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Table 2 Effects of tannin, PRP concentration on binding

From: Salivary proline-rich protein may reduce tannin-iron chelation: a systematic narrative review

Reference Method Tannin type PAC-TA comparison Conditions of assay Outcome Concentration effect
[53] DLS PAC as tetramers, pentamers, gallates No 31.2 mg/L GSE: 0.5–5 mg/L IB-8c or 3.12 mg/L IB-8c: 19.5–46.8 mg/L GSE; pH 5.0, 12% ethanol Increase in PRP concentration increases aggregation and precipitation of tannins to a maxima, then increased protein concentrations favors dissociation due to reductions in tannin-cross linking Tannin stacking and crosslinking at higher concentrations
[55] SDS-PAGE, HPLC, tryptic digestion PAC as dimers, trimers, tetramers No 0.00–1.5 mM GSE in saliva; pH 5.0, 12% ETOH At higher tannin concentrations, less PRP are required for similar binding at lower tannin concentrations. Tannin stacking and crosslinking at higher concentrations
[56] ESI-MS EgCG, ECG, B2, B2 3-O gallate, reserpine No 1:10 ratio protein: polyphenol; pH 3.2 Higher tannin concentration of tannins favor tannin-PRP stability in gastric digestion Stability of tannin-PRP binding
[51] ESI-MS; DLS,SAXS EgCG No 0.336 mM (1–3.5 mg/ml) PRP (IB5); 2:1 protein: polyphenol; pH 5.5 At lower concentrations, PRP are bound to tannins, but soluble. At higher concentrations, more tannin is needed to effectively bind the same amount of PRP; this happens as binding occurs regardless of proline terminal residue numbers. Tannin stacking and crosslinking at higher concentrations
[57] HPLC-DAD PAC as monomers, dimers, trimers No 1–8 ml saliva mixed with 40 ml GSE or 20 or 40 ml sipped Increased tannin concentration increases precipitation. Tannin stacking and crosslinking at higher concentrations
[58] ITC GSE as catechin, epicatechin, epicatechin 3-O gallate No 5–25 μg PAC and 40 μl saliva with 10% ethanol Increased tannin concentration increases precipitation. Tannin stacking and crosslinking at higher concentrations
[47] NMR, DLS EgCG, EGC, PGG Yes 20 mM polyphenol with 2 mM mouse PRP; pH 3.8 The number of PRP binding sites does not correlate with the corresponding decrease in tannin concentration after tannin-PRP binding at higher concentrations Tannin stacking and crosslinking at higher concentrations
[59] NMR Tannic acid No 1:0–1:5.6 ratio of PRP to tannic acid More tannin-PRP complexes that are bound, the less that the complexes dissociate Stability of tannin-PRP binding
  1. NMR Nuclear magnetic resonance imaging, ESI-MS electrospray ionization mass spectrometry, DLS dynamic light scattering, SAXS small angle X-ray scattering, ITC isothermal titration calorimetry, SDS-PAGE sodium dodecyl polyacrylamide gel electrophoresis, HPLC high performance liquid chromatography. B1, B2, B3: proanthocyanidin B1, B2, B3, PGG pentagalloylglucose, TGG tetragalloylglucose, PAC proanthocyanidin, EgCG epigallocatechin gallate, ECG epigallocatechin, PRP proline rich protein, TA tannic acid