Abstract
In this experiment the authors have investigated with respect to the discoloration of preboiled Euphausia superba (E. superba) during the storage at a low temperature.
Autoxidized unsaturated fatty acid of pre-boiled E. superba (E. superba autoxidized USFA) was prepared with autoxidizing unsaturated fatty acid extracted from preboiled E. superba. Autoxidized methyl linoleate was made with autoxidizing a commercial methyl linoleate. Volatility basic nitrogen (VBN) and non-volatility basic nitrogen (Non-VBN) of pre-boiled E. superba were prepared according to the method by Nakamura et al. When E. superba autoxidized USFA or autoxidized methyl linoleate were reacted to VBN or Non-VBN, discolored substances were obtained as a product of reaction. These discolored substances from VBN or Non-VBN were fractionated to hydrophilic and lipophilic fractions, and the obtained fractions were hydrophilic of Non-VBN (F-1), lipophilic of Non-VBN (F-2), hydrophilic of VBN (F-3) and lipophilic of VBN (F-4). Change of discoloration and fluorescence intensity in these fractions (F-1-F-4) were measured with the passage of time. Furthermore, change of peroxide value (POV), carbonyl value (COV) and thiobarbituric acid value (TBA) in the discolored solution of VBN and Non-VBN were measured.
The following results were obtained.
(1) Discoloration of the rancid oil was effected with contents of nitrogenous substance in the VBN and Non-VBN, and absorbance at a length of 430nm of F-1 had a higher value than other fractions (F-2-F-4).
(2) The fluorescence intensity of F-1 after 72hr was 50 times of the F-2 and 500 times of the F-3 or F-4.
(3) Both POV, COV or TBA value of the rancid oil and the discolored substances tended to increase during the first 72hr. Moreover, POV, COV and TBA value of Non-VBN were appreciably higher than those of VBN.
