## 3 Results and Discussion
### Effect of Modification on the In Vitro Digestibility of Broken Rice Starch  
The starch hydrolysis rates of the broken rice starch and modified starch composite were determined by measuring the glucose content. The amylase digestion curves are shown in Figure 7. The RDS, SDS, and RS contents, as well as the kinetic parameters of the starch digestion models, were calculated for the broken rice starch and modified starch composite, with the fitted data presented. The correlation coefficients were all above 0.98, indicating a good fit [58]. As shown in Table 3, after ultrasonic treatment, the RDS content of the broken rice starch increased from 70.94% to 76.63%, while the SDS content decreased from 22.49% to 18.65% and the RS content decreased from 6.57% to 4.72%, indicating a general decrease in resistant starch content. This could be due to the increased porosity of starch granules after ultrasonic treatment, making them more susceptible to enzyme actions [59]. The destruction of the double-helical structure of the starch after the ultrasonic treatment facilitated enzyme access to the enzyme-sensitive sites, leading to the degradation of amylopectin and a decrease in RS content [32]. After complexation with quercetin, the RDS content was lower than that of unmodified broken rice starch, with a decrease of \begin{table}
\begin{tabular}{l l l l} \hline \hline \multirow{2}{*}{**Sample**} & **Solubility** & **Swelling Power** & **Average Particle Size** \\  & **(\%)** & **(\%)** & **(nm)** \\ \hline C & 20.33 \(\pm\) 0.02 a & 10.01 \(\pm\) 0.05 a & 131.5 \(\pm\) 10.65 c \\ US & 23.27 \(\pm\) 0.01 a & 10.26 \(\pm\) 0.07 a & 314.53 \(\pm\) 15.21 a \\ US-Q & 12.73 \(\pm\) 0.03 b & 9.85 \(\pm\) 0.12 b & 242.53 \(\pm\) 13.33 b \\ \hline \hline \end{tabular}
**Note:** Different letters within the same column denote a significant difference (\(p<\) 0.05).  
\end{table} 
Table 2: Comparison of solubility, swelling, and particle size results for ground rice starch, ultrasonically modified starch, and modified starch composite. 21.43%, indicating a significant reduction in rapidly digestible starch. The SDS content of the US-Q was 30.26% and the RS content was 20.23%, representing an increase of 7.77% in SDS content and 13.66% in RS content compared with C.  
As shown in Figure 7a, the hydrolysis curve of the modified starch composite was significantly lower compared to the unmodified broken rice starch. The hydrolysis rate of unmodified C at 20 min was 70.94%, while the hydrolysis rate of US-Q decreased by 21.43%. Model fitting of the starch hydrolysis curve was performed to further understand the effect of ultrasonic synergistic quercetin composite modification on in vitro digestibility, and the fitting results are shown in Figure 7b. The hydrolysis parameter C\({}_{\infty}\) and k values for US-Q were significantly lower than those for unmodified C. The fitting results indicated that when the digestion time approached infinity, the hydrolysis rate of the broken rice starch could reach 92.6%, while that of the composite-modified starch was 78.35%, representing a decrease of 14.25%. Previous studies have shown that quercetin is an effective inhibitor of pancreatic amylase, which plays a major role in starch digestion. Starch must first be correctly oriented within the active site of the enzyme, where the \(\alpha\)-1.4 glycosidic bonds of starch are cleaved [16]. Therefore, when quercetin-starch complexes form, quercetin can bind to the hydrophobic helical regions of starch, which inhibits the binding of starch to \(\alpha\)-amylase and suppresses the \(\alpha\)-amylase activity [60]. Additionally, the strong interaction between quercetin and starch, as indicated by the XRD analysis, resulted in the formation of V-type crystals. V-type crystals are highly ordered, which also contributes to reducing the starch digestibility. Thus, the ultrasonic synergistic quercetin-modified starch composite exhibited greater resistance to digestion compared to the broken rice starch, significantly delaying the starch hydrolysis. [PERSON] et al.