where Xw is the water content in dry basis; Xm is the water content
at fully occupied active sorption sites with one molecule of water,
which is secure water content for high quality preservation of
freeze-dried food; C and K are the GAB parameters associated with
the enthalpies of monolayer and multilayer, respectively. The model
parameters in GAB were estimated using non-linear regression analysis
in Origin software (version 8.6).
2.2. Determination and modeling of the thermal transitions using DSC
The glass transition and initial freezing point of the mango samples
at different moisture contents were measured using differential
scanning calorimetry (DSC-60, Shimadzu Co. Ltd., Japan),
following the method described by Xiao et al. (2012) with slight
modifications. Liquid nitrogen was used to cool the samples. The
DSC was calibrated for heat flow and temperature using distilled
water (melting point 0.0 C, 4Hm = 334 kJ/kg) and indium (melting
point 156.5 C, 4Hm = 28.5 kJ/kg). The samples (4–5 mg) were
enclosed in hermetically sealed aluminum pans and loaded onto
the equipment at room temperature. An empty aluminum pan