Effect of rice protein on the gelatinization and retrogradation properties of rice starch

In this study, rice starch (RS) was mixed with varying amounts of rice protein (RP; 0 % to 16 %) to explore the effects of protein on the gelatinization and retrogradation of starch during storage. The increased RP addition decreased the viscosity and gelatinization enthalpy of the mixtures but caused an upward trend in the gelatinization temperature, indicating that protein hampers the process of starch gelatinization. Furthermore, RP addition reduced gel hardness, decreased retrogradation enthalpy and crystallization rate constant, but increased Avrami exponent upon RS retrogradation. RP addition also facilitated the mobility of water molecules, weakened the conversion from bound water to free water in the gels, and moderately increased the uniformity and thickness of gel shape. In summary, RP had a dose-dependent effect on the gelatinization and retrogradation behavior of RS, although the anti-retrogradation concentration effect strongly weakened at protein levels exceeding 12 %. It is noteworthy, that excessive RP addition resulted in disulfide bond formation, which increased gel strength and network structure but reduced the ability of RP to facilitate water molecule mobility and restrict water migration, ultimately reducing its anti-retrogradation capability. This phenomenon can be partially attributed to spontaneous protein-protein interaction caused by excessive protein addition, replacing the starch-protein interaction.

Automated summary

This study investigates the influence of rice protein on the gelatinization and retrogradation of rice starch during storage. The addition of rice protein decreases viscosity and gelatinization enthalpy, while increasing gelatinization temperature. It also reduces gel hardness, retrogradation enthalpy, and crystallization rate constant, but increases Avrami exponent during retrogradation. Additionally, rice protein improves water molecule mobility, weakens the conversion from bound water to free water in gels, and moderately enhances gel shape uniformity and thickness. However, excessive protein addition leads to the formation of disulfide bonds, which enhance gel strength and network structure but reduce the protein's ability to facilitate water molecule mobility and restrict water migration, ultimately reducing its anti-retrogradation capability.