Heterocyclic amines and Lipid oxidation products are important classes of toxins in food. Prevention of their formation in food might minimize their dietary exposure and lower their health risk to people. This research work is to identify the potential vitamins which may inhibit the formation of these toxins. Moreover, the possible inhibition mechanism for potent inhibitor(s) is also investigated.
The first part was related to heterocyclic amines which are a class of important Maillard reaction products. The inhibitory activities of 11 water-soluble vitamins against heterocyclic amine formation were examined in a PhIP and a MeIQx producing chemical model. Six investigated vitamins (pyridoxiamine, pyridoxine, nicotinic acid, biotin, thiamine and L-ascorbic acid) out of eleven, exhibited significant inhibition (>40%) in both models. The activity of pyridoxamine, niacin, alpha-tocopherol, retinol acid and ascorbic acid was further investigated using fried beef. Moderate inhibition (20%) of the formation of PhIP, 4,8-DiMeIQx and MeIQx was found for most of them; whereas pyridoxamine reduced the levels of all three HAs by 40%. LC–MS analysis revealed that pyridoxamine directly reacts with phenylacetaldehyde to form an adduct which was characterized by LC-MS and NMR spectroscopy.
The second part was related to cholesterol oxidation products (COPs). The capacities of 15 vitamins to inhibit the formation of 7α-hydroxycholesterol, 7β-hydroxycholesterol and 7-ketocholesterol was examined in beef patties. Among them, L-ascorbic acid, retinoic acid, and α-(±)-tocopherol were found to exert a potent inhibitory effect (30−50%) on the formation of three COPs. Pyridoxamine inhibited 7-ketocholesterol formation by 60% and it could directly react with 7-ketocholesterol via the addition reaction.
Finally, the inhibitory activities of 15 vitamins against Malondialdehyde (MDA) formation were examined in beef patties samples. Solid Phase Extraction (SPE) and TBA test were performed followed by HPLC-DAD analysis. Five vitamins (pyridoxiamine, pyridoxine, retinoic acid, α-tocopherol and L-ascorbic acid) exhibited significant inhibition (>20%) in triplicate experiments. The fatty acid profile was examined by GC-MS and significant difference was only observed for three antioxidants (retinol acid, L-ascorbic acid and alpha-tocopherol) but not pyridoxamine. An alternative explanation for the inhibition mechanism against lipid oxidation was proposed for pyridoxmine. With the application of chromatographic and spectral analysis (LC–MS and NMR), it was demonstrated that pyridoxamine could directly react with Malondialdehyde via addition reaction.
In summary, certain vitamins were found to be potential inhibitors against both heterocyclic amines and lipid oxidation products formation. Mechanistic studies showed that direct-trapping of these toxins and the intermediate compounds for their formation by pyridoxamine and other vitamins was an effective way to lower the concentration of these food toxins during high-temperature processing. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/207192 |
| Date | January 2014 |
| Creators | Wong, Daniel, 汪裕軒 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | Creative Commons: Attribution 3.0 Hong Kong License, The author retains all proprietary rights, (such as patent rights) and the right to use in future works. |
| Relation | HKU Theses Online (HKUTO) |
Page generated in 0.0023 seconds