Journal
FOODS
Volume 12, Issue 6, Pages -Publisher
MDPI
DOI: 10.3390/foods12061208
Keywords
Lacticaseibacillus casei Zhang; activity detection; flow cytometry; fluorescent dyes; plate count; CFDA; propidium iodide
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Food processing, such as freeze-drying, can reduce the viability and activity of bacteria in food. We developed a staining-based flow cytometry method to accurately detect the viability/activity of Lacticaseibacillus (Lb.) casei Zhang, a commonly used probiotic. This method showed comparable results to standard plate counts and was also able to detect viable but unculturable cells in freeze-dried samples.
Food processing, e.g., freeze-drying, exerts strong pressure on bacteria in the food matrix, decreasing their viability/activity and even forcing them to become viable but unculturable (VBNC), which are often underestimated by traditional plate count. The strict standards of bacterial viability in probiotic products require accurate cell viability/activity enumeration. We developed a staining (5(6)-carboxyfluorescein diacetate succinimide ester, propidium iodide)-based flow cytometry rapid method for detecting the viability/activity of Lacticaseibacillus (Lb.) casei Zhang, a widely used probiotic in the dairy industry in China. We optimized the procedural and instrumental parameters for generating results comparable to that of standard plate counts. This method was also applied to freeze-dried Lb. casei Zhang, yielding 7.7 x 10(11) CFU/g, which was non-significantly higher than the results obtained by plate count (6.4 x 10(11) CFU/g), possibly due to the detection of VBNC cells in the freeze-dried powder. We anticipated that this method can be used for detecting lactic acid bacteria in other probiotic food/beverages.
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