In 1991, Prof. Susan Henderson of Quinnipiac College and I were beginning a joint sabbatical. Our initial plan was to study the chemical interactions of carbohydrates and lipids under conditions found in cooking. This was a natural outgrowth of Susan's thesis research on amino acid-lipid interactions and would allow us to employ the new Keck VG Trio-2 Mass Spectrometer here at Trinity. However, we had both become interested in hot foods and we were curious about the chemistry of hot foods.
We decided to divert our attention briefly to capsaicin (N-vanyl-9 methyl-6-nonenamide) and to investigate the thermal decomposition of capsaicin and its interaction with lipids at frying temperatures. The basic approach was to use oleic acid as a model system for more complex triglycerides actually used in frying. Three experiments were necessary:
1. Thermal decomposition of capsaicin
2. Thermal decomposition of oleic acid
3. Interactions of the two under identical conditions
Thermal decomposition of capsaicin indicated that the weakest part of the molecule is the amide bond. This cleaves to yield vanillin, ammonia, and a branched chain organic acid 9-methyl-6-nonenoic acid. The acid reacts with the ammonia to form the corresponding amide. The acid also reacts with the parent amide to form an imide.
Thermal decomposition of oleic acid has been widely studied. The decomposition centers on the double bond and a homologous series of acids, alcohols, and aldehydes are formed.
Interaction of capsaicin with oleic acid produced an immediate surprise. In the presence of capsaicin, all of the decomposition products of oleic acid are suppressed. Levels of these products are reduced to less than 1% of those found in the absence of capsaicin (at a 1:1 capsaicin-oleic acid ratio by weight). The normal decomposition products of capsaicin heating are all observed in the interaction systems.
There are several new compounds observed as well. The presence of ammonia leads to the formation of oleamide, the amide of oleic acid. This compound has been found by workers at the Scripps Institute to induce sound, natural sleep in cats. It is a strong natural soporific.
The oleic acid also links with the vanyl- moiety of the capsaicin to form a capsaicin like compound with an 18 carbon chain in place of the normal 9 carbon chain. This compound may have flavor significance, however, the lack of knowledge about the specific receptor geometry of capsaicin makes this difficult to predict.
The most significant observation of this study was the antioxidant properties of capsaicin. This is confirmed by other research dating back to 1955. However, our study was the first to observe this property under frying conditions and identify the specific chemicals formed.
Details of this work are published in J. Ag. And Food Chem. Volume 40, pp 2263-68, 1992.
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