MICROBIOLOGY ADDED BY: KHOLOUD AL-ROZZI 220051543 Dr. abdel Raof AL-Manama

STARCH HYDROLYSIS

Introduction starch molecules are glucose polymers linked together by the alpha-1,4 and alpha-1,6 glucosidic bonds, as opposed to the beta-1,4 glucosidic bonds for cellulose. In order to make use of the carbon and energy stored in starch, the human digestive system, with the help of the enzyme amylases, must first break down the polymer to smaller assimilable sugars, which is eventually converted to the individual basic glucose units.

Starch is generally insoluble in water at room temperature Starch is generally insoluble in water at room temperature. Because of this, starch in nature is stored in cells as small granules which can be seen under a microscope. Starch granules are quite resistant to penetration by both water and hydrolytic enzymes due to the formation of hydrogen bonds within the same molecule and with other neighboring molecules. However, these inter- and intra-hydrogen bonds can become weak as the temperature of the suspension is raised. When an aqueous suspension of starch is heated, the hydrogen bonds weaken, water is absorbed, and the starch granules swell. This process is commonly called gelatinization because the solution formed has a gelatinous, highly viscous consistency. The same process has long been employed to thicken broth in food preparation.

Starch agar is a differential medium that tests the ability of an organism to produce certain exoenzymes, including α-amylase and oligo-1,6-glucosidase, that hydrolyze starch.  Starch molecules are too large to enter the bacterial cell, so some bacteria secrete exoenzymes to degrade starch into subunits that can then be utilized by the organism. 

SIGNIFICANCE: This test is useful for bacillus starch agar.

TOOLES Starch agar plate. Loop. Gram’s iodine.

PROCEDURES : Steak each organisms across a small portion of the agar surface . Incubate at 37c for 48 hours. Cover the surface with iodine . Record your results .

Iodine has been added to this starch agar plate Iodine has been added to this starch agar plate. The zone of clearing surrounding Bacillus megaterium and Bacillus subtilis indicate that both were able to hydrolyze starch.

[ Iodine has been added to this starch agar plate. The absence of any clearing indicates that neither Streptococcus agalactiae nor Staphylococcus epidermidis were able to hydrolyze starch.

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