D-ALANINE IN FRUIT JUICES - A MOLECULAR MARKER OF BACTERIAL-ACTIVITY, HEAT-TREATMENTS AND SHELF-LIFE

Apple, grapefruit, orange, peach, pear, pineapple and other commercial juice samples were investigated by GC (chiral phase) and HPLC (chiral eluent) to detect D-amino acids as molecular markers of bacterial activity, heat treatments, and shelf life. The development of D-amino acids was followed in grapefruit juice samples inoculated with bacteria (Lactobacillus plantarum), or yeasts (Saccharomyces cerevisiae). Significant amounts of free D-alanine were found only in juices affected by bacterial contamination. The content of D-alanine was not dependent upon pasteurization or sterilization treatments and did not change during the shelf-life of the products. D-alanine may be considered as a marker of bacterial contamination occurring before or during juice processing.