Rheological and Thermal Behavior of Mixed Gelatin/Konjac Glucomannan Gels

Abstract

Mixed konjac glucomannan/gelatin gels were mechanically characterized in the linear and large deformation regimes. Differential scanning calorimetry revealed no effect of konjac addition on gelling and melting of gelatin. The elastic moduli increased with increasing konjac content, but fracture stress slightly decreased. The rheological results and confocal laser scanning microscopy support segregative phase separation, where rigid polysaccharide domains act as bound fillers which are not separated by the solvent from the matrix and increase the Young's modulus, but the fracture stress is only weakly dependent on the concentration of the filler. The melting temperature of konjac‐modified gels remains below body temperature, indicating konjac addition does not increase danger of choking. The addition of konjac to gelatin gels with or without sucrose decreased sensory hardness and stickiness. For both types of gels, the addition of konjac made mastication and swallowing easier, making konjac/gelatin mixed gels an interesting alternative for gelatin gels. Practical Applications Mixed polysaccharide and protein gels are gaining popularity in the food industry. This study investigated the rheological consequences of konjac glucomannan addition to gelatin. The mixed gels had lower sensory hardness compared with pure gelatin gels, which led to lower perceived difficulty of mastication and swallowing. The mixed gels also retained their melt‐in‐mouth properties, as konjac did not affect the thermal properties.

The extrusion test and sensory perception revisited: Some comments on generality and the effect of measurement temperature

“…The higher correlation of the sensory attribute with the logarithm of the physical property (compared with correlation with the physical quantity itself) is a manifestation of the Weber–Fechner law (Sone, ). We will look at the correlation of the sensory hardness, as reported by Tomczyńska‐Mleko et al (), with large‐deformation stress parameters from extrusion and uniaxial compression performed at 22C and large‐amplitude oscillatory shear performed at 25C. The parameters are the maximum extrusion pressure (tapering ratio 8.5, flow rate 2 ml/s), the engineering compression stress at 90% compression, σ 90, and the fracture stress in oscillatory shear, τ f .…”

“…While several sensory attributes were evaluated, we will refer only to the hardness, defined as the perceived force needed to bite completely through the sample with incisors or molars. The results of sensory evaluation of the GLT/KGM gels were reported in our earlier study (Tomczyńska‐Mleko et al, ) and are tested in our current report against extrusion test results that were not reported previously, as well as against other mechanical test results that were included in the original study.…”

“…The Young's modulus of the gels ( E ≈ E ') was measured using a Rheolograph (Toyo Seiki Seisakusho, Tokyo, Japan) at F = 3 Hz and a strain of 0.32% (Tomczyńska‐Mleko et al, ). Large‐deformation compression and extension tests were performed on an XT.T2 Texture Analyser (Stable Micro Systems, Surrey, United Kingdom), as described previously (Brenner et al, ; Tomczyńska‐Mleko et al, ). Briefly, compression of cylindrical gel specimens (height = 10 mm, diameter = 25 mm) to 10% (or less) of their original height was carried out using an aluminum plunger (diameter = 100 mm) at a speed of 10 mm/s.…”

“…The Young's modulus of the gels (E E') was measured using a Rheolograph (Toyo Seiki Seisakusho, Tokyo, Japan) at F 5 3 Hz and a strain of 0.32% (Tomczy nska-Mleko et al, 2014). Large-deformation compression and extension tests were performed on an XT.T2 Texture Analyser (Stable Micro Systems, Surrey, United Kingdom), as described previously (Brenner et al, 2013(Brenner et al, , 2015Tomczy nska-Mleko et al, 2014).…”

The Food Colloid Principle in the Design of Elderly Food

“…Tomczyńska‐Mleko et al . () studied the texture of mixed gels of gelatin, KGM and LBG, and found that the addition of KGM and LBG made gelatin gels softer but the excessive addition made the gel too sticky. They obtained a gel from 5% gelatin, 1% KGM and 0.5% LBG which was the easiest for mastication and swallowing among other combinations…”