Sun-drying system could boost nutritional and medical value of a popular Mexican food

4open study reveals how sunshine and technology could promote wider use of prickly pear cactus

Capturing the sun’s energy to dry prickly pear (Opuntia ficus-indica) opens up a cheaper and more effective route to producing Opuntia powder with greatly improved nutritional value, new research published in the open access journal 4open shows.

“We are making a bioproduct of superior quality at much lower cost than traditional combustion-based technology,” says Mario Pagliaro of Italy’s Research Council. Pagliaro is a co-author of the paper which describes an innovative system for processing the leaves of the Opuntia cactus.

Nutrition and medicine

The thick leaf-like ‘cladodes’ of the Opuntia cactus are a popular food in Mexico and are more widely used to feed livestock in many semi-arid regions worldwide. The cladodes are rich in dietary fiber, carbohydrates, antioxidants, flavonoids, minerals and vitamins.

Cladode extracts are used in the traditional medicine of many countries, especially to treat diabetes mellitus, digestive system diseases, and kidney and urinary infections. They can also be used in cosmetics.

Pagliaro believes there is great potential for wider exploitation of the nutritional, medical and cosmetic benefits of Opuntia cladodes, or ‘nopal’, as they are also known.

The old and the new

“The key to more widespread uptake is to develop new green technologies to produce large amounts of dried cladodes at low cost,” says Pagliaro. He believes his team's solar ventilation drying system could make a big contribution.

The system captures solar energy and uses it to heat a conventional ventilated kiln. The researchers report that this brings several key advantages over both traditional sun-drying and fuel-powered drying techniques.

The traditional method of leaving fresh cladodes out in the sun takes several days and exposes them to animals, insects, bird droppings and microbial infestation. The modern process of drying in fossil-fuel-powered tunnels, however, brings greatly increased expense and all the environmental problems linked to fossil-fuel use.

The solar ventilation drying process now offers speed, cleanliness, greatly reduced cost and environmental sustainability. Plentiful sunshine is readily available in all the countries where Opuntia is grown.

Natural color indicates benefits

The procedure also has the significant advantage of retaining more beneficial nutrients.

The nutritionally rich content of cladodes dried in the solar ventilation kilns is hinted at by the intact and powdered cladodes retaining their natural green-yellow color, unlike the brown material produced using other methods. This is probably due to beneficial molecules such as chlorophylls, carotenoids and other antioxidants being retained in their unmodified form, the researchers say.

“We can cheaply and effectively make the powder with unprecedented nutritional and nutraceutical value,” Pagliaro concludes. One of the most attractive aspects for potential adopters of the technology is that there are no commercial barriers to surmount. “It is available to all Opuntia-growing countries and companies,” says Pagliaro. “All they have to do is to study our work, replicate it or even try to improve it.”

Pagliaro points out, however, that the main problems in developing aspects of a bio-economy such as his team’s procedure can be lack of technical expertise and political will in the regions best-suited to exploit the technology. He reports the need for those countries to establish new solar energy and bio-economy institutes.

This “Key Summaries” article is brought to you in collaboration with SciencePOD.

Article details:

Ciriminna R., Morreale V., Pecoraino M. and Pagliaro M.: “Solar air drying for innovative Opuntia ficus-indica cladode dehydration”, 4open 2019, 2, 1