MORPHOLOGICAL AND RHEOLOGICAL IDENTIFICATION OF ROD LACTIC ACID BACTERIA
Elzeini H. M.*, Ali A. A., Nasr N. F., Awad A. A. and Hassan A. A.
ABSTRACT
Cell morphological shape and size of four strains of rod LAB grown in two different media (MRS and RSM) were studied using scanning electron microscope (SEM) and image analysis technique. Topographical images reveal rod structures with height profiles and variation in size which occurred singly or in pairs and in chains. Rod cells had a wide range of breadth (0.40 - 1.07 μm) with wide cells perimeters of 12.26 up to 5.51 μm. Both areas of Lb. helveticus 764N and Lb. casei 761N were reduced when grown in RSM than in broth medium. On the contrary, cells areas of Lb. acidophilus 791N and Lb. Paracasei 72MP were increased when grown in RSM than in broth medium. The least elongated cells are reported for Lb. acidophilus 791N in broth medium. As far as strains are concerned, the elongation varies between 0.572 and 0.790 μm. rod cells had a different orientation angles and surfaces seemed to have heights or extrudes with external boundary which was either a sharp outline or a rough surface. Cells hardness and wall thickness effected negatively or positively depending on the strain and growing medium. Rheological properties (viscosity, shear stress and torque) recorded different values. Shear stress followed the same trend as viscosity with the maximum reached at different times (11 up to13 hrs). Clotting time was 11 up to13 hrs depending on the strain. According to acid production development, the fastest strain reached the iso-electric point (pH 4.6) was Lb. helveticus (11 hrs).
Keywords: Lactic Acid Bacteria, Morphology, Topographical, Rheological properties, Shear stress.
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