Proximate biochemical composition and caloric content calculated from elemental CHN analysis: a stoichiometric concept

Abstract

Carbohydrate, lipid, and protein compositions are stoichiometrically related to organic CHN (carbon, hydrogen, nitrogen) contents. Elemental CHN analyses of total biomass and ash, therefore, provide a basis for the calculation of proximate biochemical composition and bomb caloric value. The classical nitrogen to protein conversion factor (6.25) should be replaced by 5.8±0.13. A linear relation exists between the mass fraction of non-protein carbon and the carbohydrate and lipid content. Residual water in dry organic matter can be estimated with the additional information derived from hydrogen measurements.The stoichiometric CHN method and direct biochemical analysis agreed within 10% of ash-free dry biomass (for muscle, liver and fat tissue of silver carp; gut contents composed of detritus and algae; commercial fish food). The detrital material, however, had to be corrected for non-protein nitrogen.A linear relationship between bomb caloric value and organic carbon fractions was derived on the basis of thermodynamic and stoichiometric principles, in agreement with experimental data published for bacteria, algae, protozoa and invertebrates. The highly automatic stoichiometric CHN method for the separation of nutrient contents in biomass extends existing ecophysiological concepts for the construction of balanced carbon and nitrogen, as well as biochemical and energy budgets.

Foraging by the stoplight parrotfish Sparisoma viride II. Intake and assimilation of food, protein and energy

“…Ash content was determined from replicate subsamples (n = 3) as described above. Protein and energy contents were determined from C and N weight fractions using the stoichiometric method (Gnaiger & Bitterlich 1984), following procedures described by Bruggemann et al (1994). Soluble carbohydrates were extracted by treating replicate (n = 2) subsamples of 200 mg with hot (100°C) 2 M HCl for 2.5 h (Hashimoto et al 1987).…”

The effects of artificial substrates on freshwater pond productivity and water quality and the implications for periphyton-based aquaculture

“…Due to the low biomass of the samples, proximate composition and energy content were determined stoichiometrically from C:H:N ratios, following the method of Gnaiger and Bitterlich (1984). With this method, a sample as small as 1 mg DM can be used to determine the proximate composition of the AFDM.…”

“…Each sample was used in triplicate for CHN analysis. The CHN content of the DM samples was corrected for ash fractions according to equation (1) in Gnaiger and Bitterlich (1984):…”

“…Protein content of the AFDM was calculated using the nitrogen to protein conversion factor of 5.78 proposed by Gnaiger and Bitterlich (1984) who found this to be a more appropriate value for bacteria, algae and aquatic invertebrates than that of 6.25 that is usually applied. Subsequently, lipid, carbohydrate, residual water and caloric content were calculated from the mass fractions of organic C, H and N in the AFDM (Gnaiger and Bitterlich, 1984).…”

“…Subsequently, lipid, carbohydrate, residual water and caloric content were calculated from the mass fractions of organic C, H and N in the AFDM (Gnaiger and Bitterlich, 1984).…”