Browning, Starch Gelatinization, Water Sorption, Glass Transition, and Caking Properties of Freeze-dried Maca ( Lepidium meyenii Walpers) Powders.

Abstract

The browning, gelatinization of starch, water sorption, glass transition, and caking properties of freeze-dried maca ( Lepidium meyenii Walpers) powders were investigated and compared with a commercial maca powder. The freeze-dried maca powders had lower optical density (browning) and higher enthalpy change for starch gelatinization than the commercial maca. This resulted from a difference in thermal history. The equilibrium water contents of the freeze-dried maca powders were higher than those of commercial maca at each water activity ( a w ) because of differences in amorphous part. The glass transition temperature ( T g ) was evaluated by differential scanning calorimetry. There was a negligible difference in the anhydrous T g (79.5–80.2 ºC) among the samples. The T g -depression of freeze-dried maca powders induced by water sorption was more gradual than that of the commercial maca due to a difference in water insoluble material content. From the results, critical water activity ( a wc ) was determined as the a w at which T g becomes 25 ºC. There was negligible caking below a w = 0.328. At higher a w , the degree of caking remarkably increased with a large variation depending on the samples. The degree of caking could be described uniformly as a function of a w / a wc . From these results, we propose an empirical approach to predict the caking of maca powders.