By Vladimir B. Caliguiran
The Philippines can now meet the world demand for dried mangoes. Through a newly engineered drying technology that uses a combined far-infrared and convection heating (FIRCH) system, dried mango processors can now double their production.
After two years of laboratory and pilot-scale research, the Philippine Center for Post-harvest Development and Mechanization or PHilMech engineers found that the two-stage drying technique that used FIRCH significantly reduced the drying time of mango slices from 12 hours to just eight hours.
Far-infrared is now increasingly used worldwide in variousfood processing systems because of its efficiency in heat transfer. And in the mango drying industry, this will be a first in the Philippines.
Traditional mango drying processes
According to the Food and Agriculture Organization (FAO), the country is one of the top 10 producers of mango in the world. The Philippines claims to have the world’s sweetest mango: the Philippine Carabao Mango. Philippine mangoes, whether fresh or processed are, and have constantly been, in demand in the export market.
During the peak harvest season, local processors are constrained to meet the growing demands of the dried mango export market due to their limited drying capacity. In Cebu, where a large number of dried mango processors can be found, mango drying is commonly done with the use of a convection dryer such as a cabinet dryer heated by with LPG-powered or steam boilers.
Convection dryers are suitable for mango drying because during the drying process, the circulating heated air cannot easily damage the sensitive mango slices. This method takes a longer time, though. Mango slices cannot stand high temperatures for long periods because of the risk of case hardening (an undesirable phenomenon in which the outer surface hardens while the inside remains soft), and the drying process is complicated by the addition of syrup before the mangoes are dried.
A rapid dryer
The team of Dr. Romualdo Martinez and Engr. Robelyn Daquila, both experts in drying, initiated research to find a solution to the long time required for mango drying. This led to their discoveries of the advantages of the use of far-infrared in the process.
The pilot-scale unit dryer is tunnel-shaped and made of food grade stainless steel with the following dimensions: 9.6 meters in length, 0.38 meters in width, and 0.38 meters in height. It uses ceramic heaters to produce infrared energy to achieve a temperature of 250°C.
Mindful of the sensitivity of mango slices to high temperatures, Dr. Martinez and Engr. Daquila found that far-infrared can still be used if the exposure to it was intermittent. With the use of a conveyor, mango slices are moved slowly, at the rate of 4-6 meters per hour and in the process, they are heated using far-infrared for three minutes. The mango slices undergo seven intermittent drying and cooling cycles, and 40 trays of mango slices require two hours to partially dry. At this stage, the slices’ moisture content is reduced from 60 percent to 40 percent. According to the researchers, this is the maximum length of exposure that the mango slices can handle before the surface of the product is burned.
As the mango slices are, at this point, only semi-dried, there is still a need to use a convection dryer to reduce their moisture content to 14 percent. The good news is that this process will only consume six hours in the cabinet dryers.
“As the mango slices spend only six hours in the cabinet dryer, drying time is reduced by 50 percent. This means a 100 percent increase in the usage of the dryer; the production output of the cabinet dryers is thus doubled,” Engr. Daquila explained, referring to the two-stage drying system with FIRCH technology as the first stage dryer and a cabinet dryer for the second stage.
Another significant result of their research is that the use of the FIRCH can result in 30 percent savings in overall energy consumption and a 17 percent reduction in energy costs compared to the use of the convection method alone.
In a sensory evaluation conducted by the College of Home Science and Industry at the Central Luzon State University, the FIRCH-dried mango was found to have no significant difference from the commercially available dried mango in terms of sweetness and tartness, aroma, texture, firmness, and the moist appearance of the product.
Interestingly, when the Food and Nutrition Research Institute of the Department of Science and Technology conducted a nutrient analysis on products made with the FIRCH system, it was found that the product’s beta-carotene content was higher by 15 percent compared to that of conventionally dried mangoes.
Recently, a technology demonstration was conducted among the mango industry players in Cebu. “Many showed interest in FIRCH during our techno-demo. We also gathered some ideas that could greatly improve our technology,” Engr. Daquila said.
According to him, the capacity of the far-infrared conveyor dryer can be customized to complement the capacity of the mango processors’ existing convection dryers. The FIRCH technology is set for commercialization this year.
Mango drying R&D
Through the years, mango drying technologies developed by PHilMech have been nearing optimum efficiency. Engr. Daquila started it all with the adaptation of the Multi-Commodity Solar Tunnel Dryer. This was followed by the development of a mango cabinet dryer with a biomass-fed-furnace which was pilot-tested in 2006. These two dryers are now commercially available.
With the discovery of FIRCH, PHilMech engineers continue to help improve the mango drying industry through the development of more efficient dryers.
“If the drying process is quicker and the products are of high quality, it will be a big help to the processors and to the mango farmers too,” said Engr. Daquila.
This appeared in Agriculture Monthly’s September 2013 issue.