br Conclusion The present study demonstrates the

Conclusion The present study demonstrates the hypotensive effect of red onion (A. cepa) tunic which is often discarded as wastes. Further investigation is however in progress, in the case of this study, to ascertain the effect of chronic consumption of ACTE and evaluate the individual or synergistic contribution(s) of its flavonoids to the observed hypotensive effect.
Introduction Sweet potato is a crop with rich nutritional values including carbohydrates, dietary fibers, vitamins, and minerals [1]. Currently, it is the sixth most popular and abundant staple food worldwide. It plays an important role in solving the issues of food, energy, natural resources and environment. Four commonly available colored sweet potato species in China are white, yellow, orange, and purple, which have completely different chemical compositions. The major bioactive substances in purple sweet potato are phenolics and anthocyanins. Phenolics are the antioxidant molecules with at least one aromatic ring and one or more hydroxyl groups [2]. Anthocyanins, are a group of water-soluble flavonoids. As the predominant pigments and functional phenolics in purple sweet potato, anthocyanins are the naturally strong free-radical scavengers, which provide many pharmaceutical values including anti-oxidation, anti-tumor capacities, and prevention and treatment of cardiovascular diseases. In yellow or orange sweet potato species, buy AMG 925 (such as β-carotene) act as the primary pigment molecule [3] as well as the source of provitamin A, which shows vitamin A activity [4]. Carotenoids have strong antioxidant capacity to scavenge free radicals because of their conjugated double bonds [5]. Generally, sweet potato is cooked, either by boiling, steaming or roasting, before consumption. Such thermal processing can cause impairment of the functional compounds of sweet potato. There have been reports of negative correlation between heat treatments (steaming and baking) and some bioactive substances, such as anthocyanins. Carvalho et al. [6] reported a dramatic decrease in both total carotenoid and β-carotene contents of sweet cassava after cooking.
Materials and methods
Results
Discussion
Conclusions The dominating pigments were carotenoids in yellow and orange sweet potato species, and anthocyanins can act as the principal pigment for purple sweet potato. Thermal treatment could reduce nutritional values of sweet potatoes by chemical degradation. Heat treatments can decrease bioactive compounds (phenolics and carotenoids) significantly (p<0.05). Boiling as the heat method may retain much more carotenoids; steaming may preserve greater phenolic substances (except the group of anthocyanin contents), and roasting may keep higher anthocyanins. Therefore, to maintain diverse bioavailability of active components, no cooking method can simultaneously provide a higher retention of both carotenoids and phenolics in different species of sweet potatoes. At present, there is no cooking method that can protect and retain all chemical compositions and antioxidant capacities. It is difficult to digest raw sweet potatoes and absorb their nutrients due to the existence of abundant starch. Based on current dietary habit and cooking practice, consumers need to cook sweet potato before eating. Therefore, cooking has to damage the content of bioactive substances and their antioxidant capacities. Consumers may obtain bioactive substances and health promotion effects from sweet potatoes by choosing different means of cooking.
Conflict of interest
Compliance with ethics requirements
Acknowledgements This research was jointly supported by two research grants (UICRG 201327 and UICRG 201402) from Beijing Normal University-Hong Kong Baptist University United International College, China. The authors would like to thank Guilin Agricultural Research Institute of Guangxi Province for providing the sweet potato samples.