**6.1 Carotenoid-lipid interactions**

The integration of carotenoids and lipids resulted in a number of changes in the light absorption spectrum of the former, subject to the specific nature of the interacting molecules. For example, there was a red shift in the visible part of absorption of lycopene when it was added into the sunflower oil (**Figure 1a**) or a hyperchromicity in the spectrum of lutein when it was added to the cocoa butter (**Figure 1b**). These changes indicate that the carotenoids were able to interact with the lipid molecules and created physical complexes with them, which would be thermodynamically more favourable than when all these molecules were present in free forms.

#### **Figure 1.**

*Formation of thermodynamically favourable complexes between carotenoids and lipids. a) Red shift in light absorption peaks of lycopene embedded into sunflower oil, in 1:330 m/m—blue, control lycopene—red, control sunflower oil—green. b) Hyperchromism in light absorption peaks of lutein embedded into cocoa butter, in 1:330 m/m—blue, control lutein—red, control cocoa butter—green; in all experiments above, ethanol-methylchloride 5:1 w/w was used. Typical microscopy slides at 1000× magnification: DF—dairy fat, CLO—cod liver oil, CB cocoa butter, SFO—sunflower oil, L—lycopene, m/m.*

### *Carotenoids in Thermal Adaptation of Plants and Animals DOI: http://dx.doi.org/10.5772/intechopen.104537*

To visualise how formation of these complexes affects lipids and subsequent changes in their structures, we used light microscopy. It was found that the incorporation of carotenoids into oils or fats matrix may result in a dose-dependent growth of the size of lipid droplets or fat globules. This was observed in a broad range of plant or animal oils and fats. The working concentration at which a particular carotenoid could trigger this microscopy-visual effect was dependent on the structure of carotenoid molecules and on the length and saturation level of fatty acids (FA) in the lipids used. Overall plant lipids with a higher level of unsaturated FA were more sensitive to carotenoid-induced changes than animal lipids. Within the first group, vegetable oils with longer FA were more responsive than nut oils or cocoa butter. Within animal lipids, fish oils with a higher level of unsaturated and longer FA were more responsive than the bird fats, and they, in turn, were more sensitive than mammalian fats (**Figure 1**, microscopy slides).

For example, one molecule of lycopene was able to make noticeable changes in the size of the lipid droplets of the dairy fat/butter starting with a ratio 1:30,000 of molecules of its triglycerides. For the cod liver oil, this threshold was lower at one molecule of lycopene per about 40,000 molecules of the oil, for the cocoa butter, it was at 1 per 80,000 and for the sunflower oil, it was at 1 per about 120,000 molecules of their triglycerides.
