A novel insight on the high oxidative stability of roasted mustard seed oil in relation to phospholipid, Maillard type reaction products, tocopherol and canolol contents

Abstract

The oxidative stability of the roasted and unroasted crude mustard seed oil samples collected from the Nepalese market was evaluated by monitoring the peroxide value (PV) and conjugated diene (CD) during storage in the dark at 50°C. These samples showed a wide variability in the oxidative stability as measured by PV ranging from 5.22 to 42.11meq oxygen/kg oil after 69days of storage. The PV after 40days of storage (PV40) as an index of oxidative stability of the different samples was not significantly correlated (p>0.05) both with the total radical scavenger concentration (sum of tocopherol, plastochromanol-8 and canolol) and the total radical scavenging capacity of the oil using the di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH) assay. Hence, those antioxidants were not solely responsible for the differences in the oxidative stability among the oil samples. On the other hand, the PV40 showed significant negative correlation with the canolol content (p<0.01), the phospholipid content (p<0.001) and the different browning reaction markers such as absorbance at 350nm (p<0.001), fluorescence (excitation at 350nm and emission at 440nm) (p<0.001), and the pyrrolized phospholipid content (p<0.01). Moreover, all the browning reaction markers and phospholipid content were also highly positively correlated (p<0.001) with each other. The phospholipid and its Maillard type browning reaction products together with canolol formed during seed roasting were primarily responsible for the high oxidative stability of the roasted mustard seed oil samples.