Emulsion gels are promising candidates for foods designed for at-risk
populations because they provide essential nutrients and facilitate safe
swallowing. However, few studies have examined how the blending ratios of
commonly used food hydrocolloids, xanthan gum (XG), locust bean gum (LBG),
and guar gum (GG), together with calcium ions, collectively influence the
structure–texture relationship in protein-stabilized emulsion gels suited
for diets requiring smooth and safe swallowing. This study aimed to examine
the effects of XG–LBG–GG ratio and calcium lactate (CL) addition on the
textural properties, chemical interactions, thermal behavior, and
water-holding capacity of soybean protein isolate (SPI)-stabilized emulsion
gels.
Nine cylindrical emulsion gel formulations (diameter: 16 mm, height: 12 mm)
with various XG–LBG–GG ratios (1% w/w total) were prepared. The formulations
contained 15% (w/w) dispersed oil droplets (d 4,3 = 68.3
μm) and 4% (w/w) hydrophilic SPI (bovine serum albumin standard). Texture
profile analysis (TPA) and Fourier transform infrared spectroscopy (FT-IR)
were performed to assess physicochemical properties. Subsequently, CL was
incorporated at 0–0.2% (w/w) into a formulation that exhibited high
hardness, considering the potential weakening of gel hardness by calcium
lactate while maintaining low adhesiveness and high cohesiveness to
facilitate swallowing. The samples were analyzed using TPA, FT-IR,
differential scanning calorimetry, and syneresis measurements to investigate
the effects of multivalent cations on network integrity. Two promising
formulations (3:3:3 and 3:1:3), which met the Japanese Dysphagia Diet
Standard for hardness, adhesiveness, and cohesiveness, were further
evaluated using International Dysphagia Diet Standardization Initiative
(IDDSI) testing to determine their suitability for safe swallowing.
We found that the three groups with the highest hardness had 35–60% XG and
the lowest GG content, whereas the two groups with intermediate hardness
also had 35–60% XG and GG levels equal to or lower than LBG. The four
softest groups showed no clear XG pattern, but consistently contained the
highest GG content. FT-IR analysis showed that shifts in
hydrogen-bond-associated peaks did not always correlate with macroscopic
hardness, indicating that molecular interactions alone cannot fully explain
texture formation. Although low CL (0.05% w/w) increased gel hardness and
thermal stability, possibly due to enhanced interchain crosslinking, higher
concentrations (0.1% w/w) weakened gel cohesion, likely by reducing network
connectivity. Additional CL (0.15–0.2% w/w) partly restored these
properties, potentially through nonspecific aggregation and ionic shielding
effects. Syneresis was not significantly affected by the CL level,
suggesting that water molecules predominantly occupy the available
carboxylate sites, thereby minimizing the impact of calcium ions.
The findings underline key formulation insights: (i) hardness can be
controlled by adjusting the XG and GG contents, (ii) FT-IR molecular changes
do not consistently predict bulk texture, and (iii) calcium ion effects
exhibit nonlinear behavior due to competing structural contributions. An
IDDSI test confirmed suitability at Levels 4–6, with the 3:3:3 ratio being
particularly ideal for moderate swallowing difficulty. These results support
the formulation strategies for developing nutrient-dense, cohesive, and safe
foods to enhance dietary care for at-risk populations