Investigating carotenoid loss after drying and storage of

172
8. Study under controlled conditions
transition state theory in which enthalpy of activation ($H*) and entropy of activation
($S*) are the model’s parameters. The model’s parameters were identified from
experimental data measured in triplicate using linear regressions.
−
Ea
RT
= ek (Equation 8-2 )
Where:
∞
T : temperature (K)
k: degradation constant rate at T (day -1 )
k∞: value of k at T = % (day -1 )
Ea: Activation energy (kJ.mol -1 )
R: gas constant = 8.314 J · K −1 · mol −1
k
*
*
∆−∆ STH
k
−
B RT
= . eT (Equation 8-3 )
h
Where:
kB: Boltzmann constant = 1.381·10 -23 J.K -1
h: Planck constant = 6.626·10 -34 J.s
$H*: activation enthalpy (kJ.mol -1 )
$S*: activation entropy (J.mol -1 .K -1 )
For the validation of the Arrhenius model using room temperature, the predicted data
were calculated using Equation 8-4:
=
k e
t
− Ea
RT
∞
0
−
eC !
dt
0 (Equation 8-4)
C is the carotenoid concentration at t days of storage and C0 is the initial concentration.
In order to validate the Arrhenius carotenoid degradation model under laboratory
conditions, dried samples (Ejumula variety) were stored for t = 88 days at ambient room
temperature (anisothermal or dynamic) conditions in the dark. Temperature and
humidity were recorded every hour (mean: 21.4 ºC/46.8%; min: 13.8 ºC/39.3%; max:
25.2 ºC/47.6% respectively). The Arrhenius model was also tested with dried samples
from Ejumula variety stored for t = 125 days at ambient room temperature in Uganda
(see Chapter 4).