Comparative evaluation of air, freeze and fluidised bed drying for Solid State Fermented (SSF) lactic cultures

Abstract

The present investigation was intended to preserve the optimized Solid State fermented (SSF) lactic culture by using various drying methods such as air drying, freeze drying and fluid bed drying. The SSF fermented cultures were dried with the moisture reduction from initial moisture of 96% to 81, 72 and 54% using air drying at 20⁰C, 25⁰C and 30⁰C temperatures respectively. The drying was done openly, hence, led to aerobic spore contamination in SSF lactic cultures, thus the method of air drying of SSF lactic cultures became limited. Further freeze drying was carried out to dry SSF cultures on black gram dhal in which viable counts were reduced from 8.59 to 7.15 log₁₀ cfu/g, 9.08 to 7.23 log₁₀ cfu/g and 9.50 to 7.47 log₁₀ cfu/g in dahi, yoghurt and acidophilus cultures respectively. Freeze drying on an average reduced the viable lactic accounts by 1.7 log counts mean while drying of 11 g of wet SSF lactic culture took 8 h to dry with moisture content of 11 per cent. Fluidized bed drier was found as suitable method to dry SSF lactic cultures at ambient temperature (25±1⁰C) for period of 1, 1.5 and 2 h. Out of the drying period of 1.5 h was found suitable to retain maximum viability with a satisfactory moisture content compared to 1 h and 2 h of drying. The viable counts of SSF lactic cultures maintained after fluid bed drying for 1.5 h were 8.33, 8.85 and 9.34 log₁₀ cfu/g. Among the air drying, freeze drying and fluid bed drying, the best method seemed to be the fluid bed drier to dry SSF lactic cultures on supplemented black gram dhal with respect to higher viability and less moisture retainment compared to other two.