Vitamin E in Opuntia ficus-indica (L.) Mill.: a comparative study between pulp and peel

Vitamin E is a lipid soluble vitamin, designating a group of eight naturally occurring and structurally related vitamers, namely α-, β-, δ-, and γ-tocopherol and α-, β-, δ-, and γ-tocotrienol. α- and γ-tocopherols are the two major forms of this vitamin. The main dietary sources are vegetable oils, nuts and oilseeds. According to Regulation (EU) n.º 1169/2011, the dietary reference intake for adults is 12 mg/day. The aim of this work was to evaluate the vitamin E content in the edible portion (pulp) and by-product (peel) of Opuntia ficus-indica (L.) Mill., which are commonly known as prickly pears. Samples of prickly pears were obtained at Herdade de Peliteiros Silveiras, Montemor-o-Novo, Évora. After the separation between edible and non-edible portion, samples were homogenised and lyophilised. The chromatographic analysis of vitamin E was performed by high performance liquid chromatography. The chromatographic separation of the vitamers was achieved with a normal phase SupelcosilTM LC-SI (75 x 3.0 mm, 3 μm i.d.). A mixture of n-hexane and 1,4-dioxane (98.5:1.5) was used as eluent, at 0.7 mL/min. The detection was performed by diode array detection connected in series with the fluorescence detector (λexc: 290 nm; λem: 330 nm). The compounds were identified by comparison with standards and by their individual UV spectrum. The most abundant vitamer in both parts of the fruit was α-tocopherol, being 47.97 and 208.9 µg/g of dry weight for pulp and peel, respectively. Nevertheless, the second major compound was β-tocopherol in the peel (9.32 ± 0.64 µg/g of dry weight) and γ-tocopherol in the pulp (9.35 ± 0.64 µg/g of dry weight). Concerning tocotrienols, only α-tocotrienol was possible to be quantified, since the other vitamers were not detected. Based on the results obtained for the analysed prickly pear, it is possible to conclude that it is a good source of vitamin E and it could contribute to the intake of natural antioxidants. It is a fruit with nutritional interest and its use in human diet can bring potential health benefits to consumers. Also, due to the high amounts of vitamin E in the peel, these by-products could be added as natural extracts in cosmetic, pharmaceutical and food processing industries. Furthermore, this work will contribute to maintain the biodiversity and to promote the sustainable development and exploitation of these exotic fruits.This work was funded by National Institute of Health Dr. Ricardo Jorge, I.P. under the project BioCOMP (2012DAN730) and UID/QUI/50006/2019 with funding from FCT/MCTES through national funds. R. Alves thanks to FCT the CEECIND/01120/2017 contract.