Alkylresorcinols in cereals and cereal products

Analysis of phenolic and cyclic compounds in plants using derivatization techniques in combination with GC-MS-based metabolite profiling

Metabolite profiling has been established as a modern technology platform for the description of complex chemical matrices and compound identification in biological samples. Gas chromatography coupled with mass spectrometry (GC-MS) in particular is a fast and accurate method widely applied in diagnostics, functional genomics and for screening purposes. Following solvent extraction and derivatization, hundreds of metabolites from different chemical groups can be characterized in one analytical run. Besides sugars, acids, and polyols, diverse phenolic and other cyclic metabolites can be efficiently detected by metabolite profiling. The review describes own results from plant research to exemplify the applicability of GC-MS profiling and concurrent detection and identification of phenolics and other cyclic structures.

Effect of 5-n-alkylresorcinol extracts from durum wheat whole grain on the growth of fusarium head blight (FHB) causal agents

In an approach toward the identification of ecofriendly compounds for fusarium head blight biocontrol, the in vitro antifungal activity of 5-n-alkylresorcinol (AR) extracts, obtained from durum wheat intact kernels, was tested. In comparison with ethyl acetate and acetone extracts containing AR, total inhibition of Fusarium graminearum spore germination was observed with cyclohexane extract, which also exhibited a significant fungistatic activity against F. graminearum, Fusarium culmorum, Fusarium avenaceum, and Fusarium poae. Additionally, the study of the influence of such variables as predrying of seeds and durum wheat genotype on AR cyclohexane extract properties allowed the association of its highest antifungal activity with the AR homologue composition and, in particular, with the presence of a higher C21:0/C23:0 ratio. The interesting finding of this study suggests a potential application of the AR homologues in crop protection systems and could be an important step toward the development of commercial formulations suitable to the prevention of fungal diseases.

Various effects of the photosystem II--inhibiting herbicides on 5-n-alkylresorcinol accumulation in rye seedlings

The effect of three PSII-inhibiting herbicides, lenacil, linuron, and pyrazon, on the accumulation of 5-n-alkylresorcinols in rye seedlings (Secale cereale L.) grown under various light and thermal conditions was studied. All used chemicals increased resorcinolic lipid content in both green and etiolated plants grown at 29 °C. At 22 °C pyrazon and lenacil decreased the content of alkylresorcinols in plants kept in the darkness and increased their amount in the light-grown seedlings. In turn, level of resorcinolic lipids was decreased by linuron in both etiolated and green plants. At the lowest tested temperature lenacil enhanced production of alkylresorcinols only in etiolated rye seedlings, whereas the light-independent stimulatory action of pyrazon on alkylresorcinol accumulation in rye grown at 15 °C was observed. Additionally, only the latter did not exert a negative effect on rye seedling growth under any of tested conditions. Compared with respective controls, the herbicides used also markedly modified the qualitative pattern of resorcinolic homologs. Interestingly, the observed changes generally favored the enhanced antifungal activity of these compounds. Our study provides novel information on the influence of PSII inhibitors on alkylresorcinol metabolism in rye seedlings. The unquestionable achievement of this work is the observation that low dose of pyrazon mainly stimulated both growth and alkylresorcinol synthesis in rye seedlings, a non-target plant. Moreover, our experimental work showed unambiguously that the observed pyrazon-driven accumulation and homolog pattern modification of alkylresorcinols dramatically improved the resistance of winter rye to infections caused by Rhizoctonia cerealis.

Whole grain rye intake, reflected by a biomarker, is associated with favorable blood lipid outcomes in subjects with the metabolic syndrome--a randomized study

Background and Aim

Few studies have explored the possible plasma cholesterol lowering effects of rye consumption. The aim of this secondary analysis in the SYSDIET study was to investigate the association between plasma alkylresorcinols (AR), a biomarker for whole grain wheat and rye intake, and blood lipid concentrations in a population with metabolic syndrome. Furthermore, we analyzed the associations between the AR C17∶0/C21∶0 ratio, a suggested marker of the relative intake of whole grain/bran rye, and blood lipid concentrations.

Methods

Participants were 30–65 years of age, with body mass index (BMI) 27–40 kg/m² and had metabolic syndrome. Individuals were recruited through six centers in the Nordic countries and randomized either to a healthy Nordic diet (ND, n = 93), rich in whole grain rye and wheat, as well as berries, fruits and vegetables, rapeseed oil, three fish meals per week and low-fat dairy products, or a control diet (n = 65) for 18/24 weeks. Associations between total plasma AR concentration and C17∶0/C21∶0 homologue ratio and blood lipids were investigated in pooled (ND + control group) regression analyses at 18/24 weeks adjusted for baseline value for the dependent variable, age, BMI and statin use.

