D‐alanine in Fruit Juices: A Molecular Marker of Bacterial Activity, Heat Treatments and Shelf‐life

ABSTRACT 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 plantarun ), or yeasts ( Saccharomyces cereviae ). 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.