Influence of sodium alginate on the gelatinization, rheological, and retrogradation properties of rice starch.

Adding hydrocolloids into native starch is a secure and effective method of physical modification. In this study, the effect of sodium alginate (AG) on the gelatinization, rheological, and retrogradation properties of rice starch (RS) was investigated by measuring the pasting parameters, melting enthalpy (ΔH), rheological characteristic parameters, intensity ratio of 1047 cm-1 to 1022 cm-1 (R1047/1022), and relative crystallinity (RC) of RS-AG blends. Rapid visco analysis shows that AG could significantly change the gelatinization parameters of RS. Differential scanning calorimetry results show that the ΔH values of RS initially decreased in the low AG concentration range (0.10%-0.30%), but increased in the high AG concentration range (0.30%-0.50%). Dynamic rheological analysis reveals that the modulus (G', G'') and the loss tangent (tan δ) increased with the rise of the AG concentration from 0.10% to 0.50%. Fourier transform infrared spectroscopy and X-ray diffraction patterns collectively prove that the crystallinity of RS decreased with the addition of AG during the retrogradation periods. The interactions between AG and starch molecules in RS-AG blends were hypothesized to correlate with the aforementioned results.