Results

When adjusted for confounders, total plasma AR at 18/24 weeks was not significantly associated with blood lipids but the AR ratio C17∶0/C21∶0 was inversely associated with LDL cholesterol concentrations (B (95% CI): −0.41 (−0.80 to −0.02)), log LDL/HDL cholesterol ratio (−0.20 (−0.37 to −0.03)), log non-HDL cholesterol (−0.20 (−0.37 to −0.03)), log apolipoprotein B (−0.12 (−0.24 to 0.00)) and log triglyceride concentrations (−0.35 (−0.59 to −0.12)).

Discussion

Increased proportion of whole grain rye, reflected by a biomarker, in the diet is associated with favorable blood lipid outcomes, a relationship that should be further investigated.

Trial Registration

ClinicalTrials.gov NCT00992641

The food metabolome: a window over dietary exposure

The food metabolome is defined as the part of the human metabolome directly derived from the digestion and biotransformation of foods and their constituents. With >25,000 compounds known in various foods, the food metabolome is extremely complex, with a composition varying widely according to the diet. By its very nature it represents a considerable and still largely unexploited source of novel dietary biomarkers that could be used to measure dietary exposures with a high level of detail and precision. Most dietary biomarkers currently have been identified on the basis of our knowledge of food compositions by using hypothesis-driven approaches. However, the rapid development of metabolomics resulting from the development of highly sensitive modern analytic instruments, the availability of metabolite databases, and progress in (bio)informatics has made agnostic approaches more attractive as shown by the recent identification of novel biomarkers of intakes for fruit, vegetables, beverages, meats, or complex diets. Moreover, examples also show how the scrutiny of the food metabolome can lead to the discovery of bioactive molecules and dietary factors associated with diseases. However, researchers still face hurdles, which slow progress and need to be resolved to bring this emerging field of research to maturity. These limits were discussed during the First International Workshop on the Food Metabolome held in Glasgow. Key recommendations made during the workshop included more coordination of efforts; development of new databases, software tools, and chemical libraries for the food metabolome; and shared repositories of metabolomic data. Once achieved, major progress can be expected toward a better understanding of the complex interactions between diet and human health.

Phenolic lipids affect the activity and conformation of acetylcholinesterase from Electrophorus electricus (Electric eel)

Phenolic lipids were isolated from rye grains, cashew nutshell liquid (CNSL) from Anacardium occidentale, and fruit bodies of Merrulius tremellosus, and their effects on the electric eel acetylcholinesterase activity and conformation were studied. The observed effect distinctly depended on the chemical structure of the phenolic lipids that were available for interaction with the enzyme. All of the tested compounds reduced the activity of acetylcholinesterase. The degree of inhibition varied, showing a correlation with changes in the conformation of the enzyme tested by the intrinsic fluorescence of the Trp residues of the protein.

Plasma alkylresorcinols C17:0/C21:0 ratio, a biomarker of relative whole-grain rye intake, is associated to insulin sensitivity: a randomized study

BACKGROUND/OBJECTIVES

Few studies have used biomarkers of whole-grain intake to study its relation to glucose metabolism. We aimed to investigate the association between plasma alkylresorcinols (AR), a biomarker of whole-grain rye and wheat intake, and glucose metabolism in individuals with metabolic syndrome (MetS).

SUBJECTS/METHODS

Participants were 30-65 years of age, with body mass index 27-40 kg/m(2) and had MetS without diabetes. Individuals were recruited through six centers in the Nordic countries and randomized to a healthy Nordic diet (ND, n=96), rich in whole-grain rye and wheat, or a control diet (n=70), for 18-24 weeks. In addition, associations between total plasma AR concentration and C17:0/C21:0 homolog ratio as an indication of the relative whole-grain rye intake, and glucose metabolism measures from oral glucose tolerance tests were investigated in pooled (ND+control) regression analyses at 18/24 weeks.

