Browning, Starch Gelatinization, Water Sorption, Glass Transition, and Caking Properties of Freeze-dried Maca (<i>Lepidium meyenii</i> 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.

Water Sorption Isotherm and Critical Water Activity of Amorphous Water-Soluble Carbohydrates Characterized by the Glass Transition Temperature

“…Meanwhile, above Tg, amorphous carbohydrates become rubbery and have a texture that is soft, ductile, and/or sticky. Caking (aggregation) of amorphous carbohydrate-based powders readily occurs in the rubbery state [3][4][5][6][7][8]. Because the Tg of amorphous hydrophilic carbohydrates decreases with increasing water content and/or water activity (aw) owing to water plasticization, water sorption can result in glass transition even at a constant temperature.…”

Effect of Water Vapor Sorption on Complex Formation in Amylose-lauric Acid Blend Powder

“…The storage period was set to 7 days; this period is almost enough to reach water vapor sorption equilibrium. 11) 12) AM-LA was held at various RH conditions, and ALC formation of the sample was investigated using differential scanning calorimetry (DSC) and X-ray diffraction.…”