Synergistic effects of plant protein hydrolysates and xanthan gum on the short- and long-term retrogradation of rice starch.

Controlling and delaying the retrogradation of gelatinized rice starch (GRS) can improve the quality of GRS-based foods during storage. Here, we evaluated the influence of corn protein hydrolysates (CPHs), rice protein hydrolysates (RPHs), wheat protein hydrolysates (WPHs), and soybean protein hydrolysates (SPHs) on inhibiting the short- and long- term retrogradation of RS-xanthan gum mixtures. Compared with WPHs, RPHs, CPHs, the SPHs cooperating with xanthan gum (SPHs-XT) showed the highest inhibitory effect. The increased loss tangent (tan δ) in the dynamic viscoelastic measurement suggested that SPHs-XT enhanced the liquid-like properties of GRS gel. The decreased storage modulus (G') and the reduced setback value indicated that the short-term retrogradation of GRS was restrained by SPHs-XT. Meanwhile, during a 14-day storage at 4 °C, the hardness of GRS gel was significantly decreased from 1382.5 g to 201.4 g after the addition of SPHs-XT before storage determined by using a texture profile analysis (TPA), and the relative crystallinity of the retrograded GRS was decreased from 18.18% to 8.15% determined by using a X-ray diffraction (XRD) with a corresponding decrease of the retrogradation enthalpy determined by using a differential scanning calorimetry (DSC). These results suggested that SPHs-XT could inhibit the the long-term retrogradation of GRS. Moreover, the water molecules were determined to be locked in GRS gel after the addition of SPHs-XT by using a low-field nuclear magnetic resonance (LF-NMR). In addition, thin membranes and filaments formed by the addition of SPHs-XT in GRS gel were observed by using a scanning electron microscopy (SEM), suggesting a decreased cross-linking of GRS molecules by the addition of SPHs-XT to form ordered structures. These results indicated that the addition of SPHs-XT is a potential to inhibit the short- and long-term retrogradation of GRS and further to improve the nutrition of the GRS based products.