Behavior of Enterobacter Species and Hafnia Species in Skimmilk During Fermentation by Lactic Acid Bacteria

Area of Science:

• Dairy Microbiology
• Food Safety
• Bacteriology

Background:

• Enterobacter and Hafnia species are coliforms that can contaminate dairy products.
• Lactic acid bacteria (LAB) are commonly used as starter cultures in dairy fermentation.
• Understanding the interactions between coliforms and LAB is crucial for controlling microbial populations in milk.

Purpose of the Study:

• To investigate the inhibitory effects of specific lactic acid bacteria on the growth of Enterobacter cloacae, Enterobacter aerogenes, and Hafnia species in skimmilk.
• To determine the influence of incubation temperature and lactic starter culture inoculum size on this inhibition.

Main Methods:

• Culturing Enterobacter and Hafnia species individually in skimmilk with Streptococcus lactis, Streptococcus cremoris, or commercial lactic starter cultures.
• Incubation at two different temperatures (21°C and 32°C) with varying lactic culture inoculum levels (0.25%, 1.0%, 2.0%).
• Monitoring the growth and inactivation of the target coliforms over a 15-hour incubation period.

Main Results:

• Streptococcus lactis and Streptococcus cremoris markedly inhibited Enterobacter species at 32°C, with less inhibition at 21°C.
• Commercial starter cultures showed less inhibition compared to individual lactic streptococci.
• Increased lactic acid bacteria inoculum enhanced the inhibition of Enterobacter species, particularly at 32°C.
• Hafnia species were more inhibited by S. lactis than by S. cremoris or commercial starters.
• Higher incubation temperatures (32°C) and increased starter culture amounts promoted Hafnia inhibition.
• All tested coliforms were partially or completely inactivated by the end of the incubation period under optimal conditions.

Conclusions:

• Lactic acid bacteria, especially Streptococcus lactis and Streptococcus cremoris, possess significant inhibitory capabilities against Enterobacter and Hafnia species in skimmilk.
• Incubation temperature and the concentration of lactic starter cultures are critical factors in modulating the inhibitory efficacy of LAB.
• These findings highlight the potential of selected LAB cultures for controlling coliform contamination in dairy products.