title: Mapping the Complex Phase Behaviors of Aqueous Mixtures of κ-Carrageenan and Type B Gelatin.
abstract: We report a detailed and complete phase diagram for an aqueous mixture of oppositely charged gelling biopolymers, type B gelatin and κ-carrageenan (KC) at pH 7.0. The phase diagram is studied in the ionic strength-temperature coordinate by means of turbidity, rheological and differential scanning calorimetric measurements, and macroscopic phase compositional analysis. Seven phase regions are identified, including (I) compatible region, (II) electrostatically induced associative phase separation (EIAPS) region, (III) hydrogen bonding induced associative phase separation (HBIAPS) region, (IV) coexistence of EIAPS and HBIAPS, (V) segregative phase separation (SPS) region, (VI) coexistence of HBIAPS and SPS, and (VII) SPS trapped by gelation. The HBIAPS reported for the first time here is attributed to the extensive hydrogen bonding formation between gelatin and KC above their conformational transition temperatures, as probed by addition of urea and methylene blue as well as by 2D (1)H-(1)H NOESY NMR. NaCl is found to have dual effects on HBIAPS. The electrostatic complexation at lower ionic strength facilitates the formation of hydrogen bonds between gelatin and KC and hence the HBIAPS. It is believed that the local structural arrangement of gelatin molecules or the change in local solvent environment prior to triple helix formation during cooling enables the formation of hydrogen bonds with KC.
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Cao
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Wang
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.|‡Hubei Collaborative Innovation Centre for Industrial Fermentation, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.|‡Hubei Collaborative Innovation Centre for Industrial Fermentation, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Yapeng
authors.initials: Y
authors.lastname: Fang
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.|‡Hubei Collaborative Innovation Centre for Industrial Fermentation, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Nishinari
authors.affiliation: †Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.
authors.forename: Glyn O
authors.initials: GO
authors.lastname: Phillips
mesh_terms: D002351:Carrageenan / Q000737:chemistry*; D005780:Gelatin / Q000737:chemistry*; D008751:Methylene Blue / Q000737:chemistry; D009994:Osmolar Concentration; D013696:Temperature; D014508:Urea / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D014508:Urea; D002351:Carrageenan; D005780:Gelatin; D008751:Methylene Blue