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| Lina Marcela López Rengifo y Yenifer Alejandra Correa Toro, students from the Food Engineering Program, Tuluá. Credit: students courtesy. |
The dehydration of food is a crucial process when considering the utilization of fruits that are often discarded for not being of interest to industries. This process not only allows for the preservation of the products but also opens up new opportunities for their use in different sectors. Seeking to explore this field, a study proposes the analysis of two dehydration methods. Its results aim to deepen knowledge in the field of dehydration, with the goal of expanding information on this technique and providing producers with tools to optimize the use of their harvests.
Lea este artículo en español aquí.
Conservation and extension of the shelf life of products
The dehydration of food products is a key practice in the industry, as it allows for the extension of the shelf life of foods and facilitates their subsequent use. Currently, it has become necessary to develop new technologies and refine methods that contribute to an increasingly comprehensive process, which, in addition to the aforementioned, also preserves the physicochemical properties of the products at the functional, sensory, and nutritional levels. These characteristics are fundamental to ensuring the success of initiatives developed in the future.
For this purpose, students Lina Marcela López Rengifo and Yenifer Alejandra Correa Toro, from the Food Engineering Program at the Universidad del Valle, Tuluá campus, under the direction of researcher and professor Alfredo Ayala Aponte, with the co-direction of professor Libardo Castañeda Flórez and the advice of researcher and professor Anna María Polanía Rivera, from the same academic unit, conducted a comparison of two technologies used in the field of dehydration, with the aim of determining which method was more suitable, both from an economic and functional perspective, to extend the shelf life of yellow pitahaya including the peel. This is an exotic fruit that has not been extensively studied until now, and through the research, the aim was to enhance its qualities.
With their approach, which evaluated a traditionally used technology and a more novel one, students López Rengifo and Correa Toro sought to expand the margins of knowledge about these techniques, offering results that could serve as a foundation for future initiatives from the industry and small producers looking to innovate and undertake their own projects.
The research: "Evaluation of two drying methods (hot air and refractance window) on physicochemical and functional properties in slices of yellow pitahaya (Selenicereus Megalanthus) with skin"
Within the range of possibilities related to food dehydration processes, Lina Marcela López Rengifo and Yenifer Alejandra Correa Toro considered that one of the most important variables to take into account was the economic viability of each method, as their project was focused on providing easily accessible alternatives. After conducting a literature review, they opted for hot air drying technology (widely used, but with the disadvantage of subjecting products to a rather invasive process due to its long processing times) and refractance window drying technology (a novel and economically accessible method), setting aside processes like lyophilization, as the latter presents high costs and involves long operating times.
Their purpose, in addition to setting an academic precedent in evaluative terms for an exotic product like the yellow pitahaya, was to promote the full utilization of the fruit, so for the research, the pulp, seeds, and peel of the pitahaya were used. "We were very intrigued by this approach because we are not only offering a market alternative product with potential, but we are also contributing to waste utilization," says Yenifer Alejandra Correa Toro, who highlights that this was one of the factors that led to choosing pitahaya as the research fruit.
Once the fruit was selected, the students proceeded to analyze different variants for evaluation, among which was the crunchiness of the final product; this turned out to be a key factor, as, due to the presence of pectin between the skin and the pulp, the desired crunchy texture was not achieved in the preliminary tests. To solve this problem, it was necessary to conduct a series of additional preliminary tests.
"We blanched the fruit, scraped the skin, cut off the thorns on the skin, and, in the end, we realized that a very important factor in the process was the thickness of the sample to achieve a good texture," explains student Correa Toro.
Since there was no exact maturity state of the fruit, the students had to carry out a series of evaluations to determine and characterize the basis of their study. Some of the factors evaluated at this stage were brix degrees (measure used to determine the sugar content in the fruit), texture, and color. "We also built our own shelf-life chamber. That is to say, we bought the pitahaya, placed it in a cool place to be observed, and each day its color was evaluated over the course of a week. There, we determined its ripeness according to the Colombian Technical Standard for processing yellow pitahaya, and by correlating the color with the Brix degrees," comments Lina Marcela López Rengifo, adding that after this characterization of the fruit, measurements of physicochemical and functional properties were carried out.
Evaluation and results of the two methods
The evaluation of the dehydration methods was carried out independently for each case. "To choose the temperatures to be used, we based ourselves on the principle and foundation of each drying method. We couldn't directly evaluate the same temperatures because the heat transfer to the fruit in each method is different," explains student Yenifer Alejandra Correa Toro. According to her, in the hot air drying method, heat is transferred directly to the food, causing it to reach the same temperature as the fluid (hot air), whereas in the refractance window method, heat transfer occurs through a plastic film placed in the system, creating a temperature delta between the fluid (hot water) and the food.
For the research, this delta was around 20°C. "If we analyze the temperature delta in the refractance window, we would be using the same temperatures for the food in both drying methods. For example, if the refractance window temperature is 70°C, with the existing delta, the food would actually be at 50°; this temperature was also used in the hot air drying method, which would allow for a comparison between methods," clarifies student Correa Toro.
The results obtained demonstrated that the refractance window method had better outcomes on pitahaya in aspects such as color, vitamin C preservation, retention of phenolic compounds, and antioxidant capacity. These values tended to improve when the process was carried out at a temperature of 90°C.
According to student Correa Toro, this result was due to the shorter processing times at this temperature, which allowed them to preserve the product's properties to a greater extent, something that was also influenced by the fact that in this method there is no direct contact between the product and the heat transfer.
"We also found that, in relation to the antioxidant capacity, the final result was even higher than the initial values of the food. We found this very interesting. Investigating, we found that this is due to the mechanism offered by drying, which allows these compounds to be released and there to be a higher concentration of them," comments student Yenifer Alejandra Correa Toro.
Lina Marcela López Rengifo highlights that the result obtained through the refractance window was a pleasant surprise of the research. "In the refractance window method, the properties increased, which leads us to the conclusion that this method not only provides better preservation of the physicochemical, nutritional, and functional properties, but also enhances them. That was a plus of the work."
For students López Rengifo and Correa Toro, there are currently no exhaustive records of yellow pitahaya in a refractance window; this is why, through this research, it could be consumed in the future in the form of a snack with a very pleasant taste, in addition to all the aforementioned benefits.
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| Yellow pitahaya treated with the refraction window method. Credit: courtesy of students. |
Possible future impact
Despite the fact that the scope of this research was not to develop a snack based on the qualities of the evaluated product, after the results obtained, it becomes a viable option: "The snack prototype is delicious. The yellow pitahaya is, in itself, a very fresh and appetizing fruit. And, when dehydrated, it retains a crunchy texture, with a very artisanal flavor, while also providing a high content of vitamin C and fiber. It can even be used as a complement to dairy drinks, promoting a balanced diet, becoming an alternative to cereal-based products, now that healthy eating is trending," says Lina Marcela López Rengifo.
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| Yellow pitahayas in the final stage of dehydration. Due to its properties and texture, it is believed to have high potential as a snack. Credit: courtesy of students. |
For her part, Yenifer Alejandra Correa Toro believes that, in addition to the impact on producers seeking to innovate with their ventures, the research conducted will serve as an important precedent for future researchers:
"What I found very nice about this research was the fact that, although we had no precedents or references to compare our study, we carried it out and provided the community with research that was not very present, so that in the future they can continue related research," she concludes.
If interested in being in touch with the students or any further information about the investigation, please write the Faculty of Engineering Communications Office: comunicaingenieria@correounivalle.edu.co.
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