Protective effects of organic acids

Under certain conditions, the use of organic acids may enhance the growth of some fungal strains in bakery products (Marin et al., 2002). For example, a low concentration of sorbic acid (0.025 and 0.05%), almost without exception, has been shown to enhance fungal growth, regardless of aw and temperature levels (Samelis et al., 2002). Potassium benzoate (at a concentration of 2 mM) has been found to produce an increase in growth rate of 52% in Z. bailii cells (Macpherson et al., 2005). 

Organic acids such as acetic, malic, and L-lactic acids have been found to have protective effects (1-2 log increases in survival) on the survival of E. coli 0157 H7, compared to organic acids, at concentrations between 5 and 10 mM. D-lactic has a greater protective effect ( 4-log increase in survival) over a concentration range of 1 to 20 mM. However, citric acid has not yet shown any protective effect at these concentrations (Bjomsdottir, Breidt, Jr., and McFeeters, 2006). 

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Bjornsdottir, K., Breidt, F. Jr., and McFeeters, R.F. 2006. Protective effects of organic acids on survival of Escherichia coli 0157 H7 in acidic environments. Applied and Environmental Microbiology 72 660-664. 

Samelis, J., Sofos, J.N., Kendall, P.A., and Smith, G.C. 2002. Effect of acid adaptation on survival of Escherichia coli 0157 H7 in meat decontamination washing fluids and potential effects of organic acid interventions on the microbial ecology of the meat plant environment. Journal of Food Protection 65 33M0. 

Lu, Z., Sebranek, J.G., Dickson, J.S., Mendonca, A.F., and Baily, T.B. 2005. Inhibitory effects of organic acid salts for control of Listeria monocytogenes on frankfurters. Journal of Food Protection 68 499-506. 

Intensive studies on hydrolysis and gamma radiolysis of OOD(iB)CMPO were carried out in decalin (40), n-dodecane (20, 41, 46), TCE (tetrachloroethylene) (42), and CC14 (40). The stability of CMPO in dodecane was greater than in chlorinated diluents, as shown by G-values established in the presence of an acidic aqueous phase for the disappearance of CMPO in the presence of TBP in the organic phase (to simulate solvent in TRUEX process conditions), G(-CMPO) = 1.2 0.3 in dodecane, and 4.5 0.3 molecules/100 eV in tetrachloroethylene (42). This protective effect of dodecane on CMPO was quite unusual. 

Adaptation time to an organic acid may be directly linked to the cell s ability to maintain its internal pH (pHj). The cell may be able to maintain its pH and also adapt to mildly acidic conditions but only for a short period. After this period the pH protection system fails and the cells become sensitive to the toxic effects of the acid. It is known that certain organic acids enter the cell much more easily than others and as a result more readily alter the pH of the cell. It may, therefore, be possible to explain the differences in adaptation times between acidulants by the varying abilities of organic acids to alter the pHj of the cell (Greenacre et al., 2003). 

NAD-dependent substrate oxidation. At the same time, mitoehondria of storage organs and seeds ate eharaeterized by relatively low rates of oxidation of NAD-dependent substrates. The result of maintenance high activity of NAD-dependent dehydrogenases is the support the energy processes in cell that promotes the resistance of plant to varying envirorunental conditions. Under conditions of IW, protective effect of MF is apparently determined by maintenance in the content of unsaturated fatly acids with 18 and 20 carbon atoms in lipid phase of mitochondrial membranes. 

The effect of detoxification of the medium by removal of toxic compounds with UF membranes was demonstrated by Boyaval et al. [36] in the fermentation of propionic acid. UF runs led to an eightfold increase in volumetric productivity relative to fed batch experiments. The effectiveness of membrane bioreactors in the lowering of toxicity of the compounds involved in the bioconversion system was demonstrated by Edwards and co-workers [159]. An eightfold increase in the removal of phenoHc compounds from effluents was observed when polyphenoloxidase was immobilized in a capillary poly(ether)sulfone membrane as compared to the use of the free enzyme. Butanol recovery from the fermentation medium with organic solvent extraction or membrane solvent extraction led to similar results, both processes leading to decreased product inhibition. Due to the low toxicity of the extractive solvent used (isopropyl myristate) on Clostridium beyerinckii cells, no protective effect of the membrane was observed. However, precipitates observed in two-Hquid phase extraction were not observed... 

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