RESULTS

ND did not improve glucose metabolism compared with control diet, but the AR C17:0/C21:0 ratio was inversely associated with fasting insulin concentrations (P=0.002) and positively associated with the insulin sensitivity indices Matsuda ISI (P=0.026) and disposition index (P=0.022) in pooled analyses at 18/24 weeks, even after adjustment for confounders. The AR C17:0/C21:0 ratio was not significantly associated with insulin secretion indices. Total plasma AR concentration was not related to fasting plasma glucose or fasting insulin at 18/24 weeks.

CONCLUSIONS

The AR C17:0/C21:0 ratio, an indicator of relative whole-grain rye intake, is associated with increased insulin sensitivity in a population with MetS.

Plasma alkylresorcinols, biomarkers of whole-grain wheat and rye intake, and incidence of colorectal cancer

BACKGROUND

Few studies have investigated the association between whole-grain intake and colorectal cancer. Because whole-grain intake estimation might be prone to measurement errors, more objective measures (eg, biomarkers) could assist in investigating such associations.

METHODS

The association between alkylresorcinols, biomarkers of whole-grain rye and wheat intake, and colorectal cancer incidence were investigated using prediagnostic plasma samples from colorectal cancer case patients and matched control subjects nested within the European Prospective Investigation into Cancer and Nutrition. We included 1372 incident colorectal cancer case patients and 1372 individual matched control subjects and calculated the incidence rate ratios (IRRs) for overall and anatomical subsites of colorectal cancer using conditional logistic regression adjusted for potential confounders. Regional differences (Scandinavia, the Mediterranean, Central Europe) were also explored.

RESULTS

High plasma total alkylresorcinol concentration was associated with lower incidence of distal colon cancer; the adjusted incidence rate ratio of distal colon cancer for the highest vs lowest quartile of plasma total alkylresorcinols was 0.48 (95% confidence interval [CI] = 0.28 to 0.83). An inverse association between plasma total alkylresorcinol concentrations and colon cancer was found for Scandinavian participants (IRR per doubling = 0.83; 95% CI = 0.70 to 0.98). However, plasma total alkylresorcinol concentrations were not associated with overall colorectal cancer, proximal colon cancer, or rectal cancer. Plasma alkylresorcinols concentrations were associated with colon and distal colon cancer only in Central Europe and Scandinavia (ie, areas where alkylresorcinol levels were higher).

CONCLUSIONS

High concentrations of plasma alkylresorcinols were associated with a lower incidence of distal colon cancer but not with overall colorectal cancer, proximal colon cancer, and rectal cancer.

Inhibition of wheat bran and it's active compoments on α-glucosidase in vitro

Background:

Wheat bran is a traditional Chinese medicine; however, it is mostly used as feedstuff in China. Wheat bran is widely accepted as an important ingredient in many low-glycemic index foods in modern western societies; however, its glycemic control mechanism is unknown.

Objective:

To determine potent α-glucosidase inhibitory compounds from wheat bran and to identify the inhibition on α-glucosidase.

Materials and Methods:

Ethanolic extract of wheat bran was prepared to evaluate the inhibitory activity on α-glucosidase, then fractionation of the extract was guided by in vitro enzyme-inhibition assay, and the potent α-glucosidase inhibitory compounds were identified by high performance liquid chromatography and atmospheric pressure chemical ionization-mass spectrometry; finally the enzyme inhibition process was studied using the Michaelis-Menton and the Lineweaver-Burk equations.

Results:

Both baker's yeast and rat intestinal enzymes were mostly inhibited (87.9% and 66.8% inhibition, respectively) at concentration 0.6 mg/mL of the ethanolic extract of wheat bran. The petroleum ether fraction in the ethanolic extract of wheat bran showed significant activity against rat intestinal α-glucosidase, and revealed a dose-dependent effect. The inhibition was 76.57% at 0.3 mg/mL and 100% at 0.6 mg/mL. The active fraction 13 of petroleum ether fraction was identified as alkylresorcinols (ARs). ARs showed strong inhibition towards α-glucosidase and its IC₅₀ value was found to be 37.58 μg/mL. The enzyme kinetic studies showed that, in the presence of ARs, the Michaelis-Menton constant (K_m) remains constant whereas the maximal velocity (V_max) decreases, revealing a non-competitive type of inhibition.

Conclusion:

The therapeutic potentiality of ARs in the management of the postprandial hyperglycemia will proliferate the utilization of wheat bran in controlling type 2 diabetes.

