## 3 Results and Discussion
### Correlation Analysis  
The results of Pearson correlations between the instrumentally measured parameters and the sensorial assessments are shown in Table S1 (Supplementary Materials). Strong correlations were found between the number of AE events and sensory attributes: crispness (r = 0.903), sweetness (r = 0.765), taste (r = 0.832), and overall acceptability (r = 0.836). Fracturability also showed a strong positive correlation with sweetness (r = 0.714), taste (r = 0.704), and overall acceptability (r = 0.723). Of the structural parameters, only porosity showed a positive correlation with crispness (r = 0.796). Additionally, a noteworthy negative correlation was observed between water activity and crispness (r = -0.754). These correlations demonstrate the value of measuring the number of AE events, as it strongly correlates with all the sensory attributes analysed. These results confirm the relationships between the sensory and acoustic properties of biscuits previously described in the literature [1; 49; 50].  
To determine the extent to which the biscuits differ from each other and identify which of the analysed parameters have the greatest influence, PCA was performed (Figure 2). The first two principal components (PC1 and PC2) together accounted for 82.55% of the variance, with PC1 explaining 56.95% and PC2 explaining 25.60% of the variation in the analysed biscuit quality parameters. As shown in Figure 2a, the vectors for cookie quality parameters vary in length--the shorter the vector, the smaller the contribution to PC1 and PC2. The parameter vectors shown in red were not included in the calculation of PC1 and PC2. PC1 was formed by all sensory parameters except appearance, along with porosity, apparent density, the number of AE events, brittless, and water activity, while PC2 consisted of dough rheological parameters (stickiness, work of adhesion, and dough  
Figure 1: Sensory properties of shorthead biscuits with different sweeteners (§—sucrose, T—Tagatesse, M—maltitol, ESt—erythnitol-stevia) with the addition of fibre: (**a**) wheat fibre (WF), (**b**) oat fibre (OF).  
strength). The positioning of biscuit variants next to each other in Figure 2b indicates the similarity of their comprehensive quality, as measured instrumentally and sensorially, with the distance between them representing the magnitude and nature of the differences. The biscuits in Figure 2b formed three groups. Group 1 was distinguished by the best sensory properties, the highest number of AE events, high porosity, and intermediate--neither the largest nor the smallest--rheological parameters. Group 1 included biscuits with sucrose alone, sucrose with both fibres, and maltitol with wheat fibre. Of the sweeteners used in the biscuits, maltitol is considered to have the most similar effect to sucrose [8], which was confirmed in this study, but only in combination with wheat fibre. Group 2 included Tagatesse biscuits with both fibres, which had significantly higher rheological parameters and lower sensory evaluations than Group 1, but values similar to those of Group 3. Group 3 included biscuits with maltitol and oat fibre, as well as erythroid-stevia with both fibres. This group had the lowest sensory evaluation, low porosity, and the highest rheological parameter values.