# Effects of Isochoric Freezing on the Quality Characteristics of Raw Bovine Milk
## 3 Results and Discussion
### Color and Turbidity
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Initial**} & \multicolumn{2}{c}{**RF**} & \multicolumn{2}{c}{**HTST**} & \multicolumn{3}{c}{**IF (\(-\)5 \({}^{\circ}\)C)**} & \multicolumn{3}{c}{**IF (\(-\)10 \({}^{\circ}\)C)**} \\ \cline{2-11}  & **0 Weeks** & **2 Weeks** & **0 Weeks** & **2 Weeks** & **5 Weeks** & **2 Weeks** & **5 Weeks** & **2 Weeks** & **5 Weeks** \\ \hline \multirow{2}{*}{\(L^{*}\)} & 77.55 & 77.23 & 77.82 & 77.35 & 75.49 & 76.28 & 78.23 & 77.38 & 77.57 \\  & (0.15) \({}^{\mathrm{a}}\) & (0.05) \({}^{\mathrm{a}}\) & (0.05) \({}^{\mathrm{a}}\) & (0.03) \({}^{\mathrm{a}}\) & (0.60) \({}^{\mathrm{a}}\) & (0.05) \({}^{\mathrm{a}}\) & (0.8) \({}^{\mathrm{a}}\) & (0.02) \({}^{\mathrm{a}}\) & (0.07) \({}^{\mathrm{a}}\) \\ \hline \multirow{2}{*}{\(a^{*}\)} & \(-1.78\) & \(-1.76\) & \(-1.95\) & \(-1.94\) & \(-2.28\) & \(-1.63\) & \(-2.05\) & \(-1.33\) & \(-1.56\) \\  & (0.02) \({}^{\mathrm{b}}\) & (0.02) \({}^{\mathrm{b}}\) & (0.01) \({}^{\mathrm{c}}\) & (0.03) \({}^{\mathrm{c}}\) & (0.03) \({}^{\mathrm{d}}\) & (0.01) \({}^{\mathrm{b}}\) & (0.01) \({}^{\mathrm{c}}\) & (0.02) \({}^{\mathrm{a}}\) & (0.06) \({}^{\mathrm{ab}}\) \\ \hline \multirow{2}{*}{\(b^{*}\)} & 3.38 & 3.63 & 3.00 & 2.92 & 0.03 & 3.63 & 3.95 & 4.86 & 5.14 \\  & (0.02) \({}^{\mathrm{b}}\) & (0.01) \({}^{\mathrm{b}}\) & (0.03) \({}^{\mathrm{b}}\) & (0.03) \({}^{\mathrm{b}}\) & (0.14) \({}^{\mathrm{c}}\) & (0.02) \({}^{\mathrm{b}}\) & (0.10) \({}^{\mathrm{b}}\) & (0.01) \({}^{\mathrm{a}}\) & (0.15) \({}^{\mathrm{a}}\) \\ \hline \multirow{2}{*}{\(\Delta E\)} & 0 & 0.35 & 0.49 & 0.53 & 3.84 & 1.30 & 1.50 & 1.56 & 1.88 \\  & (0.05) \({}^{\mathrm{c}}\) & (0.06) \({}^{\mathrm{c}}\) & (0.04) \({}^{\mathrm{c}}\) & (0.19) \({}^{\mathrm{a}}\) & (0.04) \({}^{\mathrm{b}}\) & (0.20) \({}^{\mathrm{b}}\) & (0.01) \({}^{\mathrm{b}}\) & (0.21) \({}^{\mathrm{b}}\) \\ \hline Turbidity & 2325 & 2302 & 2128 & 2130 & 842 & 2107 & 1720 & 2810 & 3365 \\ (NTU) & (175) \({}^{\mathrm{bc}}\) & (15) \({}^{\mathrm{c}}\) & (50) \({}^{\mathrm{cd}}\) & (83) \({}^{\mathrm{cd}}\) & (24) \({}^{\mathrm{e}}\) & (62) \({}^{\mathrm{cd}}\) & (373) \({}^{\mathrm{d}}\) & (42) \({}^{\mathrm{b}}\) & (343) \({}^{\mathrm{a}}\) \\ \hline \hline \end{The total color change (\(\Delta E\)) values for the milk samples are shown in Table 3. \(\Delta E\) is classified as not noticeable (0-0.5), slightly noticeable (0.5-1.5), noticeable (1.5-3.0), well visible (3.0-6.0), and great (6.0-12.0) [36]. According to this classification, the color difference in the HTST sample after 5 weeks is considered to be well visible to the human eye (3.84 \(\pm\) 0.19). This was mainly caused by the increase in yellowness (\(b^{\star}\)) due to the increase in microbial loading (\(\geq\)5.5 log CFU/mL). In comparison, the IF (\(-\)5 \({}^{\circ}\)C) sample had a slightly noticeable color changes after 2 and 5 weeks, with values of 1.30 \(\pm\) 0.04 and 1.50 \(\pm\) 0.2, respectively. On the other hand, the IF (\(-\)10 \({}^{\circ}\)C) sample had noticeable color changes after 2 and 5 weeks, with values of 1.56 \(\pm\) 0.01 and 1.88 \(\pm\) 0.21, respectively. The increase in total color change for the IF (\(-\)10 \({}^{\circ}\)C) sample at 5 weeks could be due to the formation of small aggregates. The initial turbidity value for raw milk was 2325 \(\pm\) 175 NTU (Table 3). HTST treatment reduced milk turbidity due to alterations of the casein micelles [37]. The turbidity of the milk after IF (\(-\)5 \({}^{\circ}\)C) treatment was significantly reduced to 2107 and 1720 NTU after 2 and 5 weeks, respectively. Previous authors also found a reduction in turbidity with pressure [38]. In contrast, the turbidity of the milk after IF (\(-\)10 \({}^{\circ}\)C) treatment increased to 2810 and 3365 NTU after 2 and 5 weeks, respectively. Milk turbidity was mainly related to the aggregation and dissociation of casein micelles [39]. The casein micelles are composed of casein molecules, colloidal calcium phosphate, and water molecules dispersed in the whey serum.