Investigating carotenoid loss after drying and storage of

175
8. Study under controlled conditions
realised that copper is a catalyst that could react with highly unsaturated β-carotene and
therefore cause a bias in the experiment (Karl Franzman; pers. comm.). The copper
gauze was therefore removed and the dried sweet potato sample was rested directly on
the plastic cup, whose height was sufficient to maintain the sample away from the salt
solution. A cotton fabric bag was used because of its inert properties toward !-carotene
(Karl Franzman chemist; pers. comm.). Prior to its use cotton fabric was washed without
detergent in a washing machine in order to remove possible additives from the fabric.
Cotton bags were then cut and sewed by hand.
The saturation of the salt was tested without and with chips. When using a jar without
chips, humidity equilibrium (between the salt water activity and atmosphere inside the
jar) was reached after 19h. When using a jar containing dried sweet potato chips at
40ºC, equilibrium with the saturated salt was reached after 6 days (Figure 8-5).
Relative humidity (%)
85 %
80 %
75 %
70 %
65 %
60 %
55 %
50 %
45 %
40 %
35 %
11 Sep 12 Sep 13 Sep 14 Sep 15 Sep 16 Sep 17 Sep 18 Sep 19 Sep 20 Sep
Date
Figure 8-5: Achievement of equilibrium in a jar containing dried chips of orangefleshed
sweet potato (Ejumula variety) and NaCl saturated solution stored in
incubator at 40ºC
Therefore the collection time of samples for analysis should be no more than 6 days but
preferably 9 days (Figure 8-5). Following these trials, the storage system was considered
acceptable for the storage of sweet potato chips under controlled conditions of
temperature and humidity.
8.3.3 Carotenoid degradation kinetics
Temperature degradation kinetics
The effect of temperature (10; 20; 30; 40ºC) on β-carotene is shown in Figure 8-6.