Effects of emulsifiers on mixing properties, viscoelastic properties and stability of zein-starch doughs

Abstract

Zein, maize protein, has ability to form viscoelastic dough but requires mixing above room temperature (35oC) and has inferior dough properties compared to wheat dough. The objective of this research was to study effect of emulsifiers on zein-starch dough’s properties, including the mixing properties, viscoelastic properties, and dough stability. Corn starch (90%, w/w of flour), zein (10%, w/w of flour), emulsifier (4-6% PATCO-3™ or 2-4% sodium stearoyl lactilates (SSL), w/w of flour) and water (optimum %) were mixed at 35oC and 28oC into dough. Farinograph results revealed that emulsifier addition decreased optimum water amount and prolonged mixing time. SSL dough exhibited lower water amount and less mixing time than PATCO-3™ dough. Dough with emulsifier showed lower storage modulus G’ transition temperature (T of G’ transition) compared to the control. More pronounced depression in T of G’ transition was shown by addition of SSL than PATCO-3™ and the higher the emulsifier concentration, the greater the decrease obtained. Small deformation test showed that the phase angle value decreased with emulsifier incorporation, indicating enhancement of its elastic characteristic. Complex modulus, storage modulus, and viscous modulus values also increased, recognized as higher dough strength. Those were more obvious in SSL dough than PATCO-3™ dough. Those trends also were shown for dough mixed at 28oC and 35oC, indicating zein could be functionalized at below room temperature through decreasing in T of G’ transition. FTIR results exhibited that PATCO-3™ dough had better stability than SSL dough, as shown by relatively higher and constant of β-sheet secondary structure amount during storage for 15 min at room temperature (25-28oC). More apparent effect was seen in dough mixed at 35oC than at 28oC. Comparison with the control was not possible due to severe phase separation. The results of this study suggested that PATCO-3™ and SSL might help to form viscoelastic zein-starch dough at room temperature. PATCO-3™ had more positive effect on G’ transition temperature, viscoelastic properties and dough stability. SSL addition even though resulted in lower G’ transition temperature and more improved viscoelastic nature, the dough was unstable during storage. Thus, structural improvement in zein cannot be attributed only by the effect of G’ transition but also the interaction between zein and emulsifier. The proper balance between hydrophobic and hydrophilic parts of emulsifier might be required to get optimum decreased T of G’ transition, viscoelastic properties, and stability of zein-starch dough.