## 3 Results  
The linearity, limit of detection (LOD) and limit of quantification (LOQ) of the spectrophotometric Folin-Ciocalteu method, are presented in Table 1. According to the values of R\({}^{2}\) (0.9932-0.9985), all quercetin derivative standards showed linear calibration curves in the studied range, with reasonably low LOD and LOQ. Table 2 shows the amounts of adsorbed quercetin derivatives (\(q_{\rm e}\), mg/mg of \(\beta\)-glucan) for the initial concentration of quercetin derivatives 25 mg/L. All three quercetin derivatives adsorbed in similar amounts (0.30, 0.25 and 0.21 mg/mg, for quercetin-3-rhamnoside, quercetin-3-glucose and quercetin-3-galactoside, respectively). The amounts of adsorbed quercetin derivatives are similar to the amounts of various polyphenols adsorbed onto \(\beta\)-glucan, which are reported in earlier studies [16; 17]. Namely, [PERSON] et al. (2012a) [16] reported the adsorption of tea polyphenols onto \(\beta\)-glucan in the amount of 0.156 to 0.405 mg/mg \(\beta\)-glucan, which is similar to our results. They also studied the adsorption of epigallocatechin gallate under various initial concentrations and the maximum adsorption capacity with higher epigallocatechin gallate concentration was around 0.25 mg/mg \(\beta\)-glucan [16]. [PERSON] et al. (2011) [17] studied the adsorption of tea polyphenols onto \(\beta\)-glucan, and the influence of different pH values, buffer concentration and temperature onto adsorption. The highest adsorption capacity of tea polyphenols under various influences of pH, temperature and buffer concentrations was 0.116 mg/mg \(\beta\)-glucan which is also similar to our results. Furthermore, adsorption of various polyphenols onto different adsorbents like cellulose [7; 10; 11], cell wall material [34; 35; 36], pectin, xyloglucan, starch and cellulose [37], and resin [38] was also investigated. Since the amount of adsorbed polyphenols depends on the initial polyphenol concentration, pH value, buffer, and temperature, it is difficult to compare the adsorption capacities in these studies, but it can be seen that the adsorbed amount from those earlier studies [7; 10; 11; 34; 35; 36; 38] was in the range of the results of this study. The adsorption of apple polyphenols to apple cell walls was in the range of 0.14 and 0.58 mg/mg of cell walls, which is also similar to our study [39]. Quercetin adsorption was further studied with more initial quercetin derivatives concentrations in order to collect the data to analyze with the adsorption isotherm equations. The results of the adsorption of quercetin derivatives with different initial concentrations are shown in Figure 1. The amount of adsorbed quercetin derivatives increases with increased initial concentration, as shown in previous studies [7; 10; 16]. Furthermore, it can still be seen that quercetin derivatives have very similar adsorption onto \(\beta\)-glucan. At higher concentrations, quercetin-3-rhamnoside adsorbed in somewhat higher concentrations than quercetin-3-glucose and quercetin-3-galactoside. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Quercetin Derivative**} & \multicolumn{2}{c}{_Langmuir_} & \multicolumn{2}{c}{_Dubitin-RadushkevidHill_} \\ \cline{2-6}  & \(q_{\rm e}\) & \(q_{\rm e(calc)}\) & \(q_{\rm e(calc)}\) & \(q_{\rm e(calc)}\) & \(q_{\rm e(calc)}\) \\ \cline{2-6}  & **(mg/mg)** & **(mg/mg)** & **(mg/mg)** & **(mg/mg)** \\ \hline quercetin-3-glucose & 0.25 \(\pm\) 0.05 & 0.35 & 0.30 & 0.25 \\ quercetin-3-galactoside & 0.21 \(\pm\) 0.19 & 0.30 & 0.28 & 0.24 \\ quercetin-3-rhamnoside & 0.30 \(\pm\) 0.07 & 0.40 & 0.27 & 0.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Quercetin derivative adsorption capacities (\(q_{\rm e}\)) and adsorption capacities calculated from the adsorption isotherm model (\(q_{\rm e,calc}\)) (modeled with improved non-linear modeling).