1 REVISIÓN BIBLIOGRÁFICA
1.2.8 INFLUENCIA DEL CONSUMO DE LA PASTA DE CACAO EN LA SALUD
- 3.0 5 0.0 Algae 12
.■lIlllUljJl
15 17 19 21 23 25 27 29 31 33 35c„
Cladonia 0- .I.
.1
15 17 19 21 23 25 27 29 31 33 35c„
4.5Aquatic bryophyte Grass
- 3.0
i
1 ^ 200I
0.0■III..
....
15 17 19 21 23 25 27 29 31 33 35c„
15 17 19 21 23 25c„
27 29 31 33 35 16 12 5 d 8 Liverwort Fern 120 ^ 80 =L 1 1 - ■ ■ ■ . ■ ■ ■ ■ M b ■ ■ 1 ____ 0 --- --- B m 15 17 19 21 23 25 27 29 31 33 35c„
15 17 19 21 23 25c„
27 29 31 33 35 30 I- 20 ÛÛ 10 Sphagnum 12 15 17 19 21 23 25 27 29 31 33 35c„
5 i W) Juniperus...nil iLid^
15 17 19 21 23 25 27 29 31 33 35c„
Figure 5.1 Distributions of n-alkanes in modern vegetation from the Lochan Uaine catchment (except for the algal specimen, which is taken from a lowland lake).
CHAPTER 5 LIPID ANALYSIS 171
>30 |Lig gdjy The lowest values are seen in the algal and aquatic bryophyte specimens, where hydrocarbons are present at <4.5 p-g gdry wt
Similar «-alkane distributions are seen in the algal, aquatic bryophyte and liverwort specimens (Figure 5.1). These distributions are bimodal, the maxima occurring at n-
Ci7 to M-Cig, and at n-Czg to W-C31. In each case the longer chain-length «-alkanes are the more abundant. These components also show a stronger odd-over-even chain- length predominance than for the less abundant short chain-length components. In liverwort, n-Cig is more abundant than «-C1 7. It is thought that all three distributions
represent contamination from organisms other than those under study. The algal sample was obtained by scraping submerged rocks from around the shoreline of a lowland lake in southern England, as similar material collected from Lochan Uaine did not provide a sufficient concentration of lipids for analysis. Rock scraping removes attached algae such as epilithic diatoms, but will also remove any sedimented detrital organic material. When algal scraping was undertaken, the rocks were seen to be covered by a layer of fine organic detritus, thought to originate mainly from catchment soil erosion. As it was not possible to separate algae from this detritus, the n-alkane distribution shown in Figure 5.1 almost certainly represents a contribution from both algal and higher plant sources. Conversely, the aquatic bryophyte and liverwort specimens from Lochan Uaine are contaminated with algal material. In both cases, microscopic inspection of the specimens reveals large numbers of attached diatoms. The extent and significance of this contamination is not known. Comparison with the literature suggests that the true algal n-alkane signal consists solely of short chain-length components, whilst the true aquatic bryophyte and liverwort signals consist of mid and longer chain-length components. The other reference vegetation specimens, which are not from submerged or semi-submerged environments and hence are less likely to be affected by algal or organic detrital contamination, show no short/long chain-length bimodality in their w-alkane distributions.
The Sphagnum specimen contains M-alkanes ranging from Cig to C3 3, but is entirely
dominated by, in order of decreasing concentration, M-C21, «-C2 3, and «-C2 5 (Figure
CHAPTER 5 LIPID ANALYSIS 172
chain-length w-alkanes in Sphagnum agrees closely with observations by Cranwell (1973b) and Quirk (1978), although M-C23 is found to be the dominant homologue in those cases. Nott et al. (2000) also find 71-C23 to predominate in Sphagnum recurvum, although a smaller n-C^i peak is seen in S. palustre and S. papillosum, and this component is dominant in S. magellanicum, S. capillifolium and S. cuspidatum
(Figure 5.3).
In the Cladonia specimen, M-C31 is slightly more dominant than M-C29, with lower concentrations of W-C2 7 and «-C3 3. Lichens are a symbiotic organism formed from
fungi and algae. Barnes and Barnes (1978) identified « - € 2 9 as predominating in many fungi, which agrees fairly well with the Cladonia results. No major peak in short chain-length w-alkanes is seen which could have derived from the algal component of
Cladonia, although the algal biomass in lichens is very small compared to that of the fungi. Both Cig and C19 «-alkanes are present in low concentrations, as are other odd chain-length n-alkanes up to «-C3 3. The grass is dominated by «-C3 1, with M-C2 9 less
abundant and shorter chain-lengths more abundant than in Cladonia. A similar dominance was seen by Cranwell et al. (1987), although in that case the grasses studied are C4 grasses, whereas all grasses in the Lochan Uaine catchment utilise the
C3 photosynthetic pathway. In the fem, the concentration of the M-C2 9 homologue is
slightly greater than W-C3 1, but other hydrocarbons are almost completely absent.
Barnes and Barnes (1978) note that ferns, which lie below flowering plants phylogenetically, exhibit bimodal n-alkane distributions maximising at Cn/Cig and
C2 5/C2 7/C2 9. In all of the above cases, a strong odd-over-even chain-length
predominance is apparent. Juniperus differs from Cladonia, grass and fem in that n-
C27 is dominant, and that the expected odd-over-even predominance is barely noticeable at shorter chain-lengths.
The only modem reference specimen to contain a significant hydrocarbon component other than M-alkanes is grass (Figure 5.4). Three homologous series of components are visible, eluting before the C23 to C2 9 «-alkanes. These components have yet to be
identified, but it is thought that they may be n-alkenes, the three series representing differing positions of the double carbon bond, or branched hydrocarbons.