Screening and Identification of Donkey Milk Probiotic Lactic Acid Bacteria Using Fourier Transform Infrared Spectroscopy (FTIR)

Lactic acid bacteria (LAB) are a heterogeneous group of gram-positive and catalase negative bacteria that produce lactic acid during fermentation of carbohydrates. These probiotic bacteria with the ability to produce industrial valuable biopolymers have a significant impact on the improvement of taste and texture of dairy products. A number of methods have been introduced to screen and identify bacteria. Among different methods, some are less reliable and some are expensive. Introduction of a reliable, cost-effective and time-saving method to identify bacteria is of great importance.
In order to identify milk probiotic LAB, donkey's milk microbiota was investigated. LAB was identified and characterized with basic microbiological methods as well as Fourier Transform Infrared Spectroscopy (FTIR). Principle Component Analysis and cluster analysis were used to validate the FTIR data.
The results of this experiment showed that LAB isolates were mostly belonging to either Enterococcus faecalis or Streptococcus devriesei species. Furthermore, PCA and cluster analysis confirmed that FTIR data are reliable to identify LAB genera and species from milk.
It is recommended to use FTIR method for mass screening of LAB from different sources before applying other complex and expensive methods such as DNA sequencing. The FTIR is a cost-effective and quick method that could distinguish bacteria at the genus and even species level. Two bacteria species were found and confirmed by both culture-dependent and FTIR methods and one of which Streptococcus devriesei is being introduced for the first time in Iran.