## 2 Materials and Methods
### Methods
#### 2.2.3 Physicochemical Properties  
The rice flour colour was determined using a colorimeter (Hunterlab CalorFlex EZ, Sunset Hills Road, Reston). The flour sample was inserted into a glass sample cup. The flour sample should entirely cover the bottom surface of a glass sample cup. Colour profiles were expressed in L*, a*, and b*. The L* value indicates the level of light (L = 100) or dark (L = 0), the a* value indicates the amount of redness (+a) or greenness (-a), and the b* value indicates the amount of yellowness (+b) or blueness (-b) [22]. The CalorFlex EZ was standardised using the standard white tile before analysing the sample to prevent errors during colour reading. The result was reported as the mean of triplicates on each sample.  
Water absorption capacity and solubility were determined according to the methods described by [PERSON] and [PERSON], and by [PERSON] et al. [23;24] with slight modification. Approximately 1.00 \(\pm\) 0.02 g of the sample was weighed and recorded as w\({}_{0}\). The sample was then filled into a 50 mL centrifugal tube and weighed again, recorded as w\({}_{1}\). Next, 10 mL of distilled water was added into a centrifugal tube. The dispersions were vortexed every 5 min within 30 min at room temperature, followed by centrifugation for 10 min at 2000 rpm (359\(\times\)\(g\)). The supernatant was removed from the centrifugal tube, subsequently weighed, and recorded as w\({}_{2}\). The amount of water bound by flour was determined by the difference and expressed as the weight of water bound by dry flour (100 g) [25]. The result was reported as the mean of triplicates on each sample. Water absorption capacity was calculated using Equation (1).  
\[\text{Water absorption capacity}=\frac{\text{w}_{2}-\text{w}_{1}}{\text{w}_{0}} \tag{1}\]where \(\rm w_{0}\) = mass of sample (g), \(\rm w_{1}\) = mass of centrifugal tube + sample (g), and \(\rm w_{2}\) = mass of centrifugal tube + residue after removing the supernatant (g).  
The swelling capacity was determined according to the method described by [PERSON] et al. [26] with slight modification. First, 1 g (\(\rm w_{1}\)) of the rice flour sample was moistened with 30 mL of distilled water in a centrifuge tube. The centrifuge tubes containing the sample were heated at 80 \({}^{\circ}\)C in the water bath while shaking continuously. The tubes were taken out and allowed to cool down until the temperature decreased to room temperature. After the cooling process, samples were centrifuged at 2200 rpm for 15 min. The supernatant was removed from the centrifuge tube, and the residue weight was recorded (\(\rm w_{2}\)). The swelling capacity (g/g) was determined using Equation (2).  
\[\rm Swelling\ capacity\ (\rm g/g)=\frac{\rm w_{2}}{\rm w_{1}} \tag{2}\]  
where \(\rm w_{1}\) = mass of dry sample (g) and \(\rm w_{2}\) = mass of residue (after removing supernatant) (g).  
Moreover, the decanted supernatant from the swelling capacity procedure was used to determine the water solubility index of the rice flour. First, the empty crucibles were weighed and recorded as \(\rm w_{4}\), and the supernatant was poured carefully into the tared crucible. Then, the oven drying method was initiated to the supernatant at 105 \({}^{\circ}\)C overnight. On the following day, the dried supernatant was cooled in a desiccator to room temperature and weighed as \(\rm w_{3}\). The result was reported as the mean of triplicates on each sample. The water solubility index was calculated using Equation (3).  
\[\rm Water\ solubility\ index,\ \%=\frac{\rm w_{3}-w_{4}}{\rm w_{1}}\times 100 \tag{3}\]  
where \(\rm w_{1}\) = mass of the sample (g), \(\rm w_{3}\) = mass of crucibles and dried supernatant (g), and \(\rm w_{4}\) = mass of crucibles (g).