Valorization of prickly pear (Opuntia ficus- indica (L.) Mill): Study of its phytochemical, nutraceutical, and functional properties

Abstract

Opuntia ficus-indica (L.) Mill.), known as prickly pear or cactus pear, is a tropical or subtropical part of the Cactaceae family. This plant, which can grow in arid and semiarid climates, is native of Mexico and nowadays is naturalized in all continents, mainly in America, the southeast of Spain and the Mediterranean basin. Prickly pear is the Cactaceae plant with the greatest economic importance, due to their fruits and cladodes are consumed, the last mainly in Mexico. Prickly pear is mainly known for the consumption of their fruits in fresh, which can also be consumed in different processed forms, such as juices, jams, and syrups. Besides, the cladodes are very popular in Mexico and can be consumed in fresh, cooked, in juices or dehydrated, among other preparations. In addition to their use for human consumption, the prickly pear botanical parts (fruits, cladodes, and seeds) can be used for other purposes, such as in the pharmaceutical and cosmetic industries, animal feeding, biofuel production and phytoremediation of soils, among other uses. In addition to the optimal nutritional properties of the prickly pear fruits, cladodes and seeds, there is ample evidence of the health benefits that its consumption entails. Both the fruits (peel and pulp) as well as the cladodes and the seeds show a high quantity of bioactive compounds, among which the polyphenolic compounds stand out, which showed antioxidant activity. Besides, prickly pear presents other interesting health-promoting compounds, such as monounsaturated and polyunsaturated fatty acids (MUFA and PUFA, respectively), mainly in its seeds, which are also related to health benefits. This crop also stands out for showed lower management and economic cost in comparison with other crops and, due to its adaptability and resistance to high environmental stress conditions, FAO promotes the cultivation of the prickly pear in arid and semi-arid areas, which could provide use to territories where is difficult to develop other crops. Therefore, the main objective of this doctoral thesis was to determine the phytochemical, nutraceutical, and functional properties of different cultivars of prickly pear which grow in the experimental field station of Miguel Hernández University, and commercial cultivars from Alicante and Murcia, as well as their economic evaluation based on production costs, its content in bioactive compounds and carbon sequestration. The antioxidant activity, polyphenolic compounds and the fatty acid profile were determined in the fruits (peel and pulp), cladodes and seeds. The results showed that the young cladodes (less than one year old) and the peel of the fruits presented a higher antioxidant activity than the cladodes of more than one year, the pulp of the fruits and the seeds. The seeds of ‘NE’ cultivar and the young cladodes and the peel of the fruits of the ‘FR’ cultivar stood out for their antioxidant activity by the three methods (DPPH·, ABTS·+ and FRAP) and for their concentration of polyphenolic compounds, presented correlation between both parameters. Linoleic acid, a polyunsaturated essential fatty acid, was the most abundant fatty acid in all cultivars and parts of the prickly pear, except young cladodes, which showed palmitic acid as the predominant fatty acid. The cladodes of the ‘FR’ cultivar showed the highest values of MUFA and PUFA, what made it the most interesting cultivar to use its cladodes in animal feed, elaboration of processed products and human consumption. Regarding the fruits, the cultivar 'NJ' stood out for its high PUFA content both in the pulp and in the peel of the fruits. The seeds stood out for their high PUFA content in comparison to the fruits and cladodes, highlighting the cultivar 'NE', although the cultivar 'NO' showed a higher fat content. The cultivars 'FR' and 'NO' stood out for their protein content, although the cultivar 'NA' showed higher values of IAAs (indispensable amino acids) and DAAs (total dispensable amino acids). Regarding the sensory analysis, the volatile compounds were determined in the pulp of the fruits, determining 35 different compounds. 'FR' and 'NT' cultivars showed the higher concentration of these compounds, which are related to the acceptance by consumers. The fruits of the cultivar 'Orito' were preserved for 28 days under cold conditions (2ºC and 85-90% relative humidity). After cold conservation, the fruits were placed three days at room temperature (20ºC) to study shelf life. The results showed that the fruits of this cultivar presented a suppressed-climacteric pattern in ethylene production and respiration rate, and their conservation were optimal under both conditions during this time, showing optimal values both in the physical parameters, such as color and firmness, as well as in the chemicals, like ºBrix, antioxidant activity, phytochemical profile and concentration of phenolic compounds. To elaborate the economic analysis of the prickly pear crop, the production in Spain was compared with that of two major producing countries, Mexico, which is the main producer and the country with the largest area under cultivation, and Italy, which showed the most developed productive sector. In addition, due to the high content of bioactive compounds in the prickly pear, its extraction could increase the profitability of the prickly pear production, although the costs of extracting these compounds would have to be analyzed. Likewise, prickly pear cultivation proved to be an effective tool to mitigate climate change in arid and semi-arid regions, with cultivation practices being a key aspect in effectively contributing to improving carbon sequestration. These results of this work showed that the different parts of the prickly pear studied (fruits, cladodes, and seeds) presented a nutritional profile and a quantity of bioactive compounds interesting both for human consumption, for consumption in fresh or processed foods, as well as for the pharmaceutical and cosmetic industries. In addition, the peel and the seeds of the fruit are obtained as waste when the pulp is extracted to elaborate processed foods, so their use both in the industries mentioned above and in animal feed would help to reduce the waste generated in this process. For all that, added to its low production cost and its optimal conservation up to one month, make the prickly pear a very interesting crop in terms of the parameters studied in this work, which could also be an effective tool for rural development in arid and semi-arid areas in production, job creation and environment issues.