Er kinetics, thus allowing the extraction of heat-sensitive compounds with minimal damage [94]. Despite the limited number of studies that investigated the applicability of these methods in marine macrophytes, it is expected that in the future they will provide higher efficiency, become time-saving, and display lower financial and environmental costs, thus becoming friendlier solutions to obtaining products from the polar lipids of marine macrophytes in a safer solvent-free environment. 4.2. Methods to Analyze Lipids Extracts from Marine Macrophytes During the last several decades, the identification of polar lipids in lipid extracts was performed based on TLC, HPLC and GC. These PD-148515 web techniques allow the screening of polar lipid classes and fatty acid profiles, as exemplified in several studies addressing the lipidome of marine macrophytes [21,30,34,38,61,63,95]. TLC allows the separation of major lipid classes, with the identification of each lipid class being based in the comparison with lipid standards applied to the same TLC plate. Some authors identified fatty acid composition within each class by running a GC analysis of FA methyl ester, obtained after methylation of the spots of each lipid class from the TLC [21,34,38,63]. Despite this strategy being widely used, its efficiency relies on the presence of a high amount of lipids and is significantly time-consuming. HPLC presents an alternative method for lipid analysis that can potentially resolve all the different lipid classes present in a crude lipid extract [96,97]. HPLC can also be coupled to several detectors, such as a light scattering detector (LSD) or a mass spectrometer. The technology of nuclear magnetic resonance (NMR) is also used in lipidomics studies, and it can be used for the structural characterization and quantification of lipid classes. However, the NMR does not provide information on the composition of the fatty acids of the individual molecular species. Usually the NMR is associated with GC-MS to achieve the detailed information of lipid species [98,99]. On the other hand, MS provides all information at the molecular species level, providing information on the chain length, degree of unsaturation and positional distribution of fatty acids at sn-1/sn-2 positions. The combination of HPLC with a mass spectrometer may result in a more detailed picture of particular lipid species within each class and of the whole lipidome in a single run [100]. 4.2.1. Thin Layer Chromatography (TLC) TLC is one of the oldest techniques used for lipid separation and fractionation, still being widely used nowadays. Distinct lipid classes are usually separated by TLC using silica as the stationary phaseMar. Drugs 2016, 14,13 of(designated normal phase TLC). Distinct elution systems can be used depending on the polarity of the lipid classes to be isolated. For separation of nonpolar lipids (triacylglycerols, free FA, cholesterol and diacylglycerols) from more complex lipids, it is necessary to employ an elution system containing ethyl ether and hexane [101]. For the separation of polar lipid classes, namely, separation of phospholipid classes, it is necessary to use a different elution system, such as a mixture of chloroform, ethanol, water and triethylamine. In this case, the separation of polar lipid classes A-836339 chemical information reflects the differences in polarity of the polar head group of polar lipids [101]. Two-dimensional TLC (2D-TLC) is also usually used for complex lipid separation. Plant lipid extrac.Er kinetics, thus allowing the extraction of heat-sensitive compounds with minimal damage [94]. Despite the limited number of studies that investigated the applicability of these methods in marine macrophytes, it is expected that in the future they will provide higher efficiency, become time-saving, and display lower financial and environmental costs, thus becoming friendlier solutions to obtaining products from the polar lipids of marine macrophytes in a safer solvent-free environment. 4.2. Methods to Analyze Lipids Extracts from Marine Macrophytes During the last several decades, the identification of polar lipids in lipid extracts was performed based on TLC, HPLC and GC. These techniques allow the screening of polar lipid classes and fatty acid profiles, as exemplified in several studies addressing the lipidome of marine macrophytes [21,30,34,38,61,63,95]. TLC allows the separation of major lipid classes, with the identification of each lipid class being based in the comparison with lipid standards applied to the same TLC plate. Some authors identified fatty acid composition within each class by running a GC analysis of FA methyl ester, obtained after methylation of the spots of each lipid class from the TLC [21,34,38,63]. Despite this strategy being widely used, its efficiency relies on the presence of a high amount of lipids and is significantly time-consuming. HPLC presents an alternative method for lipid analysis that can potentially resolve all the different lipid classes present in a crude lipid extract [96,97]. HPLC can also be coupled to several detectors, such as a light scattering detector (LSD) or a mass spectrometer. The technology of nuclear magnetic resonance (NMR) is also used in lipidomics studies, and it can be used for the structural characterization and quantification of lipid classes. However, the NMR does not provide information on the composition of the fatty acids of the individual molecular species. Usually the NMR is associated with GC-MS to achieve the detailed information of lipid species [98,99]. On the other hand, MS provides all information at the molecular species level, providing information on the chain length, degree of unsaturation and positional distribution of fatty acids at sn-1/sn-2 positions. The combination of HPLC with a mass spectrometer may result in a more detailed picture of particular lipid species within each class and of the whole lipidome in a single run [100]. 4.2.1. Thin Layer Chromatography (TLC) TLC is one of the oldest techniques used for lipid separation and fractionation, still being widely used nowadays. Distinct lipid classes are usually separated by TLC using silica as the stationary phaseMar. Drugs 2016, 14,13 of(designated normal phase TLC). Distinct elution systems can be used depending on the polarity of the lipid classes to be isolated. For separation of nonpolar lipids (triacylglycerols, free FA, cholesterol and diacylglycerols) from more complex lipids, it is necessary to employ an elution system containing ethyl ether and hexane [101]. For the separation of polar lipid classes, namely, separation of phospholipid classes, it is necessary to use a different elution system, such as a mixture of chloroform, ethanol, water and triethylamine. In this case, the separation of polar lipid classes reflects the differences in polarity of the polar head group of polar lipids [101]. Two-dimensional TLC (2D-TLC) is also usually used for complex lipid separation. Plant lipid extrac.
