Abstract
Cassava tubers suffer from postharvest physiological deterioration (PPD) which normally sets in within 72 hours of harvest. This study examines the role of scopoletin and carotenoids in the onset or delay in PPD in two transgenic varieties EC20-7 and EC20-8 compared to a wild variety TME-7. Scopoletin and carotenoids were quantified by liquid chromatography-mass spectrometry. The scopoletin content (0.10 – 0.20 nmol/g) in the fresh varieties was not significantly (P>0.05) different from the amount in stored cassava roots (12.58 – 14.90 nmol/g). The carotenoid content values in EC20-7 variety were 6.66 µg/g (α-carotene), 80.45 µg/g (β-carotene) and 5.98 µg/g (lutein). As for EC20-8, α-carotene, β-carotene and lutein values were 6.19 µg/g, 69.11 µg/g and 3.12 µg/g, respectively. There was no significant (P>0.05) difference between the varieties in α-carotene content but in their lutein content. The results indicate that carotenoids are more relevant in the delay of PPD and scopoletin content is not a major factor in PPD vascular streaking or discolouration. Hence scopoletin content of cassava varieties may not be considered as a chemical marker for determining the potential of PPD in cassava tubers.
Highlights
Cassava (Manihot esculenta Crantz) is one of the major staple crops in Africa
This study examines the role of scopoletin and carotenoids in the onset or delay in postharvest physiological deterioration (PPD) in two transgenic varieties EC20-7 and EC20-8 compared to a wild variety TME-7
The results indicate that carotenoids are more relevant in the delay of PPD and scopoletin content is not a major factor in PPD vascular streaking or discolouration
Summary
Cassava (Manihot esculenta Crantz) is one of the major staple crops in Africa. The plant is highly cultivated because of its resistance to drought and pests as well as being a rich source of starch and energy (Edoh et al, 2014). Some conventionally bred high beta-carotene varieties known as yellow cassava which were envisaged to assist in combating both vitamin A deficiency (VAD) and postharvest physiological deterioration have been introduced (Sanchez et al, 2006). Another strategy is a transgenic modification of cassava varieties to increase their carotenoid content through genetic engineering as β-carotene content is associated with a reduction in post-harvest physiological deterioration and is thought to be due to oxidative nature of carotenoids (Rudi et al.,2010; Sanchez et al, 2006). It is the hydroxycoumarins that accumulate most „dramatically‟ during PPD (Bayoumi et al, 2010)
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