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).