The state diagram of freeze-dried mango was developed using
DSC data in this investigation. It included the freezing curve,
the glass line and the ultimate maximal-freeze-concentration
condition. The freezing points increased from 21.1 C to 1.5 C
when the soluble solids content (total sugar content) decreased
from 70.36 to 16.13 g/100 g sample (w.b.). The glass transition
temperature decreased from 16.7 C to 42.2 C when the water
content increased from 0.010 to 0.14 g water/g sample (w.b.). The
state diagram provided an estimate of the ultimate maximalfreeze-
concentrated water content (X0
w, i.e. unfreezable water
content) at 0.16 g water/g sample (w.b.) with a characteristic
temperature of the end point of freezing ðT0
mÞu of 33.0 C and a
characteristic glass transition temperatures T0
g of 54.6 C. The
other characteristic glass transition temperature T00
g was 43.2 C.
The water sorption isotherm of freeze-dried mango was also established
using the GAB model, and the monolayer moisture contents
of adsorption and desorption isotherms were found to be 0.109 and
0.145 g water/g sample (d.b.) as the stability criteria based on the
water activity concept. The state diagram can be used to predict
the storage stability of frozen and dried mangoes as well as provide
the optimum processing conditions in the food industry. If mangoes
contain unfreezable water, the stability could be easily determined
from the glass transition line. However, if mangoes contain
freezable water, the stability could be determined based on the
characteristic temperatures [ðT0
mÞu, T0
g or T00
g ]. Further studies on
physicochemical changes of frozen mangoes stored at these
different characteristic temperatures may explain the differences
in the stabilities of mangoes at these temperatures. Moreover, the
BET-monolayer line should be added to update the state diagram
and determine the stability based on combining both the water
activity and glass transition concepts in the same state diagram.