LOW STORAGE TEMPERATURES MAY AFFECT DRYING AND REHYDRATION KINETICS, MORPHOLOGY AND SOLUBILITY OF YACON (Smallanthus sonchifolius) SLICES.

The drying of yacon, although it has been addressed by several researches, still needs some clarifications for its storage and possible effects. In this direction, the present study was focused on finding out if storage under refrigeration (4 ºC) and freezing (-20 ºC) conditions had any effect on drying kinetics (Page's model) and rehydration (Peleg's model), as well as on morphology, with indicators as gray scale, area and perimeter shrinkage obtained by image analysis. These experiments were applied to two cultivars, stored for ten days at low temperatures, then slices of 4x5 cm were obtained and dried at 60 ºC, and later rehydrated at 25 ºC in 100 mL per slice. Images were obtained perpendicularly (15 cm respect samples, using a Samsung Galaxy A32 smartphone), indicators were obtained using ImageJ (ImageJ-win64 software, USA). Solubility was the ratio of dry matter solubilized in distilled water at 30 ºC after centrifugation (4000 rpm x 15 minutes). In general, the drying and rehydration kinetics were only slightly different with respect to drying rate and moisture gain with cold storage. In fact, Page's indicators, such as diffusivity, remained around 1.0 for the drying treatments without storage and with refrigeration, and only slightly lower for the frozen samples. During rehydration, however, at least one treatment significantly affected moisture gain in the rehydrated samples. The morphology measured indicates an affectation of the samples stored under freezing, with a tendency to minimize the gray scale (browning) and in one treatment towards a maximum shrinkage in area (5 cm2) and perimeter. In the case of solubility, solubility was better in the refrigerated and frozen samples. Therefore, it can be verified that by storing yacon roots for 10 days in refrigeration at 4 ºC, similar indicators are obtained to drying fresh yacon and with better morphological indicators.