Bacteria, lactic acid inhibitors

Fumaric Aero Inhibition. Another means of preventing malo-lactic fermentation is to add fumaric acid after alcoholic fermentation is complete (45, 46, 47,48). The inhibition is relative and its extent is dependent on the amount added. The susceptibility to fumaric acid is also dependent on the strain of malo-lactic bacteria tested (49). However, we know of no case where fumaric acid addition at the levels suggested by Cofran and Meyer (45) (about 0.05%) did not delay malo-lactic fermentation under normal winemaking conditions. This includes several experiments from our pilot winery (50). Nevertheless, we have not been hasty to recommend the use of fumaric acid as an inhibitor because 1) of the difficulty in solubilizing the acid in wine 2) we do not know the mechanism of action of its inhibition [Pilone (47, 48) has shown that the bacteria metabolize low levels of fumaric acid to lactic acid but, at inhibitory levels at wine pH, the acid is bactericidal] and 3) of the desirability of minimizing the use of chemical additives. 

Yurdugul, S. and Bozoglu, F. 2002. Studies on an inhibitor produced by lactic acid bacteria of wines on the control of malolactic fermentation. Eur. Food Res. Technol. 215, 38-41. 

Potassium sorbate is used as a yeast inhibitor for the stabilization of table wines containing residual sugar. When conditions permit the growth of lactic acid bacteria, wines treated with sorbic acid can develop an odor resembling crushed geranium leaves (Burkhardt, 1973 Radler, 1976 Wurdig et al., 1975). This result due to bacterial reduction... 

The majority of bacteriocins from lactic acid bacteria have been characterized according to the early definition of a proteinaceous inhibitor, estimation of their molecular mass, and determination of their inhibition spectrum [1,21]. Recent developments in the biochemical and molecular biological characterization of many of these compounds have elucidated their genetic organization, structures and mode of action. Despite their heterogeneity, bacteriocins produced by lactic acid bacteria were subdivided into three distinct classes based on these genetic and biochemical resemblances [28]. 

General purpose medium to which may be added specific inhibitors such as actidione, polymyxin and phenylethanol which make it specific for lactic acid bacteria. 

It was established that a range of concentrations exists in which fermentation inhibitors derived from pretreatments of lignocellu-losic feedstocks are not affecting the yeast, but will inhibit further growth of lactic acid bacteria. By an optimization of the levels of fermentation inhibitors the fermentation of biomass can be conducted under non-sterile conditions. Here, the yield of ethanol is comparable to those achieved under sterile conditions (22). Optimized inhibitor levels can be achieved by controlling the ratio of water to biomass of a lignocellulosic biomass during and after the pretreatment. 

Spermine (15) and spermidine (16) stimulate growth of Helianthus tuberosus in explant cultures, but are effective spore inhibitors against a number of fungi, including Pewici/-lium digitatum. Spermidine is used for stimulating lactic acid bacteria in the dairy industry. Polyamines are converted into a variety of products that are summarized in Fig. 28.11 (Slocum et al., 1984). 

Silage additives can be classified into two main types fermentation stimulants, such as sugar-rich materials, inoculants and enzymes, which encourage the development of lactic acid bacteria and fermentation inhibitors, such as acids and formalin, which partially or completely inhibit microbial growth. 

Additives are used in silage making if there is any doubt as to whether natural fermentation is capable of ensuring satisfactory preservation, or routinely as an insurance against poor preservation. Stimulants provide substrate for lactic acid production or boost the population of desirable bacteria in the material to be ensiled. Fermentation inhibitors are used to render the environment inimical to the development of undesirable microorganisms. 

Splittstoesser, D.F. and Stoyla, B.O. (1989) Effect of various inhibitors on the growth of lactic acid bacteria in a model grape juice system. J. Food Protect. 52(4), 240-243. Wilson, D.L. (1988) Use of inert gases for wine quality maintenance - recent advances. Proc. 2nd Int. Cool Climate Viticulture and Oenology Symp., Auckland, New Zealand, pp. 251-253. 

Like lysozyme, nisin is an effective inhibitor of Gram-positive bacteria. Radler (1990a 1990b) determined that most lactic acid bacteria are inhibited by nisin, even in low concentrations, while alcoholic fermentation was not affected. However, the author reported that species varied in their response, with L. casei being the least sensitive. Daeschel et al. (1991) successfully used nisin-resistant strains of O. oeni to conduct MLF in a wine previously treated with nisin to control other spoilage bacteria. Others have reported that nisin killed 100% of O. oeni present as a biofilm on stainless steel (Nel et ak, 2002). Despite its potential, nisin is not currently approved for use in wine in the United States. 

Bound SO2 also exerts a growth inhibitor effect, demonstrated by Fomachon (1963) (Section 8.6.3). Lactic acid bacteria may be capable of metabolizing the aldehyde fraction of the combination and liberating SO2. The SO2 then exerts its activity on the cell, but it is less effective. From their tests, Lafon-Lafourcade and Peynaud (1974) concluded that bound SO2 is 5 to 10 times less active than free SO2. Other authors have observed that its concentration in wine can easily be 5 to 10 times more elevated. 

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