Syrups are concentrated oral solutions of sugar or nearly saturated solutions of sucrose in water or other aqueous liquids. Syrups containing 85% w/v or 66.7% w/w sucrose will retard the growth of microorganisms. It is important to note that sucrose concentration should not reach the saturation point as a saturated solution may lead to crystallization of a small amount of sucrose due to change of physical
condition viz. temperature. Dilute solution of sucrose provides an excellent nutritional source for yeast, moulds and other microorganisms. When heat is employed for the preparation of syrups, a small portion of sucrose changes to dextrose and levulose. This phenomenon is called as inversion. Sucrose solution is optically active and rotates polarized light to right while on heating optical activity decreases, rotates the light to left due to formation of other compounds (dextrose ad levulose). The rate of inversion is enhanced by the presence of acids and hydrogen ions, which act as catalyst.
Syrups are mainly of three types :
Simple Syrup:
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It contains sucrose in purified water alone or in combination of other polyols such as glycerin or sorbitol. These substances are added in syrups to reduce the crystallization of sucrose or enhance the solubility of excipients. (e.g., simple syrup etc.)
Medicated Syrups:
It contains some added medicinal substances in the syrups and used for therapeutic purpose (e.g., ephedrine sulphate syrup, chlorphineramine maleate syrup)
Flavored Syrup:
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It contains various aromatic or pleasantly flavored substances but are non-medicated and generally used as vehicle or as a flavoring agent or for preservation, (e.g., cherry syrups, tolu balsam syrup, cocoa syrup etc.)