Orange Serum Agar

Principle And Interpretation

Fruit juices are generally acidic, with pH values ranging from approximately 2.4 for lemon juice, to 4.2 for tomato juice. The low pH of these foods is selective for yeast, moulds and a few groups of aciduric bacteria. The microorganisms of greatest significance in citrus juices are the lactic acid bacteria, primarily species of Lactobacillus and Leuconostoc, yeast and moulds. Microbial spoilage of these citrus fruit juices are most commonly due to aciduric microbes such as lactic acid bacteria and yeast. The lactic acid bacteria include Lactobacillus fermentum, L.plantarum, and Leuconostoc mesenteroides. Orange Serum Agar is recommended by APHA (1) for cultivation of Lactobacilli and other aciduric organisms. Orange Serum Agar was originally developed by Murdock et al (2) and Hays (3) for examining citrus concentrates. Hays and Reister further used this medium for studying the spoilage of orange juice (4). Dehydrated agar medium containing orange serum was reported by Stevens (6). Orange Serum Broth is used to initiate growth of saprophytic, pathogenic fungi in small samples (5). Tryptone provides essential nitrogenous, carbonaceous compounds, long chain amino acids and other essential nutrients. Dextrose (Glucose) serves as the fermentable carbohydrate and energy source. Yeast extract supplies B- complex vitamins, which stimulate growth. Orange serum provides an optimal environment for the recovery of acid tolerant microorganisms from citrus fruit products.