Tannin removal from Persian gum and investigation of physicochemical properties: Comparing different methods

Abstract

Persian gum (PG) is a novel natural exudate gum and the main challenge regarding PG is tannin content of gum which limits its application in food and pharmaceutical industries. In fact, tannins are known as anti-nutrient compounds because they limit bioavailability of proteins and minerals. Hence, in this study, the effect of microwave radiation (180, 450, 600 W for 5 min), autoclaving (121 °C for 20 min), boiling (5, 10 and 15 min) and soaking either in water or saline solutions (mono- and divalent salts) was evaluated to remove tannins from Persian gum. Moreover, the effect of tannin removal on the physicochemical properties was investigated by evaluation of rheological properties (flow behavior and viscoelastic tests), zeta potential and Fourier transform infrared spectroscopy (FTIR) data. Our outcomes demonstrated that the highest tannin removal efficiency found to be 75.67 ± 0.25, 74.32 ± 0.54 and 67.08 ± 0.19 % which belonged to soaking in water (180 min), soaking in CaCl₂ solution (1% w/v, 90 min) and boiling (15 min) treatments of brownish PG granules, respectively (p < 0.05). Interestingly, removal of tannin increased apparent viscosity of PG dispersion. Based on oscillatory tests, boiling treatment caused exhibition of solid-like behavior, in contrast to control sample. Tannin removal reduced zeta potential and the lowest reduction belonged to the gums soaked in water (from -32.3 to -28.7 mV); however, formation of ion-bridging in the presence of CaCl₂ caused a remarkable decrease. FTIR analysis declared that in the boiled sample, a decrease was detected in vibration intensity within the range of 3200–3500 cm⁻¹ (-OH groups) which can be due to heat degradation. Findings of the present research confirmed that soaking in water is a low-cost and practical method for tannin removal of PG, which almost had no negative effect on physiochemical properties of gum.