Abstract
This study was planned to explore the locally available natural sources of gum hydrocolloids as a natural modifier of different starch properties. Corn (CS), sweet potato (SPS), and Turkish bean (TBS) starches were mixed with locally extracted native or acetylated cactus (CG) and acacia (AG) gums at 2 and 5% replacement levels. The binary mixtures (starch–gums) were prepared in water, freeze dried, ground to powder, and stored airtight. A rapid viscoanalyzer (RVA), differential scanning calorimeter (DSC), texture analyzer, and dynamic rheometer were used to explore their pasting, thermal, textural, and rheological properties. The presence of acetylated AG or CG increased the final viscosity (FV) in all three starches when compared to starch pastes containing native gums. Plain SPS dispersion had a higher pasting temperature (PT) than CS and TBS. The addition of AG or CG increased the PT of CS, SPS, and TBS. The thermograms revealed the overall enthalpy change of the starch and gum blends: TBS > SPS > CS. The peak temperature (Tp) of starches increased with increasing gum concentration from 2 to 5% for both AG and CG native and modified gums. When compared to the control gels, the addition of 2% CG, either native or modified, reduced the syneresis of starch gels. However, further addition (5% CG) increased the gels’ syneresis. Furthermore, the syneresis for the first cycle on the fourth day was higher than the second cycle on the eighth day for all starches. The addition of native and acetylated CG reduced the hardness of starch gels at all concentrations tested. All of the starch dispersions had higher G′ than G″ values, indicating that they were more elastic and less viscous with or without the gums. The apparent viscosity of all starch gels decreased as shear was increased, with profiles indicating time-dependent thixotropic behavior. All of the starch gels, with or without gums, showed a non-Newtonian shear thinning trend in the shear stress vs. shear rate graphs. The addition of acetylated CG gum to CS resulted in a higher activation energy (Ea) than the native counterparts and the control. More specifically, starch gels with a higher gum concentration (5%) provided greater Ea than their native counterparts.
Highlights
Long-chain polymers known as hydrocolloids are widely used in the food industry
A very strong but broader peak at 3395–3382 cm−1 was observed in native acacia gum (AG) and cactus gum (CG), indicating -OH stretching vibrations, whereas the intensity of this peak was reduced in acetylated gums, indicating OH reduction after acetylation
The acetylated CG had the highest absorption for this peak, indicating that it was better substituted than AG (Figure 1)
Summary
Long-chain polymers known as hydrocolloids (gums) are widely used in the food industry. Fluid biopolymers with high molecular weight, such as food hydrocolloids, can be used as functional ingredients for improving product texture, shelf life, and microstructure [1]. Polysaccharides that make up the majority of gums are long-chain hydrophilic molecules with high molecular weights [2]. Food hydrocolloids are increasingly being used in the baking industry to achieve a variety of functionalities. To achieve the desired synergy between specific functional properties, a variety of gums can be used. The flour mixtures can be made texturally stable, freeze-thaw stable, and age resistant by adding gums before baking [4,5]. Gums can improve bread’s water-holding capacity, texture, volume, uniformity of cell structure, and product quality during storage, among other qualities [6]
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