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09/06/20 |   Agroindustry  Plant production

Processing technique improves sorghum digestibility and increases its antioxidant potential

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Photo: Valéria Queiroz

Valéria Queiroz - Extrusion thermal treatment improves sorghum's functional properties

Extrusion thermal treatment improves sorghum's functional properties

  • Extrusion thermal treatment increases sorghum grains' antioxidant capacity.

  • It improved digestibility and carbohydrate and fiber contents, and reduced lipids.

  • Common in animal feed, sorghum is also an alternative for human diets.

  • Functional properties in the sorghum grains can help to reduce the risk of chronic diseases like diabetes and hypertension

  • The research was developed by the Embrapa and partners. The incorporation of sorghum flour to enteral feeding was assessed.

Studies have proved that the thermal extrusion treatment can increase the antioxidant capacity of sorghum grains and to improve their digestibility, that is, the absorption of the nutrients they contain. The research was developed Embrapa Maize and SorghumEmbrapa Food Technology, UFMG (Federal University of Minas Gerais) and UFSJ (Federal University of São João del-Rei).

With that result, the cereal, which is commonly used in animal feed, becomes closer to Brazilians' table staples like corn and wheat, including in terms of protein content, which was over 14%. The use of the thermoplastic extrusion also increased carbohydrate and fiber contents and reduced lipids. Therefore, the idea was to incorporate sorghum flour in an artisanal gluten-free enteral feed (a diet delivered through a feeding tube). Such enteral diet is recommended for people who cannot feed themselves through their mouths and cannot consume gluten.

The presence of compounds with functional properties in the sorghum grains has already been widely described in the literature. They are associated with promoting health and can help reduce the risk of non-transmissible chronic diseases such as obesity, diabetes and hypertension. They mostly comprise food fibers, resistant starch and phenolic compounds, such as phenolic acid and flavonoids (tannins, anthocyanins, flavones, flavanones and others). 

 

Work generated paper and thesis

Part of the research results is published in the paper Study of Thermoplastic Extrusion and Its Impact on the Chemical and Nutritional Characteristics and Two Sorghum Genotypes SC 319 and BRS 332 The work composed the Flávia Assunção Campelo's PhD thesis at the UFMG's College of Pharmacy's postgraduate programme in Food Sciences (PPPGCA). 

The thesis “Characterization and analysis of sorghum flour digestibility for use in artisanal enteral diets” was fruit of research developed jointly by UFMG, UFSJ, Embrapa Maize and Sorghum and Embrapa Food Technology.

The study was advised by UFMG professors Raquel Linhares Bello de Araújo and Inayara Lacerda (Food Department), and Gilberto Simeone (Department of Nutrition).  It also had the participation of the Embrapa researchers Valéria Vieira Queiroz, Maria Lúcia Simeone and Carlos Piler de Carvalho,as well as of professors Rodinei Augusti and Ann Kristine Jansen (UFMG), Julio Melo (UFSJ) and PhD candidate Mauro Silva (UFMG).

The sorghum cultivars with higher tannin contents are the ones that have higher levels of total phenolic compounds and thus greater antioxidant capacity, which gives them anti-inflammatory and anticarcinogenic potential.  “However, sorghum's tannins can bind to polysaccharids and proteins to form low-digestibility complexes and reduce the absorption of such nutrients. That is why it is important to solve this kind of limitation so that the health benefits  attributed to the consumption of the tannin-rich cereal surpass occasional disadvantages”, underscores the Embrapa researcher Valéria Vieira Queiroz.

The researchers have discovered that the thermal treatment through extrusion can improve sorghum's digestibility. It is a technological procedure that changes the structures and conformations of the macronutrients present in the food. This process allows an increase in the performance of digestive enzymes and improves the indices of digestion and absorption of not only these compounds, but also of proteins and starch present in relevant amounts in the food matrix.

The aim of the study was to assess the effect of thermoplastic extrusion in the nutritional composition, phenolic compound content and antioantioxidant capacity of two genotypes of sorghum grains. One of them is SC 319, selected by Embrapa Maize and Sorghum from 100 different lineages, with high tannin content and high antioxidant capacity. And BRS 332 is a tannin-less sorghum hybrid with low antioxidant capacity. 

The UFMG professor Gilbert Simeone reports that they also assessed the profiles of phenolic acids, flavonoids, sugars, aminoacids and other chemical components of the grains using the paper spray-mass spectrometry (PS-MS) technique. “At the last stage of the work, an artisanal gluten-free enteral feed was elaborated from the sorghum genotype that was more suited for that purpose. We assessed the effect of extrusion and the digestibility in vitro for the sake of incorporating the best sorghum in an enteral feed with suitable nutritional, technological and microbiological qualities”, the scientist says.

Potential for enteral nutrition

After assessing the chemical composition and physical parameters like pH, fluidity, viscosity and particle size of BRS 332 and SC319 sorghum flours, they selected the most suitable one to develop an artisanal enteral feed.

The results showed that the use of thermoplastic extrusion produced positive effects on the grain's nutritional and functional characteristics. The process increased fiber contents, which favored digestibility as simulated in vitro, even with the genotype that contains tannins (SC 319). 

“There were also higher total phenolic compound levels, which promoted an increase in their antioxidant capacity. These effects enhance the functional potential of sorghum grains, and further increase the possibility of using the cereal in human diets”, reports the author of the thesis, Flávia Assunção Campelo.

“In addition to such benefits, some results allowed us to conclude that extrusion can improve the availability of compounds with bioactive characteristics, an advantage in comparison with untreated raw sorghum”, Campelo adds. 

In vitro digestion simulates sorghum's performance in the body

Queiroz underscores that, after the in vitro digestion, the samples showed peptide profiles that suit human diets, with higher smaller peptides ratios (< 89,08 Da), especially in the extruded samples.

The digested samples also presented higher phenolic compound contents and antioxidant activities as opposed to the undigested samples. “The in vitro simulated digestion is an important trial for a better understanding of the bioavailability of sorghum components inside the organism”, the scientist reports.

Professor Gilberto Simeone adds that the experimentally developed diet offered a centesimal composition that fits the nutritional recommendations for human adults in enteral nutricional therapy. “We found characteristics that facilitate administering the feed through a tube with no risk of clogging and with microbiological results within the limits established by legislation. These results confirm that extruded sorghum also has potential to be used in enteral formulas”, the scientist asserts.

Technical innovation

There are techniques to identify the chemical compounds present in cereals, but most of them require a long time in sample preparation and analysis. According to researcher Maria Lúcia Simeone, an innovation in the mass spectrometry technique with paper spray ionization can help to solve the problem

“The new technique, conducted in environmental ionization conditions, better preserves the sample's characteristics and allows the acquisition of data in a broad range of mass. That is why it is ideal to assess the chemical profile of several compounds, such as phenolic acids, flavonoids, sugars, aminoacids and others in complex food matrixes like sorghum grains”, the scientist explains. The analyses were performed at UFMG's Department of Chemistry in partnership with UFSJ.

According to the researcher, the sorghum genotypes SC 319 and BRS 332 were initially cultivated at Embrapa Maize and Sorghum and processed at Embrapa Food Technology to obtain extruded flours and later determine their chemical compositions. 

Photo: Valéria Queiroz

 

 

Translation: Mariana Medeiros

Sandra Brito (MTb 06.230/MG)
Embrapa Maize and Sorghum

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