Journal
FOOD HYDROCOLLOIDS
Volume 62, Issue -, Pages 1-9Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.foodhyd.2016.07.029
Keywords
Complex coacervation; Bowman-Birk protease inhibitor; iota-Carrageenan; Hydrophobic interactions; Isothermal titration calorimetry
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Funding
- National Natural Science Foundation of China [21276107]
- National Great Project of Scientific and Technical Supporting Programs - Ministry of Science & Technology of China during the 12th five-year plan [2012BAD34B04-1]
- 863 Program (Hi-tech research and development program of China) [2013AA102204-3]
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Complex behavior of Bowman-Birk protease inhibitor (BBI) with iota-carrageenan (LC) as a function of pH, protein to polysaccharides ratio and salt concentration was studied by turbidimetric titration, dynamic light scattering (DLS) and isothermal titration calorimetry (ITC). At fixed BBI/LC weight ratio of 5: 1, turbidity and DLS results showed that pH(c) and pH(phi 1) shift to the lower pH values with the increase in ionic strength (I), whereas the former occurred at the pH lower than isoelectric point (pI = 4.2) of BBI at I >= 100 mM NaCl. ITC results showed that BBI binding to LC involves a two-step process with an increasing exothermic enthalpy at the first binding step. The further insight of BBI-LC complexation was studied as a function of BBI concentration, ionic strength and temperatures using ITC. The critical molar ratio (r(critical)) between two binding steps was independent of protein concentration, ionic strength and temperature, although the heat flow obviously decreased with the increasing I (0-200 mM) and slightly increased with the elevated temperature (25-45 degrees C). The negative heat capacity (Delta C-p) and the gain in nonionic contribution (Delta G(no)) indicated the involvement of nonelectrostatic interactions (e.g., hydrophobic effect) for the first binding step. (C) 2016 Elsevier Ltd. All rights reserved.
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