EFFECT OF WATER ACTIVITY AND TEMPERATURE ON THE GROWTH AND AFB1 PRODUCTION OF Aspergillus flavus ISOLATED FROM TURMERIC

Abstract

An in vitro experiment was conducted to determine the effect of water activity (aw) and temperature on lag phase prior to growth, growth rate and AFB1 production by two isolates of Aspergillus flavus (AFg and AFt). A 6 x 5 factorial experiment replicated three times where turmeric-based media (15 ml/plate) at six aw levels (0.85, 0.90, 0.93, 0.95, 0.982 and 0.995) was inoculated with a 6-day old A. flavus culture and incubated at five temperature regimes (20, 25, 30, 35 and 37° C) was carried out. Assessment of fungal growth was done daily for 10 days and lag phase prior to growth and growth rate was derived from the data. Aflatoxin B1 (AFB1) production was analysed after 10 days of incubation. Data showed that in all cases, no growth was observed at 0.85 aw at all temperatures. Optimum growth rate was at 0.982 aw in both isolates regardless of the temperature. AFB1 production profile between the two aflatoxin-producing isolates were quite different and isolate AFt produced higher concentration of toxin than AFg. The obtained data could aid in the selection of appropriate management measures against AFB1 contamination in commonly consumed turmeric and turmeric-based products.