EFFECT OF DIFFERENT DRYING METHODS ON PHYSICAL-CHEMICAL CHARACTERISTICS AND DRYING TIME OF MIXED ACAI, STRAWBERRY AND ACEROLA PULP

The pulp drying to production of fruit powders allows its preservation for a long time, allowing its use in the manufacture of instant beverages among other applications of industrial interest. This study aimed to compare three drying methods: freeze-drying of pulp mix, freeze-drying of pulp mix in foam; and foam mat drying of pulp mix in a cabinet dryer at 60 oC. Drying parameters in the freeze-dryer and in the cabinet dryer were studied. Drying time, moisture, water activity, solubility and vitamin C of powders were determined. Powder coloration was assessed using the CIELAB scale in Konica Minolta colorimeter (CM-5). The morphology of powders was evaluated by scanning electron microscopy. Based on the results, the drying time of freeze-drying of pulp mix in foam was smaller than the drying time of freeze-drying of pulp mix. The drying method influenced the moisture content, water activity and solubility of dry products. The foam mat drying at 60º C promoted greater loss of vitamin C and reddish pigments, as well as increased browning caused by chemical reactions. A more porous structure was observed in the freeze-drying processes. Such results were expected once freeze-drying causes less loss of vitamin C. The foaming process made the freeze-drying faster by increasing the surface area and porosity of the pulp mix. It is concluded that the freeze-drying of pulp mix in foam was the best of the evaluated methods to drying of pulp mix of açaí, strawberry and acerola.