Direct Photometric Assay for Copper Chlorophyll Adulterants in Edible Oil by the Aid of an Ultraviolet-Photobleaching Pretreatment

• Published in: Journal of agricultural and food chemistry Vol. 66; no. 33; pp. 8859 - 8863
• Main Authors: Wang, Hung-Cheng, Hou, Yung-Te, Hsieh, Bo-Chuan
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.08.2018
• Subjects: adulterants; adulterated products; chlorophyll; color; cooking fats and oils; copper; detection limit; diodes; fats and oils industry; food safety; high performance liquid chromatography; photobleaching; photons; screening; soybean oil; statistical analysis; spectrophotometry; copper chlorophyll; adulteration; photobleaching; edible oil
• DOI: 10.1021/acs.jafc.8b02170
• ISSN: 0021-8561; 1520-5118

Adulterating edible oil with copper chlorophyll derivatives (E141i) has made a substantial impact on the edible oil industry and food safety. This study demonstrates an efficient and reliable screening method to directly identify the color adulteration by the aid of a simple photobleaching pretreatment using a 365 nm ultraviolet-light-emitting diode working at a photon flux density of 480 mmol m–2 s–1 for 24 min. The content of copper chlorophyll [predominantly Cu-pyropheophytin a (Cu-py a)] can be calculated by A 600, A 650, and A 700 with satisfactory spike recovery [97.9–103.6%; six kinds of edible oils spiked with 1 ppm of Cu-py a; n = 3 for each kind of oil; relative standard deviation (RSD) < 5%], linearity (R 2 = 0.9961 when spiking 0.1–10 ppm of Cu-py a into soybean oil standard; n = 3 for each concentration; RSD < 5%), and reproducibility (RSD < 5% for spiking 1 ppm of Cu-py a into soybean oil standard; n = 3 over 3 days). The detection limit (S/N > 5) was 0.05 ppm. The analytical results of 50 commercially available oil samples were verified by the official high-performance liquid chromatography method.