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Opuntia spp. is an economically important crop from the Cactaceae family and native to the tropical and subtropical regions of America. It is cultivated for various uses such as fresh fruit, pharmaceutical, cosmetic, or in the form of beverage. Opuntia spp. is well known for its anatomical and physiological characters to conserve water and tolerate extreme drought conditions. The production of Opuntia has been extended around the world and it has become an alternative crop in the areas with low-quality soil and water deficit. The ability to tolerate the extreme environments of Opuntia species makes them also valuable to study molecular mechanisms underlying abiotic stress tolerance. Opuntia is crassulacean acid metabolism (CAM) species with high water-use efficiencies (WUE) that makes it to be able to grow in areas with insufficient precipitation and less water availability to support traditional C3 or C4 bioenergy crops. Studies of photosynthesis have shown that these species use a particular photosynthetic pathway known as CAM for the fixation of atmospheric CO2 during the dry season. Indeed, in the CAM pathway as an adaptation mechanism in plants to water deficit, all or part of the atmospheric CO2 uptake occurs at the nighttime that remains stomata closer at daytime when the temperature is a higher and consequent reduction in the evapotranspiration rates. Atmospheric CO2 uptake ratio can affect the biomass production in plants. Despite, CO2 fixation in CAM plants is 15% more efficient than C3 plants, CAM species often grow slowly due to their extra enzymatic reactions for carbon fixation. In C3 plants, 3 ATP and 2 NADPH require for each CO2 molecular fixation, while in CAM plants for each CO2 fixation, 5.5–6.5 ATP and 2 NADPH are required. In CAM plants net carbon fixation efficiency is 10% less than C4 plants. However, under optimal growth conditions, Opuntia has the potential to produce higher biomass rivaling that of C3 and C4 crops. Moreover, growth character and CAM pathway in genera Opuntia, allow these species to operate at near-maximum productivity with relatively low water requirement. Cultivation of CAM species from the genera Opuntia can provide an alternative to product feedstocks and food in the arid and semiarid regions. For this purpose, here in this chapter, we will discuss (a) the crassulacean acid metabolism pathway; (b) the molecular mechanism of CAM; (c) physiological attributes of CAM during the drought tolerance period; (d) CAM improve Opuntia biomass production. Furthermore, screening Opuntia species that qualify with water use efficiency and high productivity will be interesting to be reviewed in this chapter to provide the alternative feedstock bioenergy crops that preserve and expand feedstock production in water-limited areas.

Natural plant-derived phenolic extract recently received much attention in the food industry to obtain bioactive compounds for food and pharmaceutical industries. These compounds are of considerable interest due to their medicinal and nutrition properties. In this line, cactus pear (Opuntia spp.) is considered for its potentially active nutrients and its multifunctional properties to produce health-promoting food supplements. These beneficial effects are related to its potential bioactive compounds like phenolic acids and flavonoids possessing antioxidant traits. As secondary metabolites, phenolic compounds can mitigate oxidative damage caused by cancer, cardiovascular diseases, and diabetes. The phenolic structure contains an aromatic ring with one or more hydroxyl groups that cause their therapeutic activity. Two classes of phenolic compounds are extensively investigated in the plants, including hydroxybenzoic acid and hydroxycinnamic acid. However, phenylpropanoid serves as a precursor for synthesizing the other phenolic compounds. Several phenolic compounds were found to display different health benefits, including antioxidant, anti-inflammatory, and anticancer activities. Phenolic acids and flavonoids from the genus Opuntia have been recognized as antioxidants. Phenolic acids such as vanillic, ferulic, p-coumaric, p-hydroxybenzoic, syringic, protocatechuic, caffeic, salicylic, gallic, and sinapic, as well as flavonoids such as rutin, isoquercitrin, kaempferol, and narcissi are found in plants from the genus Opuntia. The antioxidant properties of phenolic compounds in Opuntia spp. plants make them an essential product for preventing human health against degenerative diseases such as cancer, diabetes, hypercholesterolemia, arteriosclerosis, cardiovascular and gastric diseases. Nowadays, the food and agricultural processing include phenolic compounds as an essential part of the human diet. This chapter discusses the medicinal importance of phenolic compounds in Opuntia spp. as a natural antioxidant. The article highlights the extractions methods and manufacturing processing, including backing, cooking, and frying, in the food and beverage industry and their effects on these compounds’ stability and activity. This information would help identify Opuntia species rich in phenolics and their therapeutic properties. Besides, the chemical structure, properties, and health benefits of phenolic compounds of cactus pear fruit and their influences in agro-industrial wastes as natural sources of antioxidants with application in food industries have been reviewed.