Investigating carotenoid loss after drying and storage of

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8. Study under controlled conditions
enthalpy was 65.8 (61.7) and 78.0 (76.3) kJ.mol-1 respectively on a dry (and fresh)
weight basis respectively (Table 8-5).
On average the energy of activation and enthalpy were both 20% higher on 5,6 epoxy-β-
carotene compared to trans-β-carotene. This means that the degradation rate of 5,6
epoxy-!-carotene was more sensitive to the variation of temperature than trans !-
carotene.
Description of total carotenoids by spectrophotometer for the Arrhenius and Eyring
models fitted well the degradation (R 2 > 0.997 and 0.997 respectively). Activation
energy for total carotenoids content (by spectrophotometric reading) was 46.3 kJ.mol -1
on a fresh weight basis and was similar to the value of 44.3 kJ.mol -1 measured on the
same basis for freeze-dried sweet potato at 60-80 ºC (Stephanovitch and Karel 1982).
Activation energy for total carotenoids content (by spectrophotometric reading) was 49.5
kJ.mol -1 on a dry weight basis and was similar to these of Serio and Monlins wholemeal
wheat flour stored between -20ºC and 38 ºC being 45.3 and 48.7 kJ.mol -1 respectively on
a dry weight basis.
Validation of model
To test the robustness of the model, it was used to predict the carotenoid content of dried
sweet potato samples that had been stored at ambient temperature in a jar and in the dark
for 88 days in a laboratory in the UK. For the total carotenoids and trans-β-carotene
under anisothermic conditions, the difference between the experimental value and value
predicted by the model was 4.6% (4.3%) and 2.7% (3.5%) respectively on a dry (and
fresh) weight basis (Table 8-6) (see calculations in Appendix 1).
For the 5,6 epoxy-β-carotene, the difference between the experimental value and model
value was higher, being 19.4% (60.7%) on a dry (and fresh) weight basis respectively
but with lower values. Lower values can be observed to be more difficult to predict
using mathematical modelling.