Anais do Simpósio Latino Americano de Ciências de Alimentos
Actas del 14 SLACA - Simposio Latinoamericano de Ciencia de los Alimentos

The perception of bitter taste has been directly related to salivary proteins. Among the compounds that cause this perception taste, there is quinine, an alkaloid that brings several health benefits. The aim of this work was to determine the thermodynamic parameters of binding between the salivary protein mucin (PSN-Porcine stomach mucin type II: Isoelectric point between 2-3) and quinine (QN: pKa 4.25 and 8.72) using the isothermal titration nanocalorimetry (ITC) technique, at pH 7.4 and 3.0. Regardless of the studied pHs, the Kb values were around 107 L.mol-1 and ∆G ° negative, showing that the formation of complexes between PSM and QN is favored at equilibrium. However, the formation of the QN-PSM complex was more favored at pH 3.0 with a lower value of ∆G° (-45.38 ± 0.51 kJ.mol-1), compared to the interaction at pH 7.4 (-41.66 ± 0.29 kJ.mol-1), which can be explained by different charges on both molecules at the studied pH values. At pH 3.0, when in its protonated form, QN seems to induce PSM aggregation when the complex is formed, as indicated by the obtained stoichiometry of ~ 1:3. At pH 7.4, 1:1 stoichiometry was obtained, since QN is no longer ionized, there is no charge neutralization on the proteins’ side chain, preventing their aggregation. The formation of the QN-PSM complex at pH 3.0, was enthalpically driven (∆H°= -66.88 ± 0.70 kJ.mol-1 and T∆S°= -21.50 ± 0.19 kJ.mol-1). With the increase of the pH value to 7.4 and consequent deprotonation of QN, the formation of complexes with PSM became less enthalpically driven (∆H°= -18.65 ± 0.13 kJ.mol-1) and occurred with an increase of entropy (T∆S°= 23.01 ± 0.16 kJ.mol-1). These results demonstrate the great influence of pH on the interaction between QN and PSN that can be useful for applications in the food industry.