Isolation and Characterization of Lactic acid Bacteria from Indigenous Dairy Product and Preparation of Starter Culture by Freeze-drying

The quality of curd varies widely within different regions of Bangladesh which primarily depends on the starter cultures that are categorized in the group of lactic acid bacteria (LAB). Maintenance, preservation and use of quality starter cultures are prerequisite for quality curd production which is poorly maintained in the country. To explore the potential and quality starter culture and preserve these starter culture with freez-drying method, different curd samples from local popular brands were collected, processed and inoculated on MRS agar. For isolation and characterization of LAB isolates, a total of 12 distinct isolates were picked up from MRS agar, subcultured to pure culture and subjected to different biochemical, cultural and morphological examinations. Among the 12 isolates, 5 different species of Lactobacillus were identified as L. acidophilus, L. casei, L. brevis, L. viridescens, and L. bulgaricus. Among these, L. brevis and L. acidophilus were freeze-dried using four different cryoprotectiveagents viz. glycerin, mannitol, sorbitol, and skim milk. Viability of these freeze dried isolates was determined immediately after the freeze drying and after one month of storage at 4°C. In all cases there was approximately one log decrease in the cell count after freeze-drying. Viability of L. acidophilus after one month was decreased approximately by two logs, although viability for the L. brevis decreased to a greater extent. The highest viability was found in L. brevis that was freeze-dried in glycerin and the lowest viability was found in L. acidophilus that was freeze-dried in mannitol. Starter potential of those freeze-dried starter culture was confirmed by curd formation with those isolates using skim milk and liquid milk as substrate. It can be concluded from our study that the isolated LAB can be used as potential starter culture for curd production and can be preserved successfully by freeze-drying for more than one month stored at 4°C.