Regarding the most important bins for group discrimination, Fig. 6 reflects the studies based on both VIP (Fig. 6(a)) and loadings of the first two components of the proposed PLS-DA model (Fig. 6(b)). From VIP, the two most important bins to distinguish the samples were d 1.57 and 1.62 ppm. Actually, these chemical shifts had been previously identified by visual inspection of the PCA loadings plot (Fig. 2) and hypothesis tests. They can be assigned to b-carboxyl methylene groups of aliphatic chains of fatty acids (Fang et al., 2013). These fatty acids can be free or linked to glycerol as esters. The methylene groups from free fatty acids are slightly more shielded than those from esters. So, the signal at d 1.57 ppm is attributed to methylene groups from free fatty acids, whilst the d 1.62 ppm is assigned to methylene groups from esters.
Furthermore, according to PLS-DA loadings plot and VIP scores (Fig. 6), the signal at d 1.57 ppm showed an increased integration area in the irradiated samples (I) when compared with the non-irradiated samples (N), whilst for the signal at d 1.62 ppm, the relationship is reversed. One possible explana- tion for the observed discrimination is the breaking of the ester bond with formation of free fatty acid. This occurs due to the ionizing radiation, which forms free radicals from air humidity and causes the hydrolysis of ester. However, this breaking is minimal and does not lead to significant changes in the acidity degree of oil, though it is detectable by a chemometric analysis of the spectra data.
Therefore, the metabonomic model herein developed was able to classify the samples as irradiated or non-irradiated and can be used to guarantee that the soybeans grains had been exposure to ionizing radiation at doses of either 1 or 5 kGy.
Regarding the most important bins for group discrimination, Fig. 6 reflects the studies based on both VIP (Fig. 6(a)) and loadings of the first two components of the proposed PLS-DA model (Fig. 6(b)). From VIP, the two most important bins to distinguish the samples were d 1.57 and 1.62 ppm. Actually, these chemical shifts had been previously identified by visual inspection of the PCA loadings plot (Fig. 2) and hypothesis tests. They can be assigned to b-carboxyl methylene groups of aliphatic chains of fatty acids (Fang et al., 2013). These fatty acids can be free or linked to glycerol as esters. The methylene groups from free fatty acids are slightly more shielded than those from esters. So, the signal at d 1.57 ppm is attributed to methylene groups from free fatty acids, whilst the d 1.62 ppm is assigned to methylene groups from esters.Furthermore, according to PLS-DA loadings plot and VIP scores (Fig. 6), the signal at d 1.57 ppm showed an increased integration area in the irradiated samples (I) when compared with the non-irradiated samples (N), whilst for the signal at d 1.62 ppm, the relationship is reversed. One possible explana- tion for the observed discrimination is the breaking of the ester bond with formation of free fatty acid. This occurs due to the ionizing radiation, which forms free radicals from air humidity and causes the hydrolysis of ester. However, this breaking is minimal and does not lead to significant changes in the acidity degree of oil, though it is detectable by a chemometric analysis of the spectra data.Therefore, the metabonomic model herein developed was able to classify the samples as irradiated or non-irradiated and can be used to guarantee that the soybeans grains had been exposure to ionizing radiation at doses of either 1 or 5 kGy.
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