Detection by coupled LC-photodiode array detection and high-resolution Orbitrap MS of dimethyl and diethyl yellow dyes used illegally in processed soymilk curd.

An efficient non-target dye-screening system consisting of a liquid chromatography photodiode array coupled with a high-resolution mass spectrometer (HRMS) is described. Visible absorption spectroscopy assisted in locating the peak of an unknown dye in HRMS chromatograms which allowed the accurate molecular weight of the unknown to be obtained. In a study of the adulteration of processed soymilk curd (tofu) with dimethyl yellow, an unexpected unknown dye was discovered. The compound was further purified by gel permeation chromatography and identified by HRMS and proton nuclear magnetic resonance (NMR) as diethyl yellow (solvent yellow 56). This is the first time that diethyl yellow has been reported in foods. The authentic diethyl yellow was then purchased and used as a quantitative standard. Tofu products and their ingredients associated with tofu processing were surveyed. Analysis showed the source of diethyl yellow could be traced to emulsifiers used as ingredient in tofu products. Surveillance work found the concentrations of diethyl yellow ranged from several µg kg(-1) (ppb) in the tofu products to up to hundreds of mg kg(-1) (ppm) in the emulsifiers.

Identification and quantification of Cu-chlorophyll adulteration of edible oils.

Cu-pyropheophytin a, the major Cu-pigment of Cu-chlorophyll, was determined in edible oil by high-resolution mass spectrometry with a high-performance liquid chromatography-quadrupole (HPLC-Q)-Orbitrap system and by HPLC coupled with a photodiode-array detector. Respective limit of detection and limit of quantification levels of 0.02 µg/g and 0.05 µg/g were obtained. Twenty-nine commercial oil products marked as olive oil, grapeseed oil and blended oil, all sourced directly from a food company that committed adulteration with Cu-chlorophyll, were investigated. In this company, four green dyes illegally used in oils were seized during factory investigation by the health authorities. The food additive Cu-pyropheophytin a was found in all confiscated samples in concentrations between 0.02 and 0.39 µg/g. Survey results of another 235 commercial oil samples manufactured from other companies, including olive pomace oil, extra virgin olive oil, olive oil, grapeseed oil and blended oil, indicated high positive incidences of 63%, 39%, 44%, 97% and 8%, respectively, with a concentration range between 0.02 and 0.54 µg/g. High Cu-chlorophyll concentrations are indications for fraudulent adulteration of oils.

Effective extraction method through alkaline hydrolysis for the detection of starch maleate in foods.

A high-performance liquid chromatography (HPLC) method was developed for the determination of maleic acid which was released from starch maleate (SM) through the alkaline hydrolysis reaction. The proper alkaline hydrolysis conditions and LC separation are reported in this study. The starch samples were treated with 50% methanol for 30 minutes, and then hydrolyzed by 0.5N KOH for 2 hours to release maleic acid. A C18 column and gradient mobile phase consisting of 0.1% phosphoric acid and methanol at a flow rate of 1.0 mL/minute were used for separation. The method showed a good linearity in the range of 0.01-1.0 ìg/mL, with a limit of quantification (LOQ) at 10 mg/kg in starch. The recoveries in corn starch, noodle, and fish balls were between 93.9% and 108.4%. The relative standard deviation (RSD) of precision was <4.9% (n = 3). This valid method was rapid, sensitive, precise, and suitable for routine monitoring of the illegal adulteration of SM in foods.

Determination of 20 synthetic dyes in chili powders and syrup-preserved fruits by liquid chromatography/tandem mass spectrometry.

A liquid chromatography/tandem mass spectrometry (LC-MS/MS) method is developed to simultaneously determine 20 synthetic dyes (New Coccine, Indigo Carmine, Erythrosine, Tartrazine, Sunset Yellow FCF, Fast Green FCF, Brilliant Blue FCF, Allura Red AC, Amaranth, Dimethyl Yellow, Fast Garnet GBC, Para Red, Sudan I, Sudan II, Sudan III, Sudan IV, Sudan Orange G, Sudan Red 7B, Sudan Red B, and Sudan Red G) in food samples. This method offers high sensitivity and selectivity through the selection of two fragment ion transitions under multiple reaction monitoring mode to satisfy the requirements of both quantitation and qualitation. Using LC-MS/MS, the newly developed extraction protocol used in this study is rapid and simple and does not require the use of solid-phase extraction cartridges. The linearities and recoveries of the method are observed at the concentration range of 0.10-200 µg/kg and more than 90% for all dyes, respectively. The method has been successfully applied to screen 18 commercial chili powders and six commercial syrup-preserved fruits purchased from retail establishments in Taipei City. The results show that three legal food dyes, Tartrazine, and/or Sunset Yellow FCF, and/or New Coccine, are present in some syrup-preserved fruits. Amaranth, an illegal food dye in certain countries but declared illegal in Taiwan, is found in an imported syrup-preserved fruit.