Abstract
The detection and changes in microbial growth in orange juices on shelf life from five brands (A, B, C, D and NFC) distributed on the Chinese market were investigated. Dilutions of 10(0), 10(-1), and 10(-2) were chosen for spreading juices on PDA or PCA, and were validated as the optimum juice concentrations for detecting colonies. Yeast, moulds, and bacteria were detected from all orange juice samples but no Salmonella. The concentrations of mould and bacteria were very low and remained at 0-4 and 0-6 cfu/ml, respectively, when these juices were stored up to 6 months, then gradually rose to 5-8 and 10-15 cfu/ml, respectively after being stored for 10 months at 4 degrees C. At 12 months, mould and bacteria concentrations reached 8-16 and 14-18 cfu/ml, respectively. Brand B juice had better hygienic quality with the lowest amount of microorganisms and no detection of yeasts. In Brand C juice, microbial populations increased quickly and yeasts were detected. All brand juices are permitted to sell and are regarded as safe for consumption within 10 months when stored on shelves. But after this time, juice quality may be problematic because the mould counts in three brand juices were more than 10 cfu/ml which exceeded the hygienic standard for fruit and vegetable juice of China (GB 19297-2003).