Enhanced microbiological safety of acidified infant formulas tested in vitro

Objectives. To determine growth behaviour of pathogens and spoilage micro-organisms in infant formulas after reconstitution, and comparison of the bacteriostatic effect of acidified formulas obtained through fermentation or by direct addition of lactic acid. Design. Four commercially available infant formulas were deliberately contaminated with eight different pathogens and stored at 4, 25 or 37°C. Growth of the micro-organisms was followed by enumeration after 0, 3 and 6 hours. In a second challenge test the fate of pathogens added to a fermented infant formula was compared with that of pathogens in a non-fermented acidified formula. Results. After a lag phase of a few hours, most of the examined micro-organisms grew well in the pH-neutral products at 37°C. At 25°C growth was clearly retarded and at 4°C no significant growth was detected within 6 hours. Fermented formula exerted an inhibitory effect on all micro-organisms. The same effect was observed with a non-fermented acidified formula. Conclusions. Because pH-neutral reconstituted infant formulas may support rapid growth of many undesirable micro-organisms, including pathogens, utmost care should be taken to prevent contamination, and storage under conditions favouring growth of pathogens should be avoided. Alternatively, prevention of rapid microbial proliferation in infant formulas may be achieved by acidification, either through fermentation or by direct addition of lactic acid, provided that the pH is lower than 5.0. South African Journal of Clinical Nutrition Vol.17(3) 2004: 87-9