Quantitative Determination of Alkylresorcinols in Cereal Grains: Independence of the Length of the Aliphatic Side Chain

Abstract

Two general spectrophotometric methods were used to analyze alkylresorcinols and determine their total amounts in rye, wheat and cereal products. Alkylresorcinols were extracted from rye bran with acetone, hydrogenated to obtain a mixture of saturated homologues, subjected to preparative high‐performance liquid chromatography (HPLC) to obtain individual species with the side chain ranging from 15 to 25 carbon atoms, and finally quantified by colorimetric reaction with the diazonium salt Fast Blue B (2‐methoxy‐4‐nitoraniline) and by HPLC. The intensity of the reaction between the same weight amounts of homologues with Fast Blue B decreased in the order C15:0 > C17:0 > C19:0 > C21:0 > C23:0 > C25:0. It was demonstrated that calibration curves based on molecular concentration instead of weight amount of the particular homologues were characterized by the same regression equation and showed an acceptable linearity in the range of 5–30 nmol of homologue in a sample. This confirmed that the colorimetric reaction of alkylresorcinols with Fast Blue B is independent of the length of the aliphatic side chain. Total alkylresorcinols were accordingly determined in cereal grain materials. Two extraction systems (acetone and ethyl acetate) were used. The results of the colorimetric method and those calculated from calibration curves based on the weight amounts of the homologues C15:0 and C19:0 were different. In contrast, the results calculated from the calibration curves based on the mole amounts of the particular homologues were very similar or even identical. PRACTICAL APPLICATIONS The color and intensity of the reaction between alkylresorcinols and the diazonium salt Fast Blue B was independent of the length of the alkyl side chain. This feature could be helpful for the differential determination of the phenolic and resorcinolic lipids present in biological samples. Most cereal material and products contain a mixture of various homologues that is characteristic not only of the source (rye, wheat, triticate, barley), but also of the variety and the growth conditions. Therefore, for accurate calibration curves independent of the composition of homologues, they should be prepared on the basis of the mole fraction of the alkylresorcinols present, similar to the quantitation of phospholipids via phosphorus determination. This procedure will also allow the direct comparison of their amounts in different sources of alkylresorcinols. Nevertheless, simultaneous determination of the homologue composition in the samples is desirable (e.g., by reverse‐phase high‐performance liquid chromatography) as different homologues may have various impacts on the biological activity of alkylresorcinols from cereal products.

Effects of Energy and Macronutrient Intake on Cognitive Function Through the Lifespan

“…This value is comparable to the previously reported data: 28.8-42 5 mg/100 g FW by Chen et al (2004), 42.0-42.1 mg/100 g FW by Landberg et al (2009). However, our results for wheat samples are lower than those obtained by Ross et al (2003) -ARs levels in common wheat grains varied from 42 to 122.9 mg/100 g FW, by Mattila et al (2005) -whole wheat flour contained 75.9 mg/100 g FW of ARs and, also by Kulawinek and Kozubek (2008) ground wheat grains contained 57.8 mg/100 g FW of ARs (for C15:0-C 19:0 homologues). This variation is probably due in part to differences in analytical methods and also the ARs content of cereals appears to be highly variable, depending on cultivar and environmental conditions.…”

“…Calibration curves were prepared with the following concentrations: 0, 5, 20, 50, 70 and 100 mg/ml. Alkylresorcinol homologues C15:0, C23:0 and C25:0 were identified according to their spectra (Kulawinek and Kozubek, 2008) and determined semiquantitatively by method of internal standard, with C21:0 homologue as an internal standard (10 mg/ml). Relative response factors for C15:0, C23:0 and C25:0 homologues were calculated by taking into account the amount of homologue (based on molecular weight) injected into chromatographic column versus homologue C21:0.…”

“…Gas chromatography -mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) are commonly used for the routine quantitative determination of ARs (Ross et al, 2001;Mattila et al, 2005;Landberg et al, 2006). For the rapid determination of total ARs content in cereal grain products, colorimetric method after formation of intense red complex with fast blue salt (the diazonium salt Fast Blue B) has been used (Mattila et al, 2005;Kulawinek and Kozubek, 2008). Fast Blue B has been used for quantitative determination of ARs in cereal grain extracts, but without reported validations of the methods used (Andersson et al, 2008).…”

Rapid and Sensitive Analysis of Alkylresorcinols from Cereal Grains and Products Using HPLC−Coularray-Based Electrochemical Detection

“…Currently, a number of methods exist, using GC (18 ), HPLC (19,20), and spectroscopy using the reaction of AR with the dye Fast Blue B (21)(22)(23).…”

Functional Properties of Triticale Bran Bioactives Using In Vitro and In Vivo Model Systems

“…In this study, the total AR contents of TB, RB, WB, and OB extracts were measured and compared by a colorimetric method involving Fast Blue B. This diazotized salt is selective for 1,3-dihydroxy-benzene rings, forming a reddish-violet coloured azo-complex is detected at 520 nm (237). This method is a reliable and effective means of comparing the total AR contents in cereal grains as it has been optimized and used for several years (108, 163-165, 167, 238).…”