Optimisation of Chitosan-Guar Gum-Whey Protein Formulations for Inhibiting Starch Retrogradation and Enhancing the Quality of Refrigerated Sushi Rice

In this study, the effects were investigated of chitosan, guar gum and whey protein isolate (WPI) on sushi rice retrogradation and quality during refrigerated storage. Using response surface methodology with a central composite design, 23 additive combinations were evaluated, and three optimal formulations were selected. Four formulations were investigated: A (2.42% chitosan, 3.19% guar gum, 7.75% WPI), B (4.30% chitosan, 10.0% guar gum, 20.0% WPI), C (2.42% chitosan, 2.05% guar gum, no WPI) and D (control, no additives). Starch retrogradation was assessed via X-ray diffraction and differential scanning calorimetry, while texture, microbiological and sensory attributes were monitored over a 15-day storage period. Formulation B most effectively suppressed retrogradation, exhibiting the lowest final enthalpy (Δ H ᵣ = 1.12 J/g) despite the overall increase observed during storage. Compared to the remaining formulations, lower hardness (13.8 N), a modest increase in retrogradation enthalpy (0.63–0.99 J/g), and microbial counts below a 5 log colony-forming unit (CFU)/g by day 8 were noted. Sensory evaluation indicated the highest acceptability up to day 8, followed by a gradual decline thereafter. A strong negative correlation ( r = − 0.71) between retrogradation enthalpy and sensory scores demonstrated the direct impact of starch recrystallisation on perceived quality. Overall, the synergistic interaction of the three additives provides a practical approach to extending the shelf-life of refrigerated sushi rice while preserving desirable quality attributes.