# Extraction of Bioactive Compounds from _Ulva lactuca_
## 3 Results and Discussion
### Extraction of Phenolics and Carotenoids--Selection of Solvent
#### 3.3.3 Effect of Temperature  
The results obtained regarding total carotenoids and phenolics, antioxidant activity, and extraction yield at different temperatures (25, 40 and 60 \({}^{\circ}\)C), for 12 h extraction and biomass to solvent ratio 1:10 _w/v_, are presented in Figure 4. Total carotenoids were increased from 25 to 40 \({}^{\circ}\)C and then remained practically constant (Figure 4A), while total phenolic content showed a significant increase with temperature (Figure 4B). Results showed that temperature increase led to a negative effect on the antioxidant activity for the solvent ratio 1:10 _w/v_ and for 12 h extraction time (Figure 4C). However, this negative effect of temperature on the antioxidant activity is not observed for other ratios and extraction times, e.g., E1-E13 and E5-E11. Furthermore, the increase in temperature has a negligible effect on the overall extraction yield (Figure 4D). Generally, plant and algal cells are surrounded by a rigid cell wall that acts as a mechanical barrier to extract carotenoids, while the strong interaction between carotenoids and other macromolecules prevents their mass transfer during the extraction [37]. Therefore, in order to break down the cell wall, the extraction occasionally involves treatments, such as heating [37]. According to [PERSON] et al., 2010 [38], the improved extractability of carotenoids as temperature increases, is possibly related to the destruction of the cellular structure. On the other hand, as the extraction temperature increases, several factors can affect the extracted carotenoids, such as degradation and isomerization from all-trans to _cis_ isomers [38]. Thus, the extraction conditions of carotenoids should be optimized, since some are more unstable than others, depending on their chemical structure. [PERSON] et al., 2014 [39] suggested carotenoid extraction temperatures lower than 70 \({}^{\circ}\)C, in order to minimize their degradation. Moreover, under higher extraction temperatures (40-50 \({}^{\circ}\)C), a significant increase in the total phenolic content was observed [37]. In like manner, it can be supported by the results presented in the current study (Figures 3 and 4), that under higher temperature and a higher biomass to  
Figure 3: Effect of biomass to solvent ratio on carotenoids content (**A**), total phenolic content (**B**), antioxidant activity (**C**) and total extraction yield (**D**) of _U.l. lactuca_ extracted with ethanol/water 70:30 _w/v_ at 25 \({}^{\circ}\)C for 12 and 16 h extraction time. Experimental data are the mean values of three replications.  
solvent ratio, the solubility of the seaweed's phenolic compounds is enhanced. Interestingly, some studies have shown that an increase in temperature favors the extraction process by enhancing both the solubility and the diffusion coefficient of the solutes; nevertheless, the phenolic compounds can be denatured beyond a certain temperature value (>50 \({}^{\circ}\)C) [40]. Consequently, the elevated carotenoid and phenolic recovery observed with the increase in the extraction temperature in the present study, does not necessarily result in a respective enhancement of antioxidant activity.