Page 206 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

aggregation mode) constitute the point of differences between the starches of

different plants. Starch granule may be simple or compound, and the description of

a starch as 2-, 3-, 4- or 5-compound refers to the number of component granules. In

some cases, the compound granules is formed by the aggregation of a large

number of simple granules (e.g. rice and cardamom). The starting point of

granule formation in the amyloplast is marked by the hilum, which may be centric

or eccentric. Granules with eccentric hilum are usually longer than broad. The

hilum takes the form of a rounded dot or of a simple, curved, or multiple clefts.

• The starch granule is built up by the deposition of successive layers around the

hilum, and concentric rings or striation are often clearly visible in large granules,

e.g. potato. The striation probably arise from the diurnal deposition of starch

giving variation in refractive index, density and crystallinity. The position and

forms of hilum and the presence or absence of well-defined striation are of

importance in the characterization of starches.

3-Chemical composition of Starch

• Simply starch is a form of water insoluble glucose polymer. Starch granules

contain two carbohydrate, amylopectin (-amylose) and amylose (-amylose).

The former is less water soluble fraction, which gives the more viscous solution and

constitutes over 80% of most starches. -amylose consists essentially of linear

chains, have a helical arrangement with each turn comprising 6 glucosyl unit while
amylopectin has a branched structure composed of about 50000 glucosyl units.

Amylose is mainly responsible for the deep blue coloration given by starch and
iodine in which the later becomes trapped as an inclusion complex in the amylose

helix. On the other hand, amylopectin gives purple color with iodine. However,
amylose has a high affinity toward iodine than amylopectin. Starch can be

hydrolyzed by mineral acids into glucose and by -amylase into maltose.

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