Reactions autolytic

Another type of chemical change is initiated by light, which may trigger autolytic, that is, free radical (Type I) or singlet oxygen (Type II) reactions. These changes are routinely classified as oxidation. Rancidity in cosmetics, especially those containing unsaturated Hpids, is commonly prevented by use of antioxidants (qv). 

The acid/base property of a molecule is a thermodynamic property and as such it is affected by temperature. This may be illustrated by the autolysis of water, in which two molecules of water react with each other, one acting as a base while the other acts as an acid. Write down the autolytic reaction of water. 

In this definition an acid is defined as a species that raises the concentration of the cation of the solvent, while a base raises the concentration of the anion of the solvent. This definition is of use when dealing with autolytic solvents such as liquid ammonia. Write down the autolytic reaction of ammonia, and so identify the solvent anion and cation. 

Sodium amide would act as a base as it would raise the concentration of the anion, namely the amide ion. This definition may be used for water as well. Suggest what is the autolytic reaction for water, and then what would be a potential acid and base using this definition. 

The main use of this definition is for solvents that are capable of forming both anions and cations by autolysis. There are other examples, such as liquid antimony pentafluoride, that do not depend upon the transfer of a proton to effect the ionisation of the solvent. Suggest the autolytic reaction for this solvent. 

As plant tissues senesce and die, three processes may ensue almost simultaneously. First, enzymes within the dead but sterile and physically intact cells cause proteolysis and other autolytic degradations. The released amino acids, sugars, tannins, phenols, and quinones may be oxidized by chemical or enzymatic catalysis to produce humus-like pigments, or proto-humus as discussed by Stevenson in Chapter 2. This was well illustrated by Cohen (Given and Dickinson, 1975) who observed cellular material of partially polymerized eaco-anthocyanins in residues of Rhizophora mangle deposited in a mangrove swamp in Florida. The autolytic reactions may be prominent in situations where microbial decomposition is slow due to acidity, anaerobiosis, or lack of basic nutrients. 

Important groups of endogenous enzymes that promote autolysis in postmortem seafoods include those originating from the gut, present in muscle tissues or synthesized and secreted in the extracellular matrix. The major autolytic reactions that cause deterioration of fresh seafood quality include proteolysis, glycolysis, nucleic acid (ATP) breakdown, and lipid hydrolysis/oxidation. 

Processes involving proteolysis play a role in the production of many foods. Proteolysis can occur as a result of proteinases in the food itself, e. g., autolytic reactions in meat, or due to microbial proteinases, e. g., the addition of pure cultures of selected microorganisms during the production of cheese. 

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