Many factors contribute to a successful natural fermentation of carbohydrate-rich food and feed products. Metabolic activities of lactic acid bacteria (LAB) play a leading role. Their ability to rapidly produce copious amounts of acidic end products with a concomitant pH reduction is the major factor in these fermentations. Although their specific effects are difficult to quantitate, other LAB metabolic products such as hydrogen peroxide and diacetyl can also contribute to the overall antibiosis and preservative potential of these products. The contribution of bacteriocins is also difficult to evaluate. It is suggested that they may play a role in selecting the microflora which initiates the fermentation. Bacteriocins are believed to be important in the ability of LAB to compete in non-fermentative ecosystems such as the gastro-intestinal tract. During the past few decades interest has arisen in the use of the varied antagonistic activities of LAB to extent the shelf-life of protein-rich products such as meats and fish. Recent findings indicate that the newly discovered Lactobacillus reuteri reuterin system may be used for this purpose.

Antagonistic activities of lactic acid bacteria in food and feed fermentations.

Article de synthese sur le role antimicrobien du dioxyde de carbone au niveau des aliments (eau, lait, poisson, fruits, legumes), et sur la croissance microbienne au cours de divers procedes de fermentation

The inhibition by CO2 of the growth and metabolism of micro-organisms

A review of effects of carbon dioxide on microbial growth and food quality

Estimation of bacterial growth rates from turbidimetric and viable count data

Effect of carbon dioxide on yeast growth and fermentation

SUMMARY— Growth rate studies were conducted with Pseudomonas aeruginosa to measure the inhibitory effect of CO2 when such variables as temperature, O2, tension, pH, and ionic strength of the glucose-salts medium were controlled. Depletion of O2 did not limit growth until more than 75% (v/v) of the air was replaced with nitrogen. Generation time increased with ionic strength of the medium. The influence of pH in the range of 6.0 to 7.4 on the growth rate was negligible. When these variables were controlled, a linear relationship between generation time and CO2 composition of the gas phase was observed. At 70% CO2 (v/v), the generation time was nearly doubled. Thus, CO2 inhibits the metabolism of the organism, and this inhibition is due to gaseous CO2 in the air only when other environmental factors are controlled.

A. Douglas King

Papers

Growth Inhibition of a Pseudomonas by Carbon Dioxide

INFLUENCE OF CARBON DIOXIDE UPON THE METABOLISM OF Pseudomonas aeruginosa