Changes in the free D-aspartic acid D-glutamic acid and D-alanine content of cheddar during cheesemaking process

Abstract

The purpose of our research was to determine the variation in free D-aspartic acid, free Dglutamic acid and free D-alanine content of dry matter; the variation in free D-amino-acid composition; and that of the ratio of free D-amino acid related to total (D+L) free amino acid during experimental cheddar cheesemaking processes with two different starter strains (Lactococcus lactis subsp. cremoris 303 or Lactococcus lactis subsp. cremoris AM2). Until the ninth week of ripening only the increase of free D-alanine content of dry matter was significant (P<0.05). The intensity of processes which are connected with lysis and responsible for release of D-aspartic acid and D-glutamic acid from cell wall and cytoplazm do not seem to increase until this stage of ripening cheddar. The dry matter of curd contained significantly higher amount of D-aspartic acid after pressing than before pressing in case of both strains (P<0.05); and more D-glutamic acid in case of strain ’303’. Probably these differences cannot be attributed to lysis. During ripening the ratio of D-enantiomer within the free alanine content did not change that is the increase of D-alanine content followed the increase of L-alanine content. One might speculate that part of the free D-alanine content derived from the free L-alanine content of cheese due to the bacterial alanine racemase if this enzyme can operate outside of the bacterial cell wall. Cheeses from cheesemaking trials with Lactococcus lactis subsp. cremoris 303 contained more D-amino acid (P<0.01) and the ratio of D-enantiomer within the total (D+L) free glutamic acid and total free alanine was higher (P<0.01) than in case of trials with Lactococcus lactis subsp. cremoris AM2. It is possible that strain ’303’ is more susceptible to lysis than strain AM2 during this sort of Cheddar making protocol and therefore releases more D-amino acid from cells or/and releases enzymes form more D-amino acid. The ratio of the individual D-amino acid related to the total amount of D-amino acids (the D-amino acid composition) changed during ripening (P<0.001) but there were no significant differences between the two strains.