IMPACT OF WATER ACTIVITY AND MOISTURE SORPTION CHARACTERISTICS ON MOULD RELATIONS IN GARRI
ABSTRACT
The moisture content of garri samples were determined by standard method at 1050C. The mean moisture content of yellow and white garri was 11.10% and 10.81%, respectively within 24 hrs of sampling from the market and 17.27% and 16.14% following 3 months of storage at room temperature in hessian bags. The water activity of the garri samples varied from 0.587 to 0.934. Moisture sorption isotherms, determined by static gravimetric techniques based on isopiestric transfer of water vapour at 200C and 300C using inorganic saturated salt solution in the range of 0.225 – 0.973 showed sigmoidal behaviour (Brunauer- Emmet- Teller, BET II type) which is typical of dry carbohydrate rich foods. There was a general increase in the equilibrium moisture content (%) with increasing water activity. Water sorption was temperature dependent as is typical of food system. The equilibrium moisture content decreased with increase in temperature at constant water activity. A total of 44 fungal (mould) species were isolated from the garri samples. Based on the examination of their macroscopic (colonial) and microscopic characteristics, the isolates were identified to belong to the following fungal genera; Mucor, Penicillium, Cephralosporium, Aspergillus, Scopulariopsis, Rhizopus and Paecilomyces, with the range of isolations increasing with increase in moisture content of the samples. Moisture migration into this food is critical to its shelf life. Therefore, to enhance shelf life they should be stored in moisture proof bags.