Production Practices and Quality Assessment of Food Crops. Vol. 1

Saffron Quality 251
Table 10. Effect of water activity (a w) and temperature on crocin degradation upon storage of saffron
powder (after Tsimidou and Biliaderis, 1997).
Temperature
25 °C 40 °C 60 °C
a w Half-life a w Half-life a w Half-life
periods (days) periods (days) periods (days)
0.11 * 0.11 1733 0.11 65
0.23 * 0.23 0866 0.23 42
0.33 * 0.33 0408 0.33 29
0.43 1733 0.43 0193 0.43 25
0.53 0462 0.53 0048 0.53 21
0.64 0031 0.64 0016 0.64 06
0.75 0105 0.75 0015 0.75 03
not attained for samples stored at 25 °C and a ws 0.11–0.43 and for those stored at
40 °C and a ws 0.11–0.23. In contrast to what is reported for the oxidation of nonpolar
carotenoids in relation to a w value of foods, the kinetic data for saffron
carotenoid degradation showed an increasing rate with increasing a w within the range
0.11–0.64. This behaviour may be the result of the polar character of crocins. An
unexpected behaviour was observed at a w 0.64 that concur with current concepts
on the mobility of reactants in foods. This deviation was confirmed in three series
of experiments and requires some further investigation.
Concerning bitterness and aroma evolution in storage it appeared that the latter
is favoured in intermediate relative humidity environment. Thus, it should be
cautiously taken into account that optimum conditions for aroma development are
not in favour of pigment stability. Thus, a w values of 0.33–0.43 and not very low
temperatures should be used if saffron is traded as a spice. In case saffron is kept
for pharmaceutical use then crocins are the active constituents that are better
preserved at low temperatures and low a ws so that the point made by Morimoto et
al. (1994) for storage in a refrigerator becomes correct.
Selim et al. (2000) presented the first attempt of increasing storability of saffron
carotenoids by encapsulation in amorphous polymer matrices. Encapsulation of
bioactive ingredients as a means of shelf life extension is one of the popular current
approaches in food technology. Spray-drying, freeze-drying, air suspension coating,
extrusion, spray-cooling and chilling, rotational suspension separation, coacervation
and inclusion complexes are some of the techniques to encapsulate photosensitive
or thermolabile ingredients such as carotenoids (Dziezak, 1988). Pullulan, PVP40
and 360 were selected for their good water solubility and ability to form an amorphous
state on dehydration. Encapsulated saffron carotenoids using freeze-drying
were studied under the unfavourable relative humidity conditions reported by
Tsimidou and Biliaderis (1997), i.e., 0.43–0.75. PVP 40 had the better protection
effect among the polymers used because it collapses rapidly in storage and becomes
in this way an effective barrier to oxygen permeation. The half-life periods in relation
to control samples increased 4, 18, 7.5 and 7.7 times at aws 0.43, 0.53, 0.64 and