# Prediction of Walnut Deterioration Using Kernel Oxidative Stability
## 3 Results and Discussion
### Relations between Kernel OSI and Quality of Kernel and Extracted Oil during Storage  
Lipid oxidation at low and high temperatures may go through different reaction pathways, depending on the reactivity of metal ions and antioxidants at different temperatures [20; 25]. Thus, it is important to mention that Rancimat methods may lead to either overprediction or underprediction of the actual shelf life depending on the type of sample tested [5]. In order to use Rancimat as a shelf-life prediction method, it is a must to compare the OSI with quality and oxidative markers of samples that have been stored under a more normal condition. Therefore, to further investigate the application of this method and operational parameters to walnut kernels, the OSI of the samples were measured after being stored at 25 \({}^{\circ}\)C for four and six months. The results were compared with other quality and oxidative parameters at the beginning and after four and six months of storage (Table 4). After four and six months of storage, moisture and fat content of the samples, demonstrated no linear correlation with OSI for all operational parameters. PV, UV absorbances, hexanal and sensory rancidity demonstrated negative and significant correlations after four and six months of storage for operational parameters using 110 \({}^{\circ}\)C (\(r<-0.5\); \(p<0.05\)). Operational parameters using 120 \({}^{\circ}\)C, had the smaller range of OSI values (6.8 to 2.7 h using 20 L h\({}^{-1}\); 6.2 to 3.2 h using 25 L h\({}^{-1}\)) compared with analysis at 110 \({}^{\circ}\)C (17.1 to \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **Operational Parameters** & **Moisture** & **Fat** & **PV** & **K232** & **K388** & **Hexanal** & **Oil OSI** & **Rancidity** \\ \hline \multirow{3}{*}{Kernel OSI} & 110 \({}^{\circ}\)C and 20 L h\({}^{-1}\) & 0.108 & \(-0.535\) \(\ast\) & \(-0.802\) \(\ast\) & \(-0.71\) \(\ast\) & \(-0.781\) \(\ast\) & \(-0.730\) \(\ast\) & \(0.813\) \(\ast\) & \(-0.730\) \(\ast\) \\  & 110 \({}^{\circ}\)C and 25 L h\({}^{-1}\) & 0.364 & \(-0.487\) \(\ast\) & \(-0.813\) \(\ast\) & \(-0.562\) \(\ast\) & \(-0.710\) \(\ast\) & \(-0.873\) \(\ast\) & \(0.741\) \(\ast\) & \(-0.799\) \(\ast\) \\  & 120 \({}^{\circ}\)C and 20 L h\({}^{-1}\) & -0.167 & \(-0.486\) \(\ast\) & \(-0.444\) \(\ast\) & \(-0.564\) \(\ast\) & \(-0.617\) \(\ast\) & \(-0.374\) \(\ast\) & \(0.317\) \(\ast\) & \(-0.298\) \\  & 120 \({}^{\circ}\)C and 25 L h\({}^{-1}\) & 0.220 & \(-0.609\) \(\ast\) & \(-0.643\) \(\ast\) & \(-0.523\) \(\ast\) & \(-0.618\) \(\ast\) & \(-0.556\) \(\ast\) & \(0.605\) \(\ast\) & \(-0.658\) \(\ast\) \\ \hline \end{tabular}
\end{table} 
Table 3: Correlations between kernel oxidative stability index (kernel OSI), quality and oxidative parameters of the walnut kernels and extracted oils. 6.1 h using 20 L h\({}^{-1}\); 14.6 to 5.6 h using 25 L h\({}^{-1}\)). The narrow range of OSI for operational parameters using 120 \({}^{\circ}\)C resulted in no significant correlations and low coefficients comparing to the range of other oxidative parameters that changed during storage. Higher temperatures shorten analysis time and distinguish lower oxidation stages from higher oxidation stages. However, it also decreases the resolution of the method, due to the narrower OSI ranges and correlations with other quality and oxidative parameters are possibly lost. Results showed that operational parameters using 110 \({}^{\circ}\)C with 25 L h\({}^{-1}\) airflow gave the best proximity to values obtained from other methods used to measure walnut oxidation (\(r>0.6\)), such as PV, hexanal and sensory evaluation of rancidity. Measuring kernel OSI at 110 \({}^{\circ}\)C with 25 L h\({}^{-1}\) also maintained the linear correlation when samples had different oxidation levels since the Pearson correlation coefficients were also significant among samples at different storage times. It is important to emphasize that measurements at 110 \({}^{\circ}\)C with 25 L h\({}^{-1}\) of airflow also gave the lowest variance among replicates (Table 1).