Starters as substitutes for additives

1 General preservative effect of starter cultures. Lactic acid bacteria have traditionally been used in food fermentation and preservation. The preservative effect of the starter culture is considerable due to the acids produced. The acids (mainly lactic acid) lower the pH and inhibit most spoilage and pathogenic organisms. In addition to lactic acid, other antimi- 

CTobials, e.g. acetic acid, propionic acid, diacetyl, CO2 and bacteriocins, may be produced by some lactic acid bacteria. 

Propionic acid is produced by Propionibacterium from lactic acid. Ripe Swiss and Jarlsberg cheese may contain up to 1% of propionic acid (Blom and Mprtvedt, 1991). 

The antimicrobial effect of an organic acid is not simply due to the ability to decrease pH (Abrahamsen, 1989 Adams, 1990). Weak organic acids only dissociate partially in aqueous media, and because of the lipophilic character of the undissociated form it freely penetrates the bacterial cell membrane. In the cell, the acid dissociates due to higher pH, acidifying the interior of the cell and releasing potentially toxic anions, which appear to be the most important factors in the antimicrobial activity of the organic acids. 

3 Preservative effect of secondary metabolites. Secondary metabolites such as diacetyl and bacteriocins can have preservative effects as follows  

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