Quantification of lycopene and its analogues in different varieties of papaya grown in Tharaka Nithi County
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Date
2015-11
Authors
Muthui, Gerald Gitonga
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Carotenoids are a group of naturally occurring phytochemicals, many of which are important in
human nutrition and health. In particular, lycopene and its analogues may have potent
antioxidant properties to protect cells and tissues from oxidative stress and free radicals, and thus
contribute to enhancement of immune functions of the body. These antioxidants may also
prevent damage to cells and DNA, as well as stimulate the repair of oxidative damage to DNA.
Diets rich in these phytochemicals appear in some studies to lower risk of certain types of
cancer, especially cancers of the prostate, lung and stomach, as well as cardiovascular diseases
and age-related eye disorders. Previous studies have shown that papaya has moderate levels of
lycopene and its analogues. Different varieties of papaya are commonly grown in Kenya but
there exist no data on levels of the different carotenoids at different ripening stages of these
varieties. Four varieties of papaya from Tharaka Nithi County referred to as export, mountain,
SP and local were studied. Lycopene and two analogues, β-carotene and β-cryptoxanthin, were
analysed using reverse phase isocratic HPLC system with UV detector. Two levels of ripening
stages were studied: first ripening stage was seven days after papaya was harvested and kept at
25.3 ± 0.9ºC temperature and 70.5 ± 4.7% relative humidity; and second ripening stage was six
days later. The results showed that there was significant difference between the levels of
lycopene from the first ripening stage to the second one in export and SP variety, while there was
no significance difference in local and mountain variety. There was significant difference in β-
cryptoxanthin between the ripening stages for local, SP and mountain varieties while there was
no significance in export variety. For β-carotene significant difference between the ripening
stages was only seen in the local variety. The highest level in second ripening stage for lycopene
was in export variety with 2.62±0.07 mg/100g and least in mountain variety with 0.84±0.07
mg/100g. β-Carotene level was highest in the local variety (1.293±0.21 mg/100g) and lowest in
the SP (0.601±0.04 mg/100g) while β-cryptoxanthin was highest in SP variety (7.03±0.10
mg/100g) and least in the export variety (2.32±0.07 mg/100g). This study shows that there is
significantly high levels of carotenoids in the four varieties of papaya. These high levels can be
exploited through consumption of different varieties of papaya which can aid in lowering the
risks of different types of cancers and cardiovascular diseases There is need to study other
carotenoids especially xanthophylls (lutein and zeaxanthin) in different varieties of papaya and
observe how agro-ecological zones affects the levels of these carotenoids. Quality controlled
processing and storage of papaya pulp during peak seasons should be used to reduce losses
during peak seasons.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Applied Analytical Chemistry) in the School of Pure and Applied Sciences of Kenyatta University. November, 2015