ARS | Publication request: LIMITING GALACTOSE REQUIREMENT FOR CITRATE UTILIZATION BY LACTOBACILLUS CASEI IS ANNULLED IN CHEDDAR CHEESE EXTRACT

Submitted to: Antonie Van Leeuwenhoek
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2006
Publication Date: N/A

Interpretive Summary: There are lactic acid bacteria that occur as contaminants in cheese in addition to the cultures intentionally added during cheese making. These bacteria can influence the flavor of cheese either positively or negatively. They also may be responsible for formation of biogenic amines that are potentially toxic compounds. This project investigated how these bacteria grow in cheese when there is little or no sugar available. We found that they are able to use citric acid in the cheese as an energy source when sugars, which are easier to use for growth, are absent. This information will be helpful in developing strategies to control the growth of these contaminating bacteria in order to consistently make high quality cheese.

Technical Abstract: Conditions required for citrate utilization by Lactobacillus casei ATCC334 were identified. Citrate is utilized by this microorganism in modified chemically defined media as an energy source, solely in the presence of limiting concentrations of other more readily metabolized carbon sources (i.e. galactose). The presence of glucose inhibited citrate utilization by this microorganism even when added in limiting concentrations. Utilization of citrate occurred at pH 6.0 plus/minus 0.2, and 5.1 plus/minus 0.2. Together these observations suggest that citrate is an energy source for Lactobacillus casei ATCC334 in ripening cheese only when the residual levels of carbohydrate post fermentation are limiting, and lactose or glucose are absent. However, citrate utilization by this organism was observed in Cheddar cheese extract (CCE), naturally containing both lactose and galactose, at the beginning of late-logarithmic phase, and in the absence of residual lactose, regardless of the galactose concentration present in the media.