Open access publications in the SLU publication database

Abstract

The main aim of this thesis was to study the formation of phytosterol oxidation products (POP) and to evaluate and optimize an analytical method for the determination of POP in food products. The cholesterol lowering effect of phytosterols (PS) and phytostanols has been known for more than half a century and many reports in this area have been published. During the last decade the intake of PS has increased and products enriched with PS and phytostanols have been launched on the commercial market. Due to their chemical structure, PS are susceptible to oxidation at various sites in their structure. In the present study, oxidation products from the major phytosterols, sitosterol, campesterol and stigmasterol, were generated through autoxidation at elevated temperature. POP from both the ring-structure and side-chain structure were separated by preparative TLC and characterized using GC, GC-MS and NMR spectroscopy. Chromatographic data for many of the products were reported for the first time. The analytical methodology investigated and optimized in the present study included transesterification of the lipid compounds. The enrichment of POP by amino SPE-technique was reported as efficient and time saving compared with the more commonly used saponification technique. In addition, highly improved separation of a mixture of 29 POP was illustrated when a combination of different polarity GC capillary columns was studied. The optimized methodology was used for the determination of the levels of POP in some food products. The levels increased in olive oil and maize oil after heated at 180 ± 5 °C for 0-2 h from 8 mg/g to 18 mg/g and 4 mg/g to 12 mg/g, respectively. However, the levels of POP were almost unchanged during heating of peanut oil. The total amount of POP in a commercial available PS ester enriched spread was calculated to around 12 mg/g spread. Overall, the findings from this thesis demonstrate that numerous oxidation products from PS are formed during heat-facilitated autoxidation. For quantification of all these POP by GC, very high efficient capillary column/columns are necessary. The development of efficient and reliable analytical methods is urgent for the determination of levels of POP in food products, and possibilities to accurately estimate the daily intake of POP.