Effect of rice protein hydrolysates on the short-term and long-term retrogradation of wheat starch.

In this study, the effect of rice protein hydrolysate (RPH) on the short-term and long-term retrogradation of wheat starch (WS) was investigated. Among the RPH produced using different proteolytic enzymes (alcalase, papain and protamex), WS incorporated protamex-hydrolyzed rice protein which hydrolyzed for 2 h (PRPH-2) exhibited the lowest gel hardness after storage for 7 and 14 days. Compared with native WS, rapid viscosity analyzer (RVA) analysis showed PRPH-2 addition significantly lowered peak viscosity, breakdown and setback values (P <0.05), whereas it increased pasting temperature of WS. Dynamic viscoelastic measurements indicated the presence of PRPH-2 resulted in a decrease in the storage modulus (G') and an increase in the loss tangent (tan δ). Differential scanning calorimetry (DSC) showed that PRPH-2 significantly decreased the retrogradation enthalpy (P < 0.05), enhanced the Avrami exponent (n), and decreased the crystallization rate constant (k) during 28 days of storage. In addition, low field nuclear magnetic resonance (LF-NMR) results showed that PRPH-2 could promote the mobility of water molecules in WS gel. These findings indicated that PRPH-2 may be used to inhibit the short-term and long-term retrogradation of WS, which can be potently used as a natural additive to improve the quality of wheat products.