# Influence of Rice Variety and Freezing on Flour Properties
## 3 Results and Discussion
### Effect of Rice Freezing on the Grinding Process
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Basmati**} & \multicolumn{2}{c}{**Arborio**} \\ \cline{2-4}  & **Raw** & **Frozen** & **Raw** & **Frozen** \\ \hline \multicolumn{4}{c}{Product after grinding} \\ \hline Particle size distribution & & & \\ \(>\)630 \(\upmu\)m, \% & 21.1 \(\pm\) 0.10 aB\({}^{\text{a}}\) & 3 \(\pm\) 0.17 bB & 21.4 \(\pm\) 0.10 aA & 13.6 \(\pm\) 0.10 bA \\ \(>\)400 \(\upmu\)m, \% & 33.3 \(\pm\) 0.17 bA & 42.4 \(\pm\) 0.10 aA & 27.8 \(\pm\) 0.10 bB & 29.9 \(\pm\) 0.10 aB \\ \(>\)315 \(\upmu\)m, \% & 12.1 \(\pm\) 0.17 aB & 9.9 \(\pm\) 0.10 bB & 14.6 \(\pm\) 0.17 aA & 13.1 \(\pm\) 0.17 bA \\ \(>\)160 \(\upmu\)m, \% & 21.9 \(\pm\) 0.17 bB & 24.9 \(\pm\) 0.17 aA & 29.7 \(\pm\) 0.26 aA & 18.2 \(\pm\) 0.20 bB \\ \(>\)125 \(\upmu\)m, \% & 6.2 \(\pm\) 0.17 bA & 12.4 \(\pm\) 0.10 aA & 4.4 \(\pm\) 0.17 bB & 10.9 \(\pm\) 0.17 aB \\ \(<\)125 \(\upmu\)m, \% & 5.4 \(\pm\) 0.44 bA & 7.3 \(\pm\) 0.20 aB & 2.2 \(\pm\) 0.10 bB & 14.3 \(\pm\) 0.17 aA \\ Fineness modules & 3.25 \(\pm\) 0.01 \({}^{\text{a}}\) & 2.77 \(\pm\) 0.01 \({}^{\text{b}}\) & 3.26 \(\pm\) 0.01 \({}^{\text{a}}\) & 2.74 \(\pm\) 0.01 \({}^{\text{b}}\) \\ \hline \multicolumn{4}{c}{Product after grinding and sieving through 315 mesh size} \\ \hline Flour yield, \% & 45.5 \(\pm\) 0.17 \({}^{\text{b}}\)B & 54.6 \(\pm\) 0.17 \({}^{\text{a}}\)B & 50.9 \(\pm\) 0.10 \({}^{\text{b}}\)B & 56.5 \(\pm\) 0.17 \({}^{\text{a}}\)B \\ Flour fineness modules & 1.89 \(\pm\) 0.01 \({}^{\text{a}}\)B & 1.36 \(\pm\) 0.02 \({}^{\text{b}}\)B & 2.11 \(\pm\) 0.02 \({}^{\text{a}}\)B & 1.53 \(\pm\) 0.02 \({}^{\text{b}}\)B \\ \hline \hline \end{tabular} Data expressed as mean \(\pm\) standard deviation (\(n=3\)). \({}^{\text{a}}\) Within a row, mean values corresponding to the same rice variety which do not share a superscript lowercase letter are significantly different (\(p<0.05\)). Within a row, mean values corresponding to the same type of treatment (raw or frozen) which do not share a superscript uppercase letter are significantly different (\(p<0.05\)).  
\end{table} 
Table 2: Influence of rice freezing on the performance of grinding process. Because of the high shearing, grinding might cause an increase in temperature, making the product rubbery and therefore more difficult to be broken into small particles [25]. Grinding the grain sample with low temperature allows overcoming these inconveniences. At freezing, the rice samples become more brittle and can be more easily broken with less mechanical action [2]. The impact of rice freezing on the performance of the grinding process is presented in Table 2. It can be observed that the freezing significantly affected the particle size distribution of both whole grinding products (\(p<0.05\)) and of hours (\(p<0.05\)) of the two commercial rice varieties. Thus, in the case of freezing the Basmati variety, the whole grinding product had the percentage of particles exceeding 630 \(\upmu\)m considerable reduced (\(p<0.05\)) compared to the corresponding raw sample (from 21.1% to 3%), while the percentage of particles of 400-630 \(\upmu\)m increased from 33.3% to 42.4% (\(p<0.05\)), and the percentage of particle smaller than 160 \(\upmu\)m increases from 11.6% to 19.7% (\(p<0.05\)). In a first grinding step, the coarse reduction of the grain occurs under compression, further shearing and friction yielding larger volumes of fine particles [26]. It appears that in the case of grinding the frozen samples by means of the disc mill, the shearing and friction forces play a major role in shaping the particle size distribution of the final product. Further, cutting forces acting in the last stage of grinding are known for giving a definite particle size with few or no fines [26]. As a result of the increase of the volume of fine fractions when grinding the frozen samples, the flour extraction significantly increased from 45.5% to 54.6% (\(p<0.05\)), and the fineness module significantly decreased from 1.89 to 1.36 (\(p<0.05\)).