Abstract
 
Prickly pear cactus (Opuntia ficus-indica) is an edible cactus plant that grows in the arid and semi-arid regions. Cactus peel makes up about 40% of the whole fruit weight and is subsequently the major by-product. The immense amount of cactus peel waste was the motivation for accomplishing the present work by presenting an informative profile of the nutritional constituents that will serve as a basis for the economical utility of cactus peel. Additionally; it may lead to the elimination of waste in a friendly environmental manner. The obtained data showed that cactus peel is a source of protein (4.75%), carbohydrates (59.25%), calcium (2.04 %), iron (80.35 mg/kg), zinc (37.49 mg/kg), copper (1.92 mg/kg), phosphorous (0.084%), mannan (7.76%), betaglucan (27.25%) and β-carotene (141.4 µg/100g). Cactus peel content of hemicellulose, cellulose and lignin was 0.5%, 10.92% and 1.2%, respectively. Amino acid profile ensured the existence of fifteen amino acids, of which seven were essentials: leucine (0.22%), valine (0.19%), lysine (0.11%), phenylalanine (0.14%), threonine (0.14%), isoleucine (0.15%) and histidine (0.09%). The remaining amino acids were aspartic acid (0.28%), argenine (0.15%), alanine (0.19%), proline (0.23%), glutamic acid (0.32%), glycine (0.18%) and serine (0.14%).
 
Phytochemical screening of the methanolic and ethanolic extracts revealed the presence of total amino acids in a range of 0.35 and 0.3%, respectively. Mannan content 9.89 and 10.48%. While, β-glucan content was 34.74% and 36.79%, respectively. Indols content were 0.052% and 0.021%, respectively. Sucrose  level were between 3.3% and 6.05%, respectively. The extraction of these bioactive compounds constitutes a key step in the manufacture of phytochemical-rich products. GC-MS analysis revealed the existence of many common compounds in both extracts as p-coumaric acid, α-isomethyl ionone, heptadecanoic acid, kaempferol, 6-octadecenoic acid and hexestrol. In vivo experiment was carried out to investigate the hypocholesterolemic activity of cactus peel extracts on the biochemical parameters, enzyme activities and lipids profile in rats fed high fat diet. Additionally, significant increase in serum calcium, iron, zinc and copper levels reflected the bioavailability of these extracts҆.
 
Moreover, in vitro cytotoxic activity of the extracts of cactus peel was assessed against brine shrimp and recorded to be 5.8% and 5.2% for methanolic and ethanolic extracts, respectively. Sulforhodamine B assay was used to evaluate the anti-cancer activity of the extracts against colon carcinoma cell line (Caco-2) and liver cancer cell line (Hep-G2). LC50 (concentration that kills 50% of the cells) were calculated. Methanolic extract exhibited cytotoxicity against Caco-2 cancer cell line with IC₅₀ = 47.5µg/ml. Contrarily, ethanolic extract did not record any cytotoxicity.  While, IC₅₀ were found to be 20 µg/ml and 22.5 µg/ml for liver cancer cell line (Hep-G2), respectively. In conclusion; cactus peel extracts may successfully be useful in cancer control. Further work is needed to develop a processing to produce it commercially.