Physcomitrella PpORS, basal to plant type III polyketide synthases in phylogenetic trees, is a very long chain 2'-oxoalkylresorcinol synthase

The plant type III polyketide synthases (PKSs), which produce diverse secondary metabolites with different biological activities, have successfully co-evolved with land plants. To gain insight into the roles that ancestral type III PKSs played during the early evolution of land plants, we cloned and characterized PpORS from the moss Physcomitrella. PpORS has been proposed to closely resemble the most recent common ancestor of the plant type III PKSs. PpORS condenses a very long chain fatty acyl-CoA with four molecules of malonyl-CoA and catalyzes decarboxylative aldol cyclization to yield the pentaketide 2'-oxoalkylresorcinol. Therefore, PpORS is a 2'-oxoalkylresorcinol synthase. Structure modeling and sequence alignments identified a unique set of amino acid residues (Gln(218), Val(277), and Ala(286)) at the putative PpORS active site. Substitution of the Ala(286) to Phe apparently constricted the active site cavity, and the A286F mutant instead produced triketide alkylpyrones from fatty acyl-CoA substrates with shorter chain lengths. Phylogenetic analysis and comparison of the active sites of PpORS and alkylresorcinol synthases from sorghum and rice suggested that the gramineous enzymes evolved independently from PpORS to have similar functions but with distinct active site architecture. Microarray analysis revealed that PpORS is exclusively expressed in nonprotonemal moss cells. The in planta function of PpORS, therefore, is probably related to a nonprotonemal structure, such as the cuticle.

Bioactive compounds in cereal grains – occurrence, structure, technological significance and nutritional benefits – a review

This review presents current information about principal, biologically active compounds contained in grains of cereals that are most popular in Europe (wheat, rye, barley and oat). The tendency to provide consumers with safe foods, which promote their health and are based on cereal grains and/or their components with the high nutritive value, has been recently observed. The intake of protective substances contained in whole grains and their fractions contributes to a decreased risk of food-dependent diseases like the coronary heart disease and insulin-dependent diabetes. This study describes the structure, occurrence in cereal grains, technological importance and beneficial influence on human health of bioactive substances such as arabinoxylans, β-glucans, alkylresorcinols, tocols and phytosterols.

Analysis of alkylresorcinols in cereal grains and products using ultrahigh-pressure liquid chromatography with fluorescence, ultraviolet, and CoulArray electrochemical detection

Alkylresorcinols are phenolic lipids, with homologues ranging from C17 to C25, found in high concentrations in whole grain wheat and rye, lower concentrations in barley, and negligible concentrations in refined wheat flour. The analysis of alkylresorcinols is of importance due to their potential as biomarkers of whole grain intake and emerging evidence for some biological effects. Present HPLC methods have insufficient resolution for accurately quantitating the mix of alkyl- and alkenylresorcinols found in rye. An ultrahigh-pressure liquid chromatography method was developed, and three detection methods (CoulArray (CAED), ultraviolet (UV), and fluorescence detection (FD)) were compared for cereal alkylresorcinol analysis. The lower limits of quantitation and detection were 50 and 20 pg injected, 5 pg and 2 pg injected, and 500 and 1250 pg injected for FD, CAED, and UV, respectively. FD and CAED provided similar results, with some bias for higher results with FD (<10% difference). UV detection generally resulted in overestimation of alkylresorcinol concentrations. The method was applied to cereal (15) and cereal product (90) samples mainly from the United States with results in the same range as previous methods. The improved resolution with this method allows facile analysis of alkylresorcinols from cereal products, including minor unsaturated homologues such as those found in rye.

Formation of phenolic microbial metabolites and short-chain fatty acids from rye, wheat, and oat bran and their fractions in the metabolical in vitro colon model

Rye bran and aleurone, wheat bran and aleurone, and oat bran and cell wall concentrate were compared in their in vitro gut fermentation patterns of individual phenolic acids and short-chain fatty acids, preceded by enzymatic in vitro digestion mimicking small intestinal events. The formation of phenolic metabolites was the most pronounced from the wheat aleurone fraction. Phenylpropionic acids, presumably derived from ferulic acid (FA), were the major phenyl metabolites formed from all bran preparations. The processed rye, wheat, and oat bran fractions contained more water-extractable dietary fiber (DF) and had smaller particle sizes and were thus more easily fermentable than the corresponding brans. Rye aleurone and bran had the highest fermentation rate and extent probably due to high fructan and water-extractable arabinoxylan content. Oat samples also had a high content of water-extractable DF, β-glucan, but their fermentation rate was lower. Enzymatic digestion prior to in vitro colon fermentation changed the structure of oat cell walls as visualized by microscopy and increased the particle size, which is suggested to have retarded the fermentability of oat samples. Wheat bran was the most slowly fermentable among the studied samples, presumably due to the high proportion of water-unextractable DF. The in vitro digestion reduced the fructan content of wheat samples, thus also decreasing their fermentability. Among the studied short-chain fatty acids, acetate dominated the profiles. The highest and lowest production of propionate was from the oat and wheat samples, respectively. Interestingly, wheat aleurone generated similar amounts of butyrate as the rye fractions even without rapid gas production.

