# Valuable Nutri from _Ulva rigida_: Modulation by Seasonal and Cultivation Factors
## 3 Results and Discussion
### Fat and Fatty Acid Profile
This trend is in accordance with that previously reported by [PERSON] and co-workers for IMTA, as well as by other authors when monitoring fat content in wild macroalgae of _Ullva_ genus [28, 56, 57, 58]. In fact, despite the taxonomic and geographical differences, the observed trends point to higher and lower lipid values during low and high temperature seasons, respectively. These observations are also in accordance with those of [PERSON] et al. [23], who concluded that temperature was one of the most important abiotic factors modulating lipids in _Ulva pertusa_ and that lipid synthesis was favored at low temperatures, as evaluated in a randomized laboratory experiment using an artificial seawater medium. In addition to seasonality, our results also suggest that cultivation conditions influence fat content. Indeed, except for summer when lipid synthesis is at minimum values, samples cultivated at \(\mathrm{L_{Fr}/H_{Sd}}\) had superior fat ratios than those of the remaining experimental conditions. To our knowledge, there are no published studies assessing the influence of growing conditions on the fat content of _U. rigida_. Nevertheless, a previous work on _U. pertusa_ have reported the increase in the fat content of the macroalgae when exposed to nitrogen deficiency conditions [59]. This fact could partially be associated with the superior levels of fat in \(\mathrm{L_{Fr}/H_{Sd}}\) samples. The authors hypothesized lipid production to be increased in these conditions, as a result of a storage mechanism or due to a continuous synthesis of lipid compounds, as this process does not require nitrogen. In the first case, excess carbon would be stored as fat, instead of being converted into protein as a result of a high C:N ratio. The fatty acid (FA) profile of _U. rigida_ was mainly composed of palmitic acid, C16:0; oleic acid, C18:1 (_n_-9); and \(\alpha\)-linolenic acid, C18:3 (_n_-3) (Table 2). Such results are consistent with those of previous studies on wild _U. rigida_[17, 19, 45, 49]. Curiously, this trend was not totally coincident with that previously reported for _U. rigida_ grown in IMTA, since the authors also demonstrated the existence of high proportions of other polyunsaturated fatty acids, particularly of C16:4 and C18:4 [28]. Differences are probably due to the different extraction conditions used and/or to the superior capacity of DB-FFAP column (used by [PERSON] et al. [28]) to analyze polyunsaturated fatty acids, compared to DB-5 ms. According to this, we must note that is possible that polyunsaturated fatty acids (n = 4) were underestimated in our study. Figure 3: Seasonal variation of fat content (% DW) in _Ulva rigida_ produced by IMTA under different conditions of flow rate, high (dark bars) and low (gray bars); and of stocking density, high (full bars) and low (lined bars). Standard deviations are represented (n = 3, in triplicate). Albeit that, ratios \(\Omega 6/\Omega 3\) (0.2-0.4) reflected higher levels of omega-3 FA than omega-6 FA, as previously reported for this species. The intake of foods with a low ratio \(\Omega 6/\Omega 3\) (below 5:1) have been proven to contribute to the prevention of certain diseases promoted by the excessive consumption of omega-6 FA relative to omega-3 FA [60]. Notably, the Atherogenic Index (AI) and Thrombogenic Index (TI), which are related to the protection against coronary artery diseases, varied between 1.5 and 3.4 and between 1 and 2.1, respectively, being then more favorable than those reported for _U. fasciata_ (2.85 and 2.78-5.48, respectively) [61]. Moreover, more beneficial fatty acid hypocholesterolem/hypercholesterolic (h/H) ratios were herein found for _U. rigida_ in comparison to those found in _U. fasciata_[61]. In addition, seasonal variations were detected in terms of FA concentration, concomitant with the temporal changes observed for total fat content. Thus, higher concentrations of FA were found in autumn and winter, whereas the lowest were observed in summer and spring.