The Effect of Water Activity and Storage Temperature on the Growth of Aspergillus flavus in Medicinal Herbs

Abstract

The quality control of medicinal herbs post harvesting or after collection becomes very critical because of susceptibility to fungal invasion during storage depending on the temperature and humidity of the storage area. The information on moisture equilibrium is important on the process and storage of foods which can be extended to medicinal herbs. In the present study, the growth of Aspergillus flavus was observed on selected ten medicinal herbs with water activity a_w above 0.81 when stored at 25 ± 2 °C, 30 ± 2 °C and 40 ± 2 °C except for Picrorhiza kurrooa and Alpinia galanga which were found to have anti-fungal properties. Aspergillus flavus did not grow in any samples of medicinal herbs with water activity a_w below 0.81 at temperatures of 25 ± 2 °C, 30 ± 2 °C and 40 ± 2 °C. Also Aspergillus flavus did not grow in any samples of medicinal herbs with water activity a_w above 0.81 when stored below 10 ± 2 °C. Therefore it can be concluded that the contamination of medicinal herbs with aflatoxins can be minimized by controlling water activity and storage temperature. Sorption isotherms (desorption) can be interpreted to determine the optimum drying which can lower the water activity to the level required for preventing growth of Aspergillus flavus and also for ensuring quality of medicinal herbs which may get destroyed upon over drying. Furthermore, it also saves incremental cost in prolonged drying over the optimum drying.

Key words

Aspergillus flavus - water activity - temperature - moisture percentage - sorption isotherms

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