Alkylresorcinol metabolism in Swedish adults is affected by factors other than intake of whole-grain wheat and rye

The urinary alkylresorcinol (AR) metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA), could potentially serve as biomarkers for intake of whole-grain (WG) wheat and rye. Excretion of AR metabolites is largely dependent on the intake of AR but may also be influenced by other factors. This study aimed to investigate the validity of free and conjugated AR metabolites as biomarkers for WG intake of wheat and rye and to identify potential determinants of AR metabolites in urine. We quantified free aglycones and conjugates of AR metabolites in 24-h urine collections from 52 free-living Swedish adults and calculated correlation coefficients between urinary AR metabolite excretion and self-reported WG intake. We used partial least-squares regression to identify possible determinants of urinary AR metabolites. Approximately 50% of urinary AR metabolites were found as conjugates. Excretions of individually quantified free and conjugated AR metabolites and their sums were correlated to self-reported intake of WG rye and wheat (r = 0.50-0.68; P < 0.001). Excretion of urinary AR metabolites was mainly dependent on intake of 2 major dietary AR homologs, C19:0 and C21:0. Sex, BMI, and vitamin C intake were identified as determinants of the proportion of free and glucuronidated DHPPA in the present study. Urinary AR metabolites may be useful in reflecting short-term to medium-term intake of WG, but urine samples should be deconjugated prior to quantification. Anthropometric and dietary factors affecting the proportion of conjugated AR metabolites in urine may to some extent influence AR elimination and thereby the performance of urinary AR metabolites as biomarkers.

Alkylresorcinols in Latvian and Finnish breads

The alkylresorcinol (AR) content and relative homologue composition were determined in 9 Latvian and 11 Finnish soft breads. ARs were extracted with hot 1-propanol and quantified, using a gas chromatography-mass spectrometry method. The total AR content (μg/g dry matter) varied from 560 to 840 in rye breads, from 500 to 700 in Finnish mixed rye and wheat flour breads, from 200 to 300 in Latvian mixed rye and wheat flour breads and from 25 to 30 in white wheat breads. Rye and white wheat breads in the two countries varied only slightly in AR content, but there were wide variations in AR content in mixed flour breads. The AR contents in soft breads could be indicators of bran or fibre content, but not of whole-grain flour content.

The effect of high-fiber rye bread enriched with nonesterified plant sterols on major serum lipids and apolipoproteins in normocholesterolemic individuals

BACKGROUND AND AIMS

Plant sterols are naturally occurring cholesterol-lowering compounds which are industrially incorporated in various foods. A novel food carrier is rye bread, the intake of which can be monitored in trials utilizing newly defined plasma biomarkers. Our aim was to determine the effects of plant sterols incorporated into high-fiber rye bread on serum total and LDL cholesterol, apoB/apoA1 and total cholesterol/HDL cholesterol ratios and lipophilic (pro)vitamins in healthy free-living normocholesterolemic individuals.

METHODS AND RESULTS

In this double-blind, dietary intervention trial the subjects (n=68) were randomized to receive a rye bread (9.3g/d fiber) with added plant sterols (2g/d) (active) or without (control). In the second phase of the study the amount of rye bread was doubled providing 18.6g/d fiber and in the active group 4g/d plant sterols. Compliance was monitored utilizing 3-day food diaries and a novel rye fiber-derived biomarker in plasma. Intake of rye bread enriched with 2g/d of plant sterols during two weeks reduced significantly serum total and LDL cholesterol, apoB/apoA1 and total cholesterol/HDL cholesterol ratios by 5.1%, 8.1%, 8.3% and 7.2%, respectively, compared to controls. Correspondingly, the following two-week treatment with 4g/d of plant sterols resulted in 6.5%, 10.4%, 5.5% and 3.7% difference compared to controls, being most pronounced for LDL (0.33 mmol/L). The treatments did not affect lipophilic (pro)vitamin levels.

