Investigating carotenoid loss after drying and storage of
Investigating carotenoid loss after drying and storage of
Investigating carotenoid loss after drying and storage of
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7. Involvement <strong>of</strong> enzymes<br />
The aim <strong>of</strong> the study was to find out whether the degradation <strong>of</strong> !-carotene in dried<br />
sweet potato resulted mainly from enzymatic activity or autoxidation. This problem was<br />
approached in two directions:<br />
• In the first place, a simplified model system consisting <strong>of</strong> a !-carotene st<strong>and</strong>ard<br />
dissolved in buffer medium at pH 6.0 <strong>and</strong> pH 7.4 at 40ºC was tested for !-carotene<br />
catabolism by enzymes including commercial horseradish peroxidase <strong>and</strong> soybean<br />
lipoxygenase <strong>and</strong> by autoxidation using H2O2 <strong>and</strong> linoleic acid. Influences <strong>of</strong> 2,4<br />
dichlorophenol (DCP), a free radical generator (that could act as an enhancer <strong>of</strong><br />
<strong>carotenoid</strong> oxidation) <strong>and</strong> ethylenediaminetetraacetic acid (EDTA), a metal chelating<br />
agent (that could inhibit oxidation due to metal interaction with <strong>carotenoid</strong>s), were<br />
also tested.<br />
• In the second place, peroxidase (<strong>and</strong> lipoxygenase) activities were determined <strong>after</strong><br />
<strong>drying</strong> <strong>and</strong> <strong>after</strong> <strong>storage</strong> <strong>of</strong> sweet potato <strong>and</strong> at different water activities in order to<br />
underst<strong>and</strong> the involvement <strong>of</strong> enzymes, <strong>and</strong> more especially peroxidases that could<br />
be responsible for the high <strong>carotenoid</strong> degradation in dried sweet potato during<br />
<strong>storage</strong>.<br />
7.2. MATERIALS AND METHODS<br />
7.2.1. Sweet potato root samples<br />
Sweet potato flour from Ejumula variety dried chips came from unpeeled roots that had<br />
been chipped using a rotary disc chipper <strong>and</strong> sun-dried for two days in Ug<strong>and</strong>a,<br />
conserved at -20ºC <strong>and</strong> milled just before the analysis using a laboratory mill (Chapter<br />
6). In order to study the effect <strong>of</strong> <strong>storage</strong> on enzymatic activity, a portion <strong>of</strong> the dried<br />
chips was stored at 40ºC at controlled humidity (50%) (see conditions in Chapter 8) <strong>and</strong><br />
analysed <strong>after</strong> 19 <strong>and</strong> 54 days. Fresh orange-fleshed sweet potato (OFSP) roots<br />
(Susskart<strong>of</strong>feln® from Israel) bought from a fruit <strong>and</strong> vegetable supplier in Chatham,<br />
UK was used for comparison with sweet potato flour assays. Roots were washed under<br />
tap water, mashed (including peel) <strong>and</strong> stored at -20ºC before being thawed at ambient<br />
temperature <strong>and</strong> analysed.
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