The Influence of the Addition of Nuts on the Thermal and Rheological Properties of Wheat Flour

Abstract

The aim of the study was to assess the influence of replacing wheat flour with hazelnuts or walnuts, in various amounts, on the thermal and rheological properties of the obtained systems. The research material were systems in which wheat flour was replaced with ground hazelnuts (H) or walnuts (W) in the amount of 5%, 10%, and 15%. The parameters of the thermodynamic gelatinization characteristics were determined by the differential scanning calorimetry method. In addition, the pasting characteristics were determined with the use of a viscosity analyzer and the viscoelastic properties were assessed. Sweep frequency and creep and recovery tests were used to assess the viscoelastic properties of the tested gels. It was found that replacing wheat flour with nuts increased the values of gelatinization temperature, gelatinization, and retrogradation enthalpy, and the degree of retrogradation. The highest viscosity was characteristic of the control sample (2039 mPa·s), and the lowest for the paste with 15% addition of walnuts (1120 mPa·s). Replacing the flour with nuts resulted in a very visible reduction in the viscosity of such systems. In addition, gels based on the systems with the addition of H and W were weak gels (tan δ = G″/G′ > 0.1), and the values of G′ and G″ parameters decreased with the increased share of nuts in the systems. Creep and recovery analysis indicated that the systems in which wheat flour was replaced with hazelnuts were less susceptible to deformation compared to the systems with the addition of W.

The Effect of the Addition of Hazelnut or Walnut Flour on the Rheological Characteristics of Wheat Dough

“…A similar trend has been shown in previous studies [22] analyzing the viscoelastic properties of gruels based on wheat flour systems with hazelnuts or walnuts. In the presence of water, gluten forms a three-dimensional net that provides the springy nature of the dough.…”

“…The values of tan δ indicate that the tested doughs have the character of weak structures, while the presence of nuts in the system intensified this tendency, which is stronger the greater the share of nuts in the system. Earlier studies by Pycia and Juszczak [22] also showed that the gels of the wheat flour-nut systems were weak gels.…”

“…This is because the dough containing shortening lipids with a liquid consistency was characterized by a lower value of the G and G modules compared to the dough with the addition of shortening lipids with a solid consistency. The ratio of the energy lost to the energy stored in each cycle is described as tan δ, which indicates the physical behavior of the system [22]. It was found that the values of the tangent of the phase shift angles (tan δ = G /G ) for both the hazelnut and walnut doughs initially decreased, and then increased as the frequency increased (Figure 3a,b).…”

“…The storage modulus (G ) describes the share of elastic features, and corresponds to the part of the energy that is stored. The loss modulus (G ) corresponds to the viscous features, and reports the part of the energy which is lost during sinusoidal deformation [4,22]. Figure 2a,b show the mechanical spectra of dough with the addition of hazelnuts and walnuts, and Figure 3a,b show changes in the tangent value of the phase shift angle with respect to the angular frequency for the tested dough.…”

“…The viscoelasticity values also significantly depend on the type of nut flour added to the dough. Immediate compliance (J 0 ) is related to the tensile energy of elastic bonds, which disappears immediately after the force dissipates [22]. The lowest value of immediate compliance was found for the control sample, while the addition of nuts increased the value of this parameter.…”