CONCLUSION

Rye bread enriched with 2-4g/d of nonesterified plant sterols beneficially modifies cardiovascular lipid risk factors in normocholesterolemic subjects compared to controls.

Accelerated solvent extraction of alkylresorcinols in food products containing uncooked and cooked wheat

This research focuses on the overall extraction process of alkylresorcinols (ARs) from uncooked grains and baked products that have been processed with wheat, corn, rice, and white flour. Previously established extraction methods developed by Ross and colleagues, as well as a semiautomated method involving accelerated solvent extraction (ASE), were applied to extract ARs within freshly ground samples. For extraction of alkylresorcinols, nonpolar solvents such as ethyl acetate have been recommended for the extraction of uncooked foods, and polar solvents such as 1-propanol:water (3:1 v/v) have been recommended for the extraction of baked foods that contain rye, wheat, or other starch-rich grains. A comparison of AR extraction methods has been investigated with the application of gas chromatography and a flame ionization detector (GC-FID) to quantify the AR content. The goal of this research was to compare the rapid accelerated solvent extraction of the alkylresorcinols (ASE-AR) method to the previous manual AR extraction methods. Results for this study as well as the investigation of the overall efficiency of ASE-AR extraction with the use of a spiking study indicated that it can be comparable to current extraction methods but with less time required. Furthermore, the extraction time for ASE (approximately 40 min) is much more convenient and less tedious and time-consuming than previously established methods, which range from 5 h for processed foods to 24 h for raw grains.

Alkylresorcinol metabolites in urine correlate with the intake of whole grains and cereal fibre in free-living Swedish adults

Alkylresorcinols (AR) have been established as short/medium-term biomarkers for whole grain (WG) wheat and rye intake; and AR metabolites, 3,5-dihydroxybenzoic acid and 3-(3,5-dihydroxyphenyl)-propanoic acid, have been suggested as complementary biomarkers to AR. The present study examined the medium-term reproducibility and relative validity of urinary AR metabolites as biomarkers for WG and cereal fibre intake. A total of sixty-six free-living Swedes completed 3 d weighed food records and provided single 24 h urine collections and morning urine spot samples on two occasions, 2-3 months apart. The medium-term reproducibility of urinary AR metabolites was moderate when assessed in 24 h collections and lower in creatinine (CR)-adjusted morning urine. Mean AR metabolite 24 h excretions correlated well with total WG (r(s) 0·31-0·52, P < 0·05) and cereal fibre (r(s) 0·46-0·58, P < 0·001) intake on both occasions. As expected, correlations with WG (r(s) 0·28-0·38, P < 0·05) and cereal fibre (r(s) 0·35-0·42, P < 0·01) were weaker for mean CR-adjusted AR metabolite concentrations in spot samples of morning urine, although the adjusted concentrations correlated well with 24 h urinary excretion (r(s) 0·69-0·73, P < 0·001). Adjustment for intra-individual variations substantially improved the correlations between intake and excretion. These findings suggest that urinary AR metabolites can successfully reflect the medium-term intake of WG and cereal fibre when adjusted for intra-individual variation in this population, where rye was the major contributor to high WG intake. The performance of urinary AR metabolites as medium-term biomarkers appears to be comparable to that of fasting plasma AR concentration in this population.

Present status and perspectives on the use of alkylresorcinols as biomarkers of wholegrain wheat and rye intake

Alkylresorcinols (ARs) were first proposed as potential biomarkers of wholegrain wheat and rye intake a decade ago. Since then there has been a considerable body of research which suggests that ARs do meet most criteria of a biomarker of these foods. Results from human studies on plasma AR and their plasma and urinary metabolites strongly indicate that these compounds are responsive to whole grain wheat and rye intake and are correlated with various measures of AR consumption. This review briefly summarises work on the bioactivities of AR and focuses on aspects related to their use as biomarkers of whole grain wheat and rye intake. Evidence suggests that they thus far broadly fulfil the criteria to act as biomarkers of these cereals. However, there are still gaps in the knowledge on factors relating to the wide interindividual variation, and application to different epidemiological cohorts. Overall, ARs are highly promising biomarkers of whole grain wheat and rye intake and add to our increasing understanding of whole grains and health.

