## 3 Results and Discussion
### Effects of Waxy Barley Bran Blend Ratio
#### 3.3.2 Height and Specific Volume  
The height and specific volume of the bread samples differed significantly (\(p\) < 0.05) among all groups (Figure 4a,b). The highest height was observed in the IBLP 10% replacement group (17.00 cm), followed by the control (14.40 cm), IBLP 30% replacement (13.20 cm), IBLP 50% replacement (9.00 cm), and OBLP 30% replacement (7.30 cm) groups (Figure 4a). Similarly, the specific volume was the highest in the IBLP 10% replacement group (5.28 cm\({}^{3}\)/g), followed by the control (4.49 cm\({}^{3}\)/g), IBLP 30% replacement (3.71 cm\({}^{3}\)/g), IBLP 50% replacement (2.46 cm\({}^{3}\)/g), and OBLP 30% replacement (2.12 cm\({}^{3}\)/g) groups (Figure 4b) (\(p\) < 0.05). Numerous studies have reported that substituting whole grain or barley flour for wheat flour reduces bread volume. For instance, [PERSON] et al. (2011) [14] demonstrated that bread volume decreased with the inclusion of normal and waxy hull-less barley flour compared to wheat flour, with a 10% replacement showing no significant difference from wheat bread, while 20-30% replacements significantly reduced volume. [PERSON] et al. (2015) [12] reported a 12-17% reduction in bread volume with as little as 5% substitution of wheat flour with external fraction and debramned inner fraction of hull-less barley. The reduction in volume is attributed to the dilution of gluten, weakening the gluten network, and the absorption of water by \(\beta\)-glucan, a soluble fiber in barley, which affects the gluten network and gas cell stability. [PERSON] et al. (2002) [13] also noted that waxy starch binds more water than normal starch, potentially leading to reduced vapor production and a smaller loaf volume. Conversely, some reports suggest that \(\beta\)-glucan can positively influence bread volume. [PERSON] et al. (2010) [35] demonstrated that adding 0.6% high molar mass \(\beta\)-glucan to wheat flour increased bread-specific volume by 37% compared to the control. [PERSON] et al. (2007) [36] observed that in gluten-free bread, 1% \(\beta\)-glucan increased volume by 22.4%, and 2% \(\beta\)-glucan resulted in an 8% increase. [PERSON] et al. (2023) [37] showed that adding 0.1-1.0% \(\beta\)-glucan enhanced gluten solid properties and polymer content, suggesting complex interactions between \(\beta\)-glucan and the gluten network. [PERSON] et al. (2018) [38] suggested that fiber-induced changes in bread quality could not solely be explained by gluten dilution, with variations likely due to the molecular size, solubility, and concentration range of polysaccharides and the type of wheat flour used. The effect of barley flour particle size has been reported by [PERSON] et al. (2022) [19]; when doughs with high water content, such as batters, were prepared with barley of small particle size, the leaching of \(\beta\)-glucan resulted in low flowability. In cases of low moisture content, such as dough, the effect of particle size on dough is limited. However, IBLP had  
Figure 4: Height (**a**) and specific volume (**b**) of bread with added waxy barley bran. Bars represent the mean \(\pm\) standard error (\(n=3\) for height, \(n=4\) for specific volume). Different letters (a–e) indicate significant differences among the groups (\(p<0.05\)). IBLP—inner bran layer powder; OBLP—outer bran layer powder. a smaller particle size, suggesting that leaching of \(\beta\)-glucan may have an impact on flour gluten and crumb formation. The IBLP and OBLP used in this study contained \(\beta\)-glucan at levels of 4.84 g/100 g and 3.91 g/100 g, respectively [9]. In this study, a 10% IBLP replacement group increased bread-specific volume by 59% compared to the control. The \(\beta\)-glucan content in the 10% IBLP replacement group was 1.21 g, suggesting that \(\beta\)-glucan contributed to maintaining bubbles and enhancing specific volume. However, specific volumes for IBLP 30-50% replacements and OBLP 30% replacement groups were reduced by 18-53% compared to the control.