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TPC: total polyphenol content, TFC: total flavonoid content, DPPH: scavenging 2, 2-diphenyl—1-picrylhydrazyl] free radical activity, *** 9 < 0.001; ** p < 0.01; * p < 0.05. Table 2. ANOVA results for model fitting. — Table 2 TPC: total polyphenol content, TFC: total flavonoid content, DPPH: scavenging 2, 2-diphenyl—1-picrylhydrazyl] free radical activity, *** 9 < 0.001; ** p < 0.01; * p < 0.05. Table 2. ANOVA results for model fitting.

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Figure 1. The process of obtaining whisky and the resulting by-products [13].

Table 1. Actual and coded values for full factorial experimental design.

TPC: total polyphenol content, TFC: total flavonoid content, DPPH: scavenging 2, 2-diphenyl-1-picrylhydrazy]l free radical activity. Table 3. Predicted and verified optimal sample characteristics.

Figure 2. Response surface plots showing the effect of extraction parameters on phenolic compounds for SG Ultra-Turrax pre-treatment (A-F), and for ultrasound-assisted pre-treatment (G-L).

Figure 3. Response surface plots showing the effect of extraction parameters on flavonoid content for SG Ultra-Turrax pre-treatment (A-F), and for ultrasound-assisted pre-treatment (G-L).

i a a SN A ee - GD iL The analysis of variance has shown that the quadratic regression model is statistically significant (p < 0.001) in both extraction pre-treatments. The 3D evolution of the antioxidant activity content function of the parameters employed is presented in Figure 4. For Ultra- Turrax the pre-treatment coefficient of regression R? is 0.9477, and the adjusted R? is 0.8868, and for the ultrasound-assisted pre-treatment coefficient of regression R* 0.9483, the adjusted R? is 0.8881.

Figure 4. Response surface plots showing the effect of extraction parameters on antioxidant activity for SG Ultra-Turrax pre-treatment (A-F), and for ultrasound-assisted pre-treatment (G-L).

Table 4. Phenolic profile of spent grain obtained in optimal conditions using the HPLC-DAD method. 2.4. FTIR Analysis

Figure 5. FTIR spectra of native SG and SG pretreated. A means for identifying functional groups in the bioliquid-to-solid ratio is FTI spectroscopy, and the FTIR spectra are presented in Figure 5. FTIR analysis was performe« to observe any alteration in the composition of the SG by assessing possible changes it functional groups after pre-treatment and compared with native 5G [45].