Abstract: Effects of adding zein, soy protein isolate (SPI) or whey protein isolate (WPI) on the retrogradation of proso millet starch were investigated by textural profile analysis (TPA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed that adding the three proteins decreased the hardness of proso millet starch gel, making the mixed gels softer. Particularly, upon the addition of WPI, the hardness decreased from 407.32 g to 196.12 g at day 7. FTIR showed that no new functional group appeared, indicating that the starch-protein system is closely linked together by hydrogen bonding interactions, forming a tightly wound three-dimensional gel network structure. XRD analysis showed that in the retrogradated sample a strong diffraction peak appeared at around 17° as a typical B-type structure. Adding the proteins significantly reduced the retrogradation enthalpy, thus suppressing the recrystallization of proso millet starch and consequently retarding its retrogradation. By fitting the aging kinetics with the Avrami equation, it was found that the rate of recrystallization was reduced upon the addition of the proteins, and the nucleation type of recrystallisation was close to rod-like growth of sporadic nuclei (1 < n ≤ 2). Overall, addition of zein, SPI and WPI affected proso millet starch in varying degrees, with the greatest effect being observed with WPI. This study shows that the proteins act not only as nutrients but also as a starchy food anti-aging agent, which provides a theoretical basis for delaying starch aging and is of guiding significance for actual production.

Key words: proso millet starch; zein; soy protein isolate; whey protein isolate; retrogradation; Avrami equation