Plasma alkylresorcinols as a biomarker of whole-grain food consumption in a large population: results from the WHOLEheart Intervention Study

BACKGROUND

Small-scale, short-term intervention studies have suggested that plasma alkylresorcinol (AR) concentrations may be biomarkers of whole grain (WG) wheat and rye intakes.

OBJECTIVE

The objective was to determine whether plasma AR concentrations reflect self-reported WG food intake in a 16-wk WG intervention study and to establish which phenotypic characteristics influence plasma AR concentrations.

DESIGN

In a randomized parallel-group dietary intervention study, 316 overweight and obese participants with a WG intake of <30 g/d were recruited and randomly assigned to 1 of 3 groups: control (no dietary change), intervention 1 (60 g WG/d for 16 wk), or intervention 2 (60 g WG/d for 8 wk followed by 120 g WG/d for 8 wk). Fasting blood samples were collected at baseline, 8 wk, and 16 wk for the measurement of plasma lipids and ARs.

RESULTS

Plasma samples from 266 study completers were analyzed. Total plasma AR concentrations increased with the WG intervention and could be used to distinguish between control subjects and those who consumed 60 or 120 g WG, but not between those who consumed 60 and 120 g WG. Plasma AR concentrations were higher in men, were positively associated with plasma triglyceride concentrations, and were negatively associated with nonesterified fatty acids.

CONCLUSIONS

Plasma AR concentrations were correlated with WG intake and could be used to distinguish between low- and high-WG consumers. Sex and plasma lipid concentrations independently influenced plasma AR concentrations, although plasma triglycerides may explain higher concentrations in men. This trial is registered as ISRCT no. 83078872.

Antioxidant activity of alkylresorcinols from rye bran and their protective effects on cell viability of PC-12 AC cells

Alkylresorcinols (ARs) are phenolic lipids that are present in high amounts in the bran layer of different cereals. Rye samples, cultivar Hazlet, and a white rye genotype, RT202, were analyzed for their antioxidant properties and AR content and composition, based on six fractions of the bran, where 1 was the outermost fraction and 6 was the bran fraction closest to the endosperm. Gas chromatography-mass spectrometry (GC-MS) analysis demonstrated that the most commonly found AR homologue in Hazlet rye is C19:0 and that the total amount of ARs decreases from the outermost to innermost fractions. The antioxidant activity using oxygen radical absorbance capacity (ORAC) for both white rye genotype RT202 and Hazlet brans was determined to decrease from the outermost fraction (136.05 μmol TE/g for Hazlet fraction 1 and 186.57 μmol TE/g for white rye genotype RT202 fraction 1) to the innermost fraction (9.84 μmol TE/g for Hazlet fraction 6 and 78.75 μmol TE/g for white rye genotype RT202 fraction 2). A positive relationship was seen with GC-MS results. Treatment of PC-12 AC cells with Hazlet fraction 1 increased mitochondrial biogenesis as determined using mitochondrial fluorescent dyes. In the presence of a prooxidant (AAPH), PC-12 AC cells were better protected from free radical attack when treated with Hazlet fraction 1 than with all other bran fractions. The results suggest that higher AR content in bran fractions confers antioxidant protection against free radical damage.

Dietary alkylresorcinols and lignans in the Spanish diet: development of the alignia database

The intake of alkylresorcinols and lignans in Spain is unknown due to the lack of information on the content of these compounds in particular foods. This paper describes the development of the first alkylresorcinol and lignan database adapted to the Spanish diet, including foods items especially relevant for this population. The values of alkylresorcinols and lignans in common foods and beverages were collected from scientific publications in refereed journals, and other foods particularly consumed in Spain, for which values were not available, were analyzed by standardized protocols and included into the database. The Alignia database presents the content of alkylresorcinols in 88 food items and the lignan content of 593 foods and beverages. Using the database, the intake of lignans in Spain, calculated using data from the Food Composition Panel based on household consumption, was estimated to be 0.76 mg/day.

Rye bran alkylresorcinols suppress adipocyte lipolysis and hormone-sensitive lipase activity

The effects of alkylresorcinols (ARs) isolated from rye bran on adipocyte lipolysis, hormone-sensitive lipase activity and phosphorylation and on phosphorylation of protein kinase A substrates were studied. Preincubation with ARs for 18 h suppressed catecholamine-stimulated lipolysis in 3T3-L1 adipocytes. Furthermore, phosphorylation of hormone-sensitive lipase (HSL), a key lipase responsible for stimulated lipolysis, and phosphorylation of protein kinase A substrates, were diminished after preincubation with ARs, whereas HSL protein expression was unaltered. ARs were also shown to inhibit HSL activity in an in vitro assay.

