Technique extracts bioproducts of straw and cob corn

Innovative and sustainable process results in by-products through water hydrolysis

Technique extracts bioproducts of straw and cob corn

Innovative and sustainable process results in by-products through water hydrolysis

Every year, the agricultural industry dumps millions of tons of straw and corn cobs in landfills and incinerators. In addition to releasing toxins and greenhouse gases, this type of action discards a product rich in high-value substances that could be used in various industrial processes. With this in mind, a study by Unicamp managed to extract these byproducts in a sustainable and cheaper way than traditional technologies, through an innovative subcritical water hydrolysis technique.

Hydrolysis is a method that uses water to break the chemical bonds of molecules, producing various types of byproducts. Although it is not new to science, the technique usually uses toxic acids as solvents, which releases residues that are harmful to the environment. However, researchers from the School of Food Engineering (FEA) decided to use subcritical water – at a high temperature, but under a pressure high enough to prevent it from boiling – instead of acid. This condition alters the physical and chemical characteristics of the water, improving the hydrolysis process.

The study, which has just been published in the journal Biofuel Research Journal (https://www.biofueljournal.com), is part of the doctoral research of food engineer Rafael da Rosa, who examined the behavior of subcritical hydrolysis of corn straw and corn cobs at different temperature and pH levels. “Doing a comparative analysis with conventional hydrolysis methods that use sulfuric acid and sodium hydroxide, we saw that pure water produced much better results. In other words, much higher concentrations of acids and bases were unable to achieve what we achieved,” reports the author.

To give you an idea, subcritical hydrolysis was able to obtain phenolic compounds in amounts ranging from 16,06 milligrams to 76,82 milligrams equivalent of gallic acid per gram – a compound used as a standard in the quantification of phenolic compounds –, while studies with acid hydrolysis obtained only 12,76 milligrams equivalent of gallic acid per gram. As they have antioxidant, anti-inflammatory and antimicrobial properties, these substances have a high added value in industries focused on the manufacture of pharmaceutical products, cosmetics and natural food preservatives.

On the other hand, the technology was also able to obtain up to 448,54 milligrams of sugar per gram of hydrolyzed straw and cob, including cellobiose, glucose, xylose and arabinose. In the case of traditional hydrolysis methods, the amount of sugar obtained did not exceed 0,0745 grams per gram of hydrolyzed straw and cob. To achieve this result, scientists needed to use only moderate temperatures (below 180º C) for a maximum of 30 minutes, a gain in terms of reducing process costs. This is because longer hydrolysis processes generate a large expenditure of energy, which harms the environment and is not always worth it in terms of the amount of by-products obtained.

Since this was a doctoral research project, Rosa had time to carry out a very exhaustive experimental design, evaluating the performance of a wide range of variables. In addition, the engineer performed cost analyses, which proved a return on investment rate of less than four years, and sustainability analyses (Ecoscale). “We compared data from our work with that of others who used conventional technologies and saw that, out of a maximum score of 100, ours obtained a score of 93 in sustainability. The second one that came closest to ours scored 83”, celebrates the engineer.

Applications

For Rosa, one of the great advantages of supercritical technology is the possibility of obtaining a wide range of byproducts from the same residue. In addition to sugars and phenolic compounds, the study also extracted organic acids, used as additives in the food industry, and inhibitors, substances capable of preventing the growth of a certain organism. Obtaining each of these byproducts depended only on variations in temperature and pH, as there is a decomposition “route” that begins with phenolic compounds, passes through sugar, goes to organic acids and reaches inhibitors.

“The higher the temperature and pH, the more we can degrade the molecule,” explains the researcher, adding that, although this does not apply to corn, if the sample is rich in proteins, it is also possible to obtain valuable amino acids for the pharmaceutical and animal feed industries. “In the case of corn straw and corncobs, I see that one of the main applications could be second-generation ethanol, due to the large amount of sugars. Any compound that has sugar can generate ethanol,” he states.

According to FEA professor Tânia Forster-Carneiro, who supervised the research, this new destination for waste is very important because today, with the concept of biorefinery and circular economy, there is no longer any interest in obtaining only one product from a given process and discarding the byproducts. Although the final disposal of corn straw residue in landfills is still permitted, the professor states that the time will come when Brazilian legislation will require the recovery or adequate treatment of these compounds.

According to Foster-Carneiro, a brewery can produce 250 tons of malt pulp per week in the summer. “A factory that makes fruit pulp in bags, for example, generates a huge amount of peels, pulp and seeds. These products are taken to landfills. But the time will come when the industry will have to invest in the treatment or recovery of organic waste,” he believes.