The Arrhenius Law, which was originally proposed to describe the temperature dependence of the specific reaction rate constant in chemical reactions, does not adequately describe the effect of temperature on bacterial growth. Microbiologists have attempted to apply a modified version of this law to bacterial growth by replacing the reaction rate constant by the growth rate constant, but the modified law relationship fits data poorly, as graphs of the logarithm of the growth rate constant against reciprocal absolute temperature result in curves rather than straight lines. Instead, a linear relationship between in square root of growth rate constant (r) and temperature (T), namely, square root = b (T - T0), where b is the regression coefficient and T0 is a hypothetical temperature which is an intrinsic property of the organism, is proposed and found to apply to the growth of a wide range of bacteria. The relationship is also applicable to nucleotide breakdown and to the growth of yeast and molds.

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Storage of frozen fish brings about a decrease of extractability of myofibrillar proteins. There is also deterioration of the texture and functional properties of the flesh. In model systems, aggregation of myosin, actin, tropomyosin, and whole myofibrils have been described. These changes are caused by concurrent action of partial dehydration due to the freezing out of water, exposure of the proteins to inorganic salts which are concentrated in the remaining nonfrozen fluid, interactions with free fatty acids liberated from phospholipids and with lipid oxidation products, and cross-linking by formaldehyde produced in some species of fish as a result of enzymic decomposition of trimethylamine oxide. The extent of protein alterations increases with time and temperature of storage as well as with advanced disintegration of the tissues and intermixing of their components. The role played by the individual factors and the significance of different types of bonds, i.e., hydrophobic adherences, ionic bonds, and covalent cross-links in particular cases are not yet fully disclosed. Retardation of the deteriorative changes of proteins in frozen fish is possible by avoiding high storage temperatures and oxidation of lipids, removing hematin compounds and other constituents promoting cross-linking reactions, and by adding cryoprotectors like sugars, several organic acids, amino acids, or peptides.

Based on a review of various production principles of fish silage, this paper discusses the prospects of introduction of this method, as an alternative to fish meal, to utilize low value fish and waste products, particularly in developing countries. The paper covers the biochemistry, microbiology, and nutritional aspects of fish silage, as well as production technology and economy.

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BackgroundMathematical models exist that quantify the effect of temperature on poikilotherm growth rate. One family of such models assumes a single rate-limiting ‘master reaction’ using terms describing the temperature-dependent denaturation of the reaction's enzyme. We consider whether such a model can describe growth in each domain of life.Methodology/Principal FindingsA new model based on this assumption and using a hierarchical Bayesian approach fits simultaneously 95 data sets for temperature-related growth rates of diverse microorganisms from all three domains of life, Bacteria, Archaea and Eukarya. Remarkably, the model produces credible estimates of fundamental thermodynamic parameters describing protein thermal stability predicted over 20 years ago.Conclusions/SignificanceThe analysis lends support to the concept of universal thermodynamic limits to microbial growth rate dictated by protein thermal stability that in turn govern biological rates. This suggests that the thermal stability of proteins is a unifying property in the evolution and adaptation of life on earth. The fundamental nature of this conclusion has importance for many fields of study including microbiology, protein chemistry, thermal biology, and ecological theory including, for example, the influence of the vast microbial biomass and activity in the biosphere that is poorly described in current climate models.

The combined effect of temperature and NaCl concentration/water activity on the growth rate of a strain of halotolerant Staphylococcus is described by the square-root models which had been used previously to model temperature dependence only. The model square root r = b(T-T min) is shown to be a special case of the Bĕlehrádek temperature function which is given by r = a(T-alpha)d. The constant alpha is the socalled 'biological zero' and equivalent to T min in the square-root models. This and the exponent d = 2 were unaffected by changing NaCl concentration/water activity. The Bĕlehrádek-type equations are preferable to the Arrhenius equation in that their parameters do not change with temperature. The constancy of T min allows derivation of a simple expression relating growth rate of strain CM21/3 to temperature and salt concentration/water activity within the range of linear response to temperature predicted by the square-root model.