Phytochemical residue profiles in rice grains fumigated with essential oils for the control of rice weevil.

In the present study, we investigated the fumigant potential of five edible essential oils
(EOs) against Sitophilus oryzae and their phytochemical residues in treated grains. Among
the tested EOs, peppermint oil proved significantly effective (P � 0.05) on S.oryzae at
400 μl/L air concentration, inducing 83 and 100% mortalities in with-food and without-food
conditions respectively over 72 h exposure. In addition, it was also observed that the binary
mixtures of peppermint + lemon oil (1:1 ratio) produced an equivalent effect to that of peppermint
oil alone treatments. The phytochemical residue analysis by GC-MS revealed the
presence of six compounds upon 72 h exposure to EOs. Further, the analysis of physicochemical
properties of the compounds indicated a positive correlation between polar surface
area (PSA) and its residual nature. The residue levels of eugenol were significantly elevated
corresponding to its high PSA value (29) in clove and cinnamon oils. On the other hand, the
compounds with zero PSA value imparted very less or no (D-Limonene, caryophyllene,
pinene and terpinolene) residues in treated grains. With respect to the most active peppermint
oil, L-menthone, menthyl acetate and eucalyptol residues were at 67, 41 and 23% levels
respectively. The outcome of the present study indicate the peppermint oil as a potent
fumigant against S. oryzae, and although the residues of phytochemicals in treated grains is
higher; they belong to the generally recognised as safe (GRAS) status leaving no harmful
effect.