds to procyanidin oligomers with high haze formation.•Higher affinity of poly-l-proline to procyanidin oligomers than bovine serum albumin.

Though many different methods have been applied to protein-tannin interactions, divergent results are often reported. To better understand the origin of these differences, we compare here haze/aggregates formation and thermodynamic parameters occurring for protein-procyanidin interactions. Proteins well referenced for interaction with polyphenols, namely a polypeptide of extended structure that resembles salivary proteins (poly-l-proline (PLP) and a standard globular protein (bovine serum albumin (BSA)) were used. Flavan-3-ols of three degrees of polymerization were tested, (-)-epicatechin (EPI), a dimer (DP2) and a procyanidin (DP8). The interactions were tested in identical conditions for both methods. The association constants determined by isothermal titration calorimetry (expressed as constitutive unit) varied with the following scale: PLP-DP8 >> BSA-DP8 ≈ BSA-DP2 ≈ PLP-DP2 > BSA-EPI (no affinity detected for PLP-EPI). However aggregates formed more readily for highly polymerized procyanidins DP8 with BSA than with PLP, and the scale (with 10 mmol/L of constitutive unit of polyphenol and 0.07 mmol/L of proteins) was: BSA-DP8 > BSA-DP2 >> PLP-DP8 > PLP-DP2 ≈ PLP-EPI, with no haze formation for BSA-EPI. However the impact of polyphenol concentration on haze formation and precipitation was different for the two proteins.