Which type of food would have lactic acid bacteria? Discuss their useful application.

(N/A) Micro-organisms such as $Lactobacillus$ and others,commonly called Lactic Acid Bacteria $(LAB)$,grow in milk and convert it into curd.
During growth,the $LAB$ produce acids that coagulate and partially digest the milk proteins.
$A$ small amount of curd added to fresh milk as an inoculum or starter contains millions of $LAB$,which multiply at suitable temperatures,thus converting milk into curd.
This process also improves the nutritional quality of curd by increasing the content of Vitamin $B_{12}$.
In our stomach,$LAB$ play a very beneficial role in checking disease-causing microbes.