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.