Effects of air drying properties on drying kinetics and stability of cactus/brewer's grains mixture fermented with lactic acid bacteria

• Effect of air drying conditions on fermented product drying kinetics was studied.
• The air drying temperature was the main factor in controlling the drying rate.
• The characteristic drying curve of the fermented product was determined.
• Temperature affected color and water activity more significantly than air velocity.
• Drying improved the microbiological quality of the fermented product.

The present work examined the effect of air drying conditions on drying kinetics of cactus/brewer's grains mixture fermented with Lactobacillus plantarum HG328248. The drying kinetics was performed in a convective dryer for three air temperatures (40, 50 and 60 °C) and three air velocities (0.7, 1.0 and 1.3 m/s). Four mathematical models were tested to fit the drying curves. The Page model seemed the most appropriate to describe experimental data. The experimental drying curves showed two periods: that at constant rate and that of falling rate. The air temperature was the main factor in controlling the drying rate. The characteristic drying curve equation was determined.The influence of air drying conditions on color, water activity and microbiological quality of the fermented product was also studied. The temperature affected these parameters more significantly than air velocity. All dehydrated products had a satisfactory microbiological quality and consequently could be introduced in ruminant feed.