Discovery of Biomarkers for Intake of Heat-treated Foods by Untargeted Metabolomics

Research output: Book/ReportPh.D. thesisResearch

Heat treatment is a widely used method for food processing. Heating directly affects the nutritional value and potentially also the health effects of the food. Some compounds formed by heating, indicative of Maillard reactions may serve as biomarkers of food intake (BFIs). These could be useful tools, complementary to traditional methods of dietary assessment, for investigating relationships between heat-treated foods and human health. However, very few studies have investigated urinary metabolites in humans after intake of heat-treated foods. Most of the work to date focuses on the food chemistry of the heating process, and selected Maillard reaction products such as NƐ-carboxymethyllysine (CML) and pyrraline. Metabolomics is theoretically a comprehensive analysis of thousands of metabolites present in biological samples, and untargeted metabolomics was therefore applied with an aim to discover new metabolites related to intake of specific foods.
This PhD study aimed to reveal the biomarkers for intake of tubers and processed tuber products, which are widely consumed staple foods with a considerable carbohydrate content. It also aimed to explore the potential of the metabolites as new urinary biomarkers reflecting the intake of heat-treated skimmed milk powder (HSMP), which has a high protein content. Paper I summarises the metabolites proposed as candidate biomarkers for intake of potato, cassava, sweet potato, yam, and Jerusalem artichoke, and their corresponding processed products. An array of biological and analytical criteria was used to assess the usefulness of candidate biomarkers as dietary assessment tools, and to indicate further work required to explore their usefulness. For potato, glycoalkaloids, including α-chaconine, αsolanine and solanidine detected in serum, plasma and saliva, were considered to be candidate biomarkers. Two acetylated anthocyanins were promising biomarkers reflecting purple sweet potato intake, and linamarin was suggested as a putative biomarker for cassava intake, though the plausibility of this was weak. No candidate biomarkers were found for yam or Jerusalem artichoke. We already know that acrylamide (AA), acrolein (AC), and their mercapturic acids, as well as pyrazines, are particularly abundant in deep-fried foods. I propose that combining the metabolites derived from the heating process with compounds specific for potato in general, is promising as a tool to assess consumption of heat-treated potato products. This is reported, in
part, in Paper II.
Paper II reports the application of an UPLC-Qtof-MS based metabolomics approach to assess the human urine metabolome resulting from four different meals tested in a randomized controlled cross-over intervention meal study. PLS-DA and ANOVA-2 were applied to detect discriminating metabolites for intake of different meals: boiled rice, boiled potato (BP), and two types of deep-fried potatoes (potato crisps (PC) and French fries (FF)). Twentytwo metabolites were found to be specific for deep-fried potatoes, two for potato in general, and one for rice. Fourteen of these 22 metabolites were tentatively identified as furans, pyrroles, and pyrazines, indicative of Maillard reactions and as such candidate BFIs for deepfried potatoes. In an animal study discriminating metabolites for intake of HSMP were discovered, and tentatively identified in the urine of 36 rats, again using an UPLC-Qtof-MS based untargeted metabolomics approach. The rats were separated into five groups fed different dosages of HSMP, untreated skimmed milk powder (SMP), and hydrolysates of HSMP and SMP. Twentyfour hour pooled urine samples were collected on day 7 or 8 for each rat. PLS-DA for the
decomposed dataset after subtraction of the effect of matrix of hydrolysis by ASCA was applied forvariable selection. Twenty-five discriminating metabolites were extracted related to intake of HSMP, 12 of which were tentatively identified as lysine- and arginine-derived advanced glycation end-products (AGEs), while six were characterized as furans, and one as a pyrrole. The new AGEs might be formed by in-vivo metabolic activities. The discovered metabolites are
potential BFIs for HSMP intake and additional work is needed to assess their usefulness in humans.
In Paper I pyrazines are proposed as promising biomarkers for deep-fried foods. Paper II reports our finding that pyrazines are found in urine, as metabolites excreted without structural change or conversion by the gut microbiota. Acrylamide, AC, and their mercapturic acids, were not found, either because of their relatively low intensity, or because the data acquisition method was not able to detect very early eluting metabolites. Glycoalkaloids were not observed in the studies presented in Paper II since they have been reported only in blood and saliva and not in urine after intake of potato products. Compounds formed by heat treatment, such as acetylformoin, 5-hydroxymethylfurfural (HMF) and 5-(hydroxymethyl)-1Hpyrrole-2-carbaldehyde (HMPC), are found in both deep-fried potatoes (Paper II), and in HSMP (Paper III). Thus, they are relatively robust markers formed by heat treatment. In combination with markers of targeted foods they could potentially reflect the intake of the targeted food after heat processing. The new metabolites, such as pyrroles and pyrazines reported in Paper II and AGEs reported in Paper III, could be useful in exploring the biochemical and physiological responses associated with consumption of heat-treated foods, in the context of food processing, nutrition, and health.
Original languageEnglish
Place of PublicationCopenhagen
PublisherDepartment of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen
Number of pages87
ISBN (Print)9788772093901
Publication statusPublished - 2020

ID: 252683069