Mass spectrometry method development and application of investigation of food safety and human health
Principal supervisor: Professor Cai Zongwei ; Thesis submitted to the Department of Chemistry
Understanding of molecular events involved in food safety and human health has become a major concern of contemporary life. Mass spectrometry (MS) is a powerful tool for characterization of complex food ingredients and biological molecules. Advances in MS-based techniques have offered new opportunities to understand the chemical changes occurring during food storage and processing as well as the molecular events perturbed by either endogenous or exogenous stimulus. In this thesis, we developed novel MS-based approaches for authentication of edible oil (i.e., edible vegetable oil, deep frying oil and gutter oil), assessment of genotoxicity of fatty acid hydroperoxides, and investigation of metabolic deregulation in pleural effusion and tissue of human lung cancer, aiming to gain a better understanding of food safety and human health. MS-based methods were developed for authentication of edible vegetable oil adulterated with used cooking oil. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that six monoglycerides could be used as the markers to discriminate the used cooking oil (e.g., deep frying oil and gutter oil) and qualified edible oil. Accumulation behavior of these six monoglycerides was detected in the repeatedly heated edible oils. Quantitation of the monoglycerides enabled authentication of commercial olive oil adulterated with a small amount of used cooking oil (approximately 1%). In addition, a matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) method was developed for visual authentication of edible oil samples, including commercial vegetable oil, used cooking oil and adulterated edible oil. The method provided the capability for quantifying major chemical composition of edible oil, such as triglycerides, diglycerides and monoglycerides. The present method required minimal sample preparation and allowed screening of oil samples with high throughput (approximately 360 samples per day), providing a simple way to authenticate different types of oil samples. Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) was applied to investigate the genotoxicity of two fatty acid hydroperoxides, i.e., 13-hydroperoxyoctadeca-cis-9,trans-11-dienoic acid (13-HPODE) and 13-hydroperoxy-9,11E,15Z-octadecatrienoic acid (13-HPOTE), which are important inducers of oxidative deterioration in oils and fats generated from the oxidation of linolenic acid and linoleic acid. The results demonstrated that the α,β-unsaturated aldehydes, such as 4-oxo-2-nonenal, dioxo-10-dodecenoic acid, 4-hydroperoxy-2-nonenal and 4-hydroxy-2-nonenal are the main degradation compounds of 13-HPODE and 13-HPOTE, which can covalently bound to deoxyribose-nucleosides and ribose-nucleosides to form adducts. This study provided evidences regarding the genotoxicity of fatty acid hydroperoxides at the molecular level. MS-based metabolomics methods were developed and applied for the investigation of metabolic signatures of pleural effusion and tissue of human lung cancer. A database-assisted global metabolomics method was established with utility of LC-Orbitrap MS, followed by automated mass spectral searching. The method enabled unbiased identification of 194 endogenous metabolites in pleural effusions caused by tuberculosis and malignancy. Among which, 33 differential metabolites involved in tryptophan catabolism, bile acid biosynthesis, and β-oxidation of fatty acids were found between tuberculous and malignant pleural effusions, which provided non-invasive biomarkers for diagnosis of pleural effusion samples with high sensitivity and specificity. In addition, a large-scale targeted metabolomics method was developed, which enabled reliable detection of over 400 biological metabolites, covering 92 metabolic pathways in human samples. The method was applied to characterize the metabolic profiles of non-small cell lung cancer (NSCLC) tissues. A number of distant metabolic pathways were found to be differentiated between tumor and normal tissues of lung squamous cell carcinoma and adenocarcinoma, including purine metabolism, citric acid cycle, amino acid metabolism, urea cycle, and ammonia recycling. In addition, several metabolites, such as adenosine, glutamate, glucose 1,6-bisphosphate, betaine, creatine and methionine sulfoxide were found to be associated with prognosis of NSCLC patients, which might provide potential biomarkers to monitor metabolic characteristics of NSCLC patients and treatment outcomes of the cancer.