Plasma alkylresorcinol concentrations correlate with whole grain wheat and rye intake and show moderate reproducibility over a 2- to 3-month period in free-living Swedish adults

Plasma alkylresorcinols (AR) are useful as dietary biomarkers of wheat and rye whole grain (WG) during interventions but need to be validated in free-living populations. This study estimated the medium-term reproducibility and relative validity of plasma AR as biomarkers of WG and cereal fiber intake. Seventy-two Swedish adults kept 3-d weighed food records on 2 occasions 2-3 mo apart. Of these men and women, 51 provided a fasting blood sample at the end of each occasion. In addition, 18 participants provided 3 fasting and 3 nonfasting samples for 3 consecutive days on the first and second occasions, respectively. Dietary and blood variables did not differ between the 2 occasions. Nonfasting plasma total AR concentration [210 nmol/L (95% CI: 140, 314)] was higher than fasting [99 nmol/L (95% CI: 72, 137)] (P < 0.0001). Mean WG intake was 70 ± 61 g/d (41% from rye) and the intra-class correlation coefficient was 0.44 (95% CI: 0.26, 0.63) for total WG intake and 0.47 (95% CI: 0.27, 0.67) for the fasting plasma total AR concentration, suggesting moderate reproducibility. Fasting plasma total AR moderately correlated with WG rye + wheat (r(s) = 0.53; P < 0.001) and cereal fiber intake (r(s) = 0.32; P < 0.05) when using mean values from both occasions. This suggests that plasma AR concentration in fasting samples can be used as a biomarker of rye + wheat WG intake in free-living populations with a high and consistent WG intake.

Pharmacokinetics of alkylresorcinol metabolites in human urine

Wholegrain cereals are reported to promote beneficial health effects. Wholegrain wheat and rye are almost exclusive sources of alkylresorcinols, and intact alkylresorcinols together with their plasma and urinary metabolites, 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA) and 3,5-dihydroxybenzoic acid (DHBA), have been proposed as biomarkers of the intake of these foods in humans. The pharmacokinetics of alkylresorcinols and their metabolites in plasma have been determined but not that of the urinary metabolites. We aimed to characterise the urinary pharmacokinetics of alkylresorcinol metabolites in humans to evaluate their potential as biomarkers of wholegrain wheat and rye. A group of fifteen volunteers followed a low-alkylresorcinol diet for 2 d before ingesting a single dose of rye bread, containing 100 mg alkylresorcinols. Urine was collected between baseline (0 h) and 25 h after administration. Thereafter alkylresorcinol metabolites were quantified by HPLC with coulometric electrode array detection. Maximum excretion rates were observed at 5-6 h for both metabolites, DHPPA being predominant over DHBA and also possessing a greater area under the curve0-25 h. Total urinary recovery between 0 and 25 h yielded 43 % of ingested alkylresorcinols, and at 25 h significant amounts of metabolites were still retained in the body, suggesting that even a spot urine sample may be sufficient to indicate whether or not wholegrain wheat or rye is a daily dietary component. These results support the use of urinary DHPPA and DHBA as biomarkers of wholegrain wheat and rye and enable new potential for studying the association between wholegrain intake and diseases, even in the absence of dietary data.

Effects of alkylresorcinols on volume and structure of yeast-leavened bread

BACKGROUND

Alkylresorcinols (AR) are amphiphilic phenolic compounds found in high amounts in wheat, durum wheat and rye, with different homologue composition for each cereal. The effect of different amounts of added AR from these cereals on bread volume, height, porosity and microstructure was studied. Breads with added rye bran (with high levels of AR) or acetone-extracted rye bran (with low levels of AR) were also baked, as well as breads with finely milled forms of each of these brans.

RESULTS

Breads with high amounts of added AR, irrespective of AR homologue composition, had a lower volume, a more compact structure and an adverse microstructure compared with breads with no or low levels of added AR. AR were also shown to inhibit the activity of baker's yeast. There was no difference in bread volume and porosity between bread baked with rye bran and acetone-extracted rye bran or with brans of different particle size.

CONCLUSION

Irrespective of homologue composition, AR had a negative effect on wheat bread properties when added in high amounts as purified extracts from wheat, durum wheat and rye. Natural levels of AR in rye bran, however, did not affect the volume and porosity of yeast-leavened wheat breads.