Composition, biomass lipids

Since the composition of the various plants tested was not determined (i.e., lipid, cutin, lignin), the differences cannot be examined in light of variable contributions. Nevertheless, the substantially different slopes observed indicate that not only the quantity but also the quality of the plant biomass was important in determining air-plant partitioning. Note that a very similar interspecies variability has been observed for the same plants in a field study (Bohme et al., 1999). 

Macromolecular biomass composition is of obvious interest when the biomass itself is the product, such as algal biomass in [18], or for production of singlecell protein, for e.g. animal feedstock. Moreover, for a precise metabolic flux analysis, changes in biomass composition should be taken in account. For example, Henriksen et al. [19] observed with E. coli under different growth rates, that the levels of DNA and lipids were relatively constant, whereas the proteins and stable RNA levels increased with the specific growth rate and the total amount of carbohydrates decreased. 

An alternative, at least semi-quantitative method to follow changes in biomass composition is infrared (IR) spectroscopy [22]. From dried samples of microbial cells, IR spectra can be obtained which contain information on all major cell components. The spectra are analysed as a multi-component mixture Characteristic bands in the spectra are identified, the extinction coefficients for each component (protein, carbohydrate, lipid, and nucleic acids) at each band are determined, and the concentrations are calculated by a system of linear equations. The method gives results on all major cell components simultaneously, and is relatively quick and easy to perform, compared to the chemical analysis methods. For details see Sect. 8.4 below. 

Biomass can be divided mainly into three compound classes - namely, lignocellulose, lipids, and proteins. These may come from different feedstocks and may differ in composition but should need only different steps in preprocessing to obtain a... 

S.3.2.2. Pretreatment for Fractionation and Anaiyticai Purposes Chemical reactions can be used to modify the composition of a lipid mixture to facilitate its fractionation. As mentioned previously, such approaches have been employed in the fractionation of soybean (117) and olive oil deodorizer distillates (87) and fish oils (97). However, although the fractionation steps in these studies were carried out under supercritical conditions, the use of SCCO2 as a reaction medium in the pretreatment reactions has not been explored. Gunnlaugsdottir et al. (151, 165-168) investigated the alcoholysis of cod liver oil in SCCO2 for the concentration of fatty acids such as EPA and DHA. A process for the purification of polyunsaturated fatty acids from biomass on an analytical scale using in situ SEE/SCF reaction and chromatography has been patented (215). 

Figure 7. The depletion of C in lipids relative to biomass as a function of cellular composition, where XcProt, XcLip, and Xcsacch are the mole fiactions of carbon in proteins, lipids, and carbohydrates, respectively (see Eqn. 5 and related discussion). The indicated relationships are based on isotopic mass-balance requirements and on concepts outlined by Laws (1991). The cross marked Redfield (Anderson) indicates the position of cells with C/NfP = 106/16/1 but with lower (and much more realistic) abundances of H and O than those specified by the conventional Redfield formula (Anderson 1995).

Thermocrinus ruber is a hyperthermophilic, hydrogen-oxidizing chemoautotroph. The pathway by which it assimilates inorganic carbon is unknown. Its biomass is depleted relative to CO2 by only 3%o. The -alkyl lipids are in turn slightly enriched relative to biomass so that their isotopic composition is very close to that of the CO2. In this case, fractionations may be minimized both by the high temperature, which reduces the magnitude of equilibrium isotope effects, and by the structure of the metabolic... 

The chemical composition shows that biomass is more reduced than CH O, in particular due to the lipid fraction. 

M. (1991) The effects of nutrients and temperature on biomass, growth, lipid production, and fatty acid composition of Cyclotella cryptica Reimann, Lewin, and Guillard. Appl Biochem. Biotechnol, 28-29, 317-326. 

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