An empirical method for estimating the entropy of formation and the absolute entropy of dried microbial biomass for use in studies on the thermodynamics of microbial growth

An empirical method is described for calculating the entropy of formation, Delta(f)S(biomass), and the absolute entropy, S-biomass, of dried biomass for which the elemental composition is known. It is established that the ratio of Delta(f)S(biomass) to the sum of the atomic entropies of the atoms comprising the biomass multiplied by their respective coefficients is a dimensionless constant. This relationship can be used in the calculation of S-biomass, giving an accuracy comparable to experimentally determined values of 100.18+/-1.94% (n=5). The calculations appear to be valid for both anhydrous and hydrated biomass, provided that the quantity of water of hydration is known. The method is applicable to any solid, organic substance for which the elemental composition is known, with lesser accuracy at small molecular weights and greater accuracy as the molecular weight increases. It can be compared to Thornton's Rule, although completely different, in that it enables a thermal quantity to be calculated without the necessity of a direct thermal measurement. (C) 1999 Elsevier Science B.V. All rights reserved.