To study the hydrolysis of starch by microorganisms by the production of the
Starch is a polysaccharide found abundantly in plants, and is usually deposited
in the form of large granules in the cytoplasm of the cell. Starch granules can
be isolated from the cell extracts by differential centrifugation. Starch consists
of 2 components—amylase and amylopectin, which are present in various
amounts. The amylase consists of D-glucose units linked in a linear fashion by
α-1,4 linkages. It has 2 nonreducing ends and a reducing end. Amylopectin is
a branched polysaccharide. In these molecules, shorter chains of glucose units
linked by α-1,4 are also joined to each other by α-1,6 linkages. The major component
of starch can be hydrolyzed by α-amylase, which is present in saliva
and pancreatics juice and participates in digestion of starch in the gastrointestinal
Starch is a polysaccharide made of 2 components, namely amylase and
amylopectin. Amylose is not truly soluble in water, but forms hydrated micelle,
which produces blue color with iodine. Amylose produces a characteristic blue
color with iodine, but the halide occupy a position in the interior of a helical
coil of glucose units. This happens when amylase is suspended in water.
Amylopectin yields a micellar which produces a violet color with iodine.
- Petri plates
- Conical flasks
- Starch agar media
- Bacterial specimen
Preparation of starch agar
- Beef extract - 3 g
- Agar agar - 15 g
- Starch - 3 g
- Tryptone - 5 g
- Distilled water - 1000 mL
- PH - 7
- Soluble starch is dissolved in a small amount of water and is heated
slowly with constant stirring. Then all the ingredients are added to it and
transferred into a conical flask and sterilized by autoclaving at 121.5°C for
- The sterilized agar medium is poured into the sterilized Petri plates and
allowed to solidify.
- Each plate is inoculated at the center with the bacterial inoculum.
- Plates are incubated at 37°C for 24–48 hrs.
- To test the hydrolysis of starch, each plate is flooded with iodine.