Investigating carotenoid loss after drying and storage of

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2. Assessment of Methods
puree. Several authors applied freeze-drying for carotenoid analysis of vegetables
(Hedrén et al. 2002) and OFSP (Bengsston et al. 2008). In accordance with our results,
Desorby et al. (1998) affirmed that freeze drying of pureed samples was one of the most
efficient ways to preserve provitamin A. These results confirmed that freeze-drying
could be favourably adopted for the air-freight transport of sweet potato roots when the
equipment is available.
2.7.4 Influence of screening plastic coverage on sweet potato flour exposed to
artificial sun light
Carotenoids have been found to be mostly photosensitive to wavelengths lower than 470
nm (Sattar et al. 1977; Lennersten and Linghert 2000). Plastic coverage used in solar-
drying experiment could be wavelength-selective and could therefore bring protection
toward destructive sun rays in UV frequency in particular. Transmittance between 200
and 800 nm of different plastic sheeting was measured by UV- visible
spectrophotometry. The characteristics of different plastic sheeting are presented in
Table 2-11.
Table 2-11: Characteristics of polythene (PE) sheeting
Name (UK Company) Material (Thickness "m)
Clear super-strength (XLs) mLLPDE*, PE (150)
Smart Blue (XLs) mLLPDE, EVA*, PE (150)
Sterilite (XLs) mLLPDE, EVA, PE (180)
Lumitherm (BPI-Visqueen) PE (200)
Green (Allpass) PE (125)
Red (Allpass) PE (125)
Dark Blue (Allpass) PE (125)
*mLLPDE: Metallocene Linear Low Density Polyethylene; PE: Polyethylene;
EVA:Ethylene Vinyl Acetate
The spectrum of the polythene sheeting was measured between 200-800 nm using a
rectangular section of 1 cm thick plastic placed in the centre of the spectrophotometric
cuvette so that beam light could perpendicularly cross the plastic sheeting (Krizek et al.
2005). Red sheeting that was analysed twice exhibited the same spectrum. Polythene
spectra are given in Figure 2-8.