PEER REVIEWED ARTICLE No 5 - EFFECT OF PROCESSING AND PRESERVATION METHODS ON VITAMIN C AND TOTAL CAROTENOID LEVELS OF SOME VERNONIA (BITTER LEAF) SPECIES
Vernonia is one of the leafy vegetables that can be used in an attempt
to alleviate the problem of micronutrient malnutrition, prominent in
tropical Africa. Commonly known as Ndole or Bitterleaf in most Central
and West African countries, it is one of the most widely consumed leafy
vegetable in Cameroon. Though eaten by a large proportion of the
population, cultivation is limited to the southern parts of the country
and mostly in the rainy season. In order to ensure availability in
nongrowing areas or seasons, the vegetable is usually processed and
preserved. Processing and preservation methods used are thought to
influence the nutrient content of these vegetables. The study was aimed
at determining the effects of processing and preservation methods on
vitamin C and total carotenoid levels of some species of Vernonia
(V.amygdalina , V.calvoana var. bitter ,
V.colorata and V.calvoana var. non bitter ) consumed
in Cameroon. The processing methods were squeeze-washing, boiling and
squeeze-washing with 0N, 1N and 2N concentrations of natron. The
methods of preservation were sun drying, oven drying at different
temperatures (45, 60 and 75°C) and freezing for 0, 10, 30 60 and
120 days. Results show that these leafy vegetables were good sources of
vitamin C and total carotenoid. Vitamin C values vary from
137.5±3.3 in V. calvoana non bitter to 197.5 ± 3.5mg/100g in
V. colorata, while total carotenoid levels range from 30.0 ± 1.0
in V. amygdalina to 41.5±0.9mg/100g in V. colorata for the raw
samples. Greater losses of both vitamins were observed for the bitter
species. Drying caused significant losses, especially in Vitamin C. The
best temperature for drying the vegetables to preserve carotenoids and
vitamin C was at 45°C, whereas sun drying and oven drying at
75°C caused the highest losses. Freezing for up to ten days had no
significant influence on total carotenoids and vitamin C levels.
Comparatively, squeezewashing proved to be the best processing method
that ensured minimum loss of both vitamins