Abstract: The objective of this study was to evaluate the effects of positively charged, neutral charged and negatively charged amino acids, represented by Lys, Ala, and Asp, respectively, on pasting and rheological properties of rice starch. The results showed that both Lys and Asp significantly increased peak viscosity (PV) and breakdown (BD) of rice starch and reduced final viscosity (FV) and setback (ST) (P < 0.05). However, Ala had little influence on pasting properties (P > 0.05). Thus, the two charged amino acids (Lys and Asp) had stronger effects on rice starch than the neutral one (Ala). In addition, all three amino acids had different effects on rheological properties of rice starch. Lys and Ala resulted in increased elasticity of starch gel, while Asp had the opposite effect. Besides, the relationship between shear stress τ and shear rate γ during the steady flow test was analyzed by using the power law model τ = kγm, and the results showed that the m values of all samples were < 1, suggesting that both starch and starch-amino acid mixture were pseudoplastic fluid. Additionally, Lys enhanced the pseudoplastic behavior, while Asp had the opposite effect.

Key words: rice starch, amino acids, pasting properties, rheological properties