3.3.2 Frequency scan of walnut butter
The linear viscoelastic region (LVE) was the region where the elastic modulus (G’) and viscous modulus (G”) of all samples did not vary with the oscillatory stress under the same conditions (Bi et al. 2020). The LVE of walnut butter could be determined by strain scanning in the dynamic rheological oscillation measurement mode. To ensure that all samples were in the linear viscoelastic region, a strain value of 0.01% was selected for subsequent experiments (Fig. 1S).
Frequency scanning is a standard method for studying the viscoelastic behavior of substances, which helped study the chemical composition and physical structure of substances (Daubert, 2017; Steffe, 1996). The results showed that the G’ values of commercial walnut butter and three groups of FLWB were always more significant than the G” values in the frequency range of 0.1-100 Hz (Fig. 3). There was no crossover between G’ and G”, which indicating that commercial walnut butter and FLWB were dominated by elastic properties. There was a weak frequency dependence of G’ and G” of the samples, suggesting that aggregation and cross-linking between the components of walnut butter occurred. The G’ and G” values of walnut butter decreased with the increase of FL addition, indicating that the particle size of the samples decreased with the increase of oil addition (Fig. 3B - D). The results showed the trend of walnut butter from elasticity to viscosity was increased, the distance between oil droplets was decreased, and the flocculating trend appeared between microdroplets. This led to enhanced fluid interaction and increased viscosity (Barnes, 1994; Sato et al., 2015). In all walnut butter samples, the G’ values were higher than the G” values in all frequency ranges. The G’ values indicated strong interparticle interactions and stable network structures within the samples, and the same phenomenon was observed in sesame butter (Çiftçi et al., 2008).