Nobuko Nakahama

Effect of monovalent and divalent cations on the rheological properties of gellan gels

Abstract The complex shear modulus of gellan solutions, with and without sodium chloride, potassium chloride, magnesium chloride, calcium chloride and calcium lactate, was measured on cooling to monitor the gelation. The gelling temperature shifted to higher temperatures with increasing salt concentration. Complex Youngs modulus and compressive break-force were observed for cylindrically moulded gellan gels as a function of salt and polymer concentration, C s and C p , and of temperature. The storage Youngs modulus and the break-force increased up to a certain C s and then decreased with increasing C s , while the melting temperature of gellan gels shifted to higher temperatures with increasing C s .

Freeze concentration of some foodstuffs using ice nucleation-active bacterial cells entrapped in calcium alginate gel

Cells of an ice nucleation-active strain of Ermnia ananas were entrapped in calcium alginate to prepare an ice-nucleating gel usable as ice nuclei for freeze concentration. The ice-nucleating gel was also adjusted as to specific gravity. When it was placed at a desired position in a liquid material such as egg white, ice formed at this position as the material was cooled. It was possible to put the ice- nucleating gel in liquid foodstuffs such as egg white and lemon juice before their temperatures reached subzero points. Application of this method produced freeze-concentrated foods whose properties were not significantly deteriorated.

Rheological and Thermal Properties of Gellan Gum Gels

Complex Young’s modulus (E‘), compressive break-force (Ph) and curves of differencial scanning calorimetry (DSC) of gel Ian gum solution, with and without salt, were observed gellan gum gels as a function of salt and polymer concentration, Cs and Cg. E’ and Ph increased up to a certain Cs and then decreased with increasing Cs. The gelling and melting temperatures shifted to higher temperatures with increasing Cs and Cg. The sol-gel transition of samples was examined numerically by using zipper model approach. The introduction of cations increases the number of junction zones or zipper N and decreases the rotational freedom G of parallel links.

Cooking properties of food hydrocolloids

Abstract In cooking, the functional properties of food hydrocolloids are a valuable means of evaluating the quality of the cooked food and detecting the changes caused in the food properties during the cooking process. The fundamental properties and structure of the hydrocolloid sols and gels are reflected, both directly and indirectly, in the cooking properties. This study focuses mainly on the roles played by various hydrocolloids in cooking. Furthermore, the cooking properties of starch are examined in detail as an example. The subjects of (i) the thermal insulating property of starch paste; (ii) transitions in the properties during the gelation process; and (iii) transitions in the properties of blancmange caused by cooking, etc. are reviewed through rheological experiments and sensory evaluations.