Fungal spoilage of starch-based foods in relation to its water activity (a(w))

Equilibrium moisture contents of starch-based foods were determined at nine levels of relative humidity ranging from 10% to 98%, using a static desicc ator technique. From the water adsorption isotherms, the critical moisture contents (% dry basis), i.e. the moisture contents to be maintained at 25 d egrees C that will not allow fungal growth were found to be 13.0% for rice grains, 12.9% for glutinous rice grains, 9.6% for rice flour, 10.6% for glu tinous rice flour, 10.7% for wheat flour and 10.5% for corn flour. To maint ain these moisture content levels, starch-based foods must be stored at wat er activity (a(w)) levels of not more than 0.65. From this study, at 0.65 a (w), visible appearance of fungi did not occur in flours until 6 months of storage. However, spoilage occurred after 57 days for ordinary rice grains and 73 days for glutinous rice grains. Hence, a moisture content lower than 13.0% for ordinary rice grains and 12.9% for glutinous rice grains must be maintained for long-term storage. (C) 2000 Elsevier Science Ltd. All right s reserved.