Sweeteners and starches

Liquid sweeteners such as sucrose and high-fructose corn syrup are commonly used as ingredients in many foods especially in beverages. Sucrose is extracted and purified from cane and beets. High-fructose corn syrup is derived from the enzymatic and acid hydrolysis of corn starch. Other sweeteners are maple syrup, honey, and molasses.

The low water activity of starches and dry sweeteners is largely responsible for their microbial stability. However, liquid sweeteners may spoil due to their higher water content. Industrial prepared syrups range from 42° to 86 Brix.

Microorganisms in starches and sweeteners come from the raw source materials or from the manufacturing environment. Organisms that are likely to survive the process are sporeforming mesophilic aerobic and anaerobic bacteria such as Bacillus sp. and Clostridium sp. Other mesophilic bacteria may be present but will not grow in these products. Osmotolerant yeasts present the greater risk for spoilage. Molds can also be present. In our experience, heat-resistant mold spores (ascospores) can be present in liquid sucrose and high fructose corn syrup and can contribute to the spoilage of beverages where these sweeteners are used.

Microbial spoilage of liquid sweeteners may be prevented by destruction of contaminating microorganisms, use of sanitizing agents on processing and storage equipment, and prevention of water vapor condensation in storage vessels. To prevent condensation, filtered air treated by ultraviolet irradiation is forced over the surface of the liquid. Prompt use of the sweeteners also helps to reduce the incidence of spoilage.

With the exception of honey, commercially produced sweeteners are not involved in outbreaks of foodborne illnesses. Honey has been implicated as the source of spores of Clostridium botulinum causing infant botulism. The sporeforming pathogen Bacillus cereus may be present in starches used as ingredients in food such as puddings and sauces. Foodborne illness could then result from consumption of such temperature-abused foods.

Recommended tests

Aerobic Plate Count
Osmophilic/Xelotolerant yeasts and molds
Aerobic sporeformers
Anaerobic sporeformers

Additional tests

Heat-resistant mold spores.
Bacillus cereus.
Clostridium botulinum spores (in honey).

 Adapted from

Smittle, R. B. and Erickson, J. P. 2015. Sweeteners and Starches, chapter 54, p. 545. In F. P. Downes and K. Ito (eds.), Compendium of Methods for the Microbiological Examination of Foods. American Public Health Association, Washington, DC.