Optimisation of carotenoids from sweet potato (Ipomoea batatas) tuberflesh and its improvement in carotenoid yield via biogenesis manipulation

Abstract

Sweet potato (lpomoea batatas) contains carotenoids compounds that can support healthy living due to its antioxidant properties. Although sweet potato is abundantly planted in Malaysia, but, the research on its carotenoid compound has not received the attention it deserves from researchers or the government. This research was conducted to optimize carotenoid extraction and improve the individual carotenoid yield through biogenesis manipulation using orange sweet potato calluses. Primarily, this research aimed to characterize carotenoids profiles in four local sweet potato tuber cultivars; orange, yellow, purple and white. Results revealed that orange sweet potato tuber flesh showed the highest total and individual carotenoids content. The second objective was conducted to optimize carotenoid extraction from orange sweet potato flesh. Results showed that the maximum yield of total carotenoid, predicted by Design Expert® v.8.0. 7 .1 was 92. 92 mg/1 OOg and would be obtained with the extraction duration of 6.00 hours, the temperature at 40.00°C and solidsolvent ratio at 1 :30 g/ml. The third objective of the research was to study the carotenoid profiles of orange sweet potato tuber flesh from different localities, storage and years of harvest. In terms of locality, the research investigated carotenoid content in orange sweet potato tuber flesh from Kelantan, Pahang, Terengganu, Selangor and Perak, and it was analyzed by using UV.Vis. Spectrophotometer and high performance liquid chromatography HPLC. Results showed that a-carotene ranged from 22.49±0.lSμg/g in Perak to 49.13±0.02 μg/g in Kelantan sample, f3-carotene; 399.40±3.62 μg/g in Perak to 1123.85±0.04μg/g in Kelantan. Lutein was absent in all sample from the mentioned sites; zeaxanthin was only in Kelantan with 13.01±0.11 μg/g. In terms of storage and years of harvest, results showed that total carotenoids content decreased from 938.08±2.98μg/g in the 1st month to 117.58±3.89 μgig in the 6th month of storage. Lutein appeared in the 2nd month 0.47±0.41 μgig and decreased in the 3ed month to 0.14±0.02 μg/g. Zeaxanthin was not detected in the 1st month, then, it was detected in fluctuate amounts ranged from (2.02±0.03 to24.17±0.35) μgig in the following months of storage. Orange sweet potato tubers that was collected during three years of harvest; 2011, 2012 and 2013, Lutein and zeaxanthin was not detected in years 2011 and 2012, a-carotene was not found in year 2013. f3-carotene was available in all samples during the three mentioned years. The fourth objective of the research was to find the optimum media for orange sweet potato callus initiation and to improve the yield of individual carotenoid in orange sweet potato calluses through biogenesis manipulation. Results showed that under controlled conditions in the laboratory, the yield of carotenoid could be improved by involving an in vitro study using orange sweet potato calluses with plant elicitor treatment under light and dark conditions. The plant elicitors used in this study were Murashige and Skoog Salt, sodium chloride, polyethylene glycol 4000 and salicylic acid. It was found that dark condition inhibited the accumulation of carotenoids in orange sweet potato calluses with the mentioned elicitors, except the doubled growth of zeaxanthin content in the low strength of MS30 under dark condition. Nutrient strength encouraged a-carotene and f3-carotene accumulation in orange sweet potato calluses under light condition, helping them to adapt to the environmental stress caused by the plant elicitors under light and dark conditions. In brief, under light condition, maximum levels of lutein and zeaxanthin compounds could be obtained from orange sweet potato calluses with moderate strength MS30, while, maximum a-carotene and f3-carotene content was found in orange sweet potato calluses with high strength MS30. Even though the carotenoid compounds in orange sweet potato calluses could be manipulated and improved with the treatments mentioned above, the mechanisms involved regarding the treatment effects on carotenoid biosynthesis has not been well studied. Thus, further study should be conducted to understand the mechanisms better.