2-acetyl-4-tetrahydroxybutylimidazole and 4-methylimidazole in caramel colours, vinegar and beverages in China.

A survey of 2-acetyl-4-tetrahydroxybutylimidazole (THI) and 4-methylimidazole (4-MeI) concentrations in caramel colours, vinegar and beverages from the Chinese market were performed by ultrahigh-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). In total, 117 samples, 78 caramel colour samples, 23 vinegar samples and 16 beverage samples, were investigated. The results indicated that 4-MeI was found in all samples. THI was found in a part of the samples and also the level range was lower compared to 4-MeI. In caramel colour samples, the concentration level range of THI was 1.0-74.3 mg/kg and of 4-MeI was 1.5-1291.8 mg/kg. In vinegar samples, the concentration level range of THI was 13.3-119.2 µg/L and for 4-MeI 111.2-2077.8 µg/L. In beverage samples, THI was only found in two samples and the concentration level range of 4-MeI was 10.8-307.1 µg/L. THI and 4-MeI levels in vinegar and beverages were rather low compared with those in caramel colour samples. These observations can be helpful for evaluating individual exposure to THI and 4-MeI from caramel colours, vinegar and beverages in China.

Evaluation of nondigested carbohydrates in hydroxypropylated tapioca starch.

In vitro and in vivo digestibilities of hydroxypropyl starch were investigated to determine an appropriate nondigested carbohydrate assaying method for hydroxypropyl starch. Hydroxypropyl tapioca starch (HPTS), with a 0.338 degree of substitution, was used as a hydroxypropyl starch source. Practically all nondigested carbohydrate in HPTS was low molecular weight and was not precipitated in 78% ethanol. The contents of nondigested carbohydrate in HPTS and in effluents of ileorectomized rats fed the HPTS diet obtained by the AOAC 2001.03 (enzyme-gravimetric-HPLC method) were almost the same, 56% and 59%, respectively. The recovery of hydroxypropyl groups from ileorectomy effluents was 98%. The AOAC 2001.03 method is suggested to be appropriate in determining the content of nondigested carbohydrates in hydroxypropyl starch.

Determination of the carbohydrate composition of mammalian glycoproteins by capillary gas chromatography/mass spectrometry.

A technique to determine the carbohydrate composition of glycoproteins using capillary gas chromatography/mass spectrometry (electron impact) with selected ion monitoring is described. This method entails hydrolysis with methanolic-HCl followed by formation of trimethylsilyl methylglycoside derivatives, extraction of the carbohydrate derivatives into hexane, and GC/MS analysis. For those carbohydrates that are present in animal glycoproteins including fucose, mannose, galactose, glucosamine, galactosamine, and N-acetylneuraminic acid (sialic acid), the sensitivity of this assay was approximately 1-3 pmol and the assay was linear over a 100-fold range. The carbohydrate compositions determined on small quantities (1-10 pmol) of various glycoproteins including human transferrin and alpha-1 acid glycoprotein, fetuin, and ovalbumin were identical to their reported carbohydrate content and compositions. Major advantages of this technique include the time required to complete the sample preparation and analysis (less than 8 h), the sensitivity and specificity of the assay, and the fact that all carbohydrate moieties, including sialic acid, can be quantitated in a single hydrolysate of a glycoprotein.