Abstract: In order to overcome the disadvantages of the traditional microbial hygiene indicator tests, a fluorescence method based on spoilage indicator bacteria for determining the spoilage of fresh-cut lotus root products was developed. The samples were refrigerated at 4 ℃. Total colony count (TCC) and the fluorescence of the indicator bacteria were measured at 3 d intervals, and their correlation was analyzed. The optimum conditions for fluorescence detection were also studied. The results showed that the TCC of the samples stored for 6 d was 6.4 × 104 CFU/g, indicating spoilage. The fluorescence of the suspension culture of lotus roots was detected starting from the sixth day, suggesting that the time point of fluorescence detection and spoilage were consistent. The fluorescence intensity detected with confocal laser scanning microscope showed an increase with storage time but a decrease with the dilution of the suspension, indicating a positive correlation between the fluorescence intensity and the number of microorganisms. Finally, the optimal conditions for this fluorescence method were determined as follows: 10-fold dilution of the suspension, and inoculum volume 5 μL. The accuracy of this method was up to 90% when it was verified with 10 randomly selected samples. It proved to be a simple and convenient method.

Key words: fresh-cut lotus roots, spoilage, fluorescence, total colony count, detection