S. A. Lisa*
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
S. Khan
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
M. A. Kabir
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
F. Islam
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
S. Mohajan
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
K. Chowdhury
Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh
Vegetable oils; Vitamin A; Fatty acid composition; Peroxide value; Free fatty acid; Iodine value
Dhaka city, Bangladesh
Food Safety and Security
Vegetable oils Total 25 edible oil samples of five types (soybean oil, sunflower oil, rice bran oil, mustard oil and palm olein, each from 5 different brands) were collected from local market of Dhaka city, Bangladesh during the month of February, 2015. The samples were coded as SB1, SB2, SB3, SB4 and SB5 for soybean oil; SF1, SF2, SF3, SF4 and SF5 for sunflower oil; RB1, RB2, RB3, RB4 and RB5 for rice bran oil; MT1, MT2, MT3, MT4 and MT5 for mustard oil, and PO1, PO2, PO3, PO4 and PO5 for palm olein oil, respectively. Standard and chemicals- Fatty Acid Methyl Ester (FAME) and vitamin A (Retinyl Palmitate) standards were collected from Sigma-Aldrich, St. Louis, Missouri, USA. All the chemicals used in this study were of analytical grade, Merck, Germany. HPLC grade Methanol and Dichloromethane were used for HPLC analysis and GC grade petroleum ether (b.p. 40-600C) was used for GC analysis. Chemical analysis Free fatty acid, peroxide value and iodine value of the samples were done following AOAC method 940.28, AOAC 965.33 and AOAC 920.158 respectively (AOAC, 2005). Analysis of fatty acid composition Preparation of fatty acid methyl ester (FAME) Relative concentration of fatty acid (FA) from oil samples were measured as their corresponding methyl esters. 5-7 drops of oil was taken in 15 ml test tube and 3 ml of 0.5 M sodium methoxide (prepared by mixing metallic sodium in methanol) was added and digested by stirring in a boiling water bath for about 15 minutes. It was allowed to cool to room temperature and 1 ml of petroleum ether (b.p 40-600C) was added followed by 10 ml deionized water, mixed gently and allowed to settle for 5-6 minutes. The distinct upper layer of methyl ester in petroleum ether was separated carefully in a capped vial and used for analysis. 200 mg of different fatty acid standard in their respective methyl ester form were dissolved separately in 10 ml petroleum ether (b.p 40-600C) in a series of screw-capped test tubes. Aliquots of 1µl fatty acid methyl ester (FAME) were injected and the peaks of fatty acids were recorded for their respective retention time and areas by the data processor unit of GC. Gas chromatography Fatty acid composition was analyzed using gas chromatograph (Shimadzu GC-14B, Japan) equipped with flame ionization detector and fused silica capillary column (FAMEWAX, Crossbond polyethylene glycol, 15m×0.25mm×0.25µm lm thickness, Restek; Pennsylvania, USA). Splitless injection technique with nitrogen as carrier gas at a constant flow rate of 20 ml/min was used. Injector temperature was 250o C, initial oven temperature was 150oC and held for 5 minutes. Temperature was increased at a rate of 8oC/min to 190oC and then increased to 200oC at a rate of 2oC/min and held for 10 minutes. The fatty acids were identified by using respective fatty acid methyl ester standards (FAME mix) and presented as relative percentage done by the automated GC software (Class GC-10,version-2.00). Vitamin A estimation Vitamin A was determined using High Performance Liquid Chromatograph (Shimadzu Corporation, Japan) equipped with a main controlling unit (SCL-10AVP), two high pressure pumps (LC-10ATVP), a degasser (DGU-14A), a column oven (CTO-10ASVP) with 20 µL injector loop and a UV detector (SPD-10AVP) controlled by a single Class VP software along with a Luna C18 column (250mm X 4.6mm I.D., 5 µm particle size). Extraction of vitamin A Samples were prepared by dissolving 10 g of each oil samples with dichloromethane and methanol in 50 ml amber color volumetric flask. The standard stock solution was prepared by dissolving 0.005 g of retinyl palmitate in 50 ml dichloromethane and methanol to get a final concentration of 100 mg/ml. Both sample and standard were sonicated in ultrasonic bath for 5 minutes and then filtered with 0.45 µm syringe lilter in a 1.5 ml glass vial and an aliquot of the overlay was injected into the HPLC column. All of the standards and samples were run in triplicate. HPLC condition Detection was performed at 325 nm using UV-VIS Detector for vitamin A as Retinyl Palmitate. Absolute methanol was used as the elution solvent. The analytical column was kept at 300 C. The separation was done using isocratic mode. Flow rate was 1 ml/min and run time for each standard and sample was 60 minutes. The sample injection volume was 20 µL. Vitamin A (as retinyl palmitate) concentration was determined with external standards. Data was collected and processed by Class-VP Automated Software (Shimadzu Corporation). Statistical analyses Data analysis was performed using Statistical Package for the Social Sciences (SPSS version 15.0 SPSS Inc. Chicago, Illinois, U.S.A). Data were expressed as mean ± SEM (standard error of the mean) and means were separated using t-test. One-way ANOVA was used for determining the significance/non-significance of results.
Bangladesh J. Sci. Ind. Res. 54(1), 11-20, 2019
Journal