Foaming Capacity and Stability
The foaming capacity (FC) and stability (FS) of the samples are reported
in Table 4. The results clearly showed that the FC and FS of the samples
by roasting and steaming treatment were higher than that of the
untreated sample (Table 4). Untreated sample had a FC (62.13%) and FS
(43.30%) significantly lower than heating samples (P <
0.05). The steaming and roasting samples both had good foaming
properties with FC (65.44-68.60% and 69.17-71.11%, respectively) and
FS (80.07- 67.48% and 80.11-48.18% respectively). With the changes of
heating methods, the FC and FS of the samples changed. The results
showed that the FC and FS of samples by steaming treatment were slightly
different than the roasting. When the roasting time was 30 min, the FC
of sample reached the maximum value, while FS with the extending of time
gradually reduced. However, FC during the steaming was not significantly
different between S15, S20 and S30, but the FS gradually decreased with
time from 15 to 30 min. The functional properties of protein can be
altered due to the changes of the secondary and tertiary structure
[22]. The conformation changes of protein also would cause the
changes of foaming properties [53]. some researchers have reported
that the partial unfolding of proteins can improve the FC and FS of
protein [22]. In the present study, the infrared data had shown that
the number of unfolded structures in protein increased. Therefore, the
application of walnut kernel flour depended on the processing
conditions, ingredient formulation